| Chinese water-chestnut(Eleocharis tuberosa)usually eats after peeling.However,the cutting surface easily turns yellow in a short term.Studies have shown that the main cause of etiolation is the production of flavonoids on the the surface tissue of fresh-cut Chinese water-chestnut.Based on that,the fresh-cut Chinese water-chestnut was taken as the experiment material in this study.At first,the extraction conditions of flavonoids from fresh-cut Chinese water-chestnut etiolated tissues were optimized by response surface method based on single factor tests.Subsequently,the relationship between flavonoids changes and etiolated degrees as well as the changes of vitro bioactivity of flavonoids in the yellowing process of fresh-cut Chinese water-chestnut are identified by studying the dynamic changes of flavonoid contents and their in vitro antioxidant,antibacterial and hypoglycemic activities in the yellowing process of fresh-cut Chinese water-chestnut.Ultimately,the relationship between etiolation of fresh-cut Chinese water-chestnut and biological activity are determined.Thereby,this thesis provides the basis for further study of the effective active ingredients of fresh-cut Chinese water-chestnut and the development and utilization of water-chestnut related health products.The results are as follows:The extraction conditions of flavonaids from fresh-cut Chinese water-chestnut etiolated tissues were optimized by using response surface method based on single factor tests.The results showed that the optimal extraction conditions were as follows:ethanol concentration is 60%,liquid to solid ratio is 30:1(mL/g),extraction temperature is 61 ℃,and extraction time is 16 minutes.Under these conditions,the extraction amount of flavonoids was 0.54 mg/g.The study of dynamic changes of flavonoids during the process of etiolation of fresh-cut Chinese water-chestnut shows that total flavonoids change trend occurred in the entire storage period was similar to the change trend of b*values,that is,rose at the beginning then reduced and the highest content was found when the b*value reached its maximum;Meanwhile,the main flavonoids of fresh-cut Chinese water-chestnut,including naringenin,eriodictyol and quercetin,showed similar change trends with total flavonoids,and they also reached their maximum when fresh-cut Chinese water-chestnut reaches the maximum etiolated degree;Myricetone appeared in the middle period and showed the similar change trend with total flavonoids.Statistical analysis showed that there were extreme significant positive correlations between the b*value and the total flavonoids(r=0.946**),and the naringenin(r=0.915**)and the quercetin(r=0.935**),and the b*value are significantly correlated with myricetin(r=0.849*).The result of the antioxidant effect test showed that the DPPH ·,ABTS+· and · OH scavenging rate,ferric reducing antioxidant power(FRAP)and total reduction capacity of flavonoids of fresh-cut Chinese water-chestnut were significantly(p<0.05)enhanced during the entire storage period.The DPPH ·,ABTS+ ·and ·OH scavenging rate,ferric reducing antioxidant power(FRAP)rose at the beginning then reduced,but the total reduction capacity rose first then stabilized.The free radical scavenging ability and reduction capacity are the strongest when etiolation got the highest degree(Maximum b*value).It indicates that the etiolation of fresh-cut Chinese water-chestnut is helpful for enhancing the antioxidation of the tissue,and the deeper the degree of yellowing,the stronger the antioxidation.The analysis of the in vitro antibacterial indicates that the extracting solution of flavonoids in fresh-cut Chinese water-chestnut has an inhibitory effect on B.subtilis,S.aureus,E.coli and Salmonella,but it has no inhibitory effect on L.monocytogenes.The change trend of inhibitory effect first rose then reduced,which is similar to the b*values during the entire storage period and the highest inhibitory effect on B.subtilis,S.aureus,E,coli and Salmonella was found when the b*value reached its maximum.The MIC of the above four bacterium are 2.5,10,2.5 and 5 mg/mL.It indicates that etiolation helps to enhance the antimicrobial capacity of the fresh-cut Chinese water-chestnut.The deeper degree of etiolation,the better antibacterial effect.In vitro glucose test showed that the inhibitory effect of extracting solution of flavonoids in fresh-cut Chinese water-chestnut on a-amylase and a-glucosidase was significantly increased during storage period.The hypoglycemic activity first rose then reduced,and the highest inhibition effect presented at the highest etiolation degree(Maximum b*value).Further studies of the inhibition types of flavonoids of fresh-cut Chinese water-chestnut at the highest etiolation degree on a-amylase and a-glucosidase showed that they were competitive inhibitions.It indicated that the hypoglycemic activity of flavonoids in fresh-cut Chinese water-chestnut was enhanced,and the deeper the etiolation degree,the stronger the hypoglycemic activity. |
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