Optimization on Decreasing High Acid Value of Yeast Oil Pseudozyma parantarctica CHC28 for Microbial Biodiesel Production

Abstract

Currently, biodiesel has been received much attention for as an important renewable energy for resolving the energy crisis and global warming problems. The microbial oil is interested to use as an alternative raw material in biodiesel production instead of conventional oils. However, the microbial oil has high acid value (AV) oil because it contained the free fatty acid as a main component which cannot convert to biodiesel directly. Firstly, oleaginous yeast Pseudozyma parantarctica CHC28 was cultured in a 10-L fermenter for 5 days. The result showed that yeast could produce the biomass and oil concentration for 11.39 and 5.48 g/L, respectively. The oil accumulation was expressed as oil content for 48.10 % of dry cell weight. The oil in yeast biomass was extracted by using HCl solution (4.0 N) with ratio of 1:1. The extracted oil was obtained for 31.80 g which had the AV was 28.14 mgKOH/g. Then, the simple pretreatment process for decreasing the AV by statistical methods based on 2-level factorial experimental design was studied. The independent variables were amount of H₂SO₄, temperature, and ratio of methanol to oil. The AV was reduced to 2.04 mgKOH/g (92.74 % decreasing) under optimum condition: 0.2 N H₂SO₄, 65 °C of temperature, and 5:1 of methanol to oil ratio. The AV of pretreated oil was in suitable level for producing biodiesel (2.0 mgKOH/g). This research demonstrated the high efficiency of pretreatment process to decrease AV of oil produced by yeast CHC28.