The Effect of Ultrasonic Pretreatment on Antioxidant Activity and Phenolic Compounds of White and Brown Rice Extracted from Lenjan Sorkhe Cultivar

Brown rice cultivars has higher nutritional values than the white rice cultivars due to the total phenolic compounds. Ultrasonic pretreatment is an efficient method for the extraction of phenolic compounds due to time saving, high performance efficiency and also less solvent consumption.
Total phenolic compounds and flavonoid contents were determined and antioxidant potential was assessed by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay. Bioactive compounds of white and brown rice were extracted under various solvents including (water, ethanol 100%, methanol 100%, ethanol 50%, methanol 50% and ethanol 50%-methanol 50%) and two extraction methods such as Soxhlet extractor and ultrasonic bath. The comparison of the test variables were performed by Duncan's test and three-way multivariate analysis of variance.
The results showed that the highest flavonoids content (162 mg gallic acid/ Kg sample), poly phenols (142.5 mg quercetin / kg sample) and radicals scavenging effect DPPH (%76.4) belonged to brown rice under ultrasonic method and ethanol:methanol (50:50) solvent extraction. The results exibited that all the main related factors such as methods of extraction, solvents and rice have significant effects on the amount of polyphenols, flavonoids and DPPH.
Under the same extraction condition, total phenol and flavonoid contents of brown rice is higher than the white rice. Ultrasonic extraction could enhance the total phenol and flavonoids contents compared to the soxhlet extraction.