Glucan from spent brewer's yeast: preparation, analysis and use as a potential immunostimulant in shrimp feed

Spent brewer's yeast was autolysed and the residual solids were further treated with hot alkali to produce a fraction containing 95% (w/w) carbohydrate, with a glycogen content of 42% and an apparent glucan content of ca. 53% (w/w). FTIR and solid state C-NMR spectra basically showed a spectrum characteristic for an impure beta-glucan. In vitro, this glucan induced release of prophenoloxidase from intact black tiger shrimp haemocytes. When fed to shrimp at 0.2% (w/w of the feed) for 3 days, significant increases in phenol oxidase, the number of haemocytes and the bacterial killing activity against the pathogen Vibrio harveyi were observed. Furthermore, this feeding resulted in the appearance of an inducible beta-(1,3)-glucanase in the liver. Methods to analyse the fractions are discussed and a number of commercial products with potential immune stimulating properties have been included for comparative purposes.