Abstract:

Three kinds of water soluble soybean polysaccharides,namely,SSPS P₁ ,SSPS P₂ and SSPS P₃ ,were extracted from soy bean dregs by using tartaric acid,sodium hexametaphosphate and sodium hydroxide.Then,the flocculation effects of the SSPS on the brewer yeast suspension with different metal cations (Al³⁺ 、Fe³⁺ 、Fe²⁺、Mg²⁺、Ca²⁺、K⁺、Na⁺ )，polysaccharide concentrations，pH values and temperatures were respectively in- vestigated.Moreover,the response surface experiment design was performed to optimize the flocculation condi- tions,and a corresponding mathematical regression model was constructed.Single factor research results show that (1) SSPS P₁ has the best effect in flocculating the brewer yeast suspension; (2) most of the metal cations increase the flocculation effects,among which Fe³⁺ shows the best performance; (3) when the Fe³⁺ concentration reaches 0. 025mmol/L,the best flocculation effect can be achieved; (4) the flocculation effects can also be influenced by the SSPS P₁ concentration and the temperature,and the effects are better at 10mg/L and 30℃; and (5) a strong alkaline environment is helpful in adopting SSPS P₁ to flocculate the brewer yeast suspension.The analytical results based on the constructed model indicate that the optimal flocculating condition is a SSPS P₁ mass concentration of 11. 56mg/L,a Fe³⁺ concentration of 0. 26mmol/L,a pH value of 9. 05 and a temperature of 30. 68℃,and the experimental value of the flocculating rate under the optimal condition is very close to the predicted one,which means that the constructed model can reflect the influence of various factors on the flocculation effect.

Key words: water soluble soybean polysaccharides, flocculation, brewer yeast suspension, metal cation, re- sponse surface methodology