Extrusion processing improves rainbow trout digestibility of microalgal Nannochloropsis oculata co-product biomass for more sustainable aquaculture diets
Pallab K. Sarker, Anne R. Kapuscinski, Devin Fitzgerald, Connor Greenwood, Pablo Nocera, Kira O’Shelski, Benjamin Lee, Abel Mkulama, Sofie Andrade, Duncan Gwynne, Diego Gonzalez Orcajo, Lydia Warkaw, Benjamin Schoffstall
Abstract
Aquaculture feeds include fishmeal (FM) and fish oil (FO), derived from wild-caught marine fish such as anchovy and sardines, and pose ecological, food security, and economic drawbacks for sustainable aquaculture, the world's fastest-growing agricultural sector. Protein-rich microalgal co-product is a promising alternative to unsustainably sourced fishmeal in aquaculture diets. Microalgal co-product is a defatted biomass left over after extracting omega-3-rich oil for human nutraceuticals and crude oil for fuels. In this study, we report the first evaluations of nutritive values and digestibility of raw, extrusion- and enzymatic-processed co-product of the marine microalga Nannochloropsis oculata (N. oculata co-product). Results allowed us to evaluate the feasibility of using processed biomass in aquafeed for rainbow trout (Oncorhynchus mykiss), an important model for all salmonid aquaculture. Extrusion processing temperature (90 °C vs 127 °C) influenced the nutritional value of N. oculata. Protein and energy levels were significantly higher in co-product from both extrusion temperature treatments than in non-extruded raw co-product. Essential amino acid levels did not differ between extrusion temperatures, except that methionine was significantly lower in coproduct from 127 °C extrusion processing than from 90 °C extrusion processing. The protein level in extrusion processed co-product was not significantly influenced by pre-cooking. We detected the highest digestibility of crude protein, energy, most of the amino acids, and omega 3 polyunsaturated fatty acids (n3 PUFA) in extruded (90 °C) N. oculata co-product ingredient. Nutrient digestibility of enzymatic processed N. oculata co-product were mostly the same as extrusion processing or lower for certain nutrients. Overall, extrusion processing of N. oculata at 90 °C provided the best outcome for digestible protein, and yielded an excellent source of digestible protein, amino acids, and long chain omega-3 profile for rainbow trout and which could be an alternative to replace fishmeal in rainbow trout diets.