Preparation of spent brewer's yeast β-glucans with a potential application as an immunostimulant for black tiger shrimp, Penaeus monodon

Spent brewer's yeast was autolysed and the insoluble yeast cell wall fraction obtained was used as a raw material for the preparation of brewer's yeast P-glucan (BYG). A simple alkaline extraction was applied and optimized. The BYG with significantly (P less than or equal to 0.05) high carbohydrate and glucan contents of 92% and 51% (w/w), respectively and with a low protein content of 1.6% (w/w) was obtained by a single alkaline extraction using 5 volumes of 1.0 N NaOH at 90degreesC for 1 h. In vitro, this glucan significantly (P less than or equal to 0.05) enhanced phenoloxidase (PO) activity of black tiger shrimp hemolymph as compared to controls without added glucan. Also in vivo, an oral administration of 0.2% (w/w) in diets for 3 days significantly (P less than or equal to 0.05) increased the PO-activity of the shrimp. The potential immunostimulating properties of a commercial and other yeast-derived products were also evaluated for comparative purposes. (C) 2002 Elsevier Science Ltd. All rights reserved.