| The yield of apple in China accounts for over 50%of that in the world,and 20%of apple are used to food deep processing industry,producing a large amount of unutilized apple pomace and thus causing resource waste.Consequently,to utilize apple resource utmostly,it is necessary to further study the utilization of apple pomace.We first produced apple wine by fermenting apple pomace,explored fermentation techniques and obtained fermented apple pomace.Likewise,we obtained another fermented apple pomace by fermenting apple pomace to produce apple vinegar.Secondly,three apple pomace polysaccharides were obtained by the method of hot water-extraction combined with ultra-assisted technique,and therefore,apple pomace polysaccharides(AP),wine pomace polysaccharides(WFP),and vinegar pomace polysaccharides(VFP)were finally prepared,respectively.Finally,by means of modern separation and purification techniques and instrumental analysis methods,physical properties,rheological properties,functional properties,viscosity average molecular weights and structural properties of three polysaccharides were fully investigated so as to provide comprehensive understanding for the utilization of apple pomace.Results are as follows:(1)solid-state fermentation at temperature of 18～19℃ had significant effects on total sugar content,total acid content and alcohol content of AP.The apple wine produced by solid-state fermentation had the final alcohol content of 7.5%(v/v),total sugar content(3.53 mg/mL),total acid content(0.47 mg/mL),total phenol content(0.32 mg/mL),dry extract content(17.21g/L)and S02 residues(<10 mg/L),all indices meeting national standard.Solid-state fermentation of apple wine has obvious advantages including the softness of fermentation process,long fermentation period,deep color,and better model fitting degree compared with liquid-state fermentation.The dynamic model fitting results suggested that correlation coefficient was 0.99.In addition,sensory evaluation results indicated that the apple wine scored 88.9,ranked B level.(2)the polysaccharide yield of AP was 5.68%,significantly lower than WFP and VFP(P<0.05),both of which were at the range of 6%～7%.The water solubility of WFP and VFP were respectively 0.1405 g/mL,0.0771 g/mL,significantly higher than AP(0.0283 g/mL).Compared with AP,WFP and VFP had superior foaming ability,foam stability,hygroscopicity and moisturizing(P<0.05),whereas oil-absorption capacity,emulsifying property and emulsifying stability were significant lower.Rheologicalanalysis suggested that AP,WFP and VFP were typical non-Newtonian fluids,and apparent viscosity significant increased with the increasing concentration.The viscosity average molecular weights of AP,WFP,VFP were all in the range of 15-130 kDa,and AP had the highest molecular weight,followed by WFP.Microstructure analysis suggested that AP consisted mainly of rod,strip,chip forms,with high degree of interweaving and network structure;the interweaving degree of WFP,comprising of rod,sheet and cog forms,was lower than AP;in comparison,VFP had the lowest interweaving degree.In conclusion,WFP and VFP had better processing properties than AP.(3)AP,WFP,and VFP all had scavenging capacity against free radicals:the higher concentration,the better scavenging capacity.When concentration was 5 mg/mL,the DPPH scavenging rates of AP,WFP,and VFP were 56.64%,48.92%,40.40%,and the OH scavenging rates were 28.58%,29.29%,41.00%,respectively.The total reducing power evaluation experiment suggested at the concentration range of 1-5 mg/mL,AP had the strongest reducing powder,significantly higher than VFP and WFP.(4)five fractions of AP by NaCl concentration elution were obtained.AP composed mainly of AP0.1,AP0.15,AP0.2,and AP0.15>AP0.2>AP0.1 in terms of yield.By NaCl concentration elution,six fractions of AP,mainly including WFP0,WFP0.1,WFP0.15,were separated and WFP0<WFP0.1<WFP0.15.Six fractions of VFP were also separatedby NaCl concentration elution,mainly composed of VFP0.15,VFP0.1,VFP0.2,VFP0,and VFP0.15>VFP0.1>VFP0.2>VFP0.(5)The particle size of AP solution significantly decreased after fermentation.Thermo-gravimetric analysis suggested that AP,WFP and VFP were stable when temperature was below 65 ℃,while AP,WFP and VFP began to decompose when temperature was beyond 200℃.XRD analysis suggested that AP,WFP and VFP was of amorphous structure,without crystalline region.Congo red experiments showed that triple helix structure in certain fractions disappeared after fermentation.HPLC analysis suggested that AP,WFP,VFP all consisted of 10 monosaccharides.After fermentation,the mono-saccharides composition changed greatly.Besides,the biological activity of the fermented polysaccharides were improved.In conclusion,solid-state fermentation is practicable to produce apple pomace wine.Fermented apple pomace have antioxidant activities.Compressive investigation of physiochemical properties,structural analysis and rheological characterization suggested that fermented apple pomace polysaccharides are superior in processing properties than AP. |
