Production and Application of Novel Sterol Esterases from Aspergillus Strains by Solid State Fermentation

Abstract

AbstractAmong numerous mesophilic fungi screened for sterol esterase activity followed by the esterification reaction between plant β‐sitosterol and lauric acid in organic solvent, six Aspergillus strains were selected as the most active producers. These fungi had not been studied previously for sterol esterase production. The fungi were cultivated under solid state fermentation (SSF) conditions. The gently dried SSF cultures as such were tested in the esterification reactions, without any special enzyme isolation and purification (downstream) processes. All the six Aspergillus SSF preparations were able to synthesize sterol esters. Sterol esterase activity of these GRAS cleared Aspergillus strains was inducible by sterol ester supplementation to the SSF medium and showed remarkably different moisture optimum during growth as compared to the production of lipase (determined by pNP‐palmitate). Genome analysis revealed that sterol esterase production might be a common feature of many Aspergillus species. The synthetic usefulness of the best SSF preparations of A. oryzae NRRL 6270 and A. sojae NRRL 6271 was demonstrated by synthesis of esters of plant sterols with lauric acid resulting in 45–63% conversions (GC) and 27–38% isolated yields of steryl laurates. The isomer preference of A. oryzae NRRL 6270 towards the 10E,12Z isomer of conjugated linoleic acid (CLA) in the esterification reaction with plant sterols was also determined.