Processing of grapefruit juice with ultrasound, mi̇crowave and combined treatments

In this thesis, freshly squeezed grapefruit juices pasteurization (PAS) (at 90 °C, 1 min.), ultrasound (US) (15 and 30 min.), microwave (MD) (300, 600 and 900 W / 30 sec.) and ultrasound-microwave combined applications (US-15 + 300 W, US-15 + 600 W, US-15 + 900 W, US-30 + 300 W, US-30 + 600W, US-30 + 900 W) has been processed. Grapefruit juices treated with different applications and control samples (untreated grapefruit juices) were stored at +4±0.5 ºC for 60 days, and microbiological and quality analyzes were performed on 0, 15, 30, and 60 days. With the data obtained as a result of the microbiological analyzes, there was a microbiological decrease in all analyzed storage days (0., 15., 30. and 60. days) compared to the control sample in US-15, 300 W and US-15 + 300 W applications. has been observed, but the safe and desired complete inactivation has not been achieved. However, in all other processes applied to grapefruit juice (PAS, US-30, 600 W, 900 W, US-15 + 600 W, US-15 + 900 W, US-30 + 300 W, US-30 + 600 W and US -30 + 900 W) and during all storage days (0., 15., 30. and 60. days) no microbiological development was observed and safe and desired complete inactivation was achieved with these applications. Considering the quality parameters of grapefruit juices processed with different applications; In the analyzed °brix values, it was observed that the grapefruit juices subjected to US and MD treatments had the lowest °brix values during the 60-day storage period (p<0.05). It was determined that grapefruit juices processed with PAS and combined applications generally gave more similar results to the control sample for all storage days (p>0.05). It was observed that the pH values of grapefruit juices on day 0 increased compared to the control (p<0.05) for grapefruit juices subjected to PAS, US and MD treatments, and results closer to the control were obtained in combined applications (p>0.05). In the analyzes performed at the end of the 60th day, it was determined that PAS and combined applications had similar (p>0.05) pH values, but lower pH values were detected in US and MD applications (p<0.05). It was observed that the titration acidity values increased as a result of the 60-day storage period, and higher acidity values (p<0.05) were analyzed with MD and combined applications compared to PAS and ultrasound. The total amount of phenolic substance, antioxidant capacity, total amount of carotenoid substance and ascorbic acid contents obtained as a result of storing grapefruit juices processed with ultrasound, microwave and combined applications for 60 days are higher than the values obtained in traditional pasteurization, that is, the effects of these innovative technologies on grapefruit juice. It was observed that it preserved and even improved its nutritional values better than pasteurization (p<0.05). It has been determined that the browning index values of grapefruit juice are generally higher in US, MD and combined applications compared to pasteurization. It was determined that L*, a*, b* and C* values, which represent the colors of grapefruit juices after different treatments, decreased during storage and the lowest color values among applications were obtained in grapefruit juice subjected to PAS (p<0.05). In the analyzed hue angle (α) values (day 0), α values obtained in all applications except 900 W microwave application were not statistically different compared to the control sample (p>0.05). Finally, it was observed that the total color change (ΔE) values of grapefruit juices increased after 60 days of storage, the maximum color change was observed with PAS, and the least color change was detected in the combined application of US-30 + 600 W (p<0.05).