Four strains of Aspergillus niger were screened for lipase production. Each was cultivated on four different media differing in their contents of mineral components and sources of carbon and nitrogen. Aspergillus niger NRRL3 produced maximal activity (325U/ml) when grown in 3% peptone , 0.05% MgSO 4 .7H 2 O, 0.05% KCl, 0.2% K 2 HPO 4 and 1% olive oil:glucose (0.5:0.5). A. niger NRRL3 lipase was partially purifi ed by ammonium sulphate precipitation. The majority of lipase activity (48%) was located in fraction IV precipitated at 50-60% of saturation with a 18-fold enzyme purifi cation. The optimal pH of the partial purifi ed lipase preparation for the hydrolysis of emulsifi ed olive oil was 7.2 and the optimum temperature was 60°C. At 70°C, the enzyme retained more than 90% of its activity. Enzyme activity was inhibited by Hg 2+ and K + , whereas Ca 2+ and Mn 2+ greatly stimulated its activity. Additionally, the formed lipase was stored for one month without any loss in the activity.

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Microorganisms have been screened for biotransformational activity against diosgenin or its precursor furostanol glycosides obtained from fenugreek seed (Trigonella foenum-graecum). Using diosgenin as the substrate, Cunninghamella elegans and Aspergillus nidulans produced some androstenes when a,a 0 -dipyridyl was supplemented to the transformation medium. Also, using the glycosides as a substrate, Rhizopus sp. produced diosgenin in [90% yield from the glycoside. The parameters were optimized to increase the yield of the androstenes.

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