Effect Of Fermentation By Lactobacillus Plantarum On Functional And Sructure Properties Of Soybean Protein To Apply

Soybean is widely planted in our country, which with high yield and abundant nutritional value, such as high content of protein and feasible amino acid. At the same time, soybean protein is used in food processing for its many functions, which benefit from high nutritional value and no cholesterol. At present, soybean protein was made from low-temperature defatted soybean meal, which is a by-product of soybean oil processing. In the processing, protein denaturation is caused by high temperature, the application was limited for its functional properties reduction. In defatted soybean meal fermentation which is induced by Lactobacillus plantarum, soybean protein composition, structure and functional properties was influenced because of the microbial metabolism product such as protease and lactic acid. The research took the defatted soybean meal as raw material, pretreatment by liquid state fermentation with the Lactobacillus plantarum for different time(0h, 3h, 6h, 9h, 12h), then extracted the protein with the method of alkali-extraction and acid-precipitation. The soybean protein structure and properties were determined by the biochemistry and spectroscopy method. The soybean protein products whi ch with the good functional properties was applied in ice cream production. The main results are as follows:(1)The optimum condition in alkali-extraction and acid-precipitation method were determined with the single factor and the response surface method, The optimum condition are as follows: The effect of factors, such as alkali-extraction p H, temperature and time, as well as acid-precipitation p H and time was optimized. The optimum condition are as follows: alkali-extraction p H is 9.28, alkali temperature is 45.55 ℃, he alkali time is 77.70 min, acid-precipitation p H is 4.5, at this point, soybean protein extraction rate was 67.12 ± 0.15%.(2) The growth situation of Lactobacillus plantarum in defatted soybean meal was explored. The pH, acidity, viable count and protease activity were measured and compared in MRS culture medium and defatted soybean milk culture medium. The results shows that p H value, acidity and viable count in two situation are both ideal, which suggest Lactobacillus plantarum can grow well in defatted soybean milk without additional nutrients, meanwhile, in this condition, protease activity can achieve higher activities.(3) Soybean protein degradation degree in defatted soybean meal fermentation was discussed. The SDS-PAGE results indicate that protease induced by Lactobacillus plantarum can cause obvious degradation of protein. 7s component are more likely to be degraded than 11 s component, the degree of hydrolysis and protein digestibility in vitro of soybean protein sample was increase d with increasing fermentation time, however, molecular size of soluble protein was reduced.(4) The research studied the impact of Lactobacillus plantarum fermentation on soybean protein structure. Fermentation for 3 h, 6 h, 9 h and 12 h, protein molecules was unfold, the beta-fold content was increased. The alpha helix content was increased in many groups except in group which was fermentation for 12 h. At the same time, hydrophobic was exposed constantly, which lead to surface hydrophobicity increased, more sulfhydryl groups was exposed. scanning electron microscope result suggests the surface of soybean protein was no more smooth as the fermentation times went on, there are some corrosive holes on the surface and structural damage is serious.(5) The research studied the impact of Lactobacillus plantarum fermentation on soybean protein functional properties. The extracting soy protein which fermented for 0 hour compared with the original soybean protein has higher emulsifying property, foamability, foam stability,gel strength and water-hold capacity significantly(P < 0.05), the solubility, emulsifying stability and the oil-hold capacity has not significantly improved(P > 0.05).the extracting soybean protein which fermented for 3 h, 6 h,9 h and12 h compared with the original soy protein has higher solubility, emulsification, foaming and gel strength significantly(P < 0.05), emulsion stability and foam stability decreased significantly(P < 0.05), the water-hold and the oil-hold capacity has not changed obviously.(P > 0.05).(6) With the comparison of functional properties,it turned out that with 9 hours fermentation, the soy protein extract has great solubility,emulsification, and foaming ability than other groups(P < 0.05), so we added it in the ice cream making processing. Optimum additive content in ice cream formula was explored by single-factor method and orthogonal method. Finally, CMC 0.2%, monostearin 0.05%,and soybean protein 3% content were added to the ice cream.