Lipid spray beads for delivery of riboflavin to first-feeding fish larvae

High nutrient loss due to leakage from microparticulate diets is an important problem in the development of artificial diets for marine fish larvae. Lipid spray beads (LSB) are promising as they can be used to deliver low-molecular weight, water-soluble nutrients. Here, we describe a simple method for the production of LSB composed of methyl palmitate (MP), a low melting point wax, for delivering riboflavin to first-feeding freshwater fish larvae of zebra fish, Brachydanio rerio, and glowlight tetra, Hemigrammus erythrozonus. Characteristics of LSB, such as inclusion, retention and delivery efficiencies as well as overall leaching patterns over time, were used to compare the performances of LSB prepared with different materials. The mean inclusion efficiency (IE) of riboflavin within LSB was 96.70% and it was improved by addition of emulsifiers to the lipid matrix. Addition of the solid (at room temperature) emulsifier, sorbitan monopalmitate (SMP) resulted in higher retention efficiencies compared to the additions of liquid emulsifier sorbitan sesquioleate (SSO). Additions of SMP were found to have a positive effect on retention and delivery efficiencies of LSB at concentrations of 10% and 25% (w/w) of lipid. LSB composed of a mixture of MP+10% SMP+10% ethyl cellulose (EC, w/w) were shown to retain riboflavin with the highest retention efficiencies over a period of 6 h of aqueous suspension. Use of MP facilitated digestive breakdown of LSB by larvae of zebrafish and glowlight tetra as indicated by release of free riboflavin from ingested LSB. There is a need to balance the wall stability of LSB with the digestion requirements of target species. The results suggest that it is possible to formulate a carrier lipid matrix that both retains riboflavin and is digested by fish larvae. Besides riboflavin delivery, LSB may also be useful as a carrier for other water-soluble nutrients, such as dietary amino acids and peptides.