Effect of ultrasonic on the chemical composition of stirred yoghurt supplemented with orange peel powder

Heat treatments in dairy processing exert undesirable effects on the final product. Alternatively, a high-intensity ultrasonic technique was applied to process stirred yoghurt supplemented with orange peel powder (OPP). For this reason, OPP was added to the fresh milk at concentrations of 0.0, 1, and 2%, and then the mixture was subjected to ultrasound waves (24 kHz at 45 ± 2 °C for 30 min) before being incubated with the starter culture w/v%. Analysis of fresh and stored samples (7 and 14 days) showed that ultrasonic-treated milk (UTM) had a longer fermentation time than the heat-treated sample (HTM). No significant differences in total solid content, protein, ash, and volatile fatty acids were observed between UTM and HTM samples, while slight differences due to the addition of OPP were detected. Treating milk with ultrasound waves improved the processed yogurt’s apparent viscosity and water-holding capacity; however, adding OPP resulted in minor reverse effects. Total flavonoid and phenolic contents and antioxidant activity increased by adding OPP and were significantly higher in yoghurt made from UTM than in HTM. Overall, the application of ultrasonication in processing OPP- supplemented yoghurt resulted in better chemical and physical properties and maintained bioactive antioxidant components compared to yogurt manufactured from HTM.