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2023 Volume 3
Article Contents
Abstract
Introduction
Materials and methods
Materials
Preparation of mixed surimi samples
Rheological characteristics of mixed surimi samples
Apparent viscosity
Dynamic rheological behavior
Strength of mixed surimi gels
Textural properties of mixed surimi gels
Cooking loss of mixed surimi gels
Low-field nuclear magnetic resonance (lf-nmr) of mixed surimi gels
Color difference of mixed surimi gels
Scanning electron microscopy (sem) of mixed surimi gels
Thiobarbituric acid-reactive substances (tbars) determination
Statistical analysis
Results and discussion
Rheological properties of surimi gels
Steady-state shear properties
Dynamic elastic properties during gelation
Strength of surimi gels
Textural properties of surimi gels
Cooking loss of mixed surimi gels
Color of surimi gels
Changes in moisture distribution of surimi gels
Scanning electron microscopy of surimi gels
Thiobarbituric acid-reactive substances (tbars) determination
Conclusions
Author contributions
Data availability
Acknowledgments
Conflict of interest
Supplementary information
Rights and permissions
References
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ARTICLE   Open Access    

Food borne toxicants in coffee: Acrylamide and furan derivative content in Arabica and Robusta coffees with different roasting profiles and varying degrees of roast

  • Institute of Food Chemistry, Schleinitzstr. 20, D-38106 Braunschweig, Germany

More Information
  • To evaluate mitigation options for both acrylamide and furan and methylfurans a Vietnam Robusta grade 2 and a Brazil Arabica (unwashed) coffee were roasted by tangential, drum and hot air roasting. Three different roasting profiles were followed and three samples (light, medium and dark roast) were obtained per profile. Decaffeinated and steam treated batches of the two coffees were roasted. Special roasts, such as double roast (on 2 days with cooling down in between) or roasting with a sudden temperature change were studied. The contaminants were analyzed by GC-MS – in case of the furans headspace GC-MS – using deuterated standards.
    The acrylamide contents were highest in light roasts, and decreased after that with longer roasting time. This was true for both the Robusta and Arabica samples. The content of furan and 2-, 3- and 2, 5-methylfurans were low in light roasts and had a maximum in dark roasts. It is possible to minimize the content of either acrylamide and furans, however, a mitigation of both could not be established by changing the roasting parameters or using pretreatments. Among the furans determined, 2-methylfuran was most abundant (average around 70%), followed by furan (average around 20%). The special roasts showed no options to minimize both contaminants as did the pretreatments. In Vietnam Robusta, furan related compounds were measured. 5-hydroxymethylfurfural and 5-hydroxymethylfurfuryl-2-carboxylic acid decreased with the degree of roast and time, while furfuryl alcohol and 2-furoic acid content increased.

  • Introduction

    Surimi gel, known as 'concentrated myofibrillar protein'[1], is a kind of gel prepared by processing fish tissue according to fixed steps, such as rinsing, dehydration, and chopping, then adding a certain number of auxiliary materials for crushing, molding, heating and cooling. Salt-soluble myofibrillar protein (mainly myosin) of surimi denatures and unfolds after heating, and then re-crosslinks and polymerizes to form large protein aggregates[2], which is the internal mechanism of forming the gel structure. To enhance the texture and taste of surimi gel products, 2%−3% salt is added to promote the formation of the protein gel network structure and enhance the solubility and functional properties of the products[3,4]. Nonetheless, numerous studies have confirmed that excessive salt intake may result in risks of disease to human health, such as hypertension, and coronary heart disease[5]. Therefore, the development of low-salt surimi products will be widely focused on in future research.

    Recently, two strategies have been innovatively proposed to improve or maintain the gel properties of low-salt surimi products: one is to use exogenous additives or sodium salt substitutes[6−8], and the other is to exploit new processing technologies[9−11]. Glutamine transaminase (TGase) is the most effective surimi quality improver to enhance the functional properties of protein, which could catalyze acyl donors in proteins (γ-Hydroxylamine group) and acyl receptors (lysine residue, primary amine compound, etc.) undergo acyl transfer reaction to form cross-linked structures[12−14]. Previous studies by Jiang et al.[15] revealed that the cross-linking effect of TGase catalysis depends on the content and spatial distribution of available substrates. In addition, lysine, as an ideal exogenous additive, has been widely used in different meat protein gel systems, which can effectively improve the gel properties of low-salt surimi gel[16] and emulsified chicken sausage[17]. Many researchers have spent a lot of time to obtain higher-quality surimi gel products through the combination of two or more exogenous additives. Many scientists devoted themselves to obtaining higher quality surimi gel products through the combination of two or more exogenous additives. For example, Cao et al.[18] demonstrated that lysine (Lys) could bring about the dissociation of actin under the condition of the presence of TGase, promoting the cooking yield and gel properties of oxidative damaged MP. Similar findings reported by Cando et al.[19] indicated that Lys could induce the changes in protein structure, which were favorable terms to heighten the cross-linking effect of TG and improve the strength of surimi gel.

    Recently, the term ε-Poly-lysine (ε-PL) was followed with interest since it's a natural amino acid polymer produced by microbial fermentation, and was speculated that it has a similar molecular structure and potential effect to Lys[20]. ε-PL, which is generally composed of 25−30 lysine residues connected by amide bonds (by ε-Amino and α-Carboxyl group), was often used as an antibacterial agent for the preservation of meat products and aquatic products[21]. Li et al.[21] explored the effect of preservative coating with ε-PL on the quality of sea bass fillets during storage. It turned out that, ε-PL treatment evidently reduced the thiobarbituric acid and volatile base nitrogen values of bass slices during storage, inhibited the growth of microorganisms, and improved the water retention, texture, and flavor characteristics of the fish. A previous study by Cai et al.[20] proved the bacteriostatic and fresh-keeping effect of the composite coating of protein and sodium alginate on Japanese sea bass, and found that the composite coating had an effect on inhibiting the proliferation of sea bass microorganisms (Escherichia coli, lactic acid bacteria, yeast, etc.), fat oxidation, protein degradation, and nucleotide decomposition. As a natural cationic polypeptide, ε-PL has the advantages of no biological toxicity and low viscosity of aqueous solution. It is noteworthy that it can produce strong electrostatic adsorption with negatively charged amino acids[22]. Its effective modification of protein helps it fully interact with gel component molecules and groups[23], which may play a role in enhancing the texture and water retention of protein gel.

    Nevertheless, few reports are based on the addition of ε-PL to explore the influence mechanism on TGase-catalyzed surimi gel properties. The current study sought to shed light on the effects of different additions of ε-PL on TGase-induced cross-linking effect and the performance of composite surimi gel, to provide a theoretical basis and reference for further research and development of 'low salt', efficient and healthy surimi products.

    Materials and methods

    Materials

    Testing materials, including marine surimi, transglutaminase (TG, enzyme activity 100 IU/g), and ε-Polylysine (ε-PL, ≥ 99% purity) were supplied by Jiangsu Yiming Biological Technology Co., Ltd (Jiangsu, China). Egg white protein was purchased from Henan Wanbang Chemical Technology Co., Ltd (Henan, China). All other chemicals were from Shanghai Yuanye Biochemical Co., Ltd (Shanghai, China) and were at least analytical grade. The ingredients of the surimi gel are shown in Table 1.

    Table 1.  Surimi samples with different treatments.
    GroupsSurimi
    (g)    		TGase
    (w/w, %)    		Egg white
    Protein
    (w/w, %)    		ε-PL
    (w/w, %)    		NaCl
    (w/w, %)
    CK300−−−0.5
    TE3000.47.0−0.5
    TE + P13000.47.00.0050.5
    TE + P23000.47.00.010.5
    TE + P33000.47.00.020.5
    TE + P43000.47.00.040.5
    TE + P53000.47.00.060.5
     | Show Table
    DownLoad: CSV

    Preparation of mixed surimi samples

    The prepared block surimi was firstly put into the chopping machine (or tissue masher) and chopped for 2 min, then different mass fractions of ingredients were added, while the chopping time was extended to 5 min (the temperature should be controlled below 10 °C during this process). The exhausted surimi paste was poured into the special mold (50 mm × 20 mm), which was heated in two stages to form the heat-induced surimi gel (40 °C water bath for 40 min; 90 °C water bath for 20 min). Above prepared surimi gel underwent an ice water bath for 30 min and finally stored overnight at 4 °C for further use.

    Rheological characteristics of mixed surimi samples

    Mixed surimi samples with different treatments were determined under a Haake Mars 60 Rheometer (Thermo Fisher Scientific, Germany) with 35 mm stainless steel parallel plates referring to the method described by Cao et al.[18], and each determination was repeated three times. After centrifugation (1,000× g, 3 min) and 4 °C, the degassed surimi sol (~2 g) was equilibrated at 4 °C for 3 min before measurement.

    Apparent viscosity

    The shear stress of the mixed surimi sol was measured at shear rates between 0−100 s−1.

    Dynamic rheological behavior

    The rheological properties of the mixed surimi sols were measured in an oscillatory mode of CD-Auto Strain at 0.02% and 0.1 Hz frequency, respectively. The heating temperature range is set to 20~90 °C while the heating rate is 1 °C·min−1.

    Strength of mixed surimi gels

    The TA-XT Plus physical property analyzer (TA-XT Plus, Stable Micro Systems Ltd, Surrey, UK) was used to analyze the mixed surimi gel strength of each group of samples (n ≥ 3) at room temperature, and the cube-shaped surimi gel samples are measured through the P/0.5 probe. Referring to the method previously described by Fang et al.[24], the test parameters are as follows, pre-test and test rate (1 mm·s−1); rate after measurement (5 mm·s−1); depressing degree (30%); trigger force (5 g); data acquisition rate (400 p/s).

    Textural properties of mixed surimi gels

    Concerning the method of Jirawat et al.[25], texture profile analysis (TPA) was employed to record the hardness, elasticity, cohesion, chewiness, and resilience of mixed surimi gels. It is well known that TPA can explore the textural properties of food through the texture analyzer (TA-XT Plus, Stable Micro Systems Ltd, Surrey, UK) equipped with a P/75 probe to simulate human oral chewing action and obtain the texture characteristic values related to human sensory evaluation. The physical property parameter settings were as follows: downforce (5 g), compression degree (50%), pre-test speed, test speed, and post-test speed (1.0 mm·s−1).

    Cooking loss of mixed surimi gels

    The cooking loss of surimi gel under different treatments was determined referring to the protocol of Dong et al.[26]. The cooked surimi gel sample was instantly absorbed dry and weighed (W5). The cooking loss (CL) is calculated as follows:

    CL(g/100g)=(M1−M2)/M1×100 (1)

    Where M1, weight of the sample before cooking; M2, weight of the sample after cooking.

    Low-field nuclear magnetic resonance (LF-NMR) of mixed surimi gels

    The LF-NMR of the mixed surimi gel was detected by a PQ001-20-025V NMR analyzer (Niumag Analytical Instruments Co., Ltd, Suzhou, China) referring to the previous method conducted by Li et al.[27]. Relevant characteristic parameters were set as follows: sampling frequency (200 KHZ), echo time (0.3 ms), and cumulative number (8). Keeping the surimi gel sample (approximately 2 g) at room temperature for 30 min, they were carefully put into a cylindrical nuclear magnetic tube (15 mm in diameter), and finally, the relaxation time (T2) was recorded using the Carr Purcell Meiboom Gill (CPMG) pulse sequence.

    Color difference of mixed surimi gels

    CM-5 colorimeter (Konica Minolta Sensing, Inc., Tokyo, Japan) was used for surimi gel with different treatments following to the procedure of Wang et al.[28]. Several 1 cm thick slices were cut from surimi samples (n = 3) selected from different treatment groups, and the gel whiteness was calculated according to the following formula:

    Whiteness=100−√(100−L∗)2+a∗2+b∗2 (2)

    Scanning electron microscopy (SEM) of mixed surimi gels

    According to the previously described procedure by Gao et al.[29], the square-shaped surimi gels (4 mm × 4 mm × 4 mm) were immersed in 0.1 mol·L−1 phosphate buffer (pH 7.2) containing 2.5% (v/v) glutaraldehyde for 24 h. The above samples were washed using phosphate buffer (0.1 mol·L−1, pH 7.2) three times and then subsequently dehydrated in a series of alcohol solutions. The microstructures of the mixed surimi gels were imaged using an FEI Verios 460 SEM (FEI Inc., Hillsboro, OR, USA).

    Thiobarbituric acid-reactive substances (TBARS) determination

    The TBARS value was analyzed by the method described by Hu et al.[30] with slight modification. Thiobarbituric acid solution (1.5 mL) and 8.5 mL of trichloroacetic acid solution were added to the sample in turn, the mixture was bathed in water at 100 °C for 30 min. The supernatant was extracted and centrifuged twice (3,000× g, 5 min): (1) The original supernatant (5 mL) was taken and the same amount of chloroform for mixed centrifugation; (2) The second supernatant (3 mL) and petroleum ether (1.5 mL) were taken for mixed centrifugation. Finally, a small amount of lower liquid was taken to determine the absorbance (A532 nm). The final result was expressed in malondialdehyde equivalent (mg·kg−1).

    Statistical analysis

    All statistical analyses of data were investigated by statistical product and service solutions IBM SPSS Statistics version 23.0 (IBM SPSS Inc., Chicago, USA). The LSD all-pairwise multiple comparison method was used for the least significance analysis, and p < 0.05 was considered to indicate significance. The experimental data are expressed as mean ± standard deviation (SD) and plotted using Origin 2019 (Origin Lab, Northampton, MA, USA) software.

    Results and discussion

    Rheological properties of surimi gels

    Steady-state shear properties

    The steady-state shear flow curve can be used to characterize the interaction between proteins. The steady shear flow changes of apparent viscosity (Pa·s) of composite surimi with shear rate (s−1) under different treatments are shown in Fig. 1a. The apparent viscosity of all samples decreased significantly (p < 0.05) with increasing shear rate, exhibiting shear-thinning behavior[31]. In the range of shear rates from 0.1 to 100 s−1, the samples with TGase addition were always higher than the control, indicating that the induction of TGase enhanced the cross-linking of surimi proteins and formed a more stable structure. The surimi samples added with a lower proportion of ε-PL (0.005% and 0.01%) were regarded as lower viscosity fluid (Fig. 1a). The possible reason was that the low concentration of ε-PL provided a weak effect on the pH value of the surimi system. As a consequence, the content of the net charge provided was relatively small and the electrostatic interaction between the surimi proteins was weakened[20].

    Figure 1.  Effect of different treatments on rheological properties of surimi.
    DownLoad: Full-Size Img PowerPoint
    Dynamic elastic properties during gelation

    The elastic modulus (G′) mainly depends on the interaction between protein molecules, which can reflect the change of elasticity in the heat-induced surimi gel. As shown in Fig. 1b, the gel process of surimi in the control group was a thermodynamic process consisting of two typical stages. In the first stage, the value of G' showed a gradual downward trend in the range of 20~50 °C. This is mainly because, (1) the activity of endogenous protease in surimi is increased; (2) the myosin light chain subunits of surimi are dissociated under the action of protease, forming myosin and actin[24]; (3) heat-induced hydrogen bonds break between protein molecules, thus enhancing the fluidity of the gel system[31]. The second stage: From 50 to 73 °C, the G' value increases rapidly. As the temperature continues to rise to 90 °C, the G 'value keeps rising steadily. At this time, the gel network structure gradually became stable and irreversible.

    Compared with several curves in Fig. 1b, TGase treatment could significantly increase the G' value. The change trend of G' value of the samples added with TGase and ε-PL were similar to that of the control group, but the former increased faster and the maximum value of G' was also significantly higher. The temperature corresponding to the first peak of G' gradually decreased (PL1≈PL2 < PL4≈TE < PL3≈PL5 < CK), indicating that the process of protein denaturation and aggregation was advanced. This result showed that the proper amount of ε-PL (0.04%) in combination with TGase can reduce the thermal denaturation temperature of protein-forming gel and improve the forming ability of composite gel, which was unanimous with the changes in texture and properties of surimi gel (Table 2). Furthermore, the addition of a small amount (0.005%) or an excessive amount (0.06%) of ε-PL made the mixed surimi protein system more unstable, affecting the ability of TG-induced gel formation as the last resort[32].

    Table 2.  Effect of different treatments on the textural properties of surimi gels.
    GroupsHardness (g)SpringinessCohesivenessChewiness (g)Resilience
    CK811.40 ± 45.28de0.81 ± 0.01a0.53 ± 0.02b498.36 ± 21.58c0.21 ± 0.01e
    TE1105.80 ± 61.83c0.83 ± 0.01a0.56 ± 0.01b510.40 ± 26.04c0.24 ± 0.00bcd
    TE + P1736.01 ± 18.49e0.80 ± 0.03a0.61 ± 0.00a348.78 ± 18.36d0.23 ± 0.01cde
    TE + P2777.45 ± 39.61de0.80 ± 0.01a0.60 ± 0.02a307.03 ± 12.97e0.22 ± 0.00de
    TE + P3869.66 ± 45.82d0.83 ± 0.02a0.63 ± 0.01a485.06 ± 22.73c0.28 ± 0.00a
    TE + P41492.80 ± 77.13a0.83 ± 0.01a0.60 ± 0.01a721.74 ± 31.55a0.26 ± 0.01ab
    TE + P51314.60 ± 84.10b0.81 ± 0.00a0.60 ± 0.02a652.36 ± 30.24b0.25 ± 0.01bc
    Different lowercase letters in the same column indicated significant differences (p < 0.05).
     | Show Table
    DownLoad: CSV

    Strength of surimi gels

    Gel strength is one of the vital indicators to test the quality of surimi products, which directly affects the texture characteristics and sensory acceptance of the products. The strength of mixed surimi gel with TGase was significantly enhanced by 23.97% (p < 0.05) compared with the control group after heat-inducing. This enhancement is probably caused by the crosslinking promotion of TGase (Fig. 2a). A deeper explanation is that under the catalysis of TGase, the ε-amino group on lysine and the γ-amide group on glutamic acid residues undergo acylation reaction inside or between proteins, forming ε-(γ-Glutamyl)-lysine covalent cross-linking bond which promotes the production of the protein gel network[26].

    Figure 2.  (a) Catalytic reaction of glutamine transaminase and (b) effect of different treatments on gel strength and cooking loss of surimi gel. a−d/A−D: values with different lowercase letters indicate significant difference (p < 0.05).
    DownLoad: Full-Size Img PowerPoint

    On the basis of adding TGase, the strength of the mixed gel with ε-PL concentration ranging from 0.005% to 0.03% was lower than that of TE (Fig. 2b). It was speculated that the surimi sample with low concentration ε-PL was a fluid with lower viscosity, and the interaction between protein and water is strengthened, while the electrostatic interaction between proteins is further weakened[33]. This was also consistent with the change in rheological properties in Fig. 1a. Nevertheless, with the increase of ε-PL content to 0.04%, the gel strength of surimi gel significantly increased and reached the highest value (781.63 g·cm), which was about 21.03% higher than that of the TE group (p < 0.05) (Fig. 2b). The increase of gel strength in this process was obtained due to the following three possible reasons, (1) ε-PL is a cationic amino acid with positive charge, which can improve the pH value of protein or meat product system; (2) The interaction between the ε-amino group of ε-PL and the aromatic residue of protein, namely the cation-π interaction, can change the structure of meat protein[34]; (3) Protein (mixed surimi system) with high ε-amino group content, TGase has strong gel improving ability[35].

    Such synergy (ε-PL = 0.04%), as a comprehensive result of different impactors, is that after the surimi was mixed under the optimal ratio conditions, the synthesis of TGase enzyme catalysis, pH value shift, changes in protein and amino acid composition, etc., increased the strength of various forces, thus forming a denser stereoscopic network structure. Note that when the content of ε-PL reached 0.06%, the gel strength of the corresponding surimi gel decreased by 10% compared with 0.04%. Similarly, others reported the result that alkaline amino acids led to the reduction of the strength of the myosin gel of bighead carp[36].

    Textural properties of surimi gels

    TPA, also known as whole texture, is a comprehensive parameter that determines the sensory quality of surimi gel, including hardness, elasticity, cohesion, chewiness, and resilience[37]. As shown in Table 2, the addition of TGase significantly improved the texture properties of surimi gel (p < 0.05), which is related to TGase's ability to induce surimi protein to form more ε-(γ-Glu)-Lys covalent bond during heating[38] (Fig. 2a). Compared with the cross-linking induced by TGase alone, the gel hardness of the mixed surimi gel treated with ε-PL showed a similar change to the gel strength (Fig. 2b). As the concentration of ε-PL increased from 0.005% to 0.04%, the hardness of surimi gel gradually increased until it reached the maximum (1,492.80 g). At the same time, we also observed that the elasticity, cohesion, and chewiness of the composite gel reached the highest values with the 0.04% ε-PL, and these were higher than those of the TGase-only group. Similar to the findings of Ali et al.[39], the author found that the combination of ε-PL and beetroot extract can effectively replace nitrite, which produced a marked effect in maintaining the color of Frankfurt sausage and improving the texture and performance. However, the data we collated above (Table 2) also showed a clear phenomenon, that is, the addition of ε-PL with lower concentration (0.005%−0.02%) or highest concentration (0.06%) was not conducive to the combination with TGase to improve the texture characteristics of mixed surimi gel.

    Cooking loss of mixed surimi gels

    Cooking loss indicates the water holding capacity of heated surimi, which usually represents the stability of the three-dimensional network structure of surimi gel[40]. The 0.4% TGase significantly reduced the cooking loss of surimi samples (p < 0.05), which was 4.91% lower than that of the control group (Fig. 2b). When the addition of PL (combined with TGase) gradually increased from 0.005% to 0.04%, the cooking loss of surimi showed a decreasing trend and reached the minimum at 0.04%. The ε-PL-added surimi gel samples had higher cooking loss compared with that of only with TGase. Most notably, this may be due to ε-PL is able to further exert the cross-linking effect of TGase. A similar finding was reported in the study by Ma et al.[22], adding ε-PL is able to improve the solubility of myofibrillar proteins. Proteins with high solubility are more easily induced by TGase during heating, which aggravates the cross-linking between ε-PL-protein or protein-protein and forms a disordered gel network structure with relatively weaker water-holding capacity.

    Color of surimi gels

    As shown in Table 3, the high lightness (L*), low yellowness (b*), and high whiteness of surimi in the control group were relatively low, with values of 72.49, 10.42, and 70.56 respectively. After TGase was added to induce cross-linking, these values increased significantly (p < 0.05), which may be related to the photochromic effect of water molecules released from gel matrix under TGase-induced surimi protein cross-linking reported in the previous study[41]. Furthermore, on the basis of adding TGase, it was interesting to see that the L* and whiteness values of surimi gel first increased and then gradually decreased with the increase in ε-PL concentration. The influence of ε-PL combined with TGase on the whiteness of gel can be attributed to three reasons: (1) The addition of ε-PL can effectively increase the substrate content of TGase, and promote the cross-linking between proteins, so as to obtain a much more compact surimi gel structure, which affects the refractive index of light; (2) The water retention performance of the high surimi gel was significantly improved with the addition of ε-PL[42] (Fig. 2b), at this time, the L* value (positively related to the whiteness) value showed a decreasing trend with the decrease of the surface free water content of the gel sample; (3) With the increase of ε-PL concentration, some colored substances, formed due to the accelerated Maillard reaction rate during the preparation of gel, may have an adverse effect on the improvement of gel whiteness[43]. After adding TGase to induce cross-linking, although the whiteness value of composite surimi was significantly enhanced, ε-PL was not enough to further improve the whiteness value of final mixed surimi gel, and high concentration so far as to have a negative impact on the whiteness value.

    Table 3.  Effect of different treatments on the color of surimi gels.
    GroupsL*a*b*Whiteness
    CK72.49 ± 0.82e−0.92 ± 0.01e10.42 ± 0.33d70.56 ± 0.65d
    TE77.82 ± 0.34ab−0.23 ± 0.02c12.29 ± 0.29bc74.64 ± 0.26ab
    TE + P178.39 ± 0.40a−0.14 ± 0.01a12.46 ± 0.12ab75.05 ± 0.41a
    TE + P278.42 ± 0.43a−0.17 ± 0.0b12.46 ± 0.15ab75.07 ± 0.32a
    TE + P377.48 ± 0.16b−0.18 ± 0.02b12.37 ± 0.09abc74.31 ± 0.11b
    TE + P476.34 ± 0.05c−0.22 ± 0.01c12.73 ± 0.02a73.13 ± 0.04c
    TE + P575.48 ± 0.18d−0.26 ± 0.01d12.01 ± 0.14c72.70 ± 0.19c
    Different lowercase letters in the same column indicated significant differences (p < 0.05).
     | Show Table
    DownLoad: CSV

    Changes in moisture distribution of surimi gels

    The water distribution in surimi gel products was measured by LF-NMR[44], and the results were inverted to obtain the transverse relaxation time (T2), which reflects the strength of water fluidity[45]. There are four fitted wave peaks which are assigned to four different water distribution states and wave peak ranges (Fig. 3, Table 4): strong bound water T21 (0.1−1 ms), weak bound water T22 (1−10 ms), non-flowing water T23 (10−100 ms) and free water T24 (100−1,000 ms)[46]. At the same time, similar characteristics (the main peak is centered on T23) are possessed by the water distribution of all surimi gel samples. The addition of TGase increased the proportion of non-flowing water, accompanying the significant decrease in the content of free water (p < 0.05), compared with the control group. It proved that the addition of TGase brought this phenomenon, namely the bound water in surimi gel was partially transferred to the non-flowing, which also indicated the reduction of cooking loss of surimi samples induced by TGase (Fig. 2). On the basis of adding TGase, the low level of ε-PL (0.005%, 0.01% and 0.02%) inhibited the transition of free water in surimi gel to non-flowing water, in which the proportion of T23 decreased by 2.05%, 2.74%, and 1.42% respectively compared with the surimi gel only with TGase, while T24 increased by 15.76%, 14.17%, and 4.43% respectively. The proportion of P23 in the surimi gel sample (ε-PL = 0.04%) was equivalent to that of the TE group, implying that the addition of appropriate ε-PL was not directly connected with the changes in water distribution in surimi after TGase-induced cross-linking, and slight addition would have a negative impact, which was unanimous with the above research results of cooking loss (Fig. 2a).

    Figure 3.  Effect of different treatments on the transverse relaxation time T2 of surimi gel.
    DownLoad: Full-Size Img PowerPoint
    Table 4.  Effect of different treatments on the transverse relaxation time T2 of surimi gel.
    GroupsP21 (%)P22 (%)P23 (%)P24 (%)
    CK2.175 ± 0.186c1.198 ± 0.012e82.863 ± 0.691bc13.764 ± 0.091a
    TE1.938 ± 0.095d2.166 ± 0.043a85.144 ± 1.336a10.752 ± 0.033e
    TE + P12.705 ± 0.067b1.414 ± 0.009d83.435 ± 1.616b12.446 ± 0.105c
    TE + P23.005 ± 0.003a1.845 ± 0.056b82.874 ± 1.739bc12.276 ± 0.108c
    TE + P33.107 ± 0.063a1.715 ± 0.033c83.950 ± 1.587ab11.228 ± 0.086d
    TE + P41.770 ± 0.018d2.099 ± 0.059a85.021 ± 1.756a11.110 ± 0.144d
    TE + P53.121 ± 0.007a1.758 ± 0.107bc82.136 ± 1.091c12.985 ± 0.018b
    Different lowercase letters in the same column indicated significant differences (p < 0.05).
     | Show Table
    DownLoad: CSV

    Scanning electron microscopy of surimi gels

    The effect of different treatment methods on the microstructure of surimi gel was observed by SEM. As shown in Fig. 4, the microstructure of the control surimi gel (Fig. 4a) was observed to be enormously loose, uneven, and irregular, with large pores, which explained the reason why the control surimi gel had low strength and large cooking loss (Fig. 2b). In addition, the morphological properties of another group of surimi gel (TGase-induced) are appreciably different from the scanning electron micrograph mentioned above (Fig. 4b). Numerous compact and evenly distributed small pores were observed, instead of the loose structure in the control sample, which accounted for the fact that TGase could interact with proteins to form a more uniform and orderly three-dimensional network structure in the process of gel formation[47]. Moreover, similar findings were also reported in the previous studies of Dong et al.[26]. When treated with TGase and ε-PL (from 0.05% to 0.04%), the surface of the surimi gel sample gradually became flat through observation (Fig. 4f). We found that some smaller pores were formed and some larger pores were slightly supplemented visually. Remarkably, when the addition of ε-PL increased to 0.06% (Fig. 4g), the structure of surimi gel was not as uniform as before, and some large and irregular holes appeared obviously. This phenomenon might be related to moderate ε-PL, especially 0.02%, which can promote the cross-linking of TGase with protein and the aggregation/denaturation of different components, which agreed with the change of coagulation strength of surimi samples.

    Figure 4.  Effect of different treatments on the microstructure of surimi.
    DownLoad: Full-Size Img PowerPoint

    Thiobarbituric acid-reactive substances (TBARS) determination

    TBARS value, which can reflect the degree of lipid oxidation and rancidity of surimi, is an important indicator for the occurrence of oxidation[48]. Some substances in surimi, such as unsaturated fatty acids, will inevitably undergo oxidative decomposition to produce a large amount of malondialdehyde (MDA), the latter reacts easily with thiobarbituric acid (TBA) reagent to produce red compounds with maximum absorbance at 532 nm. As illustrated in Fig. 5, when TGase and a certain amount of PL (from 0.005% to 0.06%) were added, the TBARs value of surimi gels decreased to 2.03 and 1.67 mg/kg respectively, compared with the control group (2.26 mg/kg). This shows that the addition of both can significantly reduce the TBARS value of surimi gel (p < 0.05), considered to be a cue for the fat oxidation of surimi being inhibited. In addition, we also found that the antioxidant effect of PL was dose-dependent. The ε-PL can be chelated by ferrous ions along with the ability to scavenge free radicals like hydroxyl radicals, ensuring its antioxidant properties[33]. The ε-PL was prospectively considered as an antioxidant additive to prevent surimi protein from deteriorating induced by oxidation[49]. Similarly, making use of lysine or ε-PL as antioxidants in plant protein and meat protein has been widely reported[33, 50]. Fan et al.[42] confirmed that ε-PL addition has a significant effect on maintaining a high total phenolic content and vitamin C levels in fresh lettuce, which also shows that it has certain antioxidant activity.

    Figure 5.  Effect of different treatments on TBARS values of surimi gel. a−f: values with different lowercase letters indicate significant difference (p < 0.05).
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    Conclusions

    The addition of ε-PL at different concentrations had an apparent impact on the characteristics of TGase-induced mixed surimi gel, accompanied by the following situations: The 0.04% ε-PL provided a synergistic effect to promote the aggregation and crosslinking of surimi proteins induced by TGase; The rheology, LF-NMR and SEM results showed that the appropriate concentration (0.04%) of ε-PL apparently enhanced the initial apparent viscosity and elasticity of surimi samples, which was conducive to the formation of a more dense and uniform three-dimensional network structure, further limiting the flow of water in surimi and the exudation of hydrophilic substances; Simultaneously, the network strength was strengthened along with the texture properties of the mixed surimi gel. Furthermore, ε-PL had a strong ability to inhibit lipid oxidation in mixed surimi gel, showing a concentration dependence. When the content of ε-PL ran to lowest (0.005%−0.01%) or highest (0.6%), the improvement of the quality of surimi mixed gel was opposite to the above. The results show that ε-PL can be perceived as a prospective polyfunctional food additive to improve the texture properties, nutritional advantages, and product stability of surimi products.

  • The authors confirm contribution to the paper as follows: study conception and design: Cao Y, Xiong YL, Yuan F, Liang G; data collection: Liang G, Cao Y, Li Z, Liu M; analysis and interpretation of results: Li Z, Cao Y, Liang G, Liu Z, Liu M; draft manuscript preparation: Li Z, Cao Y, Liu ZL. All authors reviewed the results and approved the final version of the manuscript.

  • The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

    • Acknowledgments

    This work was financially supported by the Natural Science Basic Research Program of Shaanxi (No. 2023-JC-YB-146), the fund of Cultivation Project of Double First-Class Disciplines of Food Science and Engineering, Beijing Technology & Business University (No. BTBUKF202215), the Innovation Capability Support Plan of Shaanxi (No. 2023WGZJ-YB-27), the Agricultural Technology Research and Development Project of Xi'an Science and Technology Bureau (No. 22NYYF057), and Jiangsu Yiming Biological Technology Co., Ltd. in China.

  • The authors declare that they have no conflict of interest.

  • Supplemental Table S1 Vietnam Robusta grade 2 – 1st roasting series with tangential or drum roasting.
    Supplemental Table S2 Vietnam Robusta grade 2 first hot air roasting series.
    Supplemental Table S3 Vietnam Robusta grade 2: drum or tangential roasting series with extreme profiles; T1: first partial roast, T2: final roast.
    Supplemental Table S4 Vietnam Robusta grade 2: hot air roasting series with extreme profiles; T1: first partial roast, T2: final roast.
    Supplemental Table S5 Vietnam Robusta pretreated coffees tangential or drum roasting series.
    Supplemental Table S6 Vietnam Robusta grade 2. Pretreated coffees hot air roasting series.
    Supplemental Table S7 Vietnam Robusta grade 2 quenching experiments tangential or drum roasting series.
    Supplemental Table S8 Vietnam Robusta grade 2 quenching experiments hot air roasting series.
    Supplemental Table S9 Brazil Arabica drum and tangential roasting series.
    Supplemental Table S10 Brazil Arabica drum/tangential roasting series with extreme profiles; T1: first partial roast, T2: final r.
    Supplemental Table S11 Brazil Arabica pretreated coffees tangential or drum roasting series.
    Supplemental Table S12 Brazil Arabica drum and tangential roast-Quenching.
    Supplemental Table S13 Kenia Arabica drum and tangential roast series.
    Supplemental Table S14 Summary Brazil Arabica hot air roasting series.
    Supplemental Table S15 Brazil Arabica hot air roasting series alternate profiles.
    Supplemental Table S16 Brazil Arabica hot air roasting of pretreated samples.
    Supplemental Table S17 Brazil Arabica hot air roasting - quenching.
    Supplemental Table S18 Kenia Arabica – hot air roasting.
  • [1]

    International Agency for the Research on cancer. 2016. IARC Monographs evaluate drinking coffee, maté, and very hot beverages. www.iarc.who.int/wp-content/uploads/2018/07/pr244_E.pdf (Assessed on 24.11.2022)
    [2]

    Kettlitz B, Scholz G, Theurillat V, Cselovszky J, Buck NR et al. 2019. Furan and Methylfurans in Foods: An Update on Occurrence, Mitigation, and Risk Assessment. Comprehensive Reviews in Food Science and Food Safety 18(3):738−52

    doi: 10.1111/1541-4337.12433

    CrossRef   Google Scholar

    [3]

    International Agency for the Research on cancer. 2022 IARC Monographs on the identification of carcinogenic risks to humans. https://monographs.iarc.who.int/agents-classified-by-the-iarc/ (Assessed on 21.11.2022)
    [4]

    Andrzejewski D, Roach JAG, Gay ML, Musser SM. 2004. Analysis of coffee for the presence of acrylamide by LC-MS/MS. Journal of Agricultural and Food Chemistry 52(7):1996−2002

    doi: 10.1021/jf0349634

    CrossRef   Google Scholar

    [5]

    Guenther H, Anklam E, Wenzl T, Stadler RH. 2007. Acrylamide in coffee: Review of progress in analysis, formation and level reduction. Food Additives & Contaminants 24:60−70

    doi: 10.1080/02652030701243119

    CrossRef   Google Scholar

    [6]

    Goldmann T, Périsset A, Scanlan F, Stadler RH. 2005. Rapid determination of furan in heated foodstuffs by isotope dilution solid phase micro-extraction-gas chromatography-mass spectrometry (SPME-GC-MS). Analyst 130(6):878−83

    doi: 10.1039/b419270b

    CrossRef   Google Scholar

    [7]

    Peivasteh-Roudsari L, Karami M, Barzegar-Bafrouei R, Samiee S, Karami H, et al. 2022. Toxicity, metabolism, and mitigation strategies of acrylamide: a comprehensive review. International Journal of Environmental Health Research

    doi: 10.1080/09603123.2022.2123907

    CrossRef   Google Scholar

    [8]

    Freisling H, Moskal A, Ferrari P, Nicolas G, Knaze V, et al. 2013. Dietary acrylamide intake of adults in the European Prospective Investigation into Cancer and Nutrition differs greatly according to geographical region. European Journal of Nutrition 52(4):1369−80

    doi: 10.1007/s00394-012-0446-x

    CrossRef   Google Scholar

    [9]

    European Commission. 2017. COMMISSION REGULATION (EU) 2017/2158 establishing mitigation measures and benchmark levels for the reduction of the presence ofacrylamide in food. https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32017R2158&from=DE (Assessed on 24.11.2022)
    [10]

    European Food Safety Authority (EFSA). 2017. Risks for public health related to the presence of furan and methylfurans in food. EFSA Journal 15(10):e05005

    doi: 10.2903/j.efsa.2017.5005

    CrossRef   Google Scholar

    [11]

    Stadler RH, Robert F, Riediker S, Varga N, Davidek T, et al. 2004. In-depth mechanistic study on the formation of acrylamide and other vinylogous compounds by the maillard reaction. Journal of Agricultural and Food Chemistry 52:5550−58

    doi: 10.1021/jf0495486

    CrossRef   Google Scholar

    [12]

    Yaylayan VA, Perez C, Andrzej L, Brien JO. 2005. Mechanistic pathways of formation of acrylamide from different amino acids. In Chemistry and Safety of Acrylamide in Food, eds. Friedman M, Mottram D. Berlin: Springer Science + Business Media. pp. 191 – 203. https://doi.org/10.1007/0-387-24980-X_15
    [13]

    Schouten MA, Tappi S, Romani S. 2020. Acrylamide in coffee: formation and possible mitigation strategies - a review. Critical Reviews in Food Science and Nutrition 60(22):3807−21

    doi: 10.1080/10408398.2019.1708264

    CrossRef   Google Scholar

    [14]

    Perez Locas C, Yaylayan VA. 2004. Origin and mechanistic pathways of formation of the parent furan - A food toxicant. Agricultural and Food Chemistry 52(22):6830−36

    doi: 10.1021/jf0490403

    CrossRef   Google Scholar

    [15]

    Batool Z, Xu D, Zhang X, Li X, Li Y et al. 2021. A review on furan: Formation, analysis, occurrence, carcinogenicity, genotoxicity and reduction methods. Critical Reviews in Food Science and Nutrition 61(3):395−406

    doi: 10.1080/10408398.2020.1734532

    CrossRef   Google Scholar

    [16]

    Kim YJ, Choi J, Lee G, Lee KG. 2021. Analysis of furan and monosaccharides in various coffee beans. Journal of Food Science and Technology 58(3):862−69

    doi: 10.1007/s13197-020-04600-5

    CrossRef   Google Scholar

    [17]

    Delatour T, Huertas-Pérez JF, Dubois M, Theurillat X, Desmarchelier A et al. 2019. Thermal degradation of 2-furoic acid and furfuryl alcohol as pathways in the formation of furan and 2-methylfuran in food. Food Chemistry 303:125406

    doi: 10.1016/j.foodchem.2019.125406

    CrossRef   Google Scholar

    [18]

    Albouchi A, Murkovic M. 2018. Formation kinetics of furfuryl alcohol in a coffee model system. Food Chemistry 243:91−95

    doi: 10.1016/j.foodchem.2017.09.112

    CrossRef   Google Scholar

    [19]

    Zhu M, Long Y, Ma Y, Huang Y, Wan Y et al. 2022. Investigation of thermal contaminants in coffee beans induced by roasting: A kinetic modeling approach. Food Chemistry 378:132063

    doi: 10.1016/j.foodchem.2022.132063

    CrossRef   Google Scholar

    [20]

    Bahar I, Delker U, Engelhardt UH. 2020. Acrylamide, Furan and Methylfurans in Coffees with different degree of roast. Dtsch. Lebensm. Rdschau 116:435−40

    Google Scholar

    [21]

    ISO 18862: 2016. Coffee and coffee products — Determination of acrylamide — Methods using HPLC-MS/MS and GC-MS after derivatization. https://www.iso.org/standard/63615.html

    [22]

    Beuth publishing DIN . Food Analysis - Determination of furan in coffee and coffee products by headspace gas chromatography and mass spectrometry (HS GC-MS); German version EN 16620: 2015. https://dx.doi.org/10.31030/2249125
    [23]

    Salamon K, 2014. Furan-Gehalt in Abhängigkeit von Provenienzen, Vorbehandlungsverfahren und Röstparametern. Master-Thesis. Technische Hochschule Ostwestfalen-Lippe, Germany (in German)
    [24]

    Bahar I. 2022. Untersuchungen zum Vorkommen von Acrylamid, Furan und Furanderivaten in Vietnam Robusta Röstkaffee. Thesis. Technische Universität Braunschweig, Germany. (in German)
    [25]

    Delker U. 2022. Untersuchungen von Prozesskontaminanten und Chlorogensäuren in Arabica Röstkaffee. Thesis. Technische Universität Braunschweig, Germany. (in German)
    [26]

    Guenther H, Hoenicke K, Biesterveld S, Gerhard-Rieben E, Lantz I. 2010. Furan in coffee: Pilot studies on formation during roasting and losses during production steps and consumer handling. Food Additives & Contaminants 27(3):283−90

    doi: 10.1080/19440040903317505

    CrossRef   Google Scholar

    [27]

    Fromberg A, Mariotti MS, Pedreschi, F, Fagt S, Granby K. 2014. Furan and alkylated furans in heat processed food, including home cooked products. Czech Journal of Food Sciences 32(5):443−48

    doi: 10.17221/341/2013-CJFS

    CrossRef   Google Scholar

    [28]

    Albouchi A, Murkovic M. 2019. LC method for the direct and simultaneous determination of four major furan derivatives in coffee grounds and brews. Journal of Separation Science 42(9):1695−701

    doi: 10.1002/jssc.201900061

    CrossRef   Google Scholar

    [29]

    Bertuzzi T, Martinelli E, Mulazzi A, Rastelli S. 2020. Acrylamide determination during an industrial roasting process of coffee and the influence of asparagine and low molecular weight sugars. Food Chemistry 303:125372

    doi: 10.1016/j.foodchem.2019.125372

    CrossRef   Google Scholar

    [30]

    Esposito F, Fasano E, De Vivo A, Velotto S, Sarghini F, et al. 2020. Processing effects on acrylamide content in roasted coffee production. Food Chemistry 319:126550

    doi: 10.1016/j.foodchem.2020.126550

    CrossRef   Google Scholar

    [31]

    Cao P, Zhang L, Yang Y, Wang X, Liu Z, et al. 2022. Analysis of furan and its major furan derivatives in coffee products on the Chinese market using HS-GC-MS and the estimated exposure of the Chinese population. Food Chemistry 387:132823

    doi: 10.1016/j.foodchem.2022.132823

    CrossRef   Google Scholar

    [32]

    Alsafra Z, Scholl G, De Meulenaer B, Eppe G, Saegerman C. 2022. Hazard ratio and hazard index as preliminary estimators associated to the presence of furans and alkylfurans in belgian foodstuffs. Foods 11(16):2453

    doi: 10.3390/foods11162453

    CrossRef   Google Scholar

    [33]

    Rahn A, Yeretzian C. 2019. Impact of consumer behavior on furan and furan-derivative exposure during coffee consumption: A comparison between brewing methods and drinking preferences. Food Chemistry 272:514−22

    doi: 10.1016/j.foodchem.2018.08.078

    CrossRef   Google Scholar

    [34]

    Altaki MS, Santos FJ, Galceran MT. 2011. Occurrence of furan in coffee from Spanish market: Contribution of brewing and roasting. Food Chemistry 126(4):1527−32

    doi: 10.1016/j.foodchem.2010.11.134

    CrossRef   Google Scholar

    [35]

    Han JW, Boo H, Chung MS. 2020. Effects of extraction conditions on acrylamide/furan content, antioxidant activity, and sensory properties of cold brew coffee. Food Science and Biotechnology 29(8):1071−80

    doi: 10.1007/s10068-020-00747-1

    CrossRef   Google Scholar

    [36]

    Waizenegger J, Winkler G, Kuballa T, Ruge W, Kersting M et al. 2012. Analysis and risk assessment of furan in coffee products targeted to adolescents. Food Additives & Contaminants 29(1):19−28

    doi: 10.1080/19440049.2011.617012

    CrossRef   Google Scholar

    [37]

    Corrêa CLO, das Merces Penha E, dos Anjos MR, Pacheco S, Freitas-Silva O, et al. 2021. Use of asparaginase for acrylamide mitigation in coffee and its influence on the content of caffeine, chlorogenic acid, and caffeic acid. Food Chemistry 338:128045

    doi: 10.1016/j.foodchem.2020.128045

    CrossRef   Google Scholar

    [38]

    Albouchi A, Murkovic M. 2020. Investigation on the mitigation effects of furfuryl alcohol and 5-hydroxymethylfurfural and their carboxylic acid derivatives in coffee and coffee-related model systems. Food Research International 137:109444

    doi: 10.1016/j.foodres.2020.109444

    CrossRef   Google Scholar

  • Cite this article

    Engelhardt UH, Bahar I, Delker U. 2023. Food borne toxicants in coffee: Acrylamide and furan derivative content in Arabica and Robusta coffees with different roasting profiles and varying degrees of roast. Beverage Plant Research 3:8 doi: 10.48130/BPR-2023-0008
    Engelhardt UH, Bahar I, Delker U. 2023. Food borne toxicants in coffee: Acrylamide and furan derivative content in Arabica and Robusta coffees with different roasting profiles and varying degrees of roast. Beverage Plant Research 3:8 doi: 10.48130/BPR-2023-0008
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Food borne toxicants in coffee: Acrylamide and furan derivative content in Arabica and Robusta coffees with different roasting profiles and varying degrees of roast

  • Institute of Food Chemistry, Schleinitzstr. 20, D-38106 Braunschweig, Germany

  • Received: 08 January 2023
  • Revised: 05 February 2023
  • Accepted: 09 February 2023
  • Published online: 03 April 2023
Beverage Plant Research  3,  Article number: 8  (2023)  |  Cite this article

Abstract: 

To evaluate mitigation options for both acrylamide and furan and methylfurans a Vietnam Robusta grade 2 and a Brazil Arabica (unwashed) coffee were roasted by tangential, drum and hot air roasting. Three different roasting profiles were followed and three samples (light, medium and dark roast) were obtained per profile. Decaffeinated and steam treated batches of the two coffees were roasted. Special roasts, such as double roast (on 2 days with cooling down in between) or roasting with a sudden temperature change were studied. The contaminants were analyzed by GC-MS – in case of the furans headspace GC-MS – using deuterated standards.
The acrylamide contents were highest in light roasts, and decreased after that with longer roasting time. This was true for both the Robusta and Arabica samples. The content of furan and 2-, 3- and 2, 5-methylfurans were low in light roasts and had a maximum in dark roasts. It is possible to minimize the content of either acrylamide and furans, however, a mitigation of both could not be established by changing the roasting parameters or using pretreatments. Among the furans determined, 2-methylfuran was most abundant (average around 70%), followed by furan (average around 20%). The special roasts showed no options to minimize both contaminants as did the pretreatments. In Vietnam Robusta, furan related compounds were measured. 5-hydroxymethylfurfural and 5-hydroxymethylfurfuryl-2-carboxylic acid decreased with the degree of roast and time, while furfuryl alcohol and 2-furoic acid content increased.

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    INTRODUCTION

    • Coffee is one of the most widely consumed beverages worldwide. The average consumption varies from country to country as does the type of coffee and the style of consumption, as well as the brewing procedures. In the last decade, coffee beverages with higher amounts of milk, like latte macciato or cappuccino, became more popular. The brewing techniques include the classical manual or machine brewing with paper or gold filter, French press, fully automated machines, capsule machines or espresso machines with portafilter. The degree of roast determines the sensory characteristics to a certain degree. Light and medium roasted types are popular in some countries as are coffee crema or espresso type coffees e.g. in some Mediterranean countries.

      Coffee contains antioxidants (chlorogenic acids) which are believed to be beneficial to human health and also process contaminants due to the thermal treatment. Coffee consumption in 2016 was re-evaluated by the IARC (international agency for research on cancer) and judged as 'not classifiable as to its carcinogenicity to humans (Group 3)'. An earlier classification from 1991 was that coffee drinking is probably carcinogenic to humans[1].

      Both acrylamide and furan/methylfurans are in the group of food borne toxicants, also named process contaminants or food processing contaminants[2]. Acrylamide is classified by the IARC as probably carcinogen to humans (group 2A), while furan is in group 2B (possibly carcinogenic to humans)[3]. The occurrence of acrylamide and furan in coffee has beeni known for a number of years[4−6]. Coffee is one of the major sources of acrylamide intake, depending on the country[7]. This was also shown in a greater detail for European countries and regions, where it was also found that coffee, together with bread, was the major contributor of acrylamide[8]. Within the European Union a benchmark value of 400 µg/kg applies for roasted coffee[9] while there is currently no limit for furan itself and methylfurans. The EFSA made a call for data on methylfurans in foods including coffee and published statements on the risks of furan and methylfurans in foods[10]. Acrylamide is generated by the Maillard reaction during roasting. Figure 1 shows the possible formation pathways of acrylamide[11,12].

      Figure 1. 

      Possible formation pathways of acrylamide according to the literature[11,12].

      The precursors are amino acids, foremost asparagine, however, there are further pathways of formation. Mitigation strategies for acrylamide have been reviewed recently[13].

      In Fig. 2 the formation of furan is shown according to the literature[14, 15]. Data for methyl furanes concentrations in coffee are more scarce as the latter, even in more recent studies, are not determined and only data for furan are provided[16]. In model systems a formation of 2-methylfuran by the degradation of furfuryl alcohol was found[17].

      Figure 2. 

      Possible formation pathways of furan.

      Other process contaminants, such as furfuryl alcohol are currently not in focus, however, their formation has been studied[18, 19].

      The aim of this study was to evaluate mitigation options for both acrylamide and furan/methylfurans by varying the roasting parameters, including special procedures. As the roasting was the focus of the work, two green coffees were selected for the experiments including pretreatments such as decaffeination. The extraction of the contaminants under different conditions using various techniques are not included in the study.

      Preliminary results of the projects have been published in our previous study[20].

    MATERIALS AND METHODS

      Coffee

    • A Vietnam Robusta grade 2 and an unwashed Brazil Arabica were used as the starting material. Different production areas and treatments can give rise to a variation of coffee constituents and consequently also the formation of food born toxicants. This was not the subject of our study. For some experiments a Kenya Arabica speciality coffee was analyzed. The coffees were roasted on a smaller scale (1 kg and 4 kg) in two different industry plants using drum and tangential roasting or hot air roasting devices. Tangential roasts were used for short roasting times as the drum roaster was not capable to work with shorter roasting times.

      This approach was to ensure the possibility of a scale-up because using roasting on the lab scale will not allow this. To understand the influence of decaffeination, the samples were also decaffeinated using dichloromethane and some samples with water in an industrial plant. Another treatment analyzed was steam treatment, which is also carried out industrially. The following parameters were employed:

      Reference roast

    • The coffees were roasted according to three different profiles[20]. Briefly, profile 1 includes a linear temperature increase, while roasting profile 2 the temperature is higher in the early phase of roast. Profile 3 is characterized by a small increase of the temperature in the beginning and a fast increase at the end. Figure 3 shows the different profiles.

      Figure 3. 

      The roasting profiles of the first series[[20]].

      The coffees were roasted to a light, medium and dark roast by varying the roasting time (5, 10, 15 and 20 min) within the individual profiles. The roasts were characterized by evaluating the color by measuring the light reflectance on two different devices (see below). Overall in the first roasting series, 72 samples of Brazil Arabica and 71 Vietnam Robusta samples were produced from each green coffee.

      Double roast

    • The coffees were roasted on day 1 until 150 °C according to the corresponding roasting profile and completely cooled down (ambient air). On the next day the samples were roasted to the final degree of roast according to the profiles.

      Roasting with sudden temperature change

    • Within the capabilities of the roasters a more rapid rise of the temperature compared to the normal profiles was employed.

      Decaffeination

    • Both coffees were decaffeinated in an industrial plant using dichloromethane and roasted according to all three profiles. For the Robusta samples, a water decaffeination was also employed in an industrial plant .

      Steam treatment

    • Steam treatments are used to remove coffee wax. This treatment is believed to improve the tolerability of coffee even in sensitive subjects. The steam treatment was also carried out under typical industrial conditions (NKG Kala, Hamburg, Germany).

      Color measurements of ground coffee to determine the degree of roast

    • The ground samples were characterized using a Colorette 4 (reflected light is measured). Data are given as Colorette scale units (0–200 / 0 = dark; 200 = light), also the L* a* b*- color data have been recorded. For some samples, the roasting loss/organic roasting loss was determined gravimetrically.

      Chemicals

    • The solvents were of HPLC or MS grade, gases and all reagents used were of analytical grade. Acrylamide was obtained from VWR Int. S.A.S. (Darmstadt, Germany). Acrylamide-d3, sodium tetraborate decahydrate, sodium thiosulfate pentahydrate, triethylamine, hydrobromic acid, furan (99%), furan-d4 (≥ 99.9%), 2-methylfuran (99.1%), 3-methylfuran (99.1%), 2,5-dimethylfuran (99%) were supplied by Sigma Aldrich (Steinheim, Germany). 2,5-dimethylfuran-d3 (≥ 95%), 2-methylfuran-d3 (≥ 95%) and 3-methylfuran-d3 (≥ 95%) were supplied by Toronto Research Chemicals (Toronto, Canada). Bromine and methanol were purchased from Merck KGaA (Darmstadt, Germany). Other chemicals came from Carl Roth (Karlsruhe, Germany).

      Sample preparation for acrylamide determination

    • The coffee samples were stored at –18 °C to avoid losses of acrylamide, furan and methylfurans as initial experiments had shown a degradation of acrylamide during storage at ambient temperature (see also below). DIN EN ISO 18862 was used for the quantification of acrylamide by GC-MS/MS after derivatization[21]. Briefly, the coffee beans were ground in a mill with nitrogen cooling. To the homogenized sample (2 g) 100 µL acrylamid-d3 standard solution (c = 10 µg/L), 2 ml n-hexane and 20 ml deionized water was added to a 50 ml centrifuge tube and extracted in an ultrasonic bath at 40 °C for 15 min. After that, the tube was centrifuged (4,000 rpm). Ten ml of the aqueous phase was taken in a 15 ml centrifuge tube, and 1 ml carrez I and 1 ml carrez II solution were added, followed by mixing and centrifugation at 4,000 rpm for 4 min. The supernatant was purified by SPE (using a Chromabond ABC18 SPE, Machery-Nagel, Düren, Germany). The residue was washed with 3 ml deionized water, centrifuged and again purified by SPE. For quantification an external calibration plot was used with stable isotope dilution analysis (SIDA). Concentrations were 0.0025–0.1 µg/L.

      Sample preparation for the determination of furan and methylfurans

    • The method is based on a German standard method for furan[22] and a thesis on the determination of methylfurans[23]. Briefly, the samples were ground in a mill with nitrogen cooling and 1 g of the homogenized sample was added to a 20 ml headspace vial (baked out before use) and overlaid with 9 ml of water. Under the surface, 40 µl of the deuterated standards solution was added using a syringe. After that the headspace vial was sealed with a gastight cap and measured by HS-GC-MS. The concentrations used were as follows:

      Furan 50–2,000 µg/L; furan-d4 400 µg/L; 2-methylfuran 100–4,000 µg/L, 2-methylfuran-d3 500 µg/L; 3-methylfuran 10–400 µg/L, 3-methylfuran-d3 80 µg/L; 2,5-dimethylfuran 10–400 µg/L, 2,5-dimethylfuran 80 µg/L.

      GC-MS: (used for both acrylamide and furans determination) (Table 1) :

      Table 1.  GC-MS settings for both acrylamide and furans determination.

      GCTrace 1300 GC (Thermo Fisher Scientific, Dreieich, Germany)
      PTV modeCT split
      Inlet temperature240 °C
      ColumnVF-WAXms, 30 m, ID 0.25 mm, 0.25 μm (Agilent J & W Columns, Waldbronn, Germany)
      CarrierHelium 5.0
      Mass spectrometerTSQ DUO (Thermo Fisher Scientific, Dreieich, Germany)
      Data processingThermo TraceFinder GC 3.2, Thermo Xcalibur 3.0 (Thermo Fisher Scientific, Dreieich, Germany)
      Ionisation modeEI+, 70 eV
      MS transfer line/ion source temperature250 °C
      Collision gasArgon
      ModeSRM (acrylamide) and SIM (furans)
      AutosamplerAcrylamide: TRIPLUS RSH with 10 μl Syringe,
      57 mm (Thermo Fisher Scientific, Dreieich, Germany)
      Furans: TRIPLUS RSH, Temperature
      70 °C, with 5 mL syringe, 65 mm; (Thermo Fisher Scientific, Dreieich, Germany)
      Split flow12.0 ml/min (acrylamide) and splitless (furans)
      Flow1.2 ml/min (acrylamide) and 1.0 mL/min (furans)
      Carrier modeConstant flow

      Ions used for identification and quantification of acrylamide[24] (Table 2):

      Table 2.  Ions used for the identification and quantification of acrylamide.

      2-BromopropenamideIdentification + quantification: m/z 149 [C3H479BrON]+
      → 106 [C2H379Br]+ (identification)
      D2-BromopropenamideIdentification and quantification: m/z 153 [C32H21H381BrON]+
      → 110 [C22H21H181Br]+ (identification)

      Ions used for identification and quantification of furans[25] (Table 3):

      Table 3.  Ions used for the identification and quantification of furans.

      AnalyteIons [m/z]
      Furan68 [C4H4O]+ (identification and quantification)
      2-methylfuran/
      3-methylfuran      		82 [C5H6O]+ (identification and quantification)
      81 (identification)
      2,5-dimethylfuran95 [C6H7O]+ (identification and quantification)
      96 (identification)
      D4-furan72 [C4D4O]+ (identification and quantification)
      D3-2-methylfuran/
      D3-3-methylfuran      		85 [C5H3D3O]+ (identification and quantification)
      84 (identification)
      D3-2,5-dimethylfuran98 [C6H4D3O]+ (identification and quantification)
      99 (identification)

      Statistical analysis

    • Principal Component Analysis was used to evaluate the possible correlations between the concentrations of process contaminants and roasting parameters. The results are not presented in detail here but can be withdrawn from Bahar and Delker[24, 25].

      All samples were evaluated by a sensory panel (in-house, 10 panelists) to check whether or not the samples are within consumer's expectation. As there were no deviations the results are not given here[24, 25].

    RESULTS

    • The first roasting series showed, that acrylamide was highest in the light roasted samples, and decreased after that. This is true for both Arabica and Robusta samples and also for the different roasting technologies (tangential, drum and hot air roasting). As an example, Fig. 4 gives data for a Brazil Arabica after tangential or drum roasting. The sum of the furans detected was higher the darker the roasts and the longer the roasting time. This is inline with other studies[26].

      Figure 4. 

      Acrylamide and furan content of Brazil Arabica (drum roast – medium and dark).

      Another finding of this series was that in the furan fraction, 2-methylfuran was always the most abundant compound. This is also in line with the most recent literature[27]. Furan was higher in light roasts compared to the dark roasts while the opposite was true for 2-methylfuran. This might be due to the higher volatility of furan.

      The overall concentrations of the sum of furans in the Arabica samples were in light roasts in the order of magnitude of 10.000 µg/kg and as high as 40.000 µg/kg in longer and/or darker roasted samples.

      The bottom line is that the opposite behavior of the formation of acrylamide and the furans was confirmed by this roasting series. The roasting time and the profile do affect the concentration of process contaminants. All data used in the current studies[24,25] can be found in Supplemental Tables S1−S18. The individual data of the first roasting series can be found in Supplemental Tables S1 (drum roasting Vietnam Robusta), S2 (hot air roasting Vietnam Robusta), S8 (drum roasting Brazil Arabica) and S9 (hot air roasting Brazil Arabica).

      Based on that findings a number of treatments were employed to achieve a reduction of process contaminants.

      All individual results can be found in the electronic supplementary material.

      Double roasts

    • After the first roasting series, special roasts were evaluated, firstly double roasting/DR). Selected profiles from series 1 were tested. Figure 5 shows the content of Brazil Arabica in comparison. As can be seen for tangential and drum roasting, in light roasts the concentration of acrylamide is reduced up to 36%, while this trend was not true in dark roasts. In the 5 min DR sample (not shown in Fig. 5) the content is higher compared to the reference. This is probably due to the use of a tangential roaster. As regards the furans, no decrease but a trend to an increase is observed. Furhter details can be drawn from Fig. 5 in that acrylamide is high after the first roast/day 1 while the 2nd roast yields a degradation.

      Figure 5. 

      Comparison of acrylamide content of Brazil Arabica after day 1 and 2.

      Data for furans are not shown here as on the first day maximum temperature was 150 °C and under these conditions no formation is expected (below detection limits).

      Hot air roasting

    • Similar trends are found here. The furans are higher in dark roasts (48%−192%), in medium roast the increase is smaller (6%−35%).

      The same trend was observed with the Vietnam Robusta samples in the tangential and drum roasts. An acrylamide reduction by double roasts seems to be possible, while no reduction of furans was observed. The hot air roasted samples did not show a significant acrylamide reduction.

      Roasting with sudden change of temperature

    • For these samples, the tangential roaster was used as the drum roaster could not realize such rapid temperature changes. In Brazil Arabica, acrylamide is reduced in the samples between 22% and 76%. The furans are higher compared to the reference. Both results are in line with the assumption that higher temperatures accelerate the degradation of acrylamide and the formation of furans. Similar results are true for hot air roasts. It is worth mentioning that the medium and dark 5 min samples have much higher (88% and 102%) compared to the reference. This can at least in part be explained by the different color (lighter) which means a lower degradation of acrylamide.

      It was shown for the Vietnam Robusta that smaller changes of temperature resulted in a decrease of acrylamide degradation. The content was higher in coffees which were initially roasted with lower and later with higher thermal energy.

      The special roasting profiles are consequently no option for the simultaneous mitigation of the process contaminants.

      Dichloromethane decaffeinated samples

    • In drum roasted Brazil Arabica samples, acrylamide is higher. This might be in part due to a higher asparagine concentration in the decaffeinated sample. This is in principle also true for the hot air roasted samples. The possible reasons and the comparison to literature data can be found in the discussion.

      The content of asparagine was higher in decaffeinated green Vietnam Robusta coffee (781 vs 652 mg/kg). Again, in decaffeinated samples, acrylamide was higher in both tangential, drum and hot air roasted samples. With the exception of the short light roasted coffees, furans are higher in caffeine –containing (caf) samples.

      Water decaffeinated samples

    • Only water decaffeinated Vietnam Robusta samples were available. Acrylamide was often higher in decaffeinated (decaf) samples, while furans were higher in caffeine-containing (caf) samples. This is shown in Fig. 6 for the Vietnam Robusta. This might be due to a possible loss of precursors during the decaffeination. The water decaffeinated green coffee had 37 µg/kg acrylamide. The decaffeinated coffee was darker: slightly different roasting conditions are possible as the endpoint of roasting was determined by the color.

      Figure 6. 

      Water decaffeinated samples vs non decaffeinated samples.

      A more comprehensive study on the food borne toxicants with a wider variety of coffees is underway and will be published in due course.

      Steam treated coffees

    • The samples were treated in an industrial plant at elevated temperature and pressure. Details of the process are not available. As can be seen from Fig. 7, the color of the untreated and treated coffee is different. This certainly affects the results as the roasting is controlled by the color. Consequently, the treated samples are roasted with less thermal energy than the reference samples (see the discussion).

      Figure 7. 

      Steam treated unroasted sample (left), and untreated sample (right).

      Drum roasted Brazil Arabica samples had a lower content of acrylamide, which was more significant in light roasted samples (6%–30% less) compared to dark roasts (max 17%). The furan content is slightly lower, only in the dark roast profile 1/10 mins is it slightly lower. Hot air roasting also gave a tendency to lower acrylamide concentrations, with the exception of light roast profile 1/10 mins, where the concentration was significantly higher. Furans are also lower, foremost in light roasts, while in dark roasts the reduction is not significant.

      The steam treated Vietnam Robusta unroasted sample had already an acrylamide content of 73 µg/kg. Acrylamide content was higher in tangential and drum roasted untreated coffees (111–403 µg/kg) compared to treated (113–319 µg/kg). The hot air roasted samples did not show this trend. Furans were higher in untreated coffees (tangential and drum 10,608–43,714 µg/kg; hot air: 15,201–49,688µg/kg) compared to treated samples (tangential and drum 1,709–33,266 µg/kg; hot air: 3,671–20,907 µg/kg). Interestingly, the proportion of furan is higher in the steamed samples while 2-methylfuran is lower.

      Quenching vs air cooling

    • Quenching means a fast cooling down of the coffee after roasting using water. It is also used to adjust the desired moisture in the final product. A comparison was made between air cooling and quenching with respect to the process contaminants.

      The acrylamide content of Brazil Arabica samples correlates with the moisture content, while Furan/methylfurans did not show a trend.

      Quenching led to higher content of acrylamide in Vietnam Robusta, e.g. a volume of 250 ml yielded 543 µg/kg in the light roast sample compared to 371 µg/kg in the air cooled sample. The furan content was slightly lower in the water cooled samples. Dark roasted coffees did not show significant content, with the exception of the 800 ml sample. The reason for that is not known.

      Other furan related compounds were also determined by a HPLC-DAD method adapted from the literature[28]. 5-hydroxymethylfurfural and 5-hydroxymethylfurfuryl-2-carboxylic acid decreased with the degree of roast and time, while furfuryl alcohol and 2-furoic acid content increased. The results are only available for the Vietnam Robusta and more detail can be found in Supplemental Tables S1−S8.

    DISCUSSION

    • The overall conclusion from the data in this study is the confirmation that a simultaneous mitigation of acrylamide and furan/methyl furans by varying the roasting parameters is not possible. This proved to be true for both the analyzed Brazil Arabica and Vietnam Robusta samples. For lower content of acrylamide. darker and longer roasts can be recommended. On the other hand, the characteristics of the coffee will be completely changed and most consumers will not accept that due to lower acrylamide content resulting in only dark roasted (espresso type) coffees on the market. Moreover, furans will be higher in darker roasts. For the time being, guiding values only apply for acrylamide while no such limits exist for furan. However, it is not unlikely that this might change in the future.

      In the literature for acrylamide, similar formation kinetics compared to this study were described[29]. Under the conditions used the maximum value of acrylamide was reached after 10 min. After that a degradation took place[29]. Another study tried to optimize the roasting conditions and a decrease in acrylamide content was achieved[30].

      In Chinese coffee products, levels of furan were n.d. –6,569 μg/kg and 2-methylfuran 2–29,639 μg/kg[31], which is comparable to the results of this study with respect to both the order of magnitude or the furan concentration and the proportions of the individual furans. In a study from Belgium, it was also stated that coffee and coffee products were relevant contributors to the overall intake and that the ratio of 2-methylfuran/furan was 3.71 in average, which is in tune with the findings of the present study[32].

      The extraction procedures and techniques are relevant in case of the furans, however, it was not included in this study. It was shown that coffees brewed with a fully automatic machine had the highest levels of furan and furan derivative concentrations (9,905 µg/L furan, 263.91 µg/L 2-methylfuran, 13.15 µg/L 3-methylfuran and 8.44 µg/L 2,5-dimethylfuran) while instant coffee had neglectable concentrations only[33]. Another study stated that furan concentrations in ground coffee brews from an espresso machine were higher (43–146 µg/L) compared to brews from a home drip coffee maker (20 and 78 µg/L). The furan level from decaffeinated coffee (14–65 µg/L) were similar to the brews from a home drip coffee maker[34].

      Studies are also available for the extraction efficiency of acrylamide and furan in coffees, e.g. cold brews[35]. It was shown that the temperature (here 5–20 °C) and time (5 min – 24 h) had a strong influence on the content of the process contaminants.

      A risk assessment for coffee and coffee related products for adolescents indicated that for some of the products health problems might occur due to the fact that the MOE was below 10.000[36]. Methyl furans were not included in that research.

      Studies on a asparaginase treatment of coffee indicate that a reduction of acrylamide is possible without relevant changes of other constituents[37].

      It was shown in a model study that mitigation options for HMF and other furan related compounds could not be transferred from the model to the coffee[38].

    CONCLUSIONS

    • It can be finally concluded that Arabica and Robusta samples behaved similar to each other. The acrylamide content was negligible in green coffee and increased rapidly in the early stage with a maximum in light roast. After that, the acrylamide content decreased with increasing degree of roast. Furan and methylfurans content increased during roasting and was highest in dark roasted coffees.

      It can be concluded that mitigation options are available for acrylamide or furan/methylfurans, however, a simultaneous mitigation seems to not be possible. This has to be taken in account if limits or guiding values are be set in the future.

      Acknowledgments

      • This IGF project (AIF 200049 N) is supported via AIF within the program for promoting the Industrial Collective Research (IGF) of the German Ministry of Economics and Energy (BMWi), bases on a resolution of the German Parliament. We thank all members of the project accompanying committee for their support. Special thanks are due to Coffein Compagnie for delivering the coffee and decaffeination and also to NKG Kala for delivering the steam treated samples. The support of Probat Werke and Neuhaus Neotec is gratefully acknowledged.

      Conflict of interest

      • The authors declare that they have no conflict of interest.

      Supplementary information
      Rights and permissions
      • Copyright: © 2023 by the author(s). Published by Maximum Academic Press, Fayetteville, GA. This article is an open access article distributed under Creative Commons Attribution License (CC BY 4.0), visit https://creativecommons.org/licenses/by/4.0/.
    Figure (7)  Table (3) References (38)
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    Engelhardt UH, Bahar I, Delker U. 2023. Food borne toxicants in coffee: Acrylamide and furan derivative content in Arabica and Robusta coffees with different roasting profiles and varying degrees of roast. Beverage Plant Research 3:8 doi: 10.48130/BPR-2023-0008
    Engelhardt UH, Bahar I, Delker U. 2023. Food borne toxicants in coffee: Acrylamide and furan derivative content in Arabica and Robusta coffees with different roasting profiles and varying degrees of roast. Beverage Plant Research 3:8 doi: 10.48130/BPR-2023-0008
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  • Introduction
  • Materials and methods

  • Coffee

  • Reference roast

  • Double roast

  • Roasting with sudden temperature change

  • Decaffeination

  • Steam treatment

  • Color measurements of ground coffee to determine the degree of roast

  • Chemicals

  • Sample preparation for acrylamide determination

  • Sample preparation for the determination of furan and methylfurans

  • Statistical analysis

  • Results

  • Double roasts

  • Hot air roasting

  • Roasting with sudden change of temperature

  • Dichloromethane decaffeinated samples

  • Water decaffeinated samples

  • Steam treated coffees

  • Quenching vs air cooling

  • Discussion
  • Conclusions
  • Acknowledgments
  • Conflict of interest
  • Supplementary information
  • Rights and permissions
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