Comparison of biochemical composition and non-volatile taste active compounds in raw, high hydrostatic pressure-treated and steamed oysters Crassostrea hongkongensis.

In this study, the effects of high hydrostatic pressure (HHP) and steam on biochemical composition and non-volatile taste active compounds of oysters Crassostrea hongkongensis were investigated. The moisture content in steamed oysters significantly decreased when compared to raw samples, subsequently their crude protein, crude lipid, glycogen and ash contents (% wet weight) were all increased (P < 0.05). In addition, though the moisture content in HHP oysters decreased, no significant differences were observed in proximate compositions compared to raw oysters, except crude protein. There were no significant differences in saturated fatty acids (SFA), monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) profiles between raw and HHP oysters, however, C20:3n6 content in HHP oysters was significantly higher than that in raw samples (P < 0.05). The PUFA profile of steamed oysters, mostly contributed by n-3 PUFA, was significantly higher than that of both raw and HHP samples (P < 0.05). Major free amino acids (FAA) (taste activity value, TAV > 1) in oysters with three treatments were alanine, glycine, glutamic acid and histidine, and their contents were significantly higher in raw and HHP groups than that in steamed group. The 5'-inosine monophosphate (IMP) and 5'-guanosine monophosphate (GMP) in HHP and steamed oysters decreased compared to raw samples, while AMP content in steam oysters were significantly increased (P < 0.05). The equivalent umami concentration (EUC) of oysters of raw, HHP and steamed groups were 8.80, 3.66 and 1.44 g MSG/100 g, respectively, with significant differences observed among different treatments (P < 0.05). Succinic acid was the major organic acid in raw and HHP oysters, while lactic acid was the major organic acid in steamed groups. Further, Na+, K+, PO43- and Cl- were the main inorganic ions (TAV > 1), and their contents were significantly higher in raw and HHP groups than that in steamed group (P < 0.05). This study demonstrated that HHP treatment slightly influenced the changes in the biochemical composition and non-volatile taste active compounds to raw oysters, compared to steamed process.