Study Of Extraction, Separation,Purification, Biological Activity, And Structure Of Strawberry Phenolics

Recent years, China’s strawberry production has being developed rapidly and become the first strawberry production country in the world, both in cultivation area and output. However, the development of the industry is very slow in our country. The product only are sold in the fresh or frozen to exports. Most strawberries are exported as frozen fruit to overseas markets, while small amount are processed into strawberry juice, wine, etc. Researches of storage, post-harvest preservation in strawberries are common in our country, and the researches of bioactive substances and physiological functions of strawberries are rising. With the certain gap to the international advanced level, it is needed for the further development of strawberry phenolic active products to open up potential market.In this paper, extraction process of strawberry phenolics was explored. The optimal extraction technique of strawberry phenolics was determined; the in vitro antioxidant activity of crude extract and fractions of strawberry phenolicss were evaluated; preliminary separation and purification conditions of strawberry phenolics by silica gel chromatography was studied; and analysis on the composition of strawberry phenolics by HPLC and LC-MS technique was done. The results are as follows:Single-factor experiment was taken to study the effects of extraction temperature, ethanol concentration, ratio of sample to solution, extraction time, the oscillation frequency, the number of extraction times, and other factors on the extraction rate of strawberry phenolics. Then significant factors were selected by the Plackett-Burman experiment. The optimum extraction process of strawberry phenolics was confirmed by L9(34) orthogonal experiments:extraction temperature was40℃; the ethanol concentration was70%; the ratio was1:20; and extraction time was30min.The total phenolic content of the strawberries, and blueberries, blackberries were determined by Folin-Ciocalteu method. The results showed that total phenolic content of strawberry was lower than blackberry and blueberry. In vitro antioxidant activity of crude phenolics extract and each group of chromatography separation from strawberry were determined using DPPH method, TEAC method, determination on ability of scavenging superoxide anion radical (O2-·), determination on reducing power, and determination on ability of scavenging hydroxyl radicals. Analysis of the relation between in vitro antioxidant activity of phenolics and the total phenolics content showed a significantly positive linear correlation for the strawberries(R2>0.91), which indicated that the phenolic compounds were the major antioxidant components in strawberry crude materials extracted by ethanol. Among7fractions of strawberry phenlics extracted by ethanol, SBPP4had the strongest antioxidant capacity.In the ORAC evaluation of strawberries, the results showed that antioxidant capacity of strawberry changed based on tested part, developmental stage, variety, and collected time. Different varieties of strawberry possessed different antioxidant capacity, and Benihope, Ningfeng, and Ningyu cultivars had higher ORAC values than the others. Strawberry fruits had higher ORAC values during the green unripe stages compared to the half red stages and red ripe stages. The calyx has a higher ORAC value than the fruit. In the experiment of the impact of storage time and temperature on the oxygen free radicals, strawberries got higher ORAC values during short-time storage, and then decreased during long-time storage. Strawberries storaged at-18℃showed exhibited higher ORAC value and antioxidant stability than those storaged at4℃. In addition, the vacuum treatment may play a facilitating role in protecting the antioxidant capacity during storage period.Analysis of strawberry crude phenolic extract and its components by HPLC and LC-MS, indicated that strawberry phenolics mainly were phenolic acids, flavonoids, and their sugar-based derivatives. The total phenolics content of different varieties of strawberries were different, but phenolics constituents basically were the same. The purity of crude materials of strawberry extracted by ethanol was significantly improved after preliminary purification by silica gel column.