| As the medicinal and edible fruit, longan has high nutritional value and nourishing effect, which can be regarded as "the holy one of all fruit". Due to optimal concentration, the turning brown rotten and difficult preservation of longan, the dried longan occupy a major share of the market in addition to fresh. The longan pulp is fragment, rich in nutrients and easily processing, but the changes of the components and activity caused by the processing has not been paid enough attention. Now, previous researches have focused on the process optimization of drying, little researches are available on the changes of components and activity caused by drying. In order to understand the differences of constituents and biological activity in liposoluble and water-soluble constituents caused by different drying methods, in this study, we determined the changes of phospholipids and volatile substances profiles in liposoluble fraction by HPLC and GC-MS methods; then analyzed the changes of phenolic and nucleoside profiles by fractional extraction; finally use phytochemical separation means to identified the main substances of longan pulp using the antioxidant activity as a guide. The main findings are as follows:1. Comparison of the liposoluble constituents of longan dried by different methods:The dried longan fruit was prepared by two ways:hot air dried and hot air-sun dried. Using petroleum ether solvent to get the liposoluble constituents, we determined the total phospholipids in liposoluble constituents of longan by molybdenum blue colorimetric method which dried by different methods, and analyzed the differences of phospholipid monomers and content by HPLC methods. The results showed no significant differences were observed for total phospholipids of longan dried by different methods, ranging from9.04to10.89mg/g. In fat-soluble components, the content of phosphatidyl choline in the hot air-sun dried is significantly higher than that of hot air dried, but the content of phosphatidyl ethanolamine, phosphatidyl inositol and phosphatidic acid were found no significant. Determining the composition and content of volatile substances in fat-soluble by GC-MS methods, we detected25,20, and28kinds of volatile substances from fresh longan, hot air dried longan and hot air-sun dried longan. The results demonstrated that the types of ester materials were as following:fresh longan<hot air dried longan <hot air-sun dried longan.2. Comparison of the water-soluble constituents of longan dried by different methods:The longan pulp was dried with different methods and the alcohol extracts were fractionally extracted with ethyl acetate, n-butanol and water. The content of total phenolics and flavonoids in different polarity dried by different methods was determined by Foin-Ciocaiteu and colorimetric methods The antioxidant activity was determined by ORAC and CAA methods. The results showed that the content of total phenolics and flavonoids and its ORAC and CAA antioxidant activities in ethyl acetate extract were significantly higher than that in n-butyl alcohol extract and water extract (P<0.05). In ethyl acetate extract, the content of total phenolics was as following:fresh longan<hot air dried longan <hot air-sun dried longan, and ORAC antioxidant activity showed the same trend, but the trend of CAA antioxidant activity was fresh longan<hot air-sun dried longan <hot air dried longan. The content and composition of phenolics in different polarity dried by different methods were determined by HPLC method. The results showed that phenolics were rich in ethyl acetate extract, which included12kinds of phenolics in flash longan and rutin was the highest;16kinds of phenolics in hot air dried longan and ellagic acid and gallic acid were the highest;16kinds of phenolics in hot-sun air dried longan and ellagic acid and catechins were the highest. The content and composition of nucleoside in different polarity dried by different methods was determined by HPLC method. The results showed that nucleoside were rich in n-butyl alcohol extract. The content of uridine and adenosine were the highest in n-butyl alcohol extract, and the trend was fresh longan<hot air-sun dried longan <hot air dried longan.3. The separation and identification of the main antioxidant active component in longan pulp:We separated the ethyl acetate extract with phytochemical separation methods by column chromatography and the antioxidant activity were measured by ORAC and CAA assays. Meanwhile, we separated the n-butyl alcohol extract by D101macroporous adsorption resin and polyamide resin chromatography. The results showed that Fr.2had the highest content of phenolics and the activity of ORAC in the ethyl acetate extract, and the content of flavonoids and the activity of CAA were also the highest. Choosing this component for further separation, protocatechuic acid was identified.60%alcohol elution part showed the highest activity of ORAC and CAA in the n-butyl alcohol extract, and the content of phenolics and flavonoids were also the highest. Choosing this component for further separation, protocatechuic acid, ellagic acid, rutin and luteolin5-O-β-rutinoside were identified. |
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