| Polyphenols,which are nutrients found in abundance in plants and fruits,have a wide range of anti-ageing,anti-inflammatory and anti-tumour properties that have great potential to maintain human health and reduce the risk of disease.Polyphenols are generally classified as free polyphenols and bound polyphenols,with free polyphenols receiving most of the attention,but bound polyphenols(BP)also contain value that should not be overlooked.BPs are often chemically bonded to macromolecules such as dietary fibre and proteins.The traditional extraction methods to separate BPs from macromolecules are generally acid hydrolysis,alkaline hydrolysis and enzymatic hydrolysis,each of which has its own advantages but also has different limitations.In order to release BPs more efficiently and in large quantities,this study proposes a mixed solid-state fermentation method,which is a method of releasing bound polyphenols by breaking down macromolecules with carbohydrate hydrolysis enzymes released by microorganisms on a solid medium.The process for different modes of mixed solid-state fermentation was firstly optimised and the type and content of BPs released was compared in the two different modes,which determined that the release of BPs from carrot dietary fibre was carried out in a Sequential inoculation mixed solid-state fermentation(SMSF)mode.On this basis,the release mechanism of BPs was further investigated.Then the study investigated the inhibition of amylase by BPs,and demonstrated in vitro and in vivo that BPs have strong antioxidant properties.This study provides a theoretical basis and practical prospect for the development of nutritional functional foods with bound polyphenols,and also provides a new direction for the reuse of carrot processing by-products.The main findings are as follows:(1)Optimizing the release of bound polyphenols from carrot dietary fiber while mixed solid-state fermentation(CMSF)with optimal conditions of inoculum size =105,fermentation time = 3 d,initial p H = 7,inoculation ratio of Trichoderma viride and Aspergillus niger = 1:1,the simulated maximum BP release would be 80.8759mg/10 g GAE.The optimum conditions for SMSF were inoculum size = 105,initial p H = 6,fermentation time = 6 d,interval = 36 h,inoculation ratio of Trichoderma viride and Aspergillus niger = 1:2,and the simulated maximum release of BP would be 86.2706 mg/10 g GAE.(2)Analysis of the type and content of BPs released by CMSF and SMSF.17 different phenolic acids were identified during the CMSF,while SMSF was slightly higher,with 19 different phenolic acids identified.More notably,the SMSF released significant amounts of antioxidants ferulic acid and p-coumaric acid,and the maximum release of BP by the SMSF reached slightly higher levels than the CMSF.In summary,it was concluded that the SMSF method was superior to the CMSF method in terms of the release of BP from carrot insoluble dietary fibre,and the further study would build on the SMSF to investigate the mechanism of SMSF and the nutritional properties of the released BPs.(3)The mechanism of BP release from SMSF was investigated by exploring the dynamic relationship between enzyme activity and the amount of BPs released,as well as comparing changes in the physical properties of dietary fibre before and after fermentation.It was found that carbohydrate hydrolases secreted by mycobacteria more severely disrupted the fibrous reticulation of the cell wall during SMSF,while the penetration of mycobacteria and enzymes acted to shorten the fermentation time and promoted the breakdown of IDF components..However,SMSF did not disrupt the overall structure of the cell wall,only facilitated the dissociation of carboxyl groups and the release of BP by breaking ester groups,ether groups and intermolecular hydrogen bonds of cellulose,lignin and hemicellulose.(4)the in vitro antioxidant capacity of BP by DPPH,FRAP and FRAP were measured,and it was observed that the changes in antioxidant enzyme activity,lifespan and egg production capacity in Caenorhabditis elegans model after its ingestion of BP.It was finally found that BP had a strong amylase inhibitory effect,and it greatly increased the concentration of antioxidant enzymes in the Caenorhabditis elegans and prolonged their lifespan,which has a considerable antioxidant potential.(5)The soluble dietary fibre produced during the mixed solid fermentation process was used for the preparation of handmade instant noodles.The physical properties of the noodles with different dietary fibre additions and the comprehensive sensory evaluation were compared to finally obtain the optimal amount of dietary fibre addition. |
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