Changes in lipids of shrimp (Acetes vulgaris) during salting and fermentation

Changes in lipids of shrimp Acetes vulgaris during production of Kapi (salted shrimp paste of Thailand) were investigated. Shrimp had lipid content of 4.21% (dry weight basis). Lipids mainly consisted of triacylglycerol (TAG) 28.03g/100g and sterol (ST) 24.03g/100g. Lipid content decreased during salting, drying and the first period of fermentation (p<0.05). Both TAG and ST gradually decreased, while free fatty acid (FFA) increased and became dominant in the final product (49.29%). Phospholipids including phosphatidylethanolamine (PE) 4.80g/100g and phosphatidylcholine (PC) 5.67g/100g were also found in fresh shrimp and still remained in the final product. Palmitic acid (C16:0) was the major fatty acid in shrimp (27.95%). Eicosapentaenoic acid (EPA) (C20:5(n-3)) and docosahexaenoic acid (DHA) (C22:6(n-3)) were found at high content (19.03%). When different fractions were isolated from crude lipids, varying fatty acid profiles were obtained. TAG and FFA fractions mainly consisted of saturated and monounsaturated fatty acids. Polyunsaturated fatty acids were accumulated in PE and PC fractions. Peroxide value and TBARS value increased during Kapi production, suggesting that lipid oxidation took place. Overall, lipolysis and oxidation of shrimp lipids occurred throughout the processes, thereby affecting lipid constituents. Those changes might partially contribute to the Kapi characteristics, especially flavor.