Study On Preparation,Structural Characterization And Functional Properties Of Soluble Dietary Fiber From Okara

Okara is a by-product produced during the processing of soy products,because it is perishable and difficult to store,so mostly used for feed or directly discarded,with low utilization,but okara are rich in dietary fiber,which is an important source of dietary fiber.Dietary fiber has specific metabolic and physiological effects on humans,which can reduce the risk of hyperglycemia,hyperlipidemia,hypertension,intestinal diseases and cardiovascular diseases,etc.among these health benefits,soluble dietary fiber(SDF)plays a major role.Therefore,it is important to choose a suitable extraction method to improve the extraction rate of SDF in soybean residue,solve the problem of low utilization of soybean residue,improve the comprehensive utilization rate of okara and realize the resource utilization and high value recycling of the by-products of agricultural products processing.In this paper,using soybean dregs as raw materials.microwave treatment,mixed fermentation of lactic acid bacteria and Neurospora crassa,and microwave-fermentation combined treatment are used to increase the content of SDF in okara,then,the optimal extraction conditions were optimized by response surfaces and the effects of different extraction methods on the structure,composition,and functional properties of SDF were compared and studied.The main results are as follows:(1)Combined with the single-factor test results and using three-factor and three-level response surface tests to optimize the optimal process conditions for the three methods for extracting and preparing of SDF from okara.The results show that the optimal conditions for extracting SDF from okara by microwave treatment are: microwave power of 600 W,microwave time of 4 min,and liquid-to-material ratio of 20:1,under these conditions,the SDF content is 5.36%;the optimal conditions for extracting SDF from okara by mixed fermentation of Lactobacillus and Neurospora crassa are: fermentation temperature is30℃,fermentation time is 2 d,inoculation amount is 5.5%,and under these conditions,the SDF content is 7.09%;the optimal conditions for extracting SDF from okara by the microwave-fermentation combined treatment are: the fermentation temperature is 30℃,the fermentation time is 2 d,and the inoculation amount is 5.5%,after the fermentation treatment,the microwave treatment was performed at a microwave power of 600 W,a microwave time of 2.5 min,and a liquid-to-material ratio of 15:1,finally,the content of SDF was further increased to 7.69%.(2)Structure characterization and monosaccharide composition are determined of SDF preparation from different methods and SDF in raw materials,the results show that compared with SDF in raw materials,the microstructure of SDF prepared by extraction is more porous and rough;the results of infrared spectrum and X-ray diffraction pattern showed that the functional group,group structure and crystalline region of SDF were less affected by fermentation treatment,microwave treatment and microwave-fermentation combined treatment will increase the intensity of some bands in the infrared spectrum and reduce the intensity of diffraction peaks in the X-ray diffraction pattern or partially disappear of SDF.It shows that it has a certain effect on the functional group structure and crystal structure of SDF,which is more obvious than fermentation,in addition,the three extraction and preparation methods will redistribute the monosaccharide content of SDF from okara.(3)The functional properties of SDF preparation from different methods and SDF in raw materials were measured.The results show that SDF prepared by three different methods have a good effect on reducing blood glucose,blood lipids and antioxidant activity in vitro and have a value-added effect on the growth of intestinal probiotics such as lactic acid bacteria,among them,SDF prepared by microwave-fermentation combined treatment had the best effect on glucose adsorption capacity(407.14 mg/g),sodium cholate adsorption capacity(14.13 mg/g)and cholesterol adsorption capacity(8.89 mg/g(p H=7)and 7.69 mg/g(p H=2)).SDF prepared by fermentation treatment had the best α-Amylase activity inhibition ration(11.69%)and antioxidant activity,among them,at a concentration of 2.5 mg/g,the DPPH free radical,ABTS free radical scavenging rate and reducing power reached 53.5%,59.71% and 0.28,respectively.The four types of SDF have a good value-added effect on probiotics such as lactic acid bacteria in vitro,among them,the SDF prepared by fermentation and microwave-fermentation combined treatment had the best proliferation effect.It shows that the SDF prepared by extraction has better functional properties.In summary,three different methods have significantly increased the content of SDF in okara,and the structural change of SDF is also closely related to the functional properties;different preparation methods have different effects on the functional properties of SDF,and you can choose the appropriate preparation method according to your needs.So as to improve the comprehensive utilization rate of soybean residue and realize high value utilization of resources.