Biotechnology processing of lignocellulosic biomass such as Norwegian spruce trees and chicken hydrolysates to produce high-quality microbial ingredients such as yeast can help address the protein deficit, reduce environmental footprint and improve fish health and welfare. The yeast obtained contains about 50-55% crude protein with a favorable amino acid composition and bioactive components like β-glucans, mannoproteins and nucleic acids, which can modulate the immune response of the fish.
In general, our studies with Atlantic salmon showed that fish perform well when fed yeast-based diets. Dietary yeast has also shown to have positive health effects in salmon, including improved gut barrier function, immunity, and gut microbiota composition. Documenting value-added effects beyond the nutritional value such as effect on health is important for the overall profitability of yeast, as yeast cannot compete with the cheap prices of plant proteins such as soy protein concentrate. However, yield, nutritional value and health effects of yeast depend on species, fermentation and downstream processing (DSP) conditions.
We evaluated the structure and physicochemical properties of the cell wall of three non-saccharomyces yeast species (Cyberlindnera jadinii (CJ), Blastobotrys adeninivorans and Wickerhamomyces anomalus (WA)) produced from spruce tree sugars and chicken hydrolysates and then exposed to DSP by autolysis. The yeasts were evaluated in diets for Atlantic salmon fry. Fish were fed a fish meal-based control diet or a challenge diet with 40% soybean meal (SBM), and 6 test diets with 40% SBM and 5% of the three whole yeast species or their autolysates. Adding yeast to a challenge SBM-based diet did not affect growth performance, but CJ and WA reduced the severity of enteritis in the distal intestine (DI) and modulated gut microbiota composition in DI and immune responses in DI and spleen. Best effects were observed with autolyzed WA. Processing by autolysis affected the length, accessibility and binding properties of the cell wall components β-glucans and mannoproteins, which improved the health effects of yeast.
CJ was also evaluated in a salmon trial during sea water transfer. Adding 25% CJ to a commercial-like diet increased feed intake and growth rate, reduced secretion of cytokines in DI (IFNγ, TNF-α, IL-1β and IL-8) on both a transcriptional and a protein level, prevented morphological changes, and maintained numbers of CD3 cells in DI after seawater transfer, suggesting reduced inflammatory processes in yeast fed fish. Thus, yeast, depending on the species and processing conditions, is a promising protein source with health-beneficial properties during critical life stages.
The fermentation technology has now been scaled up and a field trial with Atlantic salmon in sea cages is being performed. This will provide important information on growth performance, health and sustainability and economical aspects of yeast as a novel feed resource for Atlantic salmon.