Poly (hydroxybutyrate–co–hydroxyvalerate) production in a batch fermentation of cheap substrates with co–cultures of Propionibacterium shermanii and a Bacillus strain isolated from date syrup wasteپنجمین کنگره بین المللی مهندسی شیمی
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Polyhydroxyalkanoates (PHAs) are a family of biodegradable and biocompatible polyesters which are biosynthesized and intracellularly accumulated as carbon and energy sources in numerous microorganisms. Poly(hydroxybutyrate–co–hydroxyvalerate) is a copolymer of hydroxyalkanoates with a better flexibility than polyhydroxybutyrate (PHB). With the aim of reducing substrate costs in the production of Poly (3–hydroxybutyrate–hydroxyvalerate), fermentation was carried out with co–cultures of two microorganisms. co–3–Propionic acid, necessary for the copolymer production, was obtained in the first step by separate fermentation of whey with Propionibacterium shermanii and then fed directly to the main fermentation medium. The microorganism that is responsible to produce PHA was an isolate strain from the sewage of date factory and identified as bacillus sp. The main fermentation medium for producing PHA was a mixed carbon source of cheap substrate containing (date syrup 2%, cane molasses 2% and ultra filtrate whey 20%), supplemented with corn step liquor 3% as nitrogen source, without using any mineral salt. It was found that propionic acid produced in the first medium was consumed by isolated microorganism to produce P(HB–co–HV). This strategy allowed production of 27 mol% of 3–hydroxyvalerate in 2.4 g\L of total accumulated copolymer.<\div>
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