Effects Of Compound Enzyme Treatment On Cell Wall Structure And Pulp Quality Of Lycium Barbarum

Fresh wolfberry fruit has a short preservation cycle and is easily perishable.Making it into pulp can fully retain the nutrient content of the fresh wolfberry fruit.The preparation of wolfberry pulp adopts the method of direct pressing,because wolfberry contains substances such as cellulose and high concentration of pectin,so the pulp cells cannot be completely broken,the nutrients are not fully released and the juice is not easily dissolved,which reduces the economic benefits.To change this situation,it is necessary to adopt enzymatic hydrolysis treatment for wolfberry pulp.The traditional beating and centrifugation method can be transformed into an enzymatic treatment and filtration method.Therefore,this paper explored the processing conditions of compound enzymatic preparation of wolfberry pulp,and analyzed the effect of Lycium barbarum cell wall structure changes on pulp yield,physicochemical indexes,stability and antioxidant activity during enzymatic hydrolysis.The main findings are as follows:(1)Processing optimization of preparation of wolfberry pulp by compound enzyme methodIn this chapter,the technological conditions for preparing wolfberry pulp by compound enzymatic method were studied.On the basis of single factor experiment,the optimal process conditions for improving the yield of wolfberry pulp were obtained by response surface methodology:The ratio of compound enzymes(pectinase:cellulase:hemicellulase)was 1:2:1,the amount of compound enzymes was 1%,the enzymatic hydrolysis time was 95 min,the enzymatic hydrolysis temperature was 40℃,and the pH of the pulp was 4.2.(2)The effect of compound enzyme treatment on the structure of Lycium barbarum cell wallIn this chapter,the effects of Lycium barbarum cell wall and its component structure changes on the yield of wolfberry pulp during enzymatic hydrolysis were studied.By measuring the particle size,electrical conductivity,and the specific surface area and pore structure of the wolfberry pulp residue,the changes in the structure of the Lycium barbarum cell wall during the enzymatic hydrolysis were analyzed.The structural changes of Lycium barbarum cell wall were accompanied by the structural changes of its main components,namely cellulose,hemicellulose and pectin.The FT-IR results showed that the compound enzyme treatment could weaken the hydrogen bond force between the cellulose molecular chains,and the hemicellulose xylan structure was degraded.XRD results showed that the relative crystallinity of cellulose decreased after enzymatic hydrolysis.The SEM observation showed that the pores on the surface of cellulose increased after the enzymatic hydrolysis,the structure was fluffy,and the supporting effect on the cell wall was weakened.Hemicellulose is in a disordered packing state,and the degree of looseness increases.Through AFM can be observed that the pectin nanostructure changes from flakes to long chains and short chains,and finally distributes in scattered points.After enzymatic hydrolysis,the molecular weight of pectin decreased and the RG-I structure was degraded.The structural changes of Lycium barbarum cell wall components proved that Lycium barbarum cell wall integrity was damaged.(3)Effect of compound enzyme treatment on the quality of wolfberry pulpIn this chapter,the effects of cell wall structure changes on the quality of wolfberry pulp were analyzed by measuring the changes in physical and chemical indexes,stability and antioxidant activity of wolfberry pulp during enzymatic hydrolysis.With the increased of enzymatic hydrolysis time,the content of soluble solids,total sugar,water,protein,Vc and p-coumaric acid in wolfberry pulp increased;Caffeic acid decreased with the increased of enzymatic hydrolysis time,and it could not be detected when enzymatic hydrolysis reached 35 min;When the enzymatic hydrolysis time was increased to 95 min,quercetin could not be detected;Rutin and kaempferol were not detected.When the pulp was enzymatically hydrolyzed for 35 min,the L*value was significantly higher than that of the control group(P<0.05),and the red and yellow values increased,but when the enzymatic hydrolysis time reached 55 min,the red and yellow values decreased.With the increased of enzymatic hydrolysis time,the stability of wolfberry pulp decreased.In the antioxidant experiment,the free radical scavenging rate and reducing ability of wolfberry pulp after enzymatic hydrolysis for 95 min were the highest,which might be related to the synergistic effect of components in fruit pulp.