The most common source of β-glucans is the cell wall of baker's yeast, Saccharomyces cerevisiae , and this component has been widely used as feed additive to improve immunological status in aquaculture. However, the cost to produce and purify the β-glucan is relatively high. Therefore, exploring alternative sources to produce more affordable β -glucans is desirable. A potential alternative would be the use of residual yeasts used in the production of alcohol. Another promising subject to be considered in the context of reducing production costs, would be the technological process. The cell wall of Saccharomyces cerevisiae has different polysaccharides, thus the process of purification can result in different glucans functionalities. The purpose of this study was to evaluate whether feeding fish with β-glucans of different levels of purification (BG01: 69.0% and BG02: 56.4%) would affect their immune and stress response to heat killed Aeromonas hydrophila inoculation. The fish were fed with three experimental diets for 21 days, one control diet, and two diets to which 1 g kg-1 of different β-glucan products were added. On the 22nd day, blood was drawn from the fish by caudal puncture prior and 6 and 24 hours post inoculation with Aeromonas hydrophila. Our study indicates that β-glucan (BG02) extracted from residual yeasts of the production of alcohol increases the leukocyte respiratory burst after bacterial challenge and could be considered as an alternative immuno-stimulant for fish feed. Furthermore, the sustainable and circular nature of using these residual yeasts as source of β-glucans aligns with the worldwide trend and the Green Aquaculture approach.
Acknowledgment: This work was supported by Fundação de Amparo à Pesquisa do Estado de São Paulo - Brazil (FAPESP - São Paulo Research Foundation), Grants 2013/50418-1 and CNPq 305007/2016-5.