Pullulan Fermentation By Aureobasidium Pullulans And Coating Lychee Preservation

Pullulan is a water-soluble and linear microbial exopolysaccharides produced aerobically by growing a yeast like fungus Aureobasidium pullulans, has a number of terrific performances such as film-forming, plasticity, readily biodegradability, safety, non-toxic and other characters and is widely used in food industry, environmental protection, medical industry field etc., is one of the most promising polysaccharide of microbial polysaccharides. Guangxi has rich resources of sugar cane and lychee, but high value-added sugar products have fewer, lychee preservation is a worldwide technical problems. To develop new products and new type of lychee preservation technology is especially important. In this paper, Aureobasidium pullulans 40329 and Aureobasidium pullulans 3# as production strains which to produce pullulan, optimization of fermentation substrate carbon source and culture medium, UV mutagenesis and protoplast fusion for screening of excellent strains, the dynamic processes of fermentation, the application of pullulan coating preservation techniques for lychee. The main conclusions are as follows:1. The present research investigated pullulan production under different carbon resource in Aureobasidium pullulans, and results showed that pullulan production with raw sugar as carbon resource was 16%-53% higher than that cultured in sugar, glucose, raw sugar and starch, accompanied with a reduced pullulan color value. Besides, a further culture optimization was conducted using orthogonal test, and the final pullulan production and the sugar conversion rate reached to 12.39 g/L and 26.65%, respectively. The best culture medium is: 100 mL of culture medium, raw sugar,5 g; dipotassium phosphate,0.7 g; ammonium sulfate,0.04 g; yeast extract,0.15 g; magnesium sulfate,0.01 g; sodium chloride,0.1 g.2. UV mutagenesis was studied for the two strains of Aureobasidium pullulans 40329 and Aureobasidium pullulans 3#, Screening for the three representative mutant strains:302 (14.28 g/L, Light yellow white),406 (19.57 g/L, Shallow blackish green),401 (9.18 g/L, Pure white). Through the preparation of protoplast, protoplast fusion, protoplast regeneration, the excellent strain 212 (15.86 g/L, Pure white) were screened from the fermentation and as production strain in the next study.3. Pullulan fermentation model was studied. Combined with the Logistic model and Luedeking-Piret equation to build up the fermentation model equation of pullulan, through the model test in line with experimental measurements. The model has a certain guiding significance for further expansion of industrial production.The structure of pullulan by which fermentation was studied by applying the Fourier infrared (FT-IR) spectrometer, the FT-IR spectrum of pullulan was showed that the experimental spectrum basically agrees well with the standard spectrum.4. Compare the differences of lychee preservation technology between the finished product of pullulan coating liquid and traditional method. The finished product of pullulan was used for the coating liquid to keeping fresh lychee. The experimental results showed that, under the environment of 35 degrees in summer, the rate of good fruit can maintain 80% after 84 hours, extended 72 hours than the untreated; under the low temperature environment of 5 degrees, the rate of good fruit can maintain 80% after 21 days, extended 16 days than the untreated. Pullulan preservation material has non-toxic, low cost fresh longer keeping, and maintain lychee fresh. However, SO2 slow release and chemical soaking to keep lychee fresh were not very good preservation effect.5. Preparation of pullulan coating liquid to keeping fresh lychee with three different materials:the finished product of pullulan(A), fermentation broth by Aureobasidium pullulans 40329 with no mutation(B), fermentation broth by Aureobasidium pullulans 212 with protoplast fusion mutagenesis(C). the experimental results showed that the rate of good fruit has dropped to 80% after 16 days with the coating liquid by B, but the rate of good fruit can maintain 80% after 21 days and 20 days with the coating liquid by A and C, respectively. A further pullulan coating liquid ingredients optimization was conducted using orthogonal test, the best ingredients is:100 mL of the coating liquid, pullulan,3 g; sodium alginate,0.3 g; CMC,0.2 g; calcium chloride,0.5 g; natamycin,0.04 g; ε-PL,0.04 g; vitamin C,0.1 g.