The influence of the concentration and time of addition of cosubstrate (pentanol) on the molecular weight (MW) of the polyhydroxybutyrate/valerate (PHBV) copolymer synthesized by Methylobacterium extorquens G-10 during cultivation in a methanol-containing medium has been studied. It was shown that an increase in the pentanol concentration to 20% in a mixture with methanol stimulated the biosynthesis of PHBV with a MW of approximately 1500 kDa and increased the content of valerate up to 50%, especially when pentanol was added to the log phase culture. High pentanol concentrations are toxic for the producer and reduce the total yield of PHBV. An MW increase to 1500 kDa lowers the melting temperature (from 172 to 162 degrees C) and the crystallinity degree (from 63 to 8%) of the biopolymer but increases its elasticity. The revealed variability of PHBV properties extends considerably the potential application areas of synthetic bioplastics.
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