| Camellia seed meal is the main by-product of camellia seed after oil extraction,and it contains a variety of active substances,including more than 40% of carbohydrates(polysaccharides,cellulose,etc.),which provides its potential as a natural source of dietary fiber(DF).However,the lower soluble dietary fiber(SDF)content and activity limit the application of camellia seed meal DF in the food industry.Therefore,to develop reasonable modification methods to improve the physicochemical properties of camellia seed meal DF is necessary for the utilization of this resource.Compared with other modification methods,fermentation method features the advantages of low energy consumption,no pollution to the environment and obvious action effect.Cellulose-degrading fungi can destroy the structure of lignocellulose through multiple action mechanisms,mainly enzymatic,to enhance the yield of SDF and improve its functional properties,which is a common class of microorganisms in fermentation modification of DF.However,the strains used for fermentation modification are few and poorly tolerant to tea saponins,and there is little information on the effects of cellulose-degrading fungi on the physicochemical structure and functional activities of camellia seed meal SDF.Based on the above,this research used naturally moldy camellia seed meal as the source of strains and screened strains with strong cellulose degrading activity for the fermentation modification of camellia seed meal SDF to improve its functional properties and yield,in order to provide more options for the utilization of camellia seed meal resources with high value.The main research results obtained are as follows:(1)Screening of strains for fermentation modification: Natural moldy camelina meal was used as the source of strains,and 65 strains with cellulose degradation ability and tea saponin tolerance were isolated after three consecutive generations of selective culture.The initial screening of 65 strains was performed,and the Congo red staining results showed that there were 8 strains with hyaline circle diameter to colony diameter ratio >1.5,and they entered the re-screening.The results of the re-screening showed that the strain numbered YC49 had stable and high activities of carboxymethylcellulase,β-glucosidase and filter paper enzyme,so it was used as the target strain for the fermentation modification.The comparative analysis of the 18 S r RNA sequence of YC49 showed that it had the highest similarity with Penicillium sp.and was therefore presumed to be a Penicillium fungus.(2)Optimization of fermentation modification conditions: The effects of fermentation time,inoculum amount,initial p H of fermentation medium and materialto-water ratio on the yield of SDF were determined,in which the initial p H of fermentation medium,material to water ratio and fermentation time had significant effects on the yield of SDF.The Box-Behnken experimental design principle was used for response surface optimization of the fermentation conditions,and the optimal fermentation modification conditions were obtained as follows: fermentation temperature of 28 ℃,fermentation time of 4 d,initial p H 7.0,material to water ratio of1:25,and shaker speed of 180 r/min.The yield of SDF under these conditions reached19.22%.Meanwhile,the fermentation of YC49 could efficiently degrade the main antinutritional factors in camellia meal,the degradation rates of tea saponin and tannin were 58.17% and 44.25%,respectively,which enhanced the feeding potential of camellia seed meal.(3)Physicochemical structure characterization of camellia seed meal SDF before and after fermentation modification: The SEM results showed that F-SDF(after fermentation modification)had a more porous and rougher microstructure compared to CK-SDF(without fermentation modification).The FT-IR spectra showed that both FSDF and CK-SDF had characteristic absorption peaks of fibrous polysaccharides,yet the absorption peaks corresponding to some groups in F-SDF were more obviously shifted,such as hydroxyl groups and β-glucoside bonds.In addition,the release of polysaccharide fractions such as pectin and soluble hemicellulose resulted in a significantly higher proportion of monosaccharides such as galacturonic acid,xylose,and glucuronic acid in F-SDF than in CK-SDF.The results of molecular weight distribution and XRD analysis showed that the fermentation significantly reduced the molecular weight of SDF,and the diffraction intensity of F-SDF was lower than that of CK-SDF in the diffraction angle range of 14.5° to 27.5°,and the relative crystallinity decreased from 20.20% to 17.57%.Meanwhile,the increase in the proportion of amorphous components such as pectin also led to a higher pyrolysis rate of F-SDF than CK-SDF at high temperature conditions(200-600 °C).(4)Functional properties of oil camellia seed meal SDF before and after fermentation modification: The in vitro functional properties of CK-SDF and F-SDF were compared in terms of hydration properties,rheological properties and in vitro hypolipidemic activities.The results showed that YC49 fermentation treatment significantly enhanced the water holding capacity of SDF,as well as the shear stress and apparent viscosity of F-SDF were significantly higher than those of CK-SDF at the same shear rate,indicating that F-SDF has superior hydration capacity and viscosity.In addition,the oil absorption capacity,cholesterol absorption capacity and pancreatic lipase activity inhibition capacity of F-SDF were all higher than those of CK-SDF.Moreover,F-SDF was more effective in impeding the diffusion of bile acids in the simulated intestinal environment,significantly increasing the apparent osmotic rate constant and having lower osmotic equilibrium bile acid concentrations.Overall,the physicochemical structural changes caused by the YC49 fermentation treatment significantly enhanced the potential of oil tea meal SDF as a functional component of lipid-lowering foods.In summary,fermentation with the cellulose-degrading fungus YC49 can significantly enhance the yield and functional activity of oil camellia seed meal SDF,which provides an ideal way to exploit the DF resources in oil camellia seed meal. |
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