Effectiveness of Inorganic Nitrogen on Kojic Acid Production from Fungi Aspergillus sp. BU20S

Abstract

Kojic acid is a valuable compound that contributes to various therapeutic and cosmetic applications. Organic nitrogen partially contributes to fermentation and mostly prefers cell growth as well as increases production costs. This study aims to find the effect of low-cost inorganic nitrogen in the form of ammonium chloride on kojic acid production from fungal isolate Aspergillus sp. BU20S. A 3.63-times increase in the kojic acid (4.43 ± 0.47 g/L) was found when only the ammonium chloride was supplemented in glucose (10 g/L) medium than other minimal salts. The product formation was 2.52 ± 0.56 g/L in ammonium chloride as compared to 2.02 ± 0.06 g/L yeast extract after 10 days. The carbon/nitrogen ratio (C/N) was found optimal as 15 (molecular C/N: 23.58) which gives a high titer of 5.17 ± 0.84 g/L from 10 g/L of glucose. At this optimal molecular nitrogen value, the nitrogen supplement cost can be reduced by 93–99% compared to yeast extract. The antimicrobial potential of kojic acid purified from the fermented broth was also studied against methicillin-resistant Staphylococcus aureus (MRSA). The purified kojic acid showed a ~ 20 mm zone of inhibition at a 2.5 mg dose loaded over 7.4 × 10⁹ CFU/mL of MRSA. This study concludes that only ammonium chloride is a sufficient inorganic nitrogen source to produce kojic acid and is useful in reducing production costs. The purified kojic acid is also an effective antimicrobial agent.