Preparation and characterization of a complex microencapsulated diet for striped bass Morone saxatilis larvae

The nutritional requirements of marine fish larvae are not well understood, primarily due to the lack of biochemically defined diets acceptable by the larvae. This study describes the methodology for the preparation and the characterization of a complex protein-walled microcapsule (CPWC) containing lipid-walled capsules (LWC). The CPWC were prepared by atomizing a mixture of casein, LWC and other dietary materials into a cyclohexane solution containing 1% (v/v) cross-linking reagent, adipoyl chloride. The primary purpose of complex microencapsulation was to allow the gradual release of low molecular weight phagostimulants and nutrients from the cross-linked protein wall. To determine the release kinetics of low molecular weight compounds from the complex diet, a solution of the amino acid, lysine, was encapsulated in LWC and its leaching rate from CPWC was assessed. A batch of conventional protein-walled capsules (PWC) were also prepared by mixing lysine with casein. The release of lysine from CPWC was significantly lower than that measured from conventional PWC (p < 0.05). Nearly 45% of the total lysine leached out of freeze-dried PWC within 5 min of hydration, reaching 100% after 2 h. CPWC, on the other hand, efficiently retained encapsulated lysine, releasing only 25% after 2 h. In-vitro experiments indicated that CPWC were readily digested by the crude enzyme extract from striped bass larvae and purified porcine pepsin and trypsin.