Optimization Of Sugar Production Conditions, Antibacterial Properties And Application Of Fusarium Oxysporum LD105

In this paper,we isolated and screened a wild strain producing antibacterial polysaccharide from maca rhizosphere soil.According to its colony and spore morphological characteristics and biochemical identification（28S rDNA）,the strain was identified as Fusarium oxysporum.The single factor test and Box-Behnken experiment were carried out on the conditions for antibacterial polysaccharides production.The properties of the crude polysaccharides were preliminary studied,and the liquid fermentation conditions and solid-state fermentation conditions of the strain were optimized.The antibacterial activity of its fermented polysaccharides was explored,and the application of the polysaccharide in the preservation of fruits and vegetables was explored.The main research contents and results are as follows:1.Screening and identification of bacteriostatic polysaccharide-producing strainsBased on morphological observation,and 28S r DNA biochemical tests,the strains LD105 was identified as Fusarium oxysporum.2.Optimization of liquid fermentation process conditions for producing antibacterial polysaccharide from F.oxysporum LD105With the inhibition rate and polysaccharide content as the evaluation index,based on the single factor test,the optimum conditions for producing antibacterial polysaccharide were determined by Box-Behnken software.The optimum conditions were as follows:fermentation time 4 d,sucrose5.5%,KH₂PO₄ 0.3%,yeast extract 3.0%,pH 6.5,liquid content 20.0%,fermentation temperature26°C.Under this optimum condition,the antimicrobial activity and polysaccharide content were42.12%（the predicted value was 41.90%）and 429.30 mg/L（the predicted value was 421.90 mg/L）.3.Optimization of solid state fermentation process conditions of antibacterial polysaccharides produced by F.oxysporum LD105With the inhibition rate and polysaccharide content as the evaluation indicators,based on the single factor test,the optimum conditions for producing antibacterial polysaccharide were determined by Box-Behnken software.The optimum conditions were as follows:fermentation time5 d,sucrose addition 3.0%,Moisture content 55.0%,KH₂PO₄ 0.3%,Peptone 1.5%,pH 6,inoculum volume 10%,fermentation temperature 28°C,Under this optimized condition,the antibacterial rate and polysaccharide content were 37.60%（the predicted value was 38.00%）and30.20 mg/g（the predicted value was 30.50 mg/g）.4.Study on the properties of the polysaccharidesThe bacteria were removed by centrifugation,protein removal,dialysis removal of small molecule compounds,and freeze drying to obtain crude polysaccharides.A single peak was obtained by gel permeation chromatography（GPC）,and the weight average molecular weight was154 kDa.A single microdilution method and oxford cup method were used to determine the antibacterial activity of polysaccharides against eight indicator bacteria such as Escherichia coli and Staphylococcus aureus.The results showed that the polysaccharide had the best antibacterial effect on Escherichia coli（The optimal inhibition rate of solid state fermentation polysaccharide was37.60%,and the optimal inhibition rate of liquid fermentation polysaccharide was 42.10%）,and all kinds of bacteria indicator bacteria have a certain degree of antibacterial effect,basically no inhibition of the fungus.5.Effect of polysaccharides on preservation of fresh-cut applesAdding different concentrations of polysaccharides to keep the red Fuji apples fresh,apple sensory changes,pH value,titratable acid content（TA）,soluble solids content（TSS）,total number of colonies,total phenol content,antioxidant capacity,color difference and water loss rate as evaluation indicators.Studies have shown that the addition of 3%of polysaccharides was best for apples,and the shelf life could be extended by 3 days,freshness was significantly better than chitosan.