Simultaneous Preparation Of Starch And Protein In Hot-pressed Peanut Meal And Development Of Low-GI Maltose Syrup

Hot-pressed peanut meal(HPM)is a by-product of peanut oil processing industry,with an annual output of about 4 million tons,accounting for about 25% of the peanut processed.HPM contains a large amount of nutrients,including about 50% of protein and about 20% of starch.However,protein is heavily thermal denaturized,poor processing characteristics and the starch is difficultly extracted and utilized,so HPM is mostly used as feed of low added value,which resulted in a great waste of resources.In order to developing food resources in a holistic and multifaceted way to implement the Big Food Vision,in this study,HPM was pretreated and the starch was hydrolyzed with enzyme which simultaneously utilized starch and improve the processing characteristics and the purity of protein in HPM.The prepared starch liquefaction liquid was used as raw material and processed by the enzymatic glycosylation to develop an isomaltooligosaccharide syrup of good sensory quality and low-glycemic index.The main findings are as follows:(1)Optimization of HPM pretreatment.HPM was pretreated by biological enzyme method,chemical method and physical method respectively,then the content of reducing sugar in the pretreated starch liquefaction liquid was compared.The results showed that the starch was most effectively hydrolyzed under the condition of soaking pretreatment with p H value of 2,which yielded 12.42 g liquefied reducing sugar per 100 g HPM.The single factor experiment was used to explore the influence of pretreatment parameters on the production of liquefied reducing sugar including the material to liquid ratio,time and temperature.And then the orthogonal experiment was applied to optimize and verify the pretreatment process.The results showed that the optimum pretreatment process was as follows: the ratio of material to liquid was 1:10,the soaking time was 10 hours,and the soaking temperature was 50 ℃.Under this condition,the production of reducing sugar was the highest at 13.31 g/100 g HPM.(2)Optimization of liquefaction conditions.The liquefaction process was optimized for the pretreated peanut meal by single factor experiment in which the effect of the high temperature α-amylase usage,liquefaction time,temperature,and p H on the yield of reducing sugar was evaluated.Further,the liquefaction parameters were optimized and verified by response surface experiment.The results showed that the optimum liquefaction process was the following: the additive amount of high temperature α-amylase was 149.80 U/g,the liquefaction time was 138 min,the p H was 6.00,and the temperature was 91 ℃.With this process,the production of reducing sugar reached 14.25 g/100 g HPM.(3)Preparation and evaluation of the properties of protein in peanut meal processed as described above.The protein in the precipitate after liquefaction was extracted by alkali extraction and acid precipitation method,and its solubility,emulsibility and emulsion stability,foamability and foaming stability,molecular weight and other physicochemical properties were tested.All functional properties were slightly changed after pretreatment and liquefaction.Nitrogen soluble index decreased,while emulsibility,water holding capacity and oil holding capacity increased by 26.41%,214% and 172% respectively.The surface hydrophobicity increased by 80.2,respectively.The molecular weight of protein increased.Foamability,foaming stability,Zeta potential and amino acid content remained unchanged.And no observable difference was detected by Fourier transform infrared spectrum.Hence,it is speculated that the protein structure and aggregation state of peanut meal have changed after treatment,which affects the property changes.(4)Development of isomaltooligosaccharide syrup with low glycemic index.In order to improve the utilization rate and add the value of peanut meal starch,the prepared liquefaction liquid was used to develop isomaltooligosaccharide syrup with low glycemic index by decolourisation,saccharification and transglycosylation steps.The effects of the amount of α-glucosidase,the time of transglycosylation and the temperature of transglycosylation on the hydrolysis index of syrup were investigated,and the optimal conditions of transglycosylation were determined by single factor and orthogonal experiments.The transglycosylation process was optimal when α-glucosidase was increased to 160 U/g liquefied liquid and the transglycosylation was processed at 55 ℃ for 32 h.Finally,the hydrolysis index of the syrup is0.52,and the sugar index is 40.