| Biological control is an emerging method, which utilizes antagonistic microorganisms to control post harvest diseases to reduce the decay. In recent years, biocontrol on fruit postharvest diseases using antagonistic yeasts becomes a hot topic. However, the efficacy of biocontrol formulation is not enough stable in the practical application. Because antagonisms are alive, their viability and biocontrol efficacy are easy to be effected by environmental factors during the process of formulating, distributing and applying, which limits the industrial production and commercial application of antagonistic yeasts. In order to improve their biocontrol ability, enhancing tolerance of biocontrol agents to stress conditions is a usefull approach. Alginate, a polysaccharide derived from marine brown algae, was preponderant for making edible films due to its unique colloidal properties. However, single alginate films are easy to age crack and poor antibacterial activity, which limits its application on the fruit and vegetables.An orthogonal experimental design was carried out to optimize the amounts of glycerol as a plasticizer, palmitic acid as lipids additive, glycerol monostearte, andβ-cyclodextrin as composite emulsifer. A novel edible bio-film was prepared using Cryptococcus laurentii as the active component and its effects on preserving strawberries were investigated.At 28℃in NYDB culture media, the yeast grew quickly and went to exponential phase without any lag phase.When reached 18 hour, the biocontrol efficacy reached the highest value. Among the heating treated solution,cultrued solution and washed-cell suspension at the 1×108 CFU/mL concentration, the spore germination of Penicillium spp treated by washed-cell suspension was 11±0.51%, and the spore germ tube cognation of Penicillium spp.was 23±3.11μm, significantly with the control.The concentrations of the yeast cells obviously influenced disease incidence and lesion develpoment in PDA and PDB.The higher the concentration was, the better the results was. Cryptococcus laurentii at 1×108CFU/mL and 1×109CFU/mL of washed-cell suspension effectivety inhibited Penicillium expansum in PDA and PDB. Rapid colonization of the yeast in wounds was observed at 20℃. The results indicated that Cryptococcus laurentii could be used as an antagonistic microorganisms on the preservation of strawberries.With the increase of the sodium alginate concentration, the tensile strength and elongation percentage increased, while the water vapor resistance(WVR) decreased.The concentration more than 3% had little influence on the water vapor resistance.Addition of glycerol can reduce the tensile strength and elongation percentage, increase the water vapor resistance.Results indicated that sodium alginate had litter effect on the growth of antagonist yeasts in NYDB culture. Compared other preparetion condition, the microorganism viability of the bio-film at 40℃,2h was higher. It was shown that the microorganism viability of the bio-film had no obvious change during 4℃storage. The microorganism viability of the bio-film without carbon source decreased quickly, while there was no significant difference between 3% CS and 6% CS group.For the bio-film, carbon source had litter effect on biocontrol efficacy of antagonist yeasts, while reduced tensle strength and and increased the water vapor resistance.Sodium alginate treatment maintained the firmness, inhibited the decrease of sugar content and the titratable acidity contents. Cryptococcus laurentii treatment decareased the rot rate and slowdowned the formulation of MDA.The treatment of sodium alginate film entrapped Cryptococcus laurentiican significantly reduce microbiological decay incidence, decrease weight loss, maintain the firmness and lightness, inhibit the decrease of sugar content and the titratable acidity contents, slowdown the oxidation of Vc. The bio-film can improve the qualities and storage properties of the fruit, which fully plays the function of biological control and coating preservation.
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