| Polyphenols are secondary metabolites in plants with various biological activities including antioxidant,anti-inflammatory and anti-aging.Researchers have been concentrating on the extractable free polyphenols(FP)for a long term,leaving out the bound polyphenols(BP)that closely bound to food matrix such as dietary fiber(DF),protein,starch,etc.,together with their potential benefits.Defatted rice bran,discarded as industrial waste frequently,is the residue obtained from rice bran(a byproduct of rice refining).Nevertheless,the waste of defatted rice bran give a rise to a significant waste of functional components and resources,since it retains rich nutrients such as polyphenols,DF,etc.Majority of polyphenols available in defatted rice bran are bound to DF,which is in urgent demand to search for approaches that could release BP mildly,efficiently,and economically.In addition,the increasingly aging population poses a serious challenge to the global economic and social life.Previous researches have shown that polyphenols,one of natural phytochemicals in diet,could alleviate the onset of aging and aging-related diseases.As a consequence,in this study,the optimal conditions for releasing BP from defatted rice bran insoluble dietary fiber(DRB-IDF)by solid-state fermentation(SSF)with Trichoderma viride were optimized;and the composition,total phenolic content,antioxidant and enzyme inhibitory activities of BP prepared by SSF(FT-IDF-RBP)and alkaline(AT-IDF-RBP)were analyzed,respectively.Simultaneously,the effects of SSF on the structural characteristics of DRB-IDF were evaluated,and the relationship between carbohydrate-hydrolase activities and BP content was elucidated,so as to explore the potential release mechanism of BP.On the basis of which,Caenorhabditis elegans were supplied with various concentrations of FT-IDF-RBP,and the effects of FT-IDF-RBP on aging and aging-related indicators were investigated.Moreover,the potential mechanism of the anti-aging effects of FT-IDF-RBP on nematodes was excavated from transcriptomics and further validated with mutants.This study was undertaken to provide valuable insights into utilizing rice agricultural by-products,as well as to contribute theoretical and technical guidance for the development of natural anti-aging nutritional supplements from the diet.The principal findings are as follows:(1)The method for releasing BP from DRB-IDF by SSF via Trichoderma viride was established,and the differences between the BP released by SSF and conventional alkaline method were analyzed.The optimal fermentation conditions for releasing BP from DRB-IDF optimized by response surface methodology were:initial p H 4,water content 66%,strain inoculum 10~5 spores/g,and fermentation time 4 days,under which conditions,the yield of BP was 5.55 mg GAE/g DW.Qualitative and quantitative analysis were conducted,and potential biotransformation pathways including hydroxybenzoic acid and hydroxycinnamic acid pathways during SSF were speculated.In addition,the in vitro antioxidant and enzyme inhibitory activities of BP were performed.It was found that,compared with the BP released through alkaline(AT-IDF-RBP),the BP released through SSF(FT-IDF-RBP)had more advantageous in in vitro antioxidant,α-amylase,andα-glucosidase inhibitory activities.(2)The effects of SSF on the structural characteristics of DRB-IDF were investigated,and the potential release mechanism of BP from DRB-IDF by SSF was elucidated.The structure of untreated,autoclaved and solid-state fermented DRB-IDF was characterized,and it was found that both autoclaving and SSF could loosen the IDF fiber network,while the amorphous regions such as hemicellulose and cellulose were degraded,and the infrared characteristic peaks along with the intensities of cellulose,hemicellulose and lignin were changed.Furthermore,the activities of carbohydrate-hydrolases such as xylanase,cellulase andβ-glucosidase appeared to be increased to varied degrees during SSF,and they were positively correlated with BP content.Therefore,we hypothesized that the interaction forces between BP and food matrix(cellulose,hemicellulose and lignin)were weakened during SSF,which contributed to the release of BP.(3)The effects of FT-IDF-RBP released by SSF on aging and aging-related indexes were investigated using Caenorhabditis elegans model.The results indicated that FT-IDF-RBP was able to extend the lifespan of nematodes without interfering with their reproductive capacity.However,there was a threshold value for this life-extending effect,and the optimal concentration of FT-IDF-RBP was 100μg/m L.Under this condition,the average lifespan of nematodes was prolonged by about 14.81%,while aging-related indicators of nematodes were significantly improved by FT-IDF-RBP,including the increased body bending ability,reduced oxidative stress levels,decreased lipofuscin accumulation and improved antioxidant enzyme activities.(4)The transcriptome information of C.elegans before and after FT-IDF-RBP intervention had been obtained based on RNA sequencing technology,and the potential mechanism of the anti-aging effects of FT-IDF-RBP on C.elegans had been explored.A total of 433 differentially expressed genes(DEGs)were screened,with 173 up-regulated DEGs(e.g.,gst-10 and sod-3)and 260 down-regulated DEGs(e.g.,F49E12.10).GO enrichment analysis demonstrated that most of the DEGs were mainly enriched in GO terms related to immune response and oxidoreductase.KEGG enrichment analysis identified 12 significant enrichment pathways,among which oxidoreductase and longevity regulating pathways were the main pathways involved in aging regulation.Verification of the“longevity regulating pathway-worm”revealed that FT-IDF-RBP increased the expression of fluorescent protein in the CF1553(SOD-3::GFP)mutant significantly,indicating that FT-IDF-RBP could extend the lifespan of nematodes by enhancing the endogenous antioxidant defense system.Besides,sod-3,a key gene in“longevity regulating pathway-worm”,might be the critical target for the life extension. |
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