| Carya cathayensis Sarg.(Chinese hickory)is widely distributed and mainly commercially cultivated in Zhejiang and Anhui provinces of China,which traditionally utilized for food and medicine in China,with an annual output of tens of thousands of tons.After t cracking and shelling process,a large number of Carya cathayensis Sarg.peels(CCSPs,also known as green husk)are produced as mainly by-products.If improperly disposed or careless discarded,it will cause serious environmental pollution and waste of resources.Phenolic compounds are one of the main bioactive compounds of plants,which have been paid increasing attention due to the various biological properties such as antioxidant,antibacterial,anti-obesity,potential for alleviation of type 2 diabetes and other metabolic disorders,and have been widely regarded as a great natural source of antioxidants,and functional dietary supplements.Valorization of this by-product producing high-value products meet the concept of a green circular economy,which is characterized by low environmental risk,resource-efficient and aims for sustainable development.In this study,an excellent high-efficiency natural deep eutectic solvents(NADES)was integrated with pulse-ultrasonication technique for extracting phenolic compounds from CCSPs,and the role of ultrasound in the extraction was characterized;phytochemicals in CCSPs extracted with NADES were identified using UPLC-Triple-TOF/MS,and effect of extraction solvent on phenolic composition,biological activity were evaluated;furthermore,the mechanism of the difference of extraction efficiency of CCSPs phenolics in different solvents was studied,and a food-grade multiphase emulsion with stable loading of CCSPs phenolics was constructed.The researches provide fundamental support for the development and utilization of the polyphenol resources of CCSPs.The main research contents and results are as follows:(1)An excellent high-efficiency natural deep eutectic solvent Ch Cl-MA(choline chloride-malic acid)was screened out for the efficient extraction of phenolics from CCSPs.Optimization was performed by single factor and response surface experiments,the optimal extraction conditions were as follows:extraction time 15 min,solvent/solid ratio 40 m L/g,temperature80℃,ultrasonic power 460 W.The predicted maximum yield of phenolic compounds was 61.31mg GAE/g DW,which was close to the result obtained in the scale-up experiment(59.27±0.82mg GAE/g DW),and the second-order kinetic model was developed and validated(R~2>0.99)to describe the extraction process and its mechanism;and second-order kinetic extraction rate constant(k),saturation concentration(Cs),and initial extraction rate(h)were calculated.Compared with ethanol(40%),glycerol(40%)and water,the extraction efficiency of Ch Cl-MA has been greatly improved,and significant ultrasonic synergistic effect was observed in Ch Cl-MA.In addition,the ultrasonication-synergistic effect during extraction process with NADES was characterized by FTIR,DSC and SEM.(2)A total of 29 phytochemicals were identified,including phenolic acids,flavonols,flavanones,flavan-3-ols(monomer or polymer derivatives).Quantification of 15 representative phenolic compounds in CCSPs in differing solvents was analyzed,among which(+)-catechin,procyanidins B1,2,3-dihydroxybenzoic acid,pinocembrin and procyanidins B3 were the five most abundant phenolic compounds.The contents of 15 representative phenolic compounds in Ch Cl-solvent systems are higher than other solvents,and the content in Ch Cl-MA is the highest.In addition,Ch Cl-MA extract had the highest phenolic compounds content,antioxidant capacity,and inhibitory activities ofα-amylase andα-glucosidase compared with other solvents.(3)Quantum chemical calculations combined with molecular dynamics simulations were performed to investigate the solubility,solvent accessible surface area,hydrogen bond with solvent,interaction energy with solvent,and a NCI analysis in dynamic solvents of(+)-catechin,procyanidins B1,2,3-dihydroxybenzoic acid,pinocembrin and procyanidins B3 in different solvents.In general,compared with water and ethanol as solvents,the five representative phenolic compounds in Ch Cl-MA solvent exhibited better dispersion,larger solvent accessible surface area(174.41、283.17、112.39、146.51、271.76 nm~2),longer hydrogen bond lifetime(71.26%～157.17%enhancement),shorter hydrogen bond interaction distance and lower interaction energy(-422.29、-787.21、-244.57、-264.85、-736.49 k J/mol).Moreover,a NCI analysis showed that the five phenolic compounds dissolving in surrounding solvents molecules could form a more stable interaction with Ch Cl-MA solvent in the long-time dynamic process.Based on the above-mentioned aspects,the interaction mechanism of these five phenolic substances with different solvent molecules was clarified qualitatively and quantitatively,and the efficient extraction mechanism of these phenolic substances with Ch Cl-MA was revealed by the comparative study.(4)Multiphase W/O/W emulsion stabilized by bovine whey protein/high methoxyl pectin complex was constructed to encapsulate polyphenols of CCSPs.Bovine whey protein/high methoxyl pectin ratio of 1/3(w/w)could result in stronger gel network structure formed at the interface between the water and oil,and better adsorption of the complex at the emulsion interface.The emulsion showed the highest encapsulation rate,the best emulsion stability and better encapsulation stability under high temperature treatment. |
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