Effects of ultrasound treatments on quality of grapefruit juice

Sonication is recognised as a potential technique for improvement in the quality of fruit juices. This study was initiated with the objective of evaluating the effect of sonication treatments on some important quality parameters of grapefruit juice such as physico-chemical (pH, acidity and °Brix), Hunter colour values (L∗, a∗ and b∗), cloud value, electrical conductivity, total antioxidant capacity, DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical scavenging activity, ascorbic acid, total phenolics, flavonoids and flavonols. Sonication of grapefruit juice was done in a bath type sonicator at a frequency of 28 kHz by maintaining a constant temperature of 20 °C. Results showed that there was significant improvement in the cloud value, total antioxidant capacity, DPPH free radical scavenging activity, ascorbic acid, total phenolics, flavonoids and flavonols in all the juice samples sonicated for 30, 60 and 90 min but no changes occurred in the pH, acidity and °Brix value as compared to control. Some differences in all the colour values were also observed but overall quality of grapefruit juice was improved, suggesting that sonication technique may successfully be implemented an industrial scale for the processing of grapefruit juice.