Extraction of phenolic compounds from defatted rice bran by two-step methanol-alkali process and subcritical water extraction

Rice bran is a good source of different antioxidants, namely, phenolic compounds which help fight diseases such as coronary heart diseases and cancer.Defatted rice bran (DRB) was extracted by a 2-step process, methanol extraction using 80% methanol solution followed by alkaline hydrolysis using 2M NaOH solution, and a subcritical water extraction (SWE) as control experiment. Altering of parameters such as the bran-to-solvent ratio, extraction time and temperature was done in the 2-step process (methanol extraction followed by alkaline hydrolysis) and was each analyzed for total phenolic content. In the methanol extraction part, the 10g:150ml 50 degree celcius 10hr sample (methanol extract) gave the highest amount of total phenolic content using the Folin-Ciocalteu analysis with gallic acid as standard with a value of 17.6 mg Gallic Acid Equivalent (GAE)/g Defatted Rice Bran (DRB). On the other hand, the 10g:150ml 50 degree celcius 4hr sample (alkaline extract) in the alkaline hydrolysis part gave the highest yield with a value of 14.1 mg Gallic Acid Equivalent (GAE)/g Defatted Rice Bran (DRB). The total phenolic content obtained from the 2-step process was of 31.7 mg GAE/g DRB.Comparing the two-step process and subcritical water extraction, the 2-step method gave a higher yield with a total phenolic content of 31.7 mg GAE/g compared to the yield obtained from the subcritical water extraction with only 6.91 mg GAE/g DRB. A higher yield for the subcritical water extract could have been obtained if a higher temperature was used but this study was only able to use 124 degree celcius for this was the maximum temperature available in the autoclave. HPLC analysis was used to quantify the amount of each phenolic acid: gallic acid, ferulic acid and p-coumaric acid from the extracts of the 2-step process and was found to be 6.94 mg GA+Ca+FA/g DRB and of the subcritical water extract which was 0.645 mg GA+CA+FA/g DRB. This study revealed that 2-step method (methanol extraction followed by alkaline hydrolysis) was more effective than the subcritical water extraction only at the conditions studied