Abstract: Polysaccharides were extracted from beer yeast mud with citric acid, and the effects of pH, extraction temperature and citric acid concentration on polysaccharide extraction were investigated by single factor and orthogonal array design methods to determine the optimal values of the three parameters for maximizing polysaccharide yield. The dried polysaccharide extract obtained was identified for its monosaccharide composition by thin layer chromatography (TLC) and UV spectrometrically measured for its water-soluble polysaccharide content. Additionally, chickens developed under identical feeding conditions were randomly divided into two groups, control group (given 10 mL of tap water per chicken every day) and trail group (given the same volume of tap water supplemented with the extract per chicken every day). At 20 days of age, the weights of spleen, thymus and bursa of Fabricius and cecal tonsil area of chicken were measured. The optimal extraction conditions of beer yeast polysaccharides were as follows: pH, 7.2; temperature, 40 ℃; and citric acid concentration, 20 mmol/L. The major monosaccharide in beer yeast polysaccharides was glucose. Beer yeast polysaccharides could stimulate the development of immune organs in chicken, as evidenced by higher indexes of thymus gland, spleen, bursa folds, and weight or size increase of cercal tonsil in the treatment group compared with those in the control group.

Key words: beer yeast, yeast polysaccharides, extraction, chicken, immune organs