Polyhydroxyalkanoate
(PHA) is one of the alternatively biodegradable plastics which can be
synthesized from a particular micro-organism after the fermentation process,
considering the optimization of nutrients. In this research, the yeast
strain Rhodotorula graminis TISTR 5124 was selected to be fermented with a carbon
source in the standard nutrient in order to conduct a preliminarily study on the
best conditions for this
yeast in PHA production. The growth rate curve of yeast in the composition of imbalanced
nutrients, i.e. the limitation
of phosphorus and nitrogen, was also investigated and compared with another sample cultured in standard nutrients. Experimental results indicated that the
condition that gave the maximum growth rate of this yeast strain was a
P-limited condition at 81 hours, whereby the cell number of 3.1×109cells/mL was
obtained and corresponded to the optical density (OD) of 0.95 measured at a
wavelength of 600 nm. The synthesized PHA extracted from yeast cells after 81
hours of incubation was examined by Fourier
transform infra-red (FT-IR) and nuclear magnetic resonance (1H NMR) spectroscopy. The results indicated stretching
vibrations similar to the copolymer PHBV (or a PHA derivative). Maximum PHA content of 54.4% was
found in the P-limited condition which corresponded
to 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, but
grew the most rapidly. Rhodotorula
graminis TISTR 5124 is therefore promising as a good candidate for alternatively
biodegradable plastics, considering the potential to produce PHA and its derivatives. This process can be beneficial as an option to replace conventional plastics in
the future.
