| Summary: | 碩士 === 國立中興大學 === 食品暨應用生物科技學系所 === 104 === Wheat bran, a by-product of the milling industry, contains starch, cellulose, protein and mineral. An appropriate pretreatment such as heating and enzymatic treatment on wheat can increase the contents of soluble carbohydrates and protein in wheat bran extracts, which benefits the microbial fermentation. Pullulan is a linear homopolysaccharide, produced by a yeast-like fungus, Aureobasidium pullulans extracellularly. It consists of repeating maltotriose subunits linked by α-1, 6-glycosidic bond and is non-toxic, tasteless and odorless. With its unique linkage pattern, pullulan has a considerable physico-chemical properties like biodegradability, film formability, impermeability to oxygen. Pullulan can be used as antimicrobial edible film with antimicrobial substance and applied in food packaging to extending the shelf-life of food.
In this study, wheat bran hydrolysates and extracts supplementing with 4% (w/v) sucrose were used as the substrate for cultivation in a 5 L stirred tank reactor. Cultivation condition in a stirred tank reactor for pullulan and application of pullulan coating to extending shelf-life of strawberry were investigated.
The results revealed that the highest production of pullulan (26.55 g/L) was obtained by following better shake flask conditions: 50 mL wheat bran extracts obtained after autoclaving, 4% sucrose (w/v), initial pH 6.5, 1% of A. pullulans NCH-218 was inoculated and cultured at 25℃and 120 rpm for 72 hours. Subsequently, the highest production of pullulan (12.44 g/L) was obtained by following better stirred tank reactor conditions: 3 L wheat bran extracts obtained after autoclaving, supplemented with 4% sucrose (w/v), initial pH 6.5, 7.5% (v/v) of A. pullulans NCH-218 was inoculated and cultured at 25℃, aerated and agitated at 1.5 vvm and 300 rpm respectively for 72 hours.
In addition, the results of strawberry coating test revealed that the better formula of coating solution was comprised 10% (w/v) crude exopolysaccharide, 1% (v/v) phytic acid and 3% (v/v) glycerol, and coated strawberries were stored at 4℃.
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