Abstract
The enzymatic production of isopropyl and 2-ethylhexyl esters was investigated using fungal oil produced via fermentation of nanofiltrated spent sulphite liquor (SSL). Screening of five oleaginous fungi showed that Cunninghmamella echinulata could accumulate lipids with 12 % (w/w) γ-linolenic acid content in shake flask cultures. Ester formation by the commercial lipase Novozym 435 was favored when transesterifications of fungal oil with isopropyl and 2-ethylhexyl alcohols were performed at 60 °C, 1:3 microbial oil to alcohol molar ratio and 10 % biocatalyst concentration. Transesterifications of individual neutral lipids (NL), glycolipids and sphingolipids (GL + SL) and phospholipids (PL), with isopropanol and 2-ethyl-hexanol showed that the presence of GL + SL and PL in fungal oil hindered ester production. Transesterification of the NL fraction alone with isopropanol and 2-ethylhexanol led to the highest conversion yield of 80.2 % and 73.8 %, respectively. Conversion yields to isopropyl and 2-ethylhexyl esters reached up to 90 % and 80 % (w/w), respectively, when hydrolyzed fungal oil was used. The biocatalyst showed good stability in 5 repeated enzymatic reactions. The physicochemical properties and the ICP-MS analysis of esters demonstrated their potential utilization in cosmetic formulations. This study showed a perspective of valorizing SSL towards the production of value-added fatty acid esters for chemical, cosmetic and pharmaceutical applications.
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