| Citrus peel is an important"medicinal and edible homologous"plant resource in China,which is rich in a variety of bioactive components.Citrus flavonoids have anti-cancer,anti-inflammation and anti-oxidation biological activities.Citrus essential oil has unique aroma,vasodilation,calming and refreshing,nerve relaxation and other biological effects.At present,the comprehensive evaluation and structure transformation of bioactive components extraction in processing are not clear.In order to utilize the bioactive ingredients efficiently and bring their nutritional and health value into full play,this study used different dietary extraction methods to extract the bioactive components from dried citrus peel,and different dietary extraction methods were systematically evaluated by comprehensive evaluation model,and the sensory properties of citrus peel extracts were analyzed by electronic sensory technology;furthermore,polymethoxyflavones(PMFs)were chosen to represent the bioactive components,the effects of different drying methods on the content and structure of PMFs in citrus peel and the inhibitory activity of tumor cells were studied.The results of this study provide scientific basis for the industrial application of citrus peel,and provide theoretical guidance for utilizing bioactive components to realize their potential nutritional and health value and promote the development of citrus industry.The main results are as follows:(1)Extraction efficiency of bioactive components from citrus peel by different dietary methods:the effects of hot water soaking,boiling,steaming and ethanol extraction on the extraction of flavonoids and essential oils from citrus peel were studied.Based on the weight method,the extraction and evaluation models of various bioactive components were established.The comprehensive evaluation revealed that the quantity of bioactive compounds in ethanol extraction(12976μg/g)was significantly higher than that of hot water soaking(5260μg/g),boiling(4048μg/g)and steaming(540μg/g).The sensory analysis effect of electronic eye and electronic tongue on peel extract was better than that of electronic nose.The results can fully tap the nutritional value of different citrus peel extracts,provide new ideas for the comprehensive evaluation of bioactive components extraction,and provide scientific and effective guidance for the reasonable diet of citrus peel.(2)The discovery,regularity and biological significance of PMFs hydroxylation reaction in citrus peel during drying:The effects of hot air drying,vacuum freeze drying and sun drying on the structure changes of PMFs(sinensetin,nobiletin,heptamethoxyflavone and tangeretin)in the peel of hybrid citrus and valencia orange were studied.For the first time we discovered that PMFs underwent hydroxylation at 5-position on the A ring of their flavonoid structures during drying process of citrus peel.The reaction was simulated by chemical and biological methods,which confirmed that acid hydrolysis and enzymatic catalysis were the main mechanisms of hydroxylation of PMFs.The hydroxylation rate of PMFs in sun-dried citrus peel was the highest,followed by hot air drying and vacuum freeze-drying.The optimum drying conditions were:60 ~oC hot air drying for 4 hours,vacuum freeze drying for 2 hours and sun drying for 16 days.Drying can significantly improve the inhibitory activities on tumor cells of citrus peel which significantly positive correlated with the hydroxylation rate of PMFs.The hydroxylation of PMFs may be an important reason for the nutritional and health effects of citrus peel.The results help the comprehensive development and utilization of citrus peel resources,provide scientific guidance for the directional transformation of PMFs,and support the industrialized preparation of high value-added citrus peel in theory. |
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