Synergic degradation of yeast β-glucan with a potential of immunostimulant and growth promotor for tiger shrimp

The synergic effect using γ-irradiation in combination with hydrogen peroxide was applied for preparation of water-soluble and low molecular weight (Mw) β-glucan from yeast water-insoluble β-glucans. The structural characterization by gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) suggested that the γ-irradiation did not cause any change in basic structure of β-glucans, except for the reduction in degree of polymerization. The suitable degradation conditions were determined at 10% β-glucans in pH~9% and 1% hydrogen peroxide. The water-soluble oligoβ-glucan with Mw~15 kDa showed a significantly effect on the increase of body weight and survival rate of Penaeus monodon shrimps challenged with Vibrio parahaemolyticus and White spot syndrome virus (WSSV). The oral administration of 15 kDa-oligoβ-glucan with a daily dose of 1000 ppm strongly stimulated immune factors in tested shrimps such as phagocytosis activity (PA), phenoloxidase (PO) and superoxide dismutase (SOD). Furthermore, dietary of 1000 ppm 15 kDa-oligoβ-glucan also significantly up-regulated the gene expressions of lipopolysaccharide and β-1,3-glucan-binding protein (LGLP) and prophenoloxidase (proPO). The relative percent of survivals (RPS) of shrimps fed with 1000 ppm 15 kDa-oligoβ-glucan were 56.2% and 38.1% post the challenge with V. parahaemolyticus and WSSV, respectively. These results demonstrated that the water-soluble oligoβ-glucan with Mw~15 kDa prepared by synergic degradation method showed a very promising potential for application as a natural growth promotor and immunostimulant in shrimp culture.