Evaluation of changes in nutrient composition during production of cross-linked protein microencapsulated diets for marine fish larvae and suspension feeders

Abstract

Cross-linked protein capsules as a vehicle for delivery of nutrients to marine fish larvae and marine suspension feeders were investigated. The effects of the production process on both qualitative and quantitative changes in protein, lipid and micronutrient concentrations were evaluated. There were no changes in lipid concentration and only minor (but significant) differences in crude protein concentrations as a result of the encapsulation process. However, there was nearly a complete loss of water-soluble nitrogen during capsule production — almost 100% of the water-soluble protein was cross-linked and made insoluble and 79% of the TCA-soluble N was lost. Peptides and free amino acids were lost during the capsule washing stages, but except for a 100% loss of taurine, small changes in the amino acid profile were observed. There was more than 90% loss of water-soluble micronutrients such as thiamin, vitamin C and zinc during capsule production, and only minor increase in concentration of thiamin and zinc in the diet by increasing the levels of these minerals and vitamins were possible. The fat-soluble vitamin E was not affected by the production process and can be delivered at controlled concentrations, but vitamin A had loss ranging from 4–57% with increased inclusion of vitamin A. With the existing production protocol, the results suggest that cross-linked protein capsules are not suitable for the delivery of water-soluble nutrients to fish larvae and marine suspension feeders.