Modification Of Okara Dietary Fiber And Its Application In Frozen Yogurt

As a by-product in the processing of soy products,okara is a natural source of dietary fiber,and its edibility and safety have been recognized by people.However,the low content of soluble components in okara dietary fiber(ODF)restricts its application in food industry due to its poor processing characteristics and taste.In this study,high-speed shearing combined with enzymatic hydrolysis was applied to modify ODF,and the best modification process conditions were explored.On this basis,the effects of modification methods on the composition,structure,physicochemical properties,probiotic activity and digestion resistibility of ODF were compared and analyzed;Finally,The modified ODF(HE-ODF)prepared by high-speed shearing combined with enzymatic hydrolysis was added to frozen yogurt to study its effects on the physicochemical quality,sensory quality and storage quality of frozen yogurt.The research contents and results were listed as follows:Firstly,the modification process conditions of ODF were optimized.Taking the yield of SDF as the index,through the single factor experiment and response surface experiment,combined with the actual production,the optimal process conditions for the modification of ODF by high-speed shearing combined with enzymatic hydrolysis method were determined as follows: liquid to solid ratio(water and ODF)of 24:1,shearing rate of 14000 r/min,shearing time of 16 min,complex enzyme(cellulase: xylanase=1:1,w/w)addition amount of1.6%,enzymatic hydrolysis temperature of 55 ℃,enzymatic hydrolysis time of 2.0 h,enzymatic hydrolysis p H of 5.3.Under this condition,the maximum yield of SDF was16.98%.Secondly,the effects of modification methods on the composition,structure and physicochemical properties of ODF were studied.ODF was modified by high-speed shearing method,complex enzymatic hydrolysis method and high-speed shearing combined with enzymatic hydrolysis method.The results showed that the modified okara dietary fiber had more soluble components,smaller particle size and looser microstructure;FT-IR results showed that there was no obvious change in the distribution of characteristic absorption peaks of the modified okara dietary fiber,but the intensity of some peaks was weakened.XRD results showed that the modification treatment did not change the crystal configuration of okara dietary fiber;all three modification methods could significantly improve the water holding capacity,swelling capacity and oil holding capacity(P<0.05),and HE-ODF showed the best physicochemical properties.Thirdly,the effects of modification methods on the probiotic activity and digestion resistibility of ODF were studied.In vitro fermentation experiments showed that ODF prepared by the three modification methods could enhance the proliferation of the two probiotics,and the proliferation of Lactobacillus acidophilus was more obvious than that of Bifidobacterium lactis.In addition,because the high-speed shearing combined with enzymatic hydrolysis modification could make the fiber structure finer and the content of soluble components higher,the in vitro probiotic activity of the ODF treated by it had the most significant increase,which was mainly reflected in maintaining the stability of the counts of viable bacteria,reducing the environmental p H and promoting the generation of SCFAs during fermentation.The artificial gastrointestinal juice digestion experiment showed that ODF before and after modification had better digestion resistibility than inulin,thus showing higher prebiotic potential.Finally,the application of HE-ODF in frozen yogurt was studied.The results of physicochemical quality measurement showed that the slurry viscosity,expansion rate of frozen yogurt increased and the melting rate decreased as the increase of the addition amount of HE-ODF.The sensory evaluation results showed that the sensory quality of frozen yogurt was the best when the addition amount of HE-ODF was 1.5% or 2.0%.Through the quality measurement during the storage period of 1～60 days,it was found that adding HE-ODF could effectively reduce the hardness of frozen yogurt,keep the texture soft,and maintain the counts of viable bacteria of Lactobacillus acidophilus and Bifidobacterium lactis,however,when the addition amount exceeded 1.5%,the counts of viable probiotic bacteria decreased.On the whole,the frozen yogurt with 1.5% HE-ODF not only had good physicochemical and sensory quality,but also maintained high counts of probiotics,thus showing certain health benefits.