Study On Modified Apple Peel By Solid State Fermentation With Aspergillus Oryzae

Apple peel is rich in nutrients,which is a valuable by-product in the apple processing industry.Direct discarding will undoubtedly cause a waste of resources and a huge environmental burden.However,due to the limitations of its structure and processing technology,the utilization of apple peel is still not sufficient and effective,and its comprehensive utilization value needs to be further improved.Solid-state fermentation has been shown to improve the quality and functional properties of fermentation substrates.Compared with other processing methods,such as steam blasting and extrusion,solid-state fermentation has the advantages of low cost and simple operation.Aspergillus oryzae,one of authenticated strain of food microorganisms,is widely used in manufacturing various fermented foods such as koji and soy sauce.In this experiment,Aspergillus oryzae was used for solid-state fermentation of apple peel to study the effects of different fermentation time（4d,8d,12d）on apple peel,mainly including the changes of its chemical composition,structure,antioxidant activity,in vitro fermentation characteristics,etc.Consequently,the quality of apple peel was improved to some extent,which provided a new approach and theoretical basis for the comprehensive utilization of apple peel.The main conclusions of the experiment were as follows:（1）The solid-state fermentation of Aspergillus oryzae had no effect on the apparent morphology of apple peel,but had some effect on the microstructure of apple peel.The apple peel powder before fermentation was mainly flaky and granular with dense surface,while the apple peel powder after fermentation was mainly lumpy and agglomerated with loose holes on the surface.（2）The chemical composition of apple peel had changed by the solid-state fermentation of Aspergillus oryzae.With the increase of fermentation time,the contents of fat,free polyphenols,total phenols,protein and insoluble dietary fiber in apple peel increased,while the contents of soluble dietary fiber,reducing sugar and soluble sugar decreased significantly.The chlorogenic acid,hyperin,quercetin-3-D-xyloside,quercetin-3-O-α-L-arabinoside decreased significantly,and coffee acid,quercitrin,quercetin increased significantly.（3）The solid-state fermentation of Aspergillus oryzae changed the hydration and antioxidant activity of apple peel.With the increase of fermentation time,the holding power of apple peel powder decreased and the swelling force increased significantly.The DPPH scavenging ability of apple peel fermented for 8 d was significantly reduced.,ABTS free radical scavenging ability was improved,and the scavenging ability order was12d>8d>4d>0d,and the reducing ability of Fe was also improved,among which the apple peel fermented for 12 d had the strongest reduction ability.（4）The solid-state fermentation of Aspergillus oryzae had significant effects on the content,micro morphology,monosaccharide and molecular weight of apple peel pectin.The content of apple peel pectin decreased significantly after fermentation.The pectin of unfermented apple peel was mainly a dense flake structure,while the pectin of fermented apple peel was a loose block structure,and the longer the fermentation time,the looser the structure.With the increase of fermentation time,the galacturonic acid,arabinose and fucose of pectin gradually decreased,while mannose,xylose,galacturose and glucose gradually increased.Main chain of pectin molecular ruptured,the side chain increased,and the molecular configuration was from HG type into RG-Ⅰtype.After fermentation,the high molecular weight pectin（>50k D）decreased significantly,while the low molecular weight pectin（<1k D,1～3.5k D）increased.（5）The enzymatic characteristics of pectinase produced by fermented 4d apple peel were as follows:the optimum reaction temperature of pectinase was 50℃and the optimum p H was 4.8.Methanol significantly promoted pectinase activity,while acetone significantly inhibited pectinase activity.Ethanol,acetonitrile,ethyl acetate and trichloromethane had no significant effect on pectinase activity.Ca²⁺had significant activation effect on pectinase activity,while Mg²⁺,Cu²⁺,K⁺,Fe²⁺and Zn²⁺had no significant effect on pectinase activity.（6）The solid-state fermentation of Aspergillus oryzae had an effect on the in vitro fermentation characteristics of apple peel.Compared with unfermented apple peel,the fermented apple peel slightly increased the p H of the fermentation broth and reduced the production of SCFAs.Blank samples,0d,4d,8d and 12d apple peel samples were fermented in vitro at different time,and the species of intestinal flora at the phylum level did not change,which were proteobacteria,firmicutes,bacteroidetes and actinomycetes,but the content changed with the increase of in vitro fermentation time.However,the species and content of intestinal flora at the genus level changed with the increase of in vitro fermentation time.Compared with unfermented apple peel samples,fermented apple peel increased the abundance of Escherichia-Shigella and Lactobacillus,decreased the abundance of the Megamonas and Prevotella,but did not significantly change the abundance of Bifidobacterium.In addition,apple peel could inhibit the growth of Enterobacter and Klebsiella which were harmful bacteria,among which apple peel fermented for 12d had the most significant inhibitory effect.