Anti-pathogenic Fungi & Fresh-keeping Activity Of Sophorolipids And The Development Of New Preservative

Post-harvest diseases induced by pathogenic microbe accounted for the spoilage of fruits and vegetables. In our country, because of lacking necessary cryogenic storage equipment, fungicide, especially chemical fungicide, was the mainly measure to prevent fruit postharvests diseases. However,long-term useing of chemical fungicide will not only endanger human health and environmental, but also make the pathogenic microbe resistant to drugs,which caused more serious spoilage of fruits. So we need to seek an new effective but harmless fungicide to replace the traditional chemical fungicide.Sophorolipids is a kind of glycolipids biosurfactant produced by yeast, and it was first discovered by Spencer in 1954. It has showed well application prospect in petroleum industry, environment protection, cosmetics, detergent, pharmaceutical, food and so on, since it has so many advantages, such as non-toxic, biodegradable, environmental friendly. In recent years, there are many reports about the research of sophorolipids as drugs, including bacteriostasis. But there was few report about research of ophorolipids to prevent spoilage of fruits both in patents and literature. In this research, we separate and identified the pathogenic microbe, study the antimicrobial activity and the keep-freshing of sophorolipids, and discuss the antibacterial mechanism, provide basis to the development of new harmless fungicide.The main research aspects and results are as following:1.The fermentation condition of sophorolipids were optimized. Keeping the medium compositions unchanged, namely glucose 8%, peptone 2%, yeast extract 0.3%, KH2PO4 0.1% , Na2HPO4·12H2O 0.1%, MgSO4·7H2O 0.05%,rapeseed oil 8%, under the circumstances, the fermentation period will be shortened 36 hours while adding 3.0% colza oil into seedculture in advance. Rapeseed oil is the key substrate of sophorolipids synthetic, in this article, the way to feed rapeseed oil is discussed, the sophorolipids yield is enhanced by batch addition of rapeseed oil. The concrete operations are as following: Adding 4% rapeseed oil at the beginning, then adding the left 4% rapeseed oil after permentation for 72h, under the circumstances, the sophorolipids yield reached to 43.40±1.0 g/L, which increased 4.0 g/L than one-time addition. The study also found that, dissolved oxygen is the most key factor influencing sophorolipids large-scale fermentation.2.Pathogenic microbe were separated and identified. 17 strains were isolated from the rotten fruits, while 9 strains of them were pathogenic fungi by the infection experiment. The 9 strains were classificated to genus according to their morphological characteristics by microexamination. The same as other microbial leaded to fruits rot reportted in the literature, most are corruption mold, which contains 6 of them, and the other 3 are yeast.3.Antimicrobial activity and mechanism of sophorolipids on pathogenic fungi. Antimicrobial activity of sophorolipids was studied including antimicrobial diameter, inhibition rate and mycelium growth spread. The results showed that 9 pathogenic fungi growth was well inhibited. At 0.5 g/L of sophorolipids the inhibition rate to yeast was nearly 100% while to. At 2.0 g/L of sophorolipids the inhibition rate to mold was over 80%. The study also found that sophorolipids showes well inhibition to hypha and the microorganism in the air. At 3.0 g/L of sophorolipids can inhibit more than 95% of microorganism in the air, the inhibition rate to hypha was more than 70% too. Meanwhile, the study also found sophorolipids can inhibit and delay the produce of spores. In this article,the antibacterial mechanism was studied, and it was clarified preliminary that sophorolipids can destroy the cell walls, which makes cell cracking to death.4.Preservation of sophorolipids on fruits. Preservation of sophorolipids on fruits was studied, including apple, pear, orange, mini tomato, cucumber, tomatoes, winter jujube and so on, the results showed well preservation. At 3.0 g/L of sophorolipids coating processing fruits, the weightlessness rate reduce 6% to 10% while putting 7 days at room-temperature. Taking weightlessness rate 15% as a standard, fruits processed with 3.0 g/L of sophorolipids can extend 3 to 6 days at room-temperature. We surmised that the preservation mechanism of sophorolipids is due to its hydrophobic end connecting into wax coat of pericarp while its long chain hydrophilic end exposed in the air, which moisturizes fruits.5.The dosage form of sophorolipids fungicide and preservation. Dissolve sophorolipids in ethanol at its biggest solubility 30 mg/mL, mix it with polysorbate 80 and water at the rate of 4:1:5 to 5:1:4 as original liquid, seal saving, appropriate multiples dilution when using. In this dosage form, the solvent and emulsifier both are avirulent and harmless, so it can be applied in both fruit post-harvest and field spraying. Dissolve sophorolipids in dimethyl sulfoxide at its biggest solubility 170 mg/mL, mix it with polysorbate 80 and water at the rate of 2:1:7 to 3:1:6 as original liquid, appropriate multiples dilution when using. In this dosage form, the solvent itself has some baeteriostasis,but due to its low toxieity,it ean be used in field,notsuitable for fruit Post一harvest.