In this contribution the synthesis of phosphatidylserine (PS) using a phospholipase D (PLD) produced by Streptomyces sp. isolated from soil-and wastewater-contaminated palm oil is shown. Streptomyces sp. SC734 was found to produce PLD in the culture medium and showed the highest transphosphatidylation activity. This PLD was purified and characterized. The purified PLD SC734 converted phosphatidylcholine (PC) to PS completely in a biphasic system consisting of chloroform and sodium acetate buffer (pH 6.0) at 1:5 (mol/mol) of PC to L-serine at 45°C within 40 min using 1.5 U PLD. The PLD could also synthesize PS from soybean lecithin with 100% conversion in the biphasic system at 1:7 (mol/mol) of soybean lecithin to L-serine at 45°C in 60 min. In addition, the PLD SC734 could be used to synthesize PS from soybean lecithin in an aqueous system as well with up to 94.7% conversion in the presence of 2.5 mM Triton X-100 in 100 min.
This study was aimed to investigate the optimal condition of ethanol production that has 2 major stages: acid hydrolysis and fermentation processes. These processes came from low quality sweet potato (LQSP) which was destroyed by the sweet potato weevil. The main compositions of LQSP were starch and fiber which consist of 55.25 and 10.29 %, respectively. In this case, the starch can be hydrolyzed to reduce the sugar, followed by the fermentation of the reduced sugar to ethanol. For this experiment, the effecting factors on acid hydrolysis of LQSP and the ethanol fermentation condition were optimized by S. cerevisiae using Response Surface Methodology (RSM) with Box-Behnken design in order to maximize ethanol yield. It was found that the maximum reducing sugar concentration of 390.99 ± 5.35 g/L was obtained from the hydrolysis condition with 1 % (v/v) of sulfuric acid and 25 % (w/v) of LQSP. Accordingly, the effects of ammonium sulphate content (0.05 - 0.15 %), pH (4.5 - 5.5) and inoculum content (5 - 10 %) on ethanol production was determined by RSM using Box-Behnken experiment design with a total 17 sets of all trials. The results were found that the maximum experimental ethanol productivity of 5.98 g/L was obtained from the condition at 0.05 % of ammonium sulphate, pH 5.5 and 5.0 % of inoculum size to 90 mL LQSP based medium and incubated at 30 °C for 48 h. In addition, the scale-up of ethanol production was studied in 9 L fermenter which provided the maximum ethanol yield of 5.04 g/L. Therefore, it can be concluded that LQSP had a potential as a substrate for ethanol production.
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