YEAST AS A PROTEIN SOURCE WITH HEALTH BENEFICIAL EFFECTS IN DIETS FOR ATLANTIC SALMON Salmo salar

Introduction

 Yeasts are gaining increasing focus as major protein ingredients in fish feeds. This is in part due to their ability to convert non-food biomass of low industrial applications into high valuable resources. In addition, y east cell wall contains bioactive components such as β-glucan, mannan and chitin, which are known for their health beneficial effects in fish. Yeasts also contain about 50-60% of crude protein with favourable amino acid composition . Therefore, in the present study, we examined the nutritional  value  and health effects of three non-saccharomyces yeasts  exposed to  different down-stream processing conditions  in diets for Atlantic salmon . 

Materials and methods

Cyberlindnera jadinii (CJ) , Blastobotrys adeninivorans (BA) and Wickerhamomyces anomalus (WA)  yeasts produced from wood sugars and chicken hydrolysates were either heat inactivated (I) or autoly zed (A) and the feeding quality of the resulting yeast products were evaluated through two studies with Atlantic salmon. The first trial assessed the ability of yeasts to restore intestinal health in Atlantic salmon  fry exposed to a dietary soybean meal challenge. The experimental diets consisted  of  a fish meal-based control (FM), a challenge diet with 40% soybean meal (SBM), and 6 test diets with 40% SBM and 5% of each of the yeast products (ICJ, ACJ, IBA, ABA, IWA and AWA). Fish were fed one of the experimental diets for 37 days, after which distal intestine, head-kidney and spleen were collected for histological and immune response analyses. The second trial evaluated the nutrient digestibility of the different yeast products using experimental diets containing 700g kg-1 of a FM reference diet and 300g kg-1 of each of the yeast products.

Results and discussion

 The crude protein content of the three yeasts ranged from 38-53% and  the yeasts contain cell wall components that support growth and health of Atlantic salmon.  Autolysis  modified the ultrastructure layers of the yeast cell wall (Figure 1a). Atomic force microscopy analysis demonstrated that the ability of  yeast man noprotein to bind to cell surfaces changed with the autolysis process. Histological evaluation of distal intestine based on widening of lamina propria, showed that AWA was effective in restoring gut health , while only limited effects were observed for  the other yeasts (Figure 1b) .  As determined by  indirect ELISA, i nclusion of yeasts  in Atlantic salmon diets induced production of TNFα and a concomitant reduction in Annexin 1 level compared to SBM fed fish (Figure 2a) , which suggests a modulation of the immune response . P rotein digestibility in inactivated yeast ranged from 63-72% and increas ed by 9-12% after autolysis (Figure 2b).

 Conclusion

Based on the results of this study, yeast has a high nutritional  value  and  can give positive  health effects, and could  thus be used as  major  protein ingredient in fish feeds . Ongoing analyses will  evaluate the ability of the different yeasts to modulate gut microbiota of Atlantic salmon.

 The immunological markers are presented as  fold change relative to SBM,  and the  digestibility a s percentage. 

References

 Agboola, J.O., Øverland, M., Skrede, A., Hansen, J.Ø., 2020. Yeast as major protein‐rich ingredient in aquafeeds: a review of the implications for aquaculture production. Reviews in Aquaculture, 1-22.

Agboola, J.O., Schiavone, M., Øverland, M., Morales-Lange, B., Lagos, L., Arntzen, M.Ø., Lapeña, D., Eijsink, V.G., Horn, S.J., Mydland, L.T., François, J.M., Mercado, L., Hansen, J.Ø., 2021. Impact of down-stream processing on functional properties of yeasts and the implications on gut health of Atlantic salmon (Salmo salar). Scientific Reports. 11, 1-14.