Effect Of Rhodosporidium Paludigenum On Postharvest Fruit Decay Caused By Penicillium And Patulin Degradation

Postharvest fruit decay is a serious worldwide problem. It brings huge financial losses and resource wastes, especially in developing countries. Fungal infection is one of the most important causes of fruit decay, and the fungi secrete mycotoxins during the invasion, which brings risks to human health. For instance, patulin is one of the most common mycotoxins in fruit and fruit-derived products. The major means of decreasing mycotoxin contamination in fruit is to control fruit decay. Rhodosporidium paludigenum is a promising antagonist which could control postharvest decay of winter jujube and cherry tomato, however, its control ability is not as effective as fungicides when applied alone. Besides, the efficacies of R. paludigenum in postharvest control on other kinds of fruit are unknown yet. The aims of this project are:a) enhance the biological activity of R. paludigenum by combination with other safe chemical compounds, and assess the efficacies in citrus, apple and pear, as well as mycotoxin accumulation in fruit; b) test the ability of R. paludigenum in patulin degradation, determine the degradation product, followed by toxicity assay, and study relevant mechanism of degradation.The major results are listed as following:1. R. paludigenum could inhibit green mold of citrus significantly. When combining sodium bicarbonate, R. paludigenum inhibited green mold decay of citrus (including Citrus reticulata Blanco cv. Subcompressa and C. reticulata Blanco cv. Ponkan) as efficiently as fungicide (Fungaflor). Based on orthogonal test, the agent containing R. paludigenum, Cryptococcus laurentii, Rhodotorula glutinis, indole-3-buyric acid, salicylic acid and sodium bicarbonate inhibited citrus green mold completely, which was more effective than fungicide.2. R. paludigenum inhibited blue mold decay caused by Penicillium expansum in apple and pear significantly. However, the yeast induced the pathogen to secrete more patulin in fruit.3. Patulin contamination was serious in fruit-derived product in China. In62 samples tested,56.5%samples were contaminated by patulin, while16.1%samples contained patulin more than permitted limit (50μg/L). pH value played a more important role than temperature in patulin stability. Patulin was stable in solutions with pH values lower than5. The best solvent for patulin storage was acetonitrile.4. R. paludigenum decreased patulin effectively in vitro:it removed patulin almost completely within two days under the optimal condition (pH6.0,30℃). The mechanism included physical adsorption and enzymatic degradation. R. paludigenum could also remove patulin in apple juice and pear juice.5. Patulin degradation by R. paludigenum is an enzymatic process, and it is a stable character of the yeast. Yet, patulin stimulated the yeast to produce more enzymes responsible for degradation. The degradation responsible enzyme was intracellular enzymes, which was stable under oxygen environment, and did not require a dissociable cofactor.6. Patulin degradation product was identified as desoxypatulinic acid by UPLC-MS. The toxicity (including bacterial toxicity, phytotoxicity and cytotoxicity) of the degradation product was much less than patulin.In conclusion, the strain R. paludigenum is a promising bio-agent, and its ability of patulin degradation provided a new method and resource for decreasing patulin contamination. The results of this project promote the commercial application of R. paludigenum.