Isolation And Identification Of Polysaccharides From Pythium Arrhenomanes And Application To Strawberry Fruit(Fragaria Ananassa Duch.)Preservation

Polysaccharides are a kind of high-molecular-weight carbohydrates,which have a wide range of biological activities.In recent years,they have gradually become research focuses in the food and medical industries.Many microbial exopolysaccharides are reported to have good antioxidant and film-forming properties and are used in the field of fruit and vegetable preservation.Pythium arrhenomanes is a kind of saprophytic fungi,which belongs to Pythiaceae,Pythium.Utill now,most of the studies on the metabolites of Pythium spp.metabolites are focused on the extraction of eicosapentaenoic acid,while the studies on their exopolysaccharides have rarely been reported.In this study,the extraction,purification,primary structure identification and antioxidant activity determination of exopolysaccharides of P.arrhenomanes HA-09 were completed,and try to explore its application value in natural antioxidants,microbial preservatives used in fruit and vegetable preservation,to provide theoretical and technical support for the further development and utilization of exopolysaccharides.1.Extraction and purification of Pythium arrhenomanes exopolysaccharideThe crude polysaccharide(Crude PEPS)was extracted from the fermentation broth of P.arrhenomanes,and the yield was 7.33 g/L.The dry weight ratio of polysaccharide and mycelium could reach 3.18 g/7.33 g.The total sugar content of PEPS was 83.62%,and the protein content was 6.89%.Crude PEPS were purified into three fractions: PEPS-1,PEPS-2 and PEPS-3.2.Structure identification of Pythium arrhenomanes exopolysaccharideThe primary structure analysis results show that the three purified polysaccharides have high purity and contain almost no impurities like protein;the purified polysaccharides are mainly composed of rhamnose and glucose;the average molecular weights of Crude PEPS,PEPS-1,PEPS-2 and PEPS-3 are: 8667 Da,8129 Da,9433 Da,and 9360 Da.Among them,PEPS-1mainly contains 1?,1?6 glycosidic bonds,and there are a small amount of 1?4 or 1?4,6glycosides.PEPS-2 mainly contains 1?4 or 1?4,6 glycosidic bonds,with a small amount of1?3,1?,1?6glycosidic bonds;PEPS-3 mainly contains 1?2,1?2,6,1?4,1 ?4,6glycosidic bonds;PEPS-1,PEPS-2,and PEPS-3 are all pyranose with ? configurations.3.Antioxidant activity analysis of exopolysaccharides.The antioxidant activities in vitro of crude PEPS and purified polysaccharides were evaluated by the determination of superoxide anion radical-scavenging activity,hydroxyl radical scavenging activity,ferrous ion-chelating activity and reducing power.Crude PEPS,PEPS-1,PEPS-2 and PEPS-3 showed different antioxidant activities.At high concentration(5 mg/m L),the order of the superoxide anion radical-scavenging activity,hydroxyl radical scavenging activity and ferrous ion-chelating activity is Crude PEPS <PEPS-1 <PEPS-2 <PEPS-3;the order of reducing power is PEPS-1 <Crude PEPS <PEPS-2 <PEPS-3.4.Study on the application of PEPS-2 to the preservation of postharvest strawberryPEPS-2 was selected as the experimental material for the presentation of postharvest strawberry fruit.The decay index,soluble solids content(SSC),malondialdehyde(MDA)content,anthocyanin content,vitamin C content and the DPPH radical-scavenging activity were determined in the assay.The results showed that PEPS-2 treatment reduced the decay index and MDA content,and delayed the decrease of SSC.The anthocyanin content,vitamin C content and the DPPH radical-scavenging activity of the strawberries were also imporved by the PEPS-2treatment.It has been proved that PEPS-2 treatment is an effective method to extend the shelf-life of strawberries,and to improve its postharvest physiological quality.