Study of continuous flow ultrasonication to improve total phenolic content and antioxidant activity in sorghum flour and its comparison with batch ultrasonication

Ultrasonic technology was applied to release the phenolics bound with starch and protein matrix in order to enhance total phenolic content (TPC) and antioxidant activity (AA) of the sorghum flour. Both the continuous flow and batch ultrasonication were implied with independent variables such as flour to water ratio (FWR), ultrasonication intensity (UI), and ultrasonication time (UT) with an additional variable as flow rate (FR) in continuous flow ultrasonication. All the process variables showed a significant effect on the corresponding ultrasonication process. The optimal conditions for the continuous flow ultrasonication were a FWR of 10% w/v, an UI of 20 W/cm², an UT of 130 s, and 15 ml/s FR which produced a maximum values of 70.9 mg GAE/100 g dry matter (d.m.) for TPC and 143.9 µmol TE/100 g d.m. for AA. Regarding the batch ultrasonication, the maximum values were 65.6 mg GAE/100 g d.m. and 141.0 µmol TE/100 g d.m. for TPC and AA, respectively at optimum conditions of 10% w/v FWR, 30 W/cm² UI, and 200 s UT. When comparing with the batch ultrasonication, the continuous flow process saved 35% time and 33% of energy consumption to obtain comparatively higher TPC and AA of the sorghum flour. Ultrasonication improved free phenolic acid content by releasing bound phenolics in the sorghum flour. Impact of various process parameters on specific energy was analyzed during both the processes, and influence of energy on TPC and AA of the sorghum flour was also observed for the batch and continuous flow ultrasonication.