Effect of high pressure processing on fatty acids and amino acids content of New Zealand clams
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High pressure processing (HPP) treatment is considered to be a popular non-thermal processing technology. It benefits food producers as it may maintain or increase the nutritional value of food and extend shelf life. Previous researchers have documented that HPP treatment could significantly change the physical, chemical and microbial properties of food. However, only few studies have examined the effects of HPP on chemical properties of seafood. These studies have reported variations of lipid and fatty acid aspects in seafood in terms of their oxidation level and content composition. However, no literature has investigated the effect of HPP on amino acid content. Hence, the aim of the current study was to investigate the effect of HPP treatment on the content of amino acids and fatty acids in two species of New Zealand clams, storm shell and tuatua. HPP treatment was carried out at 100, 200, 300, 500, and 600MPa, 18°C, for 5 seconds and 10 minutes. In the current research, the content of unsaturated fatty acids (UFA) and saturated fatty acids (SFA) in pressure treated storm shell clams significantly decreased at 300 and 600MPa, respectively, when held at 5s and 10min compared to controls. In comparison, TuaTua showed more significant changes in fatty acid content than storm shell when compared to controls. Specifically, in Tua Tua, a significant drop (P<0.05) in the total content of UFA occurred at 200MPa when held for 5s, and the value decreased significantly (P<0.05) in SFA at 500 and 600MPa when held for 5s. Moreover, treatment Tua Tua for 10min resulted in significantly increased (P<0.05) UFA and SFA at relatively lower pressures (100, 200, 300MPa) compared to controls. Comparison of pressurization times of 10 minutes and 5 second, revealed that the longer pressurization time (10 min) of Storm Shell clams caused a significant decrease (P<0.05) in both UFA and SFA content at relatively high pressures of 500 and 600MPa, with a significant increase (P<0.05) in SFA evident with 100MPa treatment. However, no significant changes in fatty acid contents were found in HPP treated Tua Tua clams when compared to pressurization time 10min to 5s. In general, almost all significant changes in fatty acid content of both Storm Shell and Tua Tua clams mainly occurred in the content of C18:0, C23:0, C24:0, C20:5n3, and C20:6n3 fatty acids. Nineteen free amino acids, including 7 essential and 12 non-essential amino acids were identified in both storm shell and Tua Tua clams. HPP treatment of Storm Shell clams for 5s and 10min at all pressure conditions (100-600MPa) resulted in significantly decreased (P<0.05) total essential amino acid (EAA) content when compared with the control. Moreover, only some significant increases (P<0.05) in total content of non-essential amino acid (NEAA) of Storm Shell were found in samples treated at 100, 200, and 300MPa for 5s and 10min compared to control. However, a significant decrease (P<0.05) in the content of EAA in Tua Tua was observed at 500 and 600MPa for both of 5s and 10min treatments compared to control. Additionally, compared to control, no significant changes were found in the total content of NEAA with 5s treatment of Tua Tua, but some significant decrease (P<0.05) in NEAA occurred at 500 and 600MPa when pressure-treated for 10min. The effect of pressurization times of 5s and 10min under the same pressure conditions were also compared. In storm shell clams, there were significant increases (P<0.05) in total EAA and NEAA content at 100MPa treatment for 10min when compared to 5s treated samples and a significant decrease (P<0.05) at 300, 500 and 600MPa treatments for 10min compared to 5s treatment. As for Tua Tua, the significant increase (P<0.05) in the content of EAA at 200MPa, 10min and increased significantly of content of NEAA at 300MPa for10min can be observed when compared to 5s treated samples. Besides, the significant decrease in the content of EAA and NEAA (P<0.05) can be found at both 500 and 600MPa, 10min when compared to 5s treatment samples.