Performance of microwave-assisted extraction of proanthocyanidins from red sorghum grain in various power and citric acid concentration

Proanthocyanidin is a phenolic compound in red sorghum grains that is popular as an antioxidant agent for food, supplement, and nutraceuticals. The development of microwave-assisted extraction (MAE) of proanthocyanidins (PA) from the grains is needed to maximize its potency. The performance of MAE was evaluated to accelerate the extraction by applying different MAE’s power ratings and citric acid (CA) concentrations in aquadest as a safe solvent. This research analyzed the MAE performance in various powers and CA concentrations using Peleg's and Newton’s law as the model approaches. The increase of PA content during MAE was evaluated as the effect of microwave power (640 W, 720 W, and 800 W) and the CA concentration (0%, 1%, and 2%). Using Peleg’s model, the initial extraction rates were stretched between 2.3 × 10-3 to 10.6 × 10-3 mg/ml.minute. The maximum capacity of each extraction ranged from 0.92 to 1.80 ml/mg. The increase of MAE power and CA concentration affected the increase of the initial extraction rate and the maximum extraction capacity. Peleg’s model illustrated a more complete and precise description of the effect of MAE power and CA concentration on the extraction rate and the maximum capacity of extraction than Newton’s model. Peleg’s model was also more accurate than Newton’s model in predicting the PA concentration during MAE, although both of them gave a good match in describing the MAE’s performance.