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Figure 1. High Performance Liquid Chromatogram of organic acid concentration.
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Figure 2. (a) E-nose gas chromatogram; (b) total peak area.
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Figure 3. Comparison of total peak area of different category VCs.
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Figure 4. Radar chart of coffee aroma.
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Figure 5. Comparison of coffee taste. (a) bitterness, astringency and the aftertaste of the two; (b) saltiness, umami and richness; (c) sourness.
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Figure 6. Analysis of coffee cup-testing.
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Figure 7. Radar chart of coffee sensory results.
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Category of treatment No. Method Temperature Pressure Duration Notes Sample Heat sterilization 1 Pasteurization 65 °C / 30 min / PS 2 Back pressure sterilization 121 °C 1.5 bar 30 min / BPS 3 High pressure short-term sterilization 110 °C / 5 s / HTS Non-heat sterilization 4 Membrane filtration 25 °C / / Ceramic membrane, 200 μm MF 5 High pressure processing 25 °C 5,000 bar 5 min / HPP Table 1. Parameters of each sterilization method.
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Parameters Chlorogenic acids Tartaric acid, Citric acid, Malic acid,
Succinic acid, Fumaric acidSpeed 1.0 mL/min 0.3 mL/min Column temperature 30 °C 40 °C Wavelength 327 nm 210 nm Moving phase Methanol (A) -0.1% phosphoric acid solution (B) Methanol (A) -0.1% phosphoric acid solution (B) Elution program 0.00−20.00 min: 20%A−80%B
20.01−45.00 min: 35%A−65%B
45.01−55.00 min: 40%A−60%B
55.01−60.00 min: 20%A−80%B0.00−20.00 min: 10%A−90%B
20.01−25.00 min: 100%A
25.01−35.00 min: 10%A−90%BTable 2. Chromatographic parameters for organic acid measurement.
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Sample CK PS BPS HTS MF HPP pH value 4.92 ± 0.006cd 4.89 ± 0b 4.65 ± 0a 4.91 ± 0.006bc 4.93 ± 0.021d 4.9 ± 0.006bc Neochlorogenic acid 1.45 ± 0.07a 1.49 ± 0.02ab 2.13 ± 0.02c 1.47 ± 0.01ab 1.47 ± 0.04ab 1.53 ± 0.02b Chlorogenic acid 3.39 ± 0.18b 3.46 ± 0.06b 2.87 ± 0.04a 3.42 ± 0.02b 3.45 ± 0.09b 3.48 ± 0.04b Cryptochlorogenic acid 1.8 ± 0.09a 1.84 ± 0.03a 2.12 ± 0.03b 1.82 ± 0.01a 1.83 ± 0.04a 1.87 ± 0.02a Isochlorogenic acid A 0.04 ± 0a 0.04 ± 0b 0.04 ± 0b 0.04 ± 0ab 0.04 ± 0b 0.04 ± 0b Isochlorogenic acid B 0 ± 0a 0.01 ± 0.01ab 0.02 ± 0.01ab 0 ± 0ab 0.01 ± 0.01a 0.02 ± 0b Isochlorogenic acid C 0.04 ± 0ab 0.04 ± 0c 0.04 ± 0a 0.04 ± 0bc 0.05 ± 0c 0.04 ± 0c Tartaric acid 6.71 ± 0.35a 6.88 ± 0.11a 7.21 ± 0.09b 6.78 ± 0.04a 6.85 ± 0.18a 6.98 ± 0.08ab Malic acid 5.88 ± 0.56a 5.85 ± 0.14a 6.07 ± 0.33a 5.88 ± 0.23a 5.81 ± 0.09a 5.85 ± 0.18a Citric acid 1.08 ± 0.48a 1.26 ± 0.04a 1.29 ± 0.09a 1.22 ± 0.03a 1.21 ± 0.03a 1.39 ± 0.15a Succinic acid 4.26 ± 0.18a 4.28 ± 0.46a 7.57 ± 0.82b 4.71 ± 0.12a 4.6 ± 0.04a 4.45 ± 0.18a Fumaric acid 0.19 ± 0.16a 0.2 ± 0.18a 0.29 ± 0.25a 0.19 ± 0.17a 0.21 ± 0.18a 0.18 ± 0.16a Total 0.03 ± 0ab 0.03 ± 0ab 0.03 ± 0b 0.03 ± 0a 0.03 ± 0ab 0.03 ± 0ab Different letters in the same row indicated significant difference (p < 0.05) Table 3. pH value and organic acid concentration (g/kg) of each sample.
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No. Retention time (s) Retention index Possible VCs Sensory description Category 1 15.2 415 Acetaldehyde Fruit, pleasant, spicy Aldehydes 2 15.9 430 Methanol Alcohol, spicy, strong Alcohols 3 16.5 441 Ethanol Alcohol, spicy, strong Alcohols 4 17.7 468 Propionaldehyde Cocoa, nut, plastic, spicy Aldehyde 5 19.4 502 Ethyl formate Fruit, green, spicy, rose Esters 6 21.1 537 2-methylpropionaldehyde Baked potatoes, fruit, malt, roasted Aldehyde 7 23.1 580 N-butyraldehyde Cocoa, chocolate, green, malt, musty Aldehyde 8 24.0 597 2-butanone Butter, cheese, chocolate, pleasant Ketones 9 24.8 605 2-methylfuran Charred, chocolate, metal Other 10 27.5 627 Isobutanol Alcohol, bitter, licorice, sweet Alcohols 11 29.3 641 Isopropyl acetate Bananas, fruit, sweet Esters 12 30.5 650 3-Methylbutyraldehyde Almonds, cheese, chocolate, malt, peach, roasted Aldehyde 13 31.8 661 2-ethylfuran Burnt, acidic, sweet, rubber, malt Other 14 35.1 686 2-pentanone Bananas, fruit, sweet Ketones 15 36.1 694 2,3-pentanedione Almond, apple, cream candy, caramel, cheese, cream, fruit, malt, nut Ketones 16 38.5 709 3-pentanol Fruit, green, nutty, greasy, sweet Alcohols 17 41.5 726 Glutaraldehyde Almonds, berries, fruits, green, nutty, malt, herbal Aldehyde 18 43.6 737 Pyrazine Bitter, corn, hazelnut, nutty, sweet, spicy, strong Pyrazine 19 44.8 744 Isoamyl alcohol Alcohol, sesame oil, bitterness, cheese, fruit, malt, spicy, whisky, charred Alcohols 20 46.0 750 pyridine Burnt, amine, spicy Pyridine 21 48.1 762 2-methylglutaraldehyde Cheese, fruit Aldehyde 22 49.6 771 N-pentanol Alcohol, fruit, sesame oil, fennel, sweet, spicy Alcohols 23 50.8 777 1-hexene-3-alcohol Freshly cut grass, rum Alcohols 24 52.2 784 2-hexanone Fruit, cinnamon, fungi, meat, spicy Ketones 25 54.0 794 N-hexanal Herbal, dense, sweet, oak, butter Aldehyde 26 55.0 800 2-Hexanol Broccoli, fruit, wine Alcohols 27 56.9 808 Propyl propionate Apple, fruit, pineapple, fruity (sweet) Esters 28 58.7 815 Bread ketone Nuts, coffee, bread Ketones 29 59.5 819 2-hydroxy-3-pentanone Butter, nuts, peanuts, truffles Ketones 30 60.9 824 Ethyl isovalerate Fennel, apple, fruit, sweet Esters 31 63.1 833 Furan formaldehyde Almond, aromatic, roasted, sweet, woody Aldehyde 32 68.2 855 Isovaleric acid Cheese, fruit, sour Acids 33 70.8 865 N-hexanol Medicinal, plant, branch, sweet, woody, barbecue Alcohols 34 76.3 888 2,4-dimethylthiazole Cocoa, coffee, meat, beef flavor Other 35 79.9 904 2-methoxypyrazine Chocolate, cocoa, nuts, sweet Pyrazine 36 82.7 919 Valeric acid Sour, sweet, spicy, rotten Acids 37 86.0 936 4,5-dimethylthiazole Roasted, smoked, nutty, earthy Other 38 86.8 940 Isovaleraldehyde propylene glycol acetal Caramel, fruit, sweet, sour Aldehyde 39 88.3 948 Propyl isovalerate Apple, fruit, sweet Esters 40 89.7 956 2-ethoxythiazole Nut (roasted), coffee, burning Other 41 91.0 963 Tetrahydrothiophene-3-one Roasted, garlic, onion flavored Ketones 42 93.0 973 Filbertone Hazelnut, nut Ketones 43 97.5 997 2-Acetylthiazole Bread, burnt, caramel, grain, peanuts, hazelnuts, popcorn, roasted Other 44 99.0 1007 Caproic acid Cheese, goat, sour, sweet, rotten Acids 45 100.0 1015 Heptadiene aldehyde Cinnamon, greasy, nutty, rancid Aldehyde 46 101.7 1028 2-acylpyrrole Popcorn, roasted Pyrrole 47 103.2 1040 2-acetylpyridine Biscuits, bread, greasy, popcorn, tobacco Pyridine 48 105.1 1055 Furanone methyl ether Caramel, fruit, mushroom, burning Other 49 105.8 1061 2-methyl-5-vinyl pyrazine Roasted, sweet, coffee, nut Pyrazine 50 106.3 1065 2-acetylpyrrole Nuts, walnuts, caramel, fennel, licorice Pyrrole 51 107.1 1071 3-methylcyclopentane-1,2-dione Caramel, coffee, sweet, maple Ketones 52 109.1 1086 2-acetylpyrazine Cocoa, coffee, popcorn Pyrazine 53 111.2 1104 2-Nonanol Apple, banana (ripe), cherry, orange, fruity Alcohols 54 122.7 1194 Ethyl octanoate Fennel, roasted fruit, fruit Esters 55 132.4 1269 Nonanoic acid Cheese, dairy products, sour Acids Table 4. Information of main possible VCs.
Figures
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Tables
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