Lipid nutrition of juvenile Litopenaeus vannamei: II. Active components of soybean lecithin

Abstract

Two experiments were conducted to investigate the active components of soybean lecithin for juvenile Litopenaeus vannamei. The first experiment was conducted to determine the dietary phosphatidylcholine (PC) requirement of juvenile L. vannamei, and to investigate whether other phospholipids (PL), mainly phosphatidylethanolamine (PE) and phosphatidylinositol (PI) were the active fractions of soybean lecithin. Seven levels of PC (0%, 0.35%, 0.7%, 1.4%, 2.1%, 2.8%, 4.2%) extracted from soybean lecithin (PC purity 93%) were used to determine the PC requirement; also, PE and PI (in a 25:22 proportion) were tested at 0.84% and 1.68% levels with PC levels controlled at 0.35% and 0.52% of diet to investigate the combined PE and PI effects. Results showed that no dietary PC requirement was evident based on shrimp growth and survival. Increasing purified PC in the diet decreased total lipid, free fatty acid and other PL levels in shrimp hepatopancreas (mid-gut gland) and increased PC level in shrimp muscle. However, other PL, mainly PE and PI, showed significant enhancing effects on shrimp growth when PC was provided at 0.35% or 0.52% of diet. Another 4×2 factorial experiment was concluded to reevaluate the requirement of shrimp for PC by including purified PC at 0%, 0.7%, 1.4 % and 2.8% of diet with or without 0.1% cholesterol in the diet. A diet containing 1.4% PC provided by deoiled lecithin also was tested for comparison. Results showed no interaction between PC and cholesterol on shrimp growth, survival and feed conversion ratio (FCR). Compared with the apparent growth-enhancing effect of dietary cholesterol, the effect of purified PC was negligible. With PC at 1.4% of diet, the presence of other PL from lecithin or 0.1% cholesterol significantly enhanced shrimp growth and FCR. In summary, purified soybean PC showed different effects from deoiled lecithin on shrimp growth, lipid composition, and relationship with dietary cholesterol. Beneficial effects of soybean lecithin on growth of L. vannamei could be attributed to the presence of PL other than PC in the diet under the experimental conditions of this study.