Reduction of raffinose oligosaccharides in red gram flour by microbial α-galactosidase

The effect of crude α-galactosidase from Aspergillus oryzae, Gibberella fujikuroi and Lactobacillus brevis in reducing the raffinose, stachyose and verbascose content in red gram flour was studied. The optimum pH for α-galactosidase was found to be 4.8 for A. oryzae, 5.0 for G. fujikuroi and L. brevis, while the optimum temperature of enzyme activity was 55°C for A. oryzae, 60°C for G. fujikuroi and 40°C for L. brevis. The specific activities of α-galactosidase from A. oryzae, G. fujikuroi and L. brevis were 1.54, 0.73 and 0.93 unit mg⁻¹ protein respectively. These enzymes were thermostable when incubated at temperature ranges of 40–60°C for A. oryzae, 40–65°C for G. fujikuroi and 35–45°C for L. brevis. The optimum conditions for removing the raffinose, stachyose and verbascose were obtained by incubating red gram flour with 50 ml of crude microbial α-galactosidase extract (0.67, 0.55 and 0.67 units ml⁻¹ for A. oryzae, G. fujikuroi and L. brevis respectively) for 3 hr at the optimum conditions of each strain. Crude A. oryzae and G. fujikuroi α-galactosidase reduced the raffinose oligosaccharide content in red gram flour by 100%, while crude α-galactosidase treatment from L. brevis reduced the raffinose content by 70.20%, stachyose 58.14% and verbascose by 71.56%.