FUNGAL-MEDIATED VANILLIC ACID PRODUCTION THROUGH BIOCONVERSION OF GALLIC ACID OBTAINED FROM RICE BRAN

Abstract

Gallic and vanillic acids are naturally occurring phenolic compounds widely used in the pharmaceutical, food, and cosmetic industries due to their antioxidant properties. Rice bran is a nutrient-rich agro-industrial by-product. However, there are challenges of improper disposal and underutilization as a substrate for the production of valuable bioactive compounds. This study investigated the fungal-mediated bioconversion of rice bran into gallic acid under solid-state fermentation (SSF) and its subsequent transformation into vanillic acid through submerged fermentation (SMF) using Aspergillus niger. It was inoculated into a fermentation medium containing pre-treated rice bran and mineral salts and incubated for 5 days at 30 °C. Fermentation was monitored for pH, temperature, UV-Vis absorbance (276nm), and titration. The produced gallic acid was characterized using HPLC, GC-MS, and FTIR. Thereafter, 1% Methanol was introduced into a mineral salt medium containing the produced gallic acid as the substrate, and inoculated 1ml of the inoculum and incubated at 30 °C for 5 days. This was monitored and characterized as in the gallic acid production. During fermentation, the temperature ranged 28-33 °C, pH decreased from 6.5 to 5.2, the absorbance rose from 0.205 to 0.681 nm, and titration increased from 0.016 to 0.075 mol (p<0.05). HPLC quantified 6552.2 mg/L total phenolics, with gallic acid at 2569.8 mg/L. FTIR revealed gallic acid functional groups such as O–H, C=O, and C=C, while GC-MS identified volatile compounds including O-toluic acid, 2(1H)-naphthalene derivatives, and 3H-Cyclodeca[b]furan-2-one. For the vanillic acid production, fermentation filtrate temperature stayed at 29-30 oC, with the pH increasing in acidity from 6.5 to 4.3 through the 5-day period. This corresponded with the results of the titration, showing 0.016 to 0.079 mol results.The GC-MS showed volatile organic compounds present in vanillic acid, including protocatechuic, catechol, and syringic acids. HPLC quantified a total of 15,31203 mg/L of vanillic acid. FTIR revealed vanillic acid functional groups such as OCH₃, OH, and C=O. The results of this study provides strategic insights for sustainable bioprocess approaches in support of SDGs 3 and 12.