| Longan is a popular subtropical fruit and has high nutritional value and health care function.Longan pulp mainly contains sugars,amino acids,peptides,polyphenols,lipids and trace elements.It has high research value such as anti-oxidation,anti-aging,anti-cancer,immune regulation and lipid-lowering heart and other physiological activities.Polyphenols are a group of polyhydric phenols and their derivatives.They are widely distributed in plants and have strong antioxidant activity and are important for human health and disease prevention.In this paper,the dried pulp of longan were used as experimental materials to extract,separate and purify the polyphenols,identify the structure,and determine the antioxidant activity in vitro.Below are the main research findings:1.50% methanol,50% ethanol,ethyl acetate and distilled water were used to determine the amount of polyphenols extracted from longan pulp,and 50% ethanol was selected as the extraction solvent.The extraction of polyphenols in longan pulp was carried out by organic solvent extraction,Soxhlet extraction and ultrasonic-assisted extraction respectively.Soxhlet extraction method was selected as the extraction method.The effects of ethanol concentration,feed-liquid ratio,extraction temperature and extraction time on the extraction of polyphenols were investigated.Use the Response Surface Analysis of Design Expert to find out the Optimum Process Conditions for Extraction of Polyphenols from Longan pulp.The ethanol concentration is 50.238%,the extraction temperature is 58.099 °C,and the extraction time is2.105 h.The primary and secondary effects of the three factors on the extraction of polyphenols were extraction time,extraction temperature,ethanol concentration.The response surface method predicts that the extracted polyphenol content is 25.600 mg/g,and the actual extracted polyphenol content according to the optimum process is 25.581 mg/g,which indicates that the prediction model is reliable.2.The extracted crude polyphenols were extracted with three organic solvents such as petroleum ether,ethyl acetate and n-butanol.The in vitro antioxidant activity of each sample was determined.The n-butanol extraction phase with the strongest antioxidant activity was selected and further purified by silica gel column gradient elution.Collected fractions arecombined by thin layer chromatography analysis.The nine fractions obtained were subjected to high performance liquid chromatography analysis and in vitro antioxidant activity determination.The fraction Fr6 with the strongest antioxidant activity was selected for further separation and purification,and three monomer compounds A,B,C were obtained.3.Compounds A,B,and C were identified by color reaction,ultraviolet spectroscopy,high performance liquid chromatography,mass spectrometry and nuclear magnetic resonance.These three monomeric substances were preliminarily judged as chlorogenic acid,catechin,and gallic acid.It provides a theoretical basis for the antioxidation and deep processing of longan pulp. |
