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Doses of aminoethoxyvinylglycine (AVG) in tomato postharvest storage

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  • Tomatoes are one of the main vegetables found daily in world cuisine and are highly perishable. The aim of this study was to evaluate the quality of 'Débora' tomato fruits over the post-harvest period in refrigerated storage, after immersion in solutions with different concentrations of aminoethoxyvinylglycine (AVG). The experimental design was entirely randomized in a 4 × 5 double factorial scheme, with four treatments, AVG doses 0 (control), 500, 1,000, and 1,500 mg·L−1, and five days of evaluation during the 28 d of refrigerated storage (days 0, 7, 14, 21 and 28) with three replications. Physicochemical analyses were carried out on weight loss, respiration rate, firmness, hydrogen potential (pH), soluble solids, titratable acidity and external and internal fruit color parameters, luminosity, chroma, and °hue. Two-way ANOVA, Tukey's mean test (p < 0.05), and multivariate statistical analysis by principal components (PCA) were carried out. The PCA allowed us to infer that, as weight loss increased, firmness decreased, an effect that was minimized with AVG at a dose of 1,500 mg·L−1, which may be related to the inhibition of the fruit's ethylene production rate. AVG delayed the post-harvest ripening of tomato fruit, reduced the respiration rate of the fruit, and the changes in external and internal chroma. The doses of AVG did not affect the luminosity and pH of the fruit pulp.
  • Hypertension refers to a long-term elevated blood pressure that mainly results from either nonspecific lifestyle change, genetic factors, or an identifiable cause[1,2]. Hypertension is a common chronic medical problem worldwide and has been confirmed as a leading factor in the cause of cardiovascular mortality[35]. Globally, 17 million people die annually due to cardiovascular disease, which is nearly a third of all deaths. Annually, hypertension has been linked to an estimated 9.4 million fatalities worldwide. It is believed to have caused at least 45% of coronary heart disease deaths and the majority of stroke deaths (51%)[6]. Hypertension has also been reported as a major risk factor for many other chronic diseases, such as vision loss, chronic kidney disease, atrial fibrillation, and dementia[7]. During the initial phase of hypertension, certain biomarkers in the bloodstream can be beneficial in understanding the mechanism of hypertension and may be used as potential treatments, including Angiotensin A, Vasoconstruction Inhibiting Factor (VIF), EndoThelin 1,2, Leptin, IL-1, IL-6, Nitric Oxide (NO), CRP, Renin, BNP, Uric Acid, and VCAM-1[8]. It is well known that hypertension plays an essential role in vascular endothelial dysfunction. Moreover, prolonged high blood pressure can increase the shear stress on blood vessels, leading to structural and functional damage to the vascular endothelium[9,10]. Vascular endothelial cells take charge in secreting vasoconstrictive factors, including NO, Prostaglandin-I-2 (PGI2), endothelin (ET) and Angiotensin II (Ang II)[1113]. These vasoconstrictive factors regulate the vasoconstriction of vascular endothelium and they exist in an equilibrium state under a normal physiological condition[1416]. For example, NO, ET and Ang II have been confirmed to possess vasoconstrictive functions, whereas PGl2 is a key factor that could regulate vascular tone[17]. It has been reported that hypertension could alter the synthesis of these vasoconstrictive factors, which could result in the collapse of their equilibrium in vascular endothelium[16]. Additionally, hypertension could take place with systemic inflammation, and thus some inflammatory mediators could be used to indicate the vascular damage caused by high blood pressure[18]. For example, interleukin 6 (IL-6) and tumor necrosis factor-α (TNF-α) are two inflammatory mediators that can be secreted into vascular endothelium by vasoactive substances (adrenaline and Ang II). IL-6 could activate platelet activating factors to enhance platelet aggregation and produce blood clots, whereas TNF-α could damage the integrity of vascular endothelial cells and trigger the inflammation to the vascular wall[1922].

    Medicinal plants have gained more attention in the field of medical science due to their potential health beneficial features. Gaocha is one of the most traditional tea beverages in China and other Asian countries. Gaocha is made of the tender shoots of A.ginnala Maxim, and it has been reported to contain various health promoting nutrients, such as alkaloids, tannins, flavonoids, and organic acids[2326]. Previous studies have reported that Gaocha possesses antioxidant activity and the consumption of Gaocha could inhibit tumor activity[27,28], hypoglycemic effect[29,30] and bacteriostatic action[31]. Gaocha has been used as a folk medicine to alleviate blood pressure. However, to the best of our knowledge, its antihypertensive mechanism has not been well studied. To this end, we treated spontaneously hypertensive rats (SHRs) with Gaocha extract at different doses and assessed the alteration of their blood pressure. Meanwhile, the vascular endothelial function factors (NO, ET, PGl2 and Ang II) and inflammatory mediators (IL-6 and TNF-α) of these SHRs under different Gaocha dose treatments were analyzed and compared. The findings from this study could provide useful insight on elucidating the mechanism of Gaocha on the hypertension alleviation.

    Catechin, epicatechin, gallocatechin, epigallocatechin, galloyl acid and β-glucogallin were purchased from Sigma-Aldrich (St. Louis, MO, USA) with a purity of 99%. Methanol, acetonitrile, and acetic acid were of HPLC grade and purchased from Tedia Co., Ltd. (Fairfield, OH, USA). Captopril tablets are a product of Changzhou Pharmaceutical Co., Ltd (Jiangsu, China). Normal saline and chloral hydrate were purchased from Kaiyuan Pharmaceutical Co., Ltd (Tianjin, China) and Shanghai Qiangshun Chemical Reagent Co., Ltd (Shanghai, China), respectively. Rat IL-6, ET-1, PGl2, Ang II, NO and TNF-α were all purchased from Sigma-Aldrich (St. Louis, MO, USA).

    The raw materials used for the Gaocha samples are sourced from Shucheng County, Lu'an City, Anhui Province (China) in 2017, and are processed by Anhui Lvyuan Tea Company. The production process of Gaocha involves picking, light withering, fixation, and baking to yield the final product[32]. The Gaocha sample was extracted using hot water at 100 oC with a 1:10 w/w ratio for 30 min under sonication. Afterwards, the resultant mixture was centrifuged at 12,000 rpm for 10 min to collect Gaocha extract. The Gaocha extract was then freeze-dried to yield the dryness. The dried extract was diluted using distilled water to a concentration of 1 g/mL. The resultant extract was filtered through a 0.22 μm membrane and then directly injected to liquid chromatography.

    An Agilent 1260 series UPLC (Palo Alto, Santa Clara, USA) was used to analyze the phenolic compounds composition in the Gaocha extract. The injection volume was set at 5 μL. An Agilent Eclipse PlusC18 column (Palo Alto, Santa Clara, CA, USA) was used to separate phenolic compounds under a flow rate of 1.0 mL/min. The mobile phase consisted of (A) water and (B) acetonitrile. A gradient elution program was as follows: 0−7 min, 10%B to 30%B; 7−10 min, 30%B isocratic; 10−11 min, 30%B to 13%B; 11−16 min, 13%B isocratic; 16−17 min, 13%B to 10%B; and 17−20 min, 10%B isocratic. The column was maintained at 40 °C during the elution program. The detection wavelength on the diode array detection was set at 280 nm. The detected individual phenolic compounds were quantified using their corresponding standard.

    A total of 40 pathogen-free male spontaneously hypertensive rats (SHRs) were provided from Beijing Vital River Laboratory Animal Technology Co., Ltd with its laboratory animal production license of SCXK(Jing) 2012-0001 (Beijing, China). These SHRs were 12-weeks-old with a body weight of 250 ± 20 g. Meanwhile, 8-12-week-old pathogen-free normal male rats were also purchased from Beijing Vital River Laboratory Animal Technology Co. Ltd with the same body weight as the SHRs. Both SHRs and normal rats were acclimated on a AIN93 G diet at 24−26 °C in a 12 h light/dark cycle for 7 d before administration. The SHRs were randomly divided into five groups and eight rats in each group was placed into two cages with four rats per cage. The normal rats were also put into two cages with four rats per cage. The SHRs in the first group (disease control group) were fed with an equal volume of distilled water as the treated SHRs. The second SHRs group was fed with captopril (6.25 mg/kg of rat weight). The rats in the third, fourth, and fifth SHRs group were gavaged with the Gaocha extract with a dose of 12.0 mg/kg (high dose), 6.0 mg/kg (mid dose) and 3.0 mg/kg (low dose) per rat weight, respectively. The Gaocha dried extract was dissolved using distilled water to a concentration of 1.2, 0.6, and 0.3 mg/mL for oral gavage. The normal rats (healthy control group) were fed with an equal volume of distilled water as the treated SHRs. The drug/extract administration took place at 9:00 am once per day for 16 d. During the experiment these rats had access to the same diet and water, and hair color, growth and general behavior of the rats were monitored. All rats were penned individually and randomly assigned to the pens.

    Tail artery blood pressure of all the rats were measured using the tail-cuff method at 0, 3, 7, 10, and 15 d under ALC-NIBP system (Shanghai Alcott Biotech. Co. Ltd., Shanghai, China). Each pressure measurement was conducted three times at 60 min intervals.

    After the last oral gavage, all the rats were fasted for 12 h without any food or water. The rats were then intravenously administered with 0.01 ml/g 10% chloral hydrate to induce anesthesia and then 5 mL of blood was collected and sampled from their aorta abdominals. Subsequently, the blood sample was transferred to EDTA tubes and then to vacuum blood collection tubes. The blood samples were centrifuged at 3,000 r/min for 30 min to separate plasma and serum. The targets (Ang II, NO, ET, PGl2, IL-6 and TNF-α) were analyzed using ELISA on an RT-6000 ELISA analyzer (Rayto Life and Analytical Sciences Co. Ltd, Shenzhen, China) according to the manufacturer’s instructions.

    After the blood was sampled, the corresponding organs were resected and soaked in 4% formaldehyde for 24 h. Afterwards, the organs (heart and kidneys) of the rats were placed in a Petri dish. The collected organ samples were washed with normal saline, dried using filter papers, and then fixed by 10% methanol. The fixed organs were dehydrated using a gradient series of ethanol and then passed through xylene solution to remove the ethanol and facilitate molten paraffin wax infiltration at 55 °C. Subsequently, the organs were embedded into a wax block and then cut into 4 mm thickness paraffin section. The paraffin sections were then stained with hematoxylin and eosin and visualized using a high-power microscope (OlympusBX51, Olympus Medical System Corp., Tokyo, Japan).

    Data were expressed as the mean ± standard error. One-way analyses of variance (ANOVA) were used to compare the means using Duncan's range test on SPSS17.0 (Chicago, IL, USA). Homogeneity analysis was carried out using the least significant different test. A p ≤ 0.05 difference was considered significant.

    Upon analysis of the functional component composition of Gaocha extract, it was found that the dried extract was affluent in phenolic compounds, with a total polyphenol content of 75.4 mg/g. Moreover, ultra-performance liquid chromatography revealed the presence of β-glucogallin, galloyl acid, gallocatechin, epigallocatechin, catechin, and epicatechin in the extract (Table 1). The predominant phenolic compound in the dried extract of Gaocha was revealed to be epicatechin, with a content of 32.68 mg/g, followed by epigallocatechin (5.69 mg/g) and gallocatechin (3.11 mg/g). Additionally, catechin was present in the extract at 1.95 mg/g. These findings demonstrate that Gaocha is rich in multiple polyphenols, potentially contributing to its beneficial effects.

    Table 1.  Concentration of phenolic compounds in dried Gaocha extract.
    Phenolic compound Content (mg/g) Percentage (%)
    β-Glucogallin 0.50 ± 0.00 0.67 ± 0.00
    Galloyl acid 0.74 ± 0.01 0.99 ± 0.02
    Gallocatechin 3.11 ± 0.07 4.13 ± 0.14
    Epigallocatechin 5.69 ± 0.08 7.55 ± 0.15
    Catechin 1.95 ± 0.06 2.59 ± 0.05
    Epicatechin 32.68 ± 0.76 43.35 ± 1.09
    Polyphenol 75.40 ± 0.71
    Polyphenol content was analysed using Folin-Cioalteu and expressed as mg galloyl acid/g dried Gaocha extract. Individual phenolic compounds were quantified using their corresponding standard and expressed as mg/g dried Gaocha extract. Data are the mean ± standard deviation of triplicate tests.
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    To gain insight into the general behavioral effects of Gaocha extract on SHRs, we conducted the experiments involving feeding them the extract and monitoring their behavior. The rats in the healthy control group exhibited glossy hair and gentle behavior (data not shown). In contrast, the SHRs in the disease control group showed an aggressive behavior and their hairs were thinner and fluffier. The SHRs treated with the Gaocha extract had more closely distributed and glossy hair, and those with the high Gaocha dose administration had similar hair growth and behavior as the SHRs treated with captopril (positive control). All the rats were kept in the same conditions with free access to water and food during the experiment.

    In order to evaluate the potential of Gaocha extract in reducing blood pressure, we monitored the tail artery blood pressure of SHRs. The results in Table 2 showed the tail artery systolic blood pressure of these rats during the experimental period. It was observed that the rats in the healthy control group had a blood pressure ranging from 109.92 to 116.49 BP/mm Hg. The SHRs in the disease control group exhibited an elevated blood pressure compared to the normal rats during the whole experiment period and their blood pressure was about 166.34 to 167.69 BP/mm Hg. The SHRs in the positive control group (captopril) had a lower blood pressure during the study and their blood pressure remained around 110 BP/mm Hg. The Gaocha extract resulted in a significant decrease in the blood pressure of the SHRs, and such pressure alleviation relied on the administration dose of the extract (Table 2). For example, the SHRs orally gavaged with the low Gaocha extract dose reduced their pressure from 169 BP/mm Hg to about 134 BP/mm Hg. The Gaocha extract with the mid dose lowered the blood pressure of the SHRs to about 125 BP/mm Hg. It is noteworthy that the SHRs treated with the high Gaocha extract dose had a similar blood pressure as the normal control rats and the captopril treated SHRs, suggesting that the high Gaocha extract dose may be effective in reducing high blood pressure.

    Table 2.  Tail artery systolic blood pressure of normal and spontaneously hypertensive rats treated with different Gaocha extract levels during the administration period.
    Group Blood pressure during administration period (BP/mm Hg)
    0 day 3 day 7 day 10 day 15 day
    Normal rats (healthy control) 114.48 ± 2.47e 109.92 ± 5.75e 112.23 ± 2.40e 116.49 ± 6.43d 115.87 ± 3.56d
    SHRs (disease control) 166.78 ± 2.71b 167.69 ± 2.46a 166.81 ± 2.71a 167.52 ± 2.56a 166.34 ± 2.99a
    SHRs with captopril (6.25 mg/kg) 165.36 ± 3.23b 123.92 ± 7.29cd 114.65 ± 2.71de 116.86 ± 4.62d 109.72 ± 3.51e
    SHRs with high Gaocha dose (12 mg/kg) 171.77 ± 5.13a 122.18 ± 4.67b 117.77 ± 3.53b 122.75 ± 1.72b 121.82 ± 3.41b
    SHRs with mid Gaocha dose (6 mg/kg) 161.72 ± 3.77c 127.99 ± 4.67c 125.37 ± 2.25c 125.48 ± 3.07c 123.91 ± 2.12c
    SHRs with low Gaocha dose (3 mg/kg) 169.17 ± 9.12ab 139.46 ± 1.69d 134.41 ± 3.85d 134.25 ± 3.49c 133.09 ± 3.76c
    Data are the mean ± standard error. Different letters in each column represent significant difference at a 0.05 significant level.
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    To explore the potential mechanism of Gaocha extract in lowering blood pressure, we analyzed its effects on PGI2, AngII, and ET level of SHRs. The healthy rats (healthy control group) had a PGI2 level of 30 ng/L, whereas its level was only about 10 ng/L in the SHRs of disease control group (Fig. 1a). Administrating captopril (positive control) to the SHRs for 16 d resulted in a level increase of PGI2 in the SHRs. The SHRs treated with the low Gaocha extract dose exhibited a similar PGI2 level as the disease control group. However, the mid and high Gaocha extract dose significantly increased the PGl2 level in the SHRs, and the SHRs with the high extract dose administration had a similar PGl2 level as the positive control SHRs (captopril).

    Figure 1.  The serum PGI2, AngII and ET levels in normal and spontaneously hypertensive rats treated with different Gaocha extract doses. (a) Serum PGI2 level, (b) Serum AngII level, and (c) Serum ET level. Different letters represent significant difference at a significant level of 0.05.

    The Ang II level in the healthy control group rats was about 45 ng/L in this study, whereas the SHRs in the disease control group had an about 80 ng/L Ang II level (Fig. 1b). The captopril (positive control) administration significantly reduced the Ang II level to about 55 ng/L in the SHRs. Feeding the SHRs with the Gaocha extract resulted in a decrease on the Ang II level. Such a decrease was much more obvious with the higher dose administration.

    In addition, the SHRs in the disease control group exhibited the ET level two times higher than the healthy control group rats (Fig. 1c). The captopril treatment significantly lowered the ET level in the SHRs. The Gaocha extract administration with different doses also resulted in an ET level decrease in the SHRs after the experiment and the high Gaocha extract dose appeared to result in the SHRs with the similar ET level as the positive control (captopril).

    Nitric oxide (NO) is a key signaling messenger that is biosynthesized from L-arginine, oxygen, NADPH through nitric oxide synthase enzymes[33,34]. It has been reported that NO could relax the smooth muscle in the endothelial cells to widening the blood vessel and increasing blood flow[35,36]. Figure 2 shows the NO level of these rats after the whole animal study. The normal rats (healthy control group) were found to have a NO level around 8 ng/L, whereas spontaneously hypertension caused the rats to have the NO level less than 4 ng/L. After treating the SHRs with the positive control captopril for 16 d, the NO level of the SHRs was elevated to about 7 ng/L. It should be noted that the administration of the Gaocha extract for 16 d did improve the NO levels in the SHRs. The NO level in the SHRs treated with the low, mid, and high dose of the Gaocha extract appeared to be about 4, 5, and 7 ng/L, respectively. These indicated that the Gaocha extract could stimulate the biosynthesis of NO in the SHRs, which could enhance the vasodilation and reduce the blood pressure.

    Figure 2.  The serum nitric acid (NO) levels in normal and spontaneously hypertensive rats treated with different Gaocha extract doses. Different letters represent significant difference at a significant level of 0.05.

    Interleukin 6 (IL-6) is an interleukin that could be produced as a pro-inflammatory cytokine by smooth muscle cells in the tunica media of blood vessels[37]. It has been reported that muscle contraction could stimulate the secretion of IL-6 into blood stream[18]. The spontaneous hypertension significantly increased the release of IL-6 level in the rats (Fig. 3a). The healthy control group rats had a IL-6 level of about 12 ng/L, whereas its level in the SHRs control group was higher than 25 ng/L. The SHRs treated with captopril for 16 d showed its IL-6 level at around 15 ng/L, indicating that captopril inhibited the biosynthesis and secretion of IL-6 in the SHRs. The SHRs gavaged with the Gaocha extract for 16 d also reduced the secretion of IL-6. For example, the IL-6 level in the SHRs with the mid and high dose of the Gaocha extract were much lower than the SHRs control group, and the high Gaocha extract dose treated SHRs showed a similar IL-6 level as the SHRs administrated with captopril.

    Figure 3.  The serum IL-6 and TNF-α levels in normal and spontaneously hypertensive rats treated with different Gaocha extract doses. (a) Serum IL-6 level and (b) Serum TNF-α level. Different letters represent significant difference at a significant level of 0.05.

    Tumor necrosis factor-α (TNF-α) is a proinflammatory cytokine that can be elevated in an inflammatory state, such as hypertension[19,20]. It has been reported that the formation of TNF-α is associated with salt-sensitive hypertension and related renal injury, whereas Ang II increase could also promote the release of TNF-α[21,38]. In the present study, the SHRs control group showed a much higher level of TNF-α than the healthy control group rats (Fig. 3b). This indicated that hypertension stimulated the release of TNF-α in the SHRs. Both captopril and Gaocha extract inhibited the secretion of TNF-α in the SHRs after 16 d of treatment. For example, the captopril treated SHRs possessed a similar TNF-α level as the healthy control rats. The SHRs that were gavaged with Gaocha extract showed a significantly lower level of TNF-α compared to the control group. Furthermore, increasing the dose of the extract resulted in a greater inhibition of TNF-α release in the SHRs.

    Regarding the rat heart histomorphological analysis, no thickening on the cardiac muscle fiber or fibrous hyperplasia was found in the healthy control group rats (Fig. 4a). However, the cardiac muscle fibers in the SHRs control group (disease control group) were significantly thickened with the muscle tissue hyperplasia (Fig. 4c). These demonstrated that spontaneous hypertension damaged the organs in the SHRs. In the captopril treated SHRs (positive control), their cardiac muscle fibers appeared to be normal without thickening, and their blood cells were visible in the cardiac cavities. Besides, no fibrous hyperplasia was found in the mesenchyme of the rats (Fig. 4b). The administration of the Gaocha extract improved the cardiac muscle fibers compared to the SHRs control although the thickening of the fibers still occurred to these Gaocha extract fed SHRs (Fig. 4df). It should be noted that the cardiac muscle fibers in the SHRs with the high Gaocha extract dose appeared to be much thinner than the low extract dose fed SHRs. Meanwhile, the blood cells were observed in the cardiac cavities of these SHRs treated with the Gaocha extract. More importantly, no obvious tissue hyperplasia was found in these Gaocha extract treated SHRs.

    Figure 4.  Morphological feature of cardiac tissue in normal and spontaneously hypertensive rats treated with different Gaocha extract doses. (a) Normal rats in healthy control group.(b) Captopril treated spontaneously hypertensive rats. (c) Spontaneously hypertensive rats in disease control group. (d) Low Gaocha extract dose treated spontaneously hypertensive rats. (e) Mid Gaocha extract dose treated spontaneously hypertensive rats. (f) High Gaocha extract dose treated spontaneously hypertensive rats.

    The healthy control group rats possessed normal renal tubules in the kidney histomorphological biopsy (Fig. 5a). However, a significant stenosis of the renal tubules happened in the SHRs (disease control group). Meanwhile, these SHRs were found to have fibrosis in the renal interstitium with a structural alteration on the glomerulus (Fig. 5c). The captopril treated SHRs improved the structure of the renal tubules and glomerulus and the histomorphological feature of the SHRs kidney was similar to that of the healthy rats. An improvement of the kidney structure on the SHRs treated with the Gaocha extract was also found. Among these treatments, the high Gaocha extract dose resulted in SHRs with normal renal tubules and glomerulus. Meanwhile, no obvious renal interstitial fibrosis or renal tubule stenosis was found in these SHRs.

    Figure 5.  Morphological feature of renal tissue in normal and spontaneously hypertensive rats treated with different Gaocha extract doses. (a) Normal rats in healthy control group.(b) Captopril treated spontaneously hypertensive rats. (c) Spontaneously hypertensive rats in disease control group. (d) Low Gaocha extract dose treated spontaneously hypertensive rats. (e) Mid Gaocha extract dose treated spontaneously hypertensive rats. (f) High Gaocha extract dose treated spontaneously hypertensive rats.

    In this study, we explored the anti-hypertensive effects of Gaocha extract on spontaneously hypertensive (SHR) rats. It was found that the groups treated with Gaocha had lower systolic blood pressure in the tail artery compared to the control group. Additionally, the levels of certain biomarkers, such as PGI2, Angiotensin II, ET, and NO, were higher in the Gaocha-treated groups. After treatment, the levels of IL-6 and TNF-α were lower in the Gaocha-treated groups compared to the control group. Histomorphological examination of the heart and kidney indicated that Gaocha may possess a protective effect. Future research will aim to identify the active components and elucidate the associated health benefits.

    Gaocha has been reported to contain numerous nutrients that could provide multiple benefits to human health[2326]. Among these nutrients, polyphenols appear to be a major group for such beneficial activities. It has been confirmed that polyphenols are important antioxidants that could prevent the occurrence of many active and chronic diseases and these secondary metabolites could also regulate the secretion of signaling molecules in the human body[39,40]. Interestingly, our results showed that the content of EC was extremely high in Gaocha extracted solution. It was reported that the EC had a positive effect on vascular function in humans by inhibition of NO synthase[33]. Furthermore, it was also reported that epicatechin (EC) may in part contribute to the cardioprotective effects of cocoa and tea by improving insulin resistance[34]. These suggested that the high content of EC could be part of the reason for the vascular function of Gaocha. Moreover, Gallic acid (GA) was also reported as an active compound in Gaocha. Previous studies have demonstrated that GA can enhance NO production by augmenting the phosphorylation of eNOS. Additionally, GA has been found to impede the activity of ACE, leading to a reduction in the blood pressure of spontaneously hypertensive rats[35]. It can increase eNOS phosphorylation levels by influencing the Ca2+/CaM compounds, and also inhibit calcium influx into cells through the L-type calcium channel, resulting in the dilation of endothelial cells[36]. It is yet to be determined whether the GA lowers blood pressure, and this will be the focus of future research involving active ingredients, molecular and cellular studies.

    Hypertension is a progressive cardiovascular condition, caused by different factors, which can cause changes in the heart and blood vessels' structure and function. It affects one in every three adults and an increase of 1 mm of mercury in hypertension patients increases the mortality rate by 1%. Therefore, research on molecular mechanisms is essential for the prevention and treatment of hypertension[12]. Hypertension is a multi-faceted medical condition, composed of several risk factors, such as atherosclerosis, endothelial cell damage, hyperlipidemia, and subclinical diseases, that can culminate in cardiovascular events. Its development involves endothelial dysfunction, vascular remodeling, inflammation, calcification, and increased vascular stiffness[11]. Endothelial dysfunction is believed to be an important factor in the pathogenesis of hypertension[7], as it has a genetic basis and can affect target organs. Furthermore, increased shear stress in the blood vessels due to hypertension can cause changes in the structure and function of vascular endothelium[41].Vascular endothelial cells are capable of releasing a variety of active factors that can cause blood vessels to relax or contract through autocrine and paracrine pathways, such as NO, PGI2, ET, and Ang II[11].

    In hypertension, the contraction of blood vessels causes ischemia and hypoxia of the endothelial cells, leading to damage to their structure and function, and consequently, affects the production and release of NO. Oxidative stress has been identified as a major contributor to the processes of endothelial dysfunction, inflammation, hypertrophy, apoptosis, migration, fibrosis, angiogenesis, and hypertensive vascular remodeling[13]. Endothelin has a pronounced effect of decreasing vascular diameter, in comparison to Angiotensin II, which is produced by hyperpolarization of vascular endothelial cells and also has a vasoconstrictive action but with less intensity. Ang II is a peptide hormone that is basically converted from Ang I through angiotensin-converting enzyme (ACE)[42]. Ang II has been confirmed to act on venous and arterial smooth muscle to increase vasoconstriction. ACE inhibitors could restrain the conversion of Ang I to Ang II and thus improve the blood pressure[43]. Feeding the SHRs with the Gaocha extract resulted in a decrease in the Ang II level. Such a decrease was much more obvious with the higher dose administration. We speculated that phenolic compounds, such as epicatechin and epigallocatechin, in the Gaocha extract might inhibit the renin-angiotensin system (RAS) activation pathway to reduce the secretion of Ang II in the SHRs. In this way, the vascular wall of the SHRs could be protected.

    In addition, ET is a peptide that is primarily present in endothelium and its overexpression could drive hypertension, heart diseases and other organ damages[44]. ET is a vasoconstrictor that interacts with smooth muscle endothelin receptors[45]. It has been reported that epicatechin could inhibit the interaction between ET and its endothelin receptors[46]. We hypothesized that the high level of epicatechin, found in the Gaocha extract, could inhibit endothelin receptors and thus prevent the excessive production of ET in SHRs.

    PGl2 is an important prostaglandin member that could inhibit platelet activation. It is biosynthesized in endothelial cells and plays a vital role in preventing the platelet plug formation through primary hemostatsis[16]. In addition, PGl2 could exert as a vasodilator to stabilize cardiovascular homeostasis[47]. Physiologically, NO, PGI2, ET, and AngII are in a state of balance. When pathological factors disrupt this equilibrium of active substances in VEC, it can cause platelet activation and endothelial cell damage, which can contribute to or aggravate the occurrence of cardiovascular disease[1416]. Recent research has revealed that endothelial damage and dysfunction are major factors in the onset and advancement of hypertension[48,49].

    IL-6 and TNF-α are pro-inflammatory factors that can cause direct damage to vascular endothelium. TNF-α can disrupt the structure and function of vascular endothelial cells, leading to inflammatory reactions in the vascular wall[14]. IL-6 is a glycoprotein mainly produced by T cells and B cells, and it is involved in the regulation of immune response, acute phase response, and hematopoietic function. Additionally, IL-6 can activate platelet activating factors, which can enhance platelet aggregation and form thrombosis, thus damaging the endothelial cells of hematopoietic blood vessels[15].

    The present study demonstrated that the Gaocha extract is capable of effectively reducing blood pressure in SHR rats, as well as decreasing the serum levels of Ang II and ET, while increasing the levels of NO and PGI2. This protective effect on vascular endothelial function is thought to be achieved by obstructing the activation pathway of RAS, thereby diminishing the amount of Ang II produced and its consequential damage to the vascular wall. Additionally, the Gaocha extract may bind to ET and receptors in vascular endothelial cells, resulting in the release of NO and PGI2, which leads to the relaxation of blood vessels and a decrease in blood pressure. The findings hold important clinical implications for the treatment of hypertension, suggesting that Gaocha extract may have the potential to serve as a natural alternative with potentially fewer side effects and greater safety compared to conventional chemical drugs. Furthermore, the study underscores the need for further research on Gaocha to elucidate its active components and associated mechanisms. Subsequent research will seek to identify the active components of Gaocha and explore their potential for treating hypertension using vascular endothelial cell lines. This will involve evaluating changes in pertinent biomarkers and utilizing Western blot or PCR techniques to assess the influence of these active components on gene and protein expression levels relevant to vascular activity, as well as their regulatory effects on genes linked to endothelial cell function. Meanwhile, conducting animal studies can provide insights into the effects of Gaocha extract on vascular endothelial function, vascular remodeling, inflammatory factors, and its regulatory influence on blood pressure. These efforts will enhance our understanding of the antihypertensive mechanisms of Gaocha extract and its potential for treating hypertension. Overall, the study highlights the promising antihypertensive effects of Gaocha extract and underscores the need for further research to unlock its full therapeutic potential for human health.

    In this work, we discuss the effect of Gaocha extract treatment on spontaneously hypertensive (SHR) rats. Male SHR rats were randomly divided into the model (saline), positive control (captopril), low-dose Gaocha extract, medium-dose Gaocha extract and high-dose Gaocha extract groups, which were treated daily for two weeks. Tail artery systolic blood pressure (SBP) was measured before and 3, 7, 10, and 15 d after treatment. The Gaocha-treated groups had significantly lower SBP than the model group. Post-treatment abdominal aorta blood samples showed that the serum Angiotensin II, ET, IL-6, and TNF-α levels were significantly higher and the serum NO and PGI2 levels were significantly lower in the model group. Finally, haematoxylin-eosin staining of the heart and kidney showed that Gaocha extract had a protective effect. Thus, our findings indicate that Gaocha extract has obvious treatment benefits in SHR rats with regard to lowering SBP and protecting the vascular endothelium.

    The animal study protocol was conducted in compliance with the Guide for the Care and Use of Laboratory Animals in Ministry of Science and Technology of the People's Republic of China. The protocol was reviewed and approved by the ethics committee of Anhui Agricultural University (Anhui, China).

    The authors confirm contribution to the paper as follows: study conception and design: Wang H, Gao L; experiments performed: Wang W, Ma J, Ma Y, Bao Y, Long Z, Lei S, Xu Y, Dai Q; draft manuscript preparation: Wang H, Wang W. 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.

    This work was supported by the National Natural Science Foundation of China (Grant No. 31700608 and 32202551), Natural Science Foundation of Anhui Province (Grant No. 1708085MC58), the Natural Science Basic Research Program of Shaanxi (Grant No. 2022JQ-194) and the Anhui Agriculture University Pesident Fund (Grant No. 2014SKQJ020). We thank Professor Zijiang Long at the Function Experiment Center, Anhui University of Chinese Medicine for his assistance.

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

  • Supplemental Fig. S1 Correlations by color map cluster of twelve parameters evaluated in tomato fruit treated with doses of AVG and stored (15 ± 1 °C and RH 90 ± 5 %) for 28 days.
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    Rocha Lacerda V, Aparecida dos Santos J, Sílvia Angélica de Oliveira H, Gaona Acevedo AF, Lopes Vieites R. 2024. Doses of aminoethoxyvinylglycine (AVG) in tomato postharvest storage. Technology in Horticulture 4: e011 doi: 10.48130/tihort-0024-0008
    Rocha Lacerda V, Aparecida dos Santos J, Sílvia Angélica de Oliveira H, Gaona Acevedo AF, Lopes Vieites R. 2024. Doses of aminoethoxyvinylglycine (AVG) in tomato postharvest storage. Technology in Horticulture 4: e011 doi: 10.48130/tihort-0024-0008

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ARTICLE   Open Access    

Doses of aminoethoxyvinylglycine (AVG) in tomato postharvest storage

Technology in Horticulture  4 Article number: e011  (2024)  |  Cite this article

Abstract: Tomatoes are one of the main vegetables found daily in world cuisine and are highly perishable. The aim of this study was to evaluate the quality of 'Débora' tomato fruits over the post-harvest period in refrigerated storage, after immersion in solutions with different concentrations of aminoethoxyvinylglycine (AVG). The experimental design was entirely randomized in a 4 × 5 double factorial scheme, with four treatments, AVG doses 0 (control), 500, 1,000, and 1,500 mg·L−1, and five days of evaluation during the 28 d of refrigerated storage (days 0, 7, 14, 21 and 28) with three replications. Physicochemical analyses were carried out on weight loss, respiration rate, firmness, hydrogen potential (pH), soluble solids, titratable acidity and external and internal fruit color parameters, luminosity, chroma, and °hue. Two-way ANOVA, Tukey's mean test (p < 0.05), and multivariate statistical analysis by principal components (PCA) were carried out. The PCA allowed us to infer that, as weight loss increased, firmness decreased, an effect that was minimized with AVG at a dose of 1,500 mg·L−1, which may be related to the inhibition of the fruit's ethylene production rate. AVG delayed the post-harvest ripening of tomato fruit, reduced the respiration rate of the fruit, and the changes in external and internal chroma. The doses of AVG did not affect the luminosity and pH of the fruit pulp.

    • Tomato (Solanum lycopersicum L.), is one of the main vegetables found daily in the world's cuisine. It can be eaten both fresh and processed. The heightened demand for this fruit contributes significantly to job creation within the tomato production sector, and it plays a significant role in agribusiness[1]. In addition to its aroma, flavor, and texture, tomatoes are widely accepted for their many benefits for human health. It is a food rich in lycopene, vitamins A and C, and minerals such as potassium, phosphorus, and magnesium, which are important for human nutrition[2].

      Climacteric fruits, like tomatoes, are highly perishable. They show a rapid and significant increase in respiration during ripening, with a series of biochemical and visual changes occurring[3]. Post-harvest losses of fruit and vegetables begin at harvest and continue throughout the marketing stage until consumption, i.e. during packaging, transportation, storage and at the consumer level.

      Ethylene is the main hormone responsible for ripening and its control is one of the main factors in reducing post-harvest losses. There are several inhibitors used in the conservation of climacteric fruits, which control the action and/or synthesis of ethylene, extending the shelf life of the product[4]. One form of control, for example, is the compound aminoethoxyvinylglycine (AVG).

      AVG suppresses ethylene biosynthesis by inhibiting the enzymatic activity responsible for converting S-adenosyl methionine (SAM) to 1-aminocyclopropane-1-carboxylic acid (ACC)[5,6]. Several studies have used AVG to delay ripening and maintain post-harvest quality in climacteric fruits such as bananas[7] and apples[8]. In pears, AVG treatment suppressed the rate of fruit respiration, reduced the loss of firmness, reduced internal browning, senescence disorders, and consequently effectively delayed fruit ripening[9].

      Considering the quality and shelf life of the product, there are several damages caused to tomatoes, including handling, transportation, mechanical damage and exposure to high temperatures[3], resulting in rapid ripening with intensification of the red color. As such, tomatoes require a great deal of care and technology for their preservation.

      As the effect of AVG can vary depending on the dose and the type of fruit[10], and as there are few studies with AVG in tomatoes, more detailed studies are needed to better understand the issues of the feasibility of using AVG at an appropriate dose. In this context, the aim of this work was to evaluate the quality of tomato fruit cultivar 'Débora' over various postharvest times in refrigerated storage, after immersion in solutions with different concentrations of aminoethoxyvinylglycine (AVG).

    • Tomato fruits (Solanum lycopersicum L. Cultivar 'Débora') obtained from commercial cultivation were used. The fruits were harvested at the salad tomato stage of ripeness, green and ripe, and transferred to the Fruit and Vegetable PostHarvest Laboratory at the Universidade Estadual Paulista 'Júlio de Mesquita Filho', Faculdade de Ciências Agronômicas, Campus de Botucatu, São Paulo, Brazil, where they were selected to standardize the batch, eliminating those with physical damage (dented and/or cracked) and biological damage (diseases and/or pests). The fruits were randomly divided, immersed for 15 min in a solution of hypochlorite with 2% active chlorine, diluted to 7%, washed in running water, and dried in the air, remaining at rest for 24 h to remove the field heat.

    • Each treatment consisted of immersing the fruit for 5 min in a solution of AVG at four concentrations: 0 (control), 500, 1,000, and 1,500 mg·L−1. Each treatment consisted of three replicates. The commercial product used was the plant regulator ReTain®.

      After applying the treatments, the fruit was packed in expanded polystyrene trays (two fruits) covered with polyvinyl chloride film (thickness 0.020 mm), stored in a cold room at 15 ± 1 °C and 90% ± 1% RH (average of 31 °C outside) and assessed for quality every 7 d for 28 d.

    • To determine weight loss, a semi-analytical scale (Owa labor model) was used with a maximum load of 2,000 g and a division of 10 mg. The results were calculated as the percentage (%) of weight loss at the start of the experiment and at different intervals during storage using the equation: PM (%) = (Pi ‒ Pj/Pi) × 100, where PP = Weight loss (%); Pi = Initial weight of the fruit (g); Pj = Weight of the fruit in the period following Pi (g)[11].

    • The respiration rate was determined by quantifying CO2 production in a respirometer, according to a methodology adapted from Bleinroth et al.[12], using the equation: TCO2 = 2.2 × (V0 ‒ V1) × 10/P × T, where, TCO2 = Respiration rate (mL CO2 kg−1·h−1); V0 = Volume spent of HCl for potassium hydroxide titration − standard before CO2 absorption (mL); V1 = Volume spent of HCl for potassium hydroxide titration after CO2 absorption from respiration (mL); P = Fruit weight (kg−1); T = Respiration time (h−1); 2.2 = Inherent CO2 (mL) equivalent (44/2), multiplied by the concentration of hydrochloric acid at 0.1 N; 10 = Adjustment for total potassium hydroxide used in CO2 absorption (mL).

    • Firmness was measured at two different points on each fruit and determined using a Texturometer (STEVENS - LFRA Texture Analyzer), with a penetration distance of 20 mm and a speed of 2.0 mm·s−1, using a TA 9/1000 tip. The results were expressed in Newton (N).

    • The hydrogen potential (pH) of the tomato pulp obtained with the aid of a mixer was determined using a tabletop digital pH meter (model DMPH - 2), according to the methodology of AOAC[11].

      The total soluble solids (TSS) content of the extracted tomato pulp was measured using a tabletop digital refractometer (Digital Refractometer DR 202) by direct refractometric reading, according to the methodology of AOAC[11] and the results were expressed in °Brix.

      Titratable acidity (TA) was determined by titrimetry. Three milliliters of extracted tomato juice were diluted to 100 mL with distilled water and titrated with 0.1 N sodium hydroxide solution (NaOH) at pH 8.2. The results were expressed as a percentage of citric acid in the fresh pulp, according to the methodology recommended by AOAC[11]. The calculation was made using the formula: AT (%) = [(V × N × meq)/Y] × 100, where V = Volume of sodium hydroxide used in ml, N = Normality of sodium hydroxide and meq = 0.064, Y = Volume of bulk fruit juice mL[11].

    • The color of the tomato peel and pulp was determined using a Konica Minolta colorimeter (Chroma meter, CR 400) where L*, expressed as a percentage, indicates luminosity values (0% = black and 100% = white), C* is represented by Chroma which defines color intensity. The Hue angle is the value in degrees corresponding to the three-dimensional color diagram and ranges from: 0° to 18° for red-violet, 19° to 54° for red, 55° to 90° for orange, 91° to 126° for yellow, 127° to 162° for yellow-green, 163° to 198° for green, 199° to 234° for blue-green, 235° to 270° for blue, 271° to 306° for blue-violet and 307° to 342° for violet, 343° to 360° red-violet, making 360°[13]. For the approximate reproduction of the color profile, determined by the Konica Minolta colorimeter, the Luminosity, Chroma and Hue angle values of the fruit peel were used to feed into the colorizer.org platform, topic HSL(A), according to the CIELAB diagram.

    • The experimental design was entirely randomized in a 4 × 5 double factorial scheme, with four treatments being the doses of AVG 0 (control), 500, 1,000, and 1,500 mg·L−1 and 5 d of evaluation during the 28 d of refrigerated storage (0, 7, 14, 21, and 28 d) with three repetitions (n = 3).

    • The data obtained was subjected to the Shapiro-Wilk normality test using GraphPad Prism software version 8.0.1 (San Diego, CA, USA). With all the data showing normality, it was subjected to analysis of variance (Two-Way ANOVA), and the means were compared using the Tukey test, p < 0.05; and at p < 0.01; using the Sisvar software version 5.6 (Lavras, MG, Brazil). The results were presented as means with standard deviation (mean ± SD). Principal component analysis and correlations was carried out using JMP 10 statistical software (SAS Institute Inc., USA).

    • The results of the analysis of variance with the doses of AVG (0, 500, 1,000, and 1,500 mg·L−1), storage time (days 0, 7, 14, 21, and 28) and the interaction between these factors for the physicochemical parameters assessed at the post-harvest stage of the tomato fruit are presented in Table 1. Except for pH, all the parameters showed significant differences depending on the doses and storage time. There was an interaction between the factors, except for pH and total soluble solids.

      Table 1.  Results of the analysis of variance (Two-Way ANOVA) of the effect of AVG doses, storage time and the interaction of these factors on the physicochemical parameters evaluated in tomato fruits.

      Cause of variationD.F.Weight lossRespiratory rateFirmnessTotal soluble solidspHTritrable acidity
      Dose30.000**0.000**0.027*0.042*0.778ns0.046*
      Time (d)40.000**0.000**0.000**0.049*0.579ns0.000**
      Dose × time120.004**0.000**0.000**0.219ns0.988ns0.002**
      Residue400.1503.2640.0330.1220.0690.000
      ns represents not significant; * represents p ≤ 0.05 and ** represents p ≤ 0.01.

      There was an increase in weight loss in tomato fruit at all doses during storage (Fig. 1a). The control fruit (0 mg·L−1) showed less weight loss compared to the fruit treated with AVG, and on day 28 the 1,000 and 1,500 mg·L−1 doses showed greater weight loss compared to the other doses. In a similar previous study, the weight loss of 'Grando F1' tomatoes increased with longer storage time and reached 1.38% in the AVG-treated fruit and 1.21% in the control fruit after 20 d at 12 °C[14], so there seems to be no consistent effect of AVG treatments on weight loss. Different results were obtained in apple cultivar 'Eva', where the doses of 500 and 1,500 mg·L−1 were responsible for the lowest weight loss from the 21st and 28th d[15]. Although positive effects have been observed in some fruit varieties, opposite results have been obtained in other fruits[10].

      Figure 1. 

      (a) Weight loss, (b) respiration rate and (c) firmness of tomato fruit treated with doses of aminoethoxyvinylglycine (AVG) and stored (15 ± 1 °C and RH 90% ± 5 %) for 28 d. Lowercase letters differ the doses in a single storage time and capital letters differ the storage times in a single dose, according to the Tukey test (p < 0.05).

      Weight loss is a process that occurs due to the loss of water, stimulated by the process of respiration and transpiration due to the vapor pressure deficit on the surface of the fruit[16]. The loss of water leads to softening of the tissues, affecting the texture, color, and flavor of the fruit, reducing its time on the market. As reported by Taiz et al.[17], AVG also acts to inhibit enzymes that use pyridoxal phosphate as an enzyme cofactor and when applied in high doses, this may have occurred in this study by increasing weight loss, inhibiting various aspects of the plant's metabolism, especially interfering with the rind tissue.

      There was an increase in the respiration rate of the fruit on the 7th day of evaluation, with a gradual increase over time until the maximum climacteric peak of 55.31 mL CO2 kg−1·h−1 on the 14th day for the control fruit, followed by a decline on the other days (Fig. 1b). From the 7th to the 28th day, the control had a significantly higher respiration rate, 55% to 64% higher on the 28th day compared to the AVG-treated fruit, showing a positive effect of this compound. The respiration rate can be reduced using various technologies that reduce the metabolic activity of the fruit, such as refrigerated storage and inhibitors of ethylene action[6], like AVG. The continuation of the metabolic process gradually alters the composition of the product, leading to senescence, which was delayed with AVG in this study.

      Over time, there was a decrease in the firmness of the fruit from day 14 onwards, which was gradual until day 28 (Fig. 1c). AVG provided greater fruit firmness compared to the control at a dose of 1,500 mg·L−1 on day 7 and 1,000 mg·L−1 on day 21, and on the other days there was no difference between the doses. The difference in firmness between treated and untreated fruit disappears over time[18], which probably occurred on day 28. When applied as a postharvest dip treatment, AVG reduced the rate of fruit softening in 'Grando F1' tomatoes[14], 'Huangguan' pears[9] and sweet orange Citrus sinensis (L.)[19] during storage or shelf life, as a consequence of ethylene inhibition.

      The total soluble solids (TSS) content of the control fruit (0 mg·L−1) decreased over time, and for the other doses there was stability, with no significant difference (Fig. 2a). On day 28, the 1,000 mg·L−1 dose provided a 1.0 °Brix increase in SS content compared to the control. The SS content is used as an indirect estimate of sugars, as well as other compounds that are present in the vascular sap, such as vitamins, phenolics and pectin's. Like this study[20], working with 'Tommy Atkins' mangoes at room temperature, observed stability in the SS content when treated with AVG during the 12 d of storage. However, this was probably due to the ripening process of the fruit with the conversion of starch to sugar.

      Figure 2. 

      (a) Total soluble solids, (b) pH and (c) titratable acidity of tomato fruit treated with doses of aminoethoxyvinylglycine and stored (15 ± 1 °C and RH 90% ± 5 %) for 28 d. Lowercase letters differ the doses in a single storage time and capital letters differ the storage times in a single dose, according to the Tukey test (p < 0.05).

      The pH showed no statistical difference between the treatments (Fig. 2b). A previous study,[15] also found no significant difference for the doses of AVG, but found a significant effect for the storage time of the 'Eva' apple cultivar. The author observed higher pH values on the 0th and 7th day of storage, with a decrease in value from the 14th day onwards. This reported decrease was linked to the release of organic acids resulting from the degradation of the cell wall, a fact that did not occur in this study under the conditions in which the experiment was carried out.

      Titratable acidity (TA) remained stable in the fruit treated with the 1,500 mg·L−1 dose during storage; on the other hand, there was a reduction in the fruit treated with the other doses (Fig. 2c). In the fruit treated with the 1,500 mg·L−1 dose on day 28, the acidity was 0.08% and 0.05% higher, respectively, compared to the two lower doses, 0 and 500 mg·L−1. Corroborating this work, dos Santos et al.[20], working with 'Kent' mango, reported that the 300 mg·g−1 concentration of AVG resulted in fruit with a higher acidity content. Titratable acidity analysis is used to quantify acidity through a predominant acid according to the plant material, determining the percentage of organic acids.

      Corroborating the present study, it was previously reported that TA decreased over time and no significant differences were found in the pH of the pulp of 'Grando F1' tomatoes between fruit treated and untreated with 1,000 mg·L−1 AVG at −30 kPa during storage at 12 °C for 20 d and a further 2 d at 20 °C[14]. However, unlike the present study, these authors found no significant differences in SS and TA between fruit treated and not treated with AVG, reporting that changes in organic acids and sugars in tomatoes were not controlled by ethylene[21], a positive effect that certainly occurred in the present study due to the inhibition of ethylene by AVG at a dose of 1,500 mg·L−1, as it kept TA and SS stable.

      The results of the Two-Way ANOVA with the doses of AVG (0, 500, 1,000, and 1,500 mg·L−1), storage time (days 0, 7, 14, 21, and 28) and the interaction between these factors for the external and internal color parameters, assessed at post-harvest of the tomato fruit, are shown in Table 2. Except for the effect of the doses and the interaction between the factors for internal luminosity (pulp), all the other parameters showed significant differences. Storage time was significant for all parameters.

      Table 2.  Results of the analysis of variance (Two-Way ANOVA) of the effect of AVG doses, storage time and the interaction of these factors on the external and internal color parameters evaluated in tomato fruits.

      Cause of variationD.F.L peelC peelh° peelL pulpC pulph° pulp
      Dose30.001**0.000**0.000**0.866ns0.030*0.045 *
      Time (d)40.000**0.000**0.000**0.000**0.000**0.000**
      Dose × time120.038*0.010*0.000**0.695ns0.014*0.000**
      Residue401.7804.4023.2947.0972.50712.640
      ns represents not significant; * represents p ≤ 0.05 and ** represents p ≤ 0.01.

      As for peel color, external luminosity decreased over time (Fig. 3a), and on day 28, the 500 mg·L−1 dose provided significantly lower luminosity compared to the 0 mg·L−1 dose, indicating lower brightness of the fruit periderm (Fig. 3b), but both did not differ from the other doses. There was an increase in external chroma values over time, and on day 28 the AVG doses showed lower chroma compared to the control. Corroborating the present study, in a previous study with 'Grando F1' tomatoes treated with 1,000 mg·L−1 of AVG at −30 kPa during storage at 12 °C for 20 d and a further 2 d at 20 °C after refrigerated storage[14], it was reported that AVG reduced the rate of ethylene production and delayed ripening changes in peel color (L*, C* and h° values, chlorophyll and lycopene content). Therefore, C* values increased while h° and L* values decreased at a lower rate in AVG-treated fruit than in control fruit during storage and shelf life.

      Figure 3. 

      External instrumental color (peel), (a) luminosity, (b) chroma and (c) hue angle of tomato fruits treated with doses of AVG and stored (15 ± 1 °C and RH 90% ± 5 %) for 28 d. Lowercase letters differ the doses in a single storage time and capital letters differ the storage times in a single dose, according to the Tukey test (p < 0.05).

      The external °hue decreased until day 14 and remained stable for the rest of the time (Fig. 3c). This behavior leads to a change from green to red, which can possibly be attributed to the degradation of chlorophyll and the biosynthesis of lycopene, responsible for the tomato's red color. On day 14, the doses of AVG showed lower °hue compared to the control, and on day 21 there was no difference between the doses, and on day 28 the highest doses (1,000 and 1,500 mg·L−1) provided color maintenance compared to the control (Fig. 4), indicating that AVG reduced fruit ripening.

      Figure 4. 

      Approximate reproduction of the color profile of the peel of tomato fruit treated with doses of AVG and stored (15 ± 1 °C and RH 90% ± 5%) for 28 d, determined using a Konica Minolta colorimeter, with Luminosity, Chroma and °Hue values fed into the colorizer.org platform.

      For internal color, there was no statistical difference between AVG doses only for brightness, showing that there was no negative effect of AVG on fruit brightness. In relation to time, there was a decrease over the days, indicating a loss in the internal brightness of the fruit (Fig. 5a). On the 28th day, the internal chroma was higher in the 0 mg·L−1 control and the doses did not differ (Fig. 5b). There was an increase in color intensity on days 14 and 21. The internal ºhue gradually decreased until day 14 and remained stable on the other days (Fig. 5c), and there was no significant difference between the doses on days 14, 21 and 28. Aglar[22] reported that spraying 225 mg·L−1 of AVG on 'Li' jujube trees pre-harvest and keeping the fruit in cold storage for 45 d at 0 ± 0.5 °C and 90% ± 5% relative humidity (RH) reduced the development of fruit color.

      Figure 5. 

      Internal instrumental color (pulp), (a) luminosity, (b) chroma and (c) hue angle of tomato fruit treated with doses of AVG and stored (15 ± 1 °C and 90% ± 5% RH) for 28 d. Lowercase letters differ the doses in a single storage time and capital letters differ the storage times in a single dose, according to the Tukey test (p < 0.05).

      Principal component analysis (PCA) of 12 parameters evaluated in tomato fruit treated with doses of AVG (0, 500, 1,000, and 1,500 mg·L−1) and stored for 28 d (day 0, 7, 14, 21, and 28), allowed the general observation of the data in a smaller dimension, separated by treatment in different quadrants (Fig. 6). The variability was explained by two principal components (PC) with eigenvalues > 1.0. These two significant PCs (PC1 and PC2) accumulated 76.9% of the total variation.

      Figure 6. 

      (a) Score plot and (b) load plot of the principal component analysis of 12 parameters evaluated in tomato fruit treated with doses of AVG and stored (15 ± 1 °C and RH 90% ± 5%) for 28 d. Score graph (a): 0 mg·L−1 dose on days 0 (A), 7 (E), 14 (B), 21 (C) and 28 (D); 500 mg·L−1 dose on days 0 (P), 7 (T), 14 (Q), 21 (R) and 28 (S); 1,000 mg·L−1 dose on days 0 (F), 7 (J), 14 (G), 21 (H) and 28 (I); and 1,500 mg·L−1 dose on days 0 (K), 7 (O), 14 (L), 21 (M) and 28 (N). Load graph (b): weight loss (WL), respiratory rate (Resp), firmness (Firm), total soluble solids (SS), hydrogen potential (pH), titrable acidity (TA), lightness external (L peel), chroma external (C peel), hue angle external (°h peel), lightness internal (L pulp), chroma internal (C pulp) and hue angle internal (°h pulp).

      PC1 was responsible for 61.6% of the total variation and was effective in separating the treatments on days 0 and 7 into positive scores and the treatments on the remaining days (14, 21, and 28) into negative scores (Fig. 6a). Analysis of the PC1 loadings (Fig. 6b) suggests that this separation is mainly due to the analyses of firmness, external and internal luminosity and external and internal °h which have strong positive loadings (> 0.80) and the analyses of external and internal chroma with strong negative loadings in the PCA (< 0.75). The PC1 scores and loadings showed a greater effect for time than for AVG doses.

      PC2 in the score graph (Fig. 6a) was important mainly for separating dose 0 on day 28 (D), since this treatment had a positive score, from doses 1,000 and 1,500 on day 28 (I, N) which had the strongest negative scores, corroborating the respiration rate mean test (Fig. 1b). PC2 represented 15.3% of the total variation and was mainly related to positively charged respiration rate and negatively charged weight loss (Fig. 6b). Therefore, principal component analysis was effective in confirming the results presented here.

      By grouping the dependent variables via correlation, PCA indicated that there were positive correlations between weight loss, external and internal chroma, which correlated negatively with firmness, external and internal luminosity, external and internal hue angle, total soluble solids, and titratable acidity, and all the latter correlated positively with each other (Supplemental Fig. S1). This infers that, as weight loss increased, firmness decreased, an effect that was minimized with AVG, which may be related to the inhibition of the fruit's ethylene production rate and the expression of genes associated with chlorogenic acid metabolism, perception and signal transduction and membrane breakdown in the central tissue, as well as a decrease in malondialdehyde activity and polyphenol oxidase enzyme activity[9].

    • Under the conditions in which the experiment was carried out, it can be concluded that immersing 'Débora' tomato fruit in AVG solution at a dose of 1,500 mg·L−1 delayed ripening, reduced the fruit's respiration rate, and the changes in external and internal chroma, and it did not reduce weight loss. The doses of AVG did not negatively affect the luminosity and pH of the fruit pulp. The untreated fruit became soft and ripe red 7 d earlier than the treated fruit during the 28 d of storage at 15 ± 1 °C and 90% ± 1% RH. The feasibility of using AVG to market tomato fruit to distant markets or to local or retail markets for longer was demonstrated. More studies are needed on the use of AVG in different conditions and with other tomato cultivars.

    • The authors confirm contribution to the paper as follows: study conception and design: Aparecida dos Santos J, Rocha Lacerda V; methodology: Rocha Lacerda V, Aparecida dos Santos J, Gaona Acevedo AF, Lopes Vieites R; software: Rocha Lacerda V; validation: Rocha Lacerda V, Aparecida dos Santos J, Sílvia Angélica de Oliveira H, Gaona Acevedo AF, Rocha Lacerda V; formal analysis: Rocha Lacerda V, Aparecida dos Santos J, Gaona Acevedo AF; investigation: Rocha Lacerda V, Aparecida dos Santos J, Sílvia Angélica de Oliveira H; resources: Rocha Lacerda V; data curation: Rocha Lacerda V, Aparecida dos Santos J; draft manuscript preparation: Rocha Lacerda V, Aparecida dos Santos J, Sílvia Angélica de Oliveira H; final manuscript preparation: Rocha Lacerda V, Sílvia Angélica de Oliveira H, Lopes Vieites R; visualization: Rocha Lacerda V, Aparecida dos Santos J, Sílvia Angélica de Oliveira H, Gaona Acevedo AF; supervision: Lopes Vieites R; project administration: Aparecida dos Santos J; funding acquisition: Lopes Vieites R. All authors reviewed the results and approved the final version of the manuscript.

    • All data generated or analyzed during this study are included in this published article, and are available from the corresponding author on reasonable request.

      • This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brazil (CAPES) - Financing Code 001. To the Conselho Nacional de Desenvolvimento Científico e Tecnológico – CNPq, for the financial support for this work.

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

      • Supplemental Fig. S1 Correlations by color map cluster of twelve parameters evaluated in tomato fruit treated with doses of AVG and stored (15 ± 1 °C and RH 90 ± 5 %) for 28 days.
      • Copyright: © 2024 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 (6)  Table (2) References (22)
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    Rocha Lacerda V, Aparecida dos Santos J, Sílvia Angélica de Oliveira H, Gaona Acevedo AF, Lopes Vieites R. 2024. Doses of aminoethoxyvinylglycine (AVG) in tomato postharvest storage. Technology in Horticulture 4: e011 doi: 10.48130/tihort-0024-0008
    Rocha Lacerda V, Aparecida dos Santos J, Sílvia Angélica de Oliveira H, Gaona Acevedo AF, Lopes Vieites R. 2024. Doses of aminoethoxyvinylglycine (AVG) in tomato postharvest storage. Technology in Horticulture 4: e011 doi: 10.48130/tihort-0024-0008

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