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Microbial transformation is known to be useful for obtaining more active or less toxic compounds and achieving selective compounds conversion to more useful derivatives. The objective of this study is to explore several factors that affect the optimization of bioconversion of quercetin glucosides using Aspergillus acueletus LS04-3. To obtain the optimum condition of biotransformation the fungus was cultured under several conditions by varying the number of days of fermentation, the concentration of substrate, carbon, and nitrogen source. The transformation product was analyzed using HPLC and LCMS-MS. The results revealed that on the third-day biotransformation process, quercetin production reached the highest amount and the optimum concentration was at 50 ppm of quercetin glucoside based on HPLC analysis. In addition, from various carbon sources, glucose yielded the highest biotransformation product, while nitrogen accelerated the reaction. In this research, media of A. acueletus LS04-3 containing carbon and nitrogen could increased quercetin production. This research finding provided several factors for optimizing quercetin biotransformation by A. acueletus LS04-3. These factors were important in scaling up biotransformation even in other biotransformation reactions.

Sulochrin is known to have an activity as inhibitors of the α-glucosidase enzyme. In this report interaction of sulochrin to the active site of the α-glucosidase enzyme from Saccharomyces cerevisiae was studied by docking method. The crystal structure of α-glucosidase from S. cerevisiae obtained from the homology method using α-glucosidase from S. cerevisiae (Swiss-Prot code P53341) as a target and crystal structure of isomaltase from S. cerevisiae (PDB code 3A4A) as a template. These studies show that sulochrin and sulochrin-I could be bound in the active site of α-glucosidase from S. cerevisiae through the formation of hydrogen bonds with Arg213, Asp215, Glu277, Asp352. Sulochrin-I has stability and inhibition of the α-glucosidase enzyme better than sulochrin. The iodine atom in the structure of sulochrin can increase the activity as an inhibitor of the α-glucosidase enzyme.

This study aims to search for the active components from Aspergillus terreus LS07 which isolated from an Indonesian soil. Bioassay-guided fractionations of the ethyl acetate (EtOAc) extract against α-glucosidase and DPPH free radical to give four isolated compounds: oleic acid (1), ergosterol (2), butyrolactone I (3), and butyrolactone II (4). The structures of these metabolites were assigned on the basis of detailed spectroscopic analysis. Oleic acid (1) was showed significant activity toward α-glucosidase with IC50 value of 8.54 μM, but not for antioxidant. Butyrolactone I (3) and II (4) were showed significant activities against the α-glucosidase with their IC50 values at 52.17 and 96.01 μM, and those against DPPH free radicals at 51.39 and 17.64 μM, respectively. On the other hand, ergosterol (2) did not show any activities.