Effects of coating and encapsulation of crystalline amino acids on leaching in larval feeds

Abstract

Three types of microparticulate diets for marine larval fish were tested to improve retention of added amino acids after immersion in water. These particle types included microbound, microcoated, and microencapsulated particles. Binding crystalline amino acids to alginate, carrageenan or zein microparticles gave poor results, with leaching of 80–90% of the crystalline amino acids within minutes after immersion in water. Coating microbound diets or crystalline amino acids with tripalmitin had little effect on the retention of crystalline amino acids. Microencapsulation of crystalline amino acids within protein-walled capsules gave better results, with capsules retaining up to 60% of some crystalline amino acids after 2 min in water. The best results were obtained by encapsulating crystalline amino acids within lipid-walled capsules. Retention was further improved by including 2% (w/w) Span 85, a surface-active agent, in the lipid wall of the capsules. With this technique, leaching was reduced to 1.4% when capsules were suspended for 2 min in buffered water (pH 8.5). Feeding studies with olive flounder ( Paralichthys olivaceus) indicated that larvae older than 20 days could break tripalmitin-walled capsules. Lipid-walled capsules show promising potential for use in nutritional studies with marine fish larvae.