Sarocladium strictum lipase (LipSs) produced using crude glycerol as sole carbon source: A promising enzyme for biodiesel production

The production of biodiesel (fatty acid methyl esters), an environmentally safe next-generation biofuel, using a lipase from Sarocladium strictum and glycerol (a biodiesel by-product) as sole carbon source, was investigated. The fungus S. strictum showed maximum lipase production when grown in crude glycerol (3.13 U/mg protein) with 168 h of growth. Different concentrations of crude glycerol as carbon source were tested and concentrations ranging from 0.5 to 4% were completely consumed (100%) by the S. strictum. The lipase from S. strictum was purified (24.4-fold) with a specific activity of 73.2 U/mg protein showing a molecular weight of 52 kDa. The effects of pH and temperature in the lipase activity were evaluated showing optimal activity at pH 5.0 and 40 degrees C, respectively. Lipase hydrolyzed different substrates and exhibited better activity on p-nitrophenyl octanoate (30.68 U/mg protein). The detergents Triton X-100 and Tween 80 at concentration of 0.1% (v/v) increased the lipase activity by 10.45 and 8.55%, respectively. The lipase maintained 80% residual activity in the presence of methanol (1:1, v/v) after 24 h of incubation. In concentrations ranging from 1 to 5% of methanol, showed activity above 90%, maintaining 70% activity at 10% concentration. Gas chromatography mass spectrometry (GC-MS) analysis confirmed biodiesel production with soybean and sunflower oil by lipase with a conversion rate of approximately 65 and 85%, respectively. Therefore, the lipase was efficient in the conversion of low-cost plant oil to high-value biodiesel.