| Lipid oxidation is considered to be the main factor in the deterioration of oil and oilcontaining foods.Adding antioxidants is currently the most effective method,however,due to there exists some physiological toxicity in synthetic antioxidant,natural antioxidants have the characteristic of green,safety,and strong antioxidant abilities,which have attracted more and more attention of researchers and manufacturers.At present,there exists considerable phenolic compounds from natural plants have been proved possession the ability of inhibition lipid oxidation,and the application of phenolic compounds in oils has become more and more extensive.Chinese quince [Chaenomeles sinensis(Thouin)koehne] is a species belonging to Rose family and deciduous shrub.Its ripe fruits are rich in phenolic compounds.Proanthocyanidins(PAs),the main constituents of phenolics,has been proved possess excellent radical scavenging ability and various bioactive activity.However,the current research on Chinese quince PAs is mainly focused on extraction,structure identification and in vitro antioxidant activity,and there are few researches on Chinese quince PAs applications as natural antioxidants in food system.In order to enhance the oxidative stability,increase the variety of natural antioxidants as well as improve the utilization rate of Chinese quince PAs,in the present study firstly measured and analyzed the content,radical scavenging ability,composition and the structure characteristics of PAs in Chinese quince fruits at different growth stages to fully understand the dynamic changes of PAs.On this basis,oil and oil-inwater emulsion systems were selected to evaluated the ability of Chinese quince PAs to inhibit lipid oxidation.These results were useful to explore the possibility of application of Chinese quince PAs in food industry.The main works and conclusions are as follows:1.The aim of this part was to clarify the chemical composition,structure characterization and antioxidative activity changes of PAs in Chinese quince fruits at different ripening stages.A total phenolics and PAs increase was observed during ripening with the highest total phenolics content in August fruits(0.323 mg epicatechin equivalent/g extracts)and followed by fruits in October(0.312 mg epicatechin equivalent/g extracts).As for TPA,the highest PAs content in July was 0.837 g Procyanidin B1 equivalent/g extracts.UPLC-MS/MS analysis revealed the PAs in different stage fruits was mainly composed Flavan-3-ols,and the type of type of PAs were B-type procyanidins(PC).Moreover,PAs high polymers content more than95% in PAs extracts.We also found the exists of two different steric configurations prodelphinidin(PD)with lower degree of polymerization.The highest oligomers procyanidins B2 and phenolic acids were found in October fruits,and the degree of polymerization mainly concentrated between 4 ? 6.The PAs in different development stage fruits exhibited excellent antioxidant activity.The highest FRAP activity was found in August,fruits in October shown the highest DPPH radical scavenging ability.2.Three Chinese quince PAs(water extracts,ethanol extracts,acetone extracts)were extracted by water,50% ethanol,and 60% acetone,respectively.The chemical composition of three extracts was analyzed by UPLC-MS/MS.The antioxidative ability of three extracts in three vegetable oils with different saturation degrees(peanut oil,sunflower oil,and flaxseed oil)was studied and compared with BHA by Schaal oven accelerated oxidation method.The results exhibited that the PAs in the three extracts were mainly composed of polymers,and the content of dimeric flavan-3-ols was the highest among oligomers.The highest content of procyanidin B2 in oligomers.Three extracts showed stronger radical scavenging ability than ascorbic acids,and the ethanol extracts has the strongest inhibitory ability.In the process of accelerated oxidation,the addition of three proanthocyanidin(PA)-rich extracts can effectively improve the oxidative stability of three vegetable oils of different saturation levels.In peanut oil,comparing with blank sample,the water extract can reduce the content of peroxide by33.0%,which was significantly higher than ethanol extract(18.66%),and acetone extract(9.15%).In sunflower oil and linseed oil,ethanol extract and acetone extract have similar capacity to inhibit the formation of oxidation products,and were stronger than water extract.Chinese quince PAs can be used as a natural antioxidant to improve the oxidation stability of vegetable oils.3.To evaluate the effect of Chinese quince PAs on the physical and oxidative stability of sunflower oil-in-water(O/W)emulsions during storage,three PA-rich extracts,namely water extract(WE),ethanol extract(EE),and acetone extract(AE),were prepared.When added to O/W emulsions,all the three extracts inhibited the increase in droplet size and the absolute zeta-potential value during storage(55?,24 days).All three extracts also exhibited superior antioxidative activity in the O/W emulsions.WE showed the highest efficacy in retarding lipid oxidation as proved by its lower conjugated dienes(7.5 mmol/L)and thiobarbituric substances values(0.75 mg MDA/L),and such efficacy was similar to that of BHA at the same level.Lower molecular weight and degree of polymerization have a positive effect on antioxidant activity of PA-rich extracts.4.This study investigated the mechanism of PAs of Chinese quince and soybean protein isolates(SPI),and explore the effects of PAs and SPI complexes on the physical and oxidative stability of emulsions.Two proanthocyanidin fractions(F1 and F2)from Chinese quince were prepared using ethyl acetate were prepared.The fluorescence quenching experiment found that F1 and F2 could interact with tryptophan and lysine residues of SPI and thus effectively quench the intrinsic fluorescence of SPI by static quenching.Structural analysis indicated that F1 and F2 bound SPI mainly through hydrophobic interaction and the number of bond PAs molecules(n)was approximately equal to 1.Moreover,the binding of F1 and F2 towards SPI can alter the conformational structures of SPI,such as the decreases of ?-helix and ?-turn contents and the increases of ?-sheet and irregular coil contents.The properties of emulsifying,forming,and antioxidative were improved after SPI complexation with F1 and F2.Compared with SPI emulsified emulsion,the application of SPI-F1 and SPI-F2 exhibited distinctly physical and oxidative stability.The obtained results suggest that the PAs fractions from Chinese quince can enhance the stability of emulsions by improving the physicochemical properties of SPI in this study.It also expands the application extents of Chinese quince PAs as a potential natural antioxidant in food systems.In the present study,the structure characteristics and biological activity of Chinese quince PAs were systematically studied in the first time,and the application range of PAs from Chinese quince fruits was explored by using different food systems.The results showed that Chinese quince PAs,as a natural antioxidant,have strong application prospects in foods,especially in oily foods.As the same time,this study also provides theoretical support and ideas for the comprehensive utilization of Chinese quince PAs. |
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