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Polyhydroxyalkanoate(PHA) is one of the alternatively biodegradable plastics which can besynthesized from a particular micro-organism after the fermentation process,considering the optimization of nutrients. In this research, the yeaststrain Rhodotorula graminis TISTR 5124 was selected to be fermented with a carbonsource in the standard nutrient in order to conduct a preliminarily study on thebest conditions for thisyeast in PHA production. The growth rate curve of yeast in the composition of imbalancednutrients, i.e. the limitationof phosphorus and nitrogen, was also investigated and compared with another sample cultured in standard nutrients. Experimental results indicated that thecondition that gave the maximum growth rate of this yeast strain was aP-limited condition at 81 hours, whereby the cell number of 3.1×109cells/mL wasobtained and corresponded to the optical density (OD) of 0.95 measured at awavelength of 600 nm. The synthesized PHA extracted from yeast cells after 81hours of incubation was examined by Fouriertransform infra-red (FT-IR) and nuclear magnetic resonance (1H NMR) spectroscopy. The results indicated stretchingvibrations similar to the copolymer PHBV (or a PHA derivative). Maximum PHA content of 54.4% wasfound in the P-limited condition which correspondedto a PHA yield of 65.1 (g/g-total sugar consumed) in which the yeast consumed the least glucose amount of 3.2 g/L, butgrew the most rapidly. Rhodotorulagraminis TISTR 5124 is therefore promising as a good candidate for alternativelybiodegradable plastics, considering the potential to produce PHA and its derivatives. This process can be beneficial as an option to replace conventional plastics inthe future. |
