Research On Effect Of β-glucan On Properties Of Soybean Protein Mixed Gel And Application In Soymilk Yoghurt

Both of protein and polysaccharide which are biological macromolecular material not onlycan improve the nutritional characteristics of food, but also greatly affects texture, rheology andother physical and chemical properties of food. They are the main factors that form texture andprocess characteristics of food, and there is a crucial effect on structure characteristics of food. Inthis study, the rheological properties, texture properties and microstructure of soybeanprotein/β-glucan were studied systemically by combination use with dynamic rheolog, textureanalysis and scanning electron microscope analysis methods. The effect of β-glucan on propertiesof soybean protein mixed gel and application of β-glucan in soymilk yoghurt were researched. Themain results were as follows：The β-glucans were extracted by ultrasonic auxiliary water from oats. Different molecularweights of β-glucans were obtained by acid hydrolysis for different time and measured by gelfiltration chromatography, including360kDa,300kDa,250kDa,190kDa and80kDa, for OGL360,OGL300, OGL250, OGL190and OGL80respectively.The effect of different concentration and different molecular weight of β-glucan onrheological properties, texture properties and water holding capacity of SPI mixed thermal gelwere studied. The results showed that mixing with β-glucan in the SPI could make gel strengthincreased and water holding capacity decreased. And gel strength and texture parameters of mixedsystem would increase as the increase of the concentration and molecular weight of β-glucan. Highmolecular weight of β-glucan could improve water holding capacity of mixed gel. Gel strength andwater holding capacity of mixed system were reduced with the increase of the ionic strength.Under the condition of low ionic strength, the effect of concentration of β-glucan on gel strengthand water holding capacity of mixed system was remarkable.SPI was fermented by different Lactobacillus (Lactobacillus acidophilus、Streptococcusthermophilus、Lactobacillus bulgaricus) and mixture of them to prepare acid-set gel. Methods suchas rheometer and texture analyzer were used to analyze the properties of SPI acid-set gel. Asresults showed, acid production of fermentation by mixed bacteria was better than that of singlebacterium. On the basis of single factor experiment, technological parameters of SPI gel weredetermined by mixture design method to optimize fermentation conditions as following：concentration of SPI was12%, adding5%glucose, adding0.99%Lactobacillus acidophilus,adding0.95%Streptococcus thermophilus, adding1.06%Lactobacillus bulgaricus, fermentation temperature was42℃, fermentation time was5hours.Physical properties and microstructure of SPI/β-glucan mixed system acid-set gel byinduction of Lactobacillus were investigated. The effect of concentration and molecular weight ofβ-glucan on rheological properties, syneresis, texture properties and water holding capacity of SPIacid-set mixed gel were discussed. As results showed, the rate of fermented acidification byLactobacillus bulgaricus was faster. And the effect of Lactobacillus bulgaricus as being the bestfermentation strains on mixed gel properties was better than Lactobacillus acidophilus andStreptococcus thermophilus. Syneresis of mixed gel was reduced by β-glucan with highconcentration or high molecular weight, that is to say, whey separation was decreased. Mixing withβ-glucan in the SPI could make the strength and water holding capacity of mixed gel reduced, andwater holding capacity would decline as the increase of the concentration of β-glucan. Weakeningeffect of β-glucans on SPI acid-set mixed gel could be eliminated by using β-glucans with highmolecular weight, and gel strength and texture properties of mixed system even could be improvedby β-glucan with high molecular weight. And high molecular weight of β-glucan could enhancewater holding capacity.Application of β-glucan (OGL360) in soymilk yoghurt was researched by texture analyzer. Onthe basis of single factor experiment, as sensory score for indicator, technological parameters ofOGL360soymilk yoghurt were determined by response surface methodology to optimizefermentation conditions as following：adding7%sucrose, fermentation time was5.56hours,fermentation temperature was42℃, inoculum size was2.5%, adding1.89%OGL360. Under theoptimum fermentation conditions, OGL360soymilk yoghurt with less whey separation, good senseand texture could be obtained.