ENHANCEMENT OF PHENOLIC CONTENT AND ANTIOXIDANT PROPERTIES THROUGH CHEMICAL AND BIOCHEMICAL REATMENT OF LIGNIN-RICH RICE STRAW RESIDUE

Valorization of lignin in biorefineries is important as this can lead to enhancement of chemical and physical properties of lignin, making it suitable for applications in polymers, composites and adhesives. Lignin valorization requires overcoming recalcitrance and tailoring for different uses. Here, lignin was extracted from rice straw lignin-rich residue at pH 12, using 4% magnesium oxide and 6% sodium hydroxide on a dry w/w basis. The extracted lignin-rich stream, which had a pH in the range of 9-10, was used further for biochemical transformation. Towards that end, Pseudomonas putida, Sphingomonas paucimobilis, Pseudomonas fluorescens and Bacillus tequilensis were screened for their capability of aromatic dye decolourization. The results of the study show an increase in the total phenolic content in lignin between 50% and 55% after 144 h of treatment with Pseudomonas putida. Concomitant with the increase of phenolics, a four-fold increase in antioxidant activity in gallic acid equivalents was also observed when Pseudomonas putida was used.