Survival of agglomerated Saccharomyces cerevisiae in pelleted shrimp feeds

Abstract

Baker's yeast Saccharomyces cerevisiae is a potential supplement in shrimp feeds, but there are few data on yeast survival after feed manufacturing processes. Dry, active yeast cells, agglomerated in spheres of different sizes (100–200 and 800–1600 μm) were incorporated into feeds processed by a commercial pellet mill or in the laboratory using a meat grinder, in order to check their resistance to the process, storage, immersion in seawater, and their effect on the pellet stability in seawater. Total counts (cells seen alive by microscopy evaluation) and viable yeast counts (colony forming units on malt agar plates) were determined in feed samples at different stages of the process. Pelleting had no significant effect on total yeast counts but decreased the viable yeast numbers about 10-fold. The laboratory process was more destructive with a 10 5-fold decrease for both total and viable yeast counts. Immersing the feed pellets in seawater further reduced the yeast number but only by less than 10-fold. Fine yeast spheres (<200 μm) had a slightly better overall resistance and survival than large yeast spheres (>800 μm). Pellet stability in seawater was not affected by the inclusion of the yeast agglomerates.