Off-flavor compounds in IF-DHMP were identified using sensory-directed analysis. In total, 56 types of aroma-active compounds were identified in the off-flavor (OF) samples, positive control (PC) samples, and accelerated oxidation (AO) samples. The Aroma Extraction Dilution Analysis (AEDA) results showed that methional, generated via Maillard reaction , was the most important component with the highest dilution factor in OF. The results of aroma recombination, omission and spiking experiment revealed that compounds such as pentanal, methional, ( E )-2-nonenal, 3-methylbutanal, ( E )-2-heptenal, nonanal, ( E,E )-2,4-heptadienal, 1-penten-3-one, 1-octen-3-one, and ( E,E )-2,4-nonadienal were the major sources of off-flavor in OF. We observed that the off-flavor in OF samples originated due to proteolysis, Maillard reaction, or lipid oxidation during processing rather than due to lipid oxidation during storage.
Processing is an indispensable technology in the preparation of Spirulina platensis ( S. platensis ). The key odorants in liquids, muds, and powders from S. platensis (NM and GZ) were characterized. A total of 90 odorants were identified and 41 odorants were sniffed with the flavor dilution (FD) factors ranging from 1 to 729. Among them, nonanal, decanal, d -limonene, β -cyclocitral, and β -ionone with FD factors ≥1 were detected in S. platensis during the whole processing stages. In addition, heptanal, ( E , E )-2,4-nonadienal, trans -4,5-epoxy-( E )-2-decenal, 1-hepten-3-one, isophorone, 3-ethyl-2,5-dimethylpyrazine, and α -ionone exhibited higher odor activity values in powders; β -myrcene, methional, and S -methyl methanethiosulphonate were key odorants in muds; while trans -3-penten-2-ol was key odorant in liquids. Besides, the GZ-mud presented stronger earthy and fishy odor than NM - mud. S. platensis powders have the stronger grassy odor, roasted odor, and marine odor than S. platensis muds. Overall, drying process promotes the formation of aldehydes, heterocyclic compounds, and terpenoids.
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