Response surface methodology for optimization of Rhizopus stolonifer 1aNRC11 mutant F whole-cell lipase production as a biocatalyst for methanolysis of waste frying oil

Abstract

Biodiesel, fatty acid methyl ester (FAME), is an environmentally friendly alternative fuel produced by transesterification of renewable lipid feedstocks for diesel engines. Methanolysis of waste frying oil (WFO) was catalyzed by Rhizopus stolonifer 1aNRC11 mutant F whole-cell lipase that produced under solid state fermentation (SSF) using wheat bran (WB) and black cumin meal as the main substrate. Cultivation SSF parameters of R. stolonifer mutant were optimized using Plackett-Burman (PB) experimental design and Face-centred Central Composite Design (FCCD), taking FAME yield as a response for whole-cell lipase production ability. PB results showed that cultivation temperature, medium pH and moisture content were the most significant parameters, which were selected for optimization by FCCD. The optimal determined conditions were as follows: WB (10 g), black cumin meal (6%, w/w of WB), fodder yeast (1%, w/w of WB), moisture content (1.5 g water/g solid), inoculum size (3 discs), initial pH (8), and cultivation time (4 day) at 28 °C. With R. stolonifer mutant cultivated in the optimized conditions, the FAME yield reached 82.6% that was close to the predicted yield of 85.7%. The analysis of variance showed that the model was statistically significant (p value of .0001) and could explain 89% of the variability in the response. These results indicated that the optimization conditions increased biodiesel production by about 43% compared to the basal medium (57.60%). The optimization of SSF conditions using low cost components makes the whole-cell lipase production process from the R. stolonifer 1aNRC11 mutant F economically effective for application in biodiesel production from WFO.