Enhanced Extraction of Phenolics and Antioxidant Capacity from Sorghum (Sorghum bicolor L. Moench) Shell Using Ultrasonic-Assisted Ethanol-Water Binary Solvent

Abstract

Sorghum shell is a rich source of phenolic compounds. Traditionally used organic solvents for these compounds extraction are toxic and are not acceptable for food industry. This study examined the ultrasonic-assisted ethanol–water binary solvent extraction of phenolic compounds from sorghum shell. The results showed that extraction factors had significant effects on the yields of phenolic compounds. The optimum extraction conditions were solids to 80% ethanol solvent ratio of 1:15 at 50C in a 0.32-W cm−2 ultrasonic intensity bath lasting 10 min in duration and extracted twice. Under these conditions, the yield of total phenolic content (TPC) was 52.23 mg GAE/g with values of 53.22 μmol TE/g for 2,2′-azino-bis-(3-ethylbenzothiazoline-6 sulfonic acid) (ABTS) and 77.01 μmol Fe/g for ferric reducing antioxidant power (FRAP). TPC was positively correlated with ABTS and FRAP. The present study would provide theoretical basis for the deep processing and functional food development of sorghum shell comprehensive utilization. Practical Applications An investigation into the effects of ethanol concentration, ultrasonic power, extraction time, ratio of solvent to raw material, temperature and number of extraction steps on the extraction yields of total phenolic content (TPC), total flavonoid content (TFC) and proanthocyanidins content (PAC) from sorghum shell were performed using a single-factor experiment by ultrasonic assisted extraction (UAE). The UAE optimum process parameters were optimized with regard to the extraction temperature, the amount of solvent and the duration of sonication using orthogonal array design (OAD). Sorghum shell exhibited good antioxidant activity and could be a potentially useful natural source of antioxidants. The present study would provide theoretical basis for the deep processing and functional food development of sorghum shell comprehensive utilization.