Ripe and overripe pineapples were bought from a local market in Jashore, Bangladesh. According to Shamsudin et al. [18] and Ramallo and Mascheroni [19] , fruits were gently divided into two separate groups based on their maturity (ripe and overripe). Under flowing water, all pineapples were washed. The fruits were then peeled and pressed mechanically using an electrical juice separator (BL25C46, Guangdong Midea Electric Appliances Co., Ltd., Foshan, China). In order to extract the juice and remove the solid particles, the flesh was squeezed and passed through a double layer of filter cloth. The juices were then kept at −18˚C in a (400 ± 2 ml) glass jar for later analysis. Frozen fruit juices that were ripe or overripe were collected, defrosted, and given time to warm up before being pasteurized and sterilized using ultrasound. After that, the juices are divided into four categories (Group 1: Fresh raw pineapple juice without any treatment; Group 2: Juice treated with pasteurization; Group 3: Juice treated with ultrasonication, Group 4: Juice treated with combined pasteurization and ultrasonication treatment).

The following treatments were applied to the various groups. Control groups consisted of fresh pineapple juice that had not been treated. Juices were processed by pasteurization and ultrasonication treatments described by Bavisetty and Venkatachalam [20] with slight modification. For pasteurization process, juices were transported into sterilized glass jars (400 ± 2 ml). Juices were then pasteurized (≈90˚C) using a temperature-controlled water bath with a basin made of stainless steel. The water bath (Human Lab Instrument Co., Ltd., Korea) included thermostatic control, temperature resistance up to 120˚C, an operational temperature range of 25˚C - 100˚C with a precision of ±1˚C, and 220 V/50 Hz electrical supply after the pasteurization was finished, samples were gathered and quickly cooled to ambient temperature (25˚C ± 1˚C). The samples were then prepared for ultrasonic therapy.

The ultrasound therapy was carried out using an ultrasound bath (Branson Model 2510E-DHT ultrasonic cleaner, CT 06813, USA), operating at a frequency of 40 kHz with a maximum input power of 185 W (the internal dimensions: 16 × 15.5 × 14.5 inch) for 5 minutes. To prevent any interaction from light with the samples, all treatments were carried out in complete darkness. A sample of untreated juice was similarly preserved and used as a comparison standard (non-sonicated). Stainless steel container-mounted piezoelectric sandwich-type transducers convert high-frequency electricity into ultrasonic waves of the required frequency. Pineapple juice was placed in glass jars and placed in the center of the ultrasonic cleaning solution. During the ultrasonic treatment, the temperature of the demineralized water was 37˚C ± 1˚C (Figure 1).

Pineapple juices were also treated with combined treatment of pasteurization and ultrasonication. Same parameters were also set here for both pasteurization and ultrasonication as described earlier. The processed juice was stored at −18˚C until further analysis. For each treatment, three samples were created. The experiment was carried out three times.

By using a Minolta colorimeter (CR-400, Minolta Camera Co., Ltd., Osaka, Japan) and the Hunter Lab color system, the color of pineapple juice that had been treated was determined. Before the measurement, the colorimeter was calibrated using demineralized water (L = 100, a = 0, b = 0). The color value was determined using a glass cuvette (3.5 × 4 × 1.5 cm³) containing processed pineapple juice. Three Hunter parameters, “L*” (lightness), “a*” (redness and greenness), and “b*” (yellowness and blueness), were measured, and L*, a*, and b* values were used to determine total color differences.

The pH, total soluble solids, and titratable acidity of the juice are related to its sensory quality; hence, alterations in these three qualities may have a negative effect on the juice’s sensory quality. Figure 2 shows pH, TSS, and TA values for differently treated juices. The pH of ripe and overripe pineapple juices before and after processing did not differ significantly (p < 0.05) (Figure 2(a)). The pH values for treated ripe and overripe pineapple juice varied from 4.70 to 4.73 and 4.52 to 4.53 respectively. The pH of the treatment solution may change as a result of ultrasonication due to the generation of reactive oxygen species (ROS) in the aqueous medium, such as hydrogen peroxide, nitrate, and nitrite, as described by Supeno and Kruus [26] . The pH of grape juice treated with ultrasonic waves at 20 kHz and 1500 watts at temperatures ranging from 32˚C to 45˚C did not change much [27] . In a recent experiment, Bhat et al. [7] also reported that the pH of kasturi lime juice was not significantly affected by ultrasonic treatment (p > 0.05) in any of the treatments.

One important pineapple quality factor that affects the sensory qualities of pineapple juice is total soluble solids (TSSs) as illustrated in Figure 2(b). Mainly

depending on the fruit’s maturity. Initially overripe fruit juice had a higher TSS (11.5˚Brix) than ripe fruit (9.70˚Brix), but it decreased after treatment. The combination of sonication and pasteurization led to a greater drop than sonication alone (p < 0.05), but the alterations were minor. This was due to the fact that ripe juice contained much fewer fermentable sugars than overripe juice, including d-glucose, d-fructose, and sucrose [28] . Saeeduddin et al. [16] also found no discernible differences in pear juice after conventional and ultrasound pasteurization at varied temperatures.

Bavisetty and Venkatachalam [20] also reported, the reduction of TSS in wax apple juice samples sonicated with subsequent pasteurization was greater than with sonication alone. All juices showed parallel titratable acidity (TA) changes when processed, independent of maturity (Figure 2(c)). In this study, there was no considerable (p < 0.05) increase in TA for pineapple juices after sonication and pasteurization treatments. Similar patterns were discovered in the juice of Haematocarpus validus [29] . These results agreed with the previous reports of Bavisetty and Venkatachalam [20] .

Fruit juice’s color is a crucial sensory characteristic that can indicate nutritional quality or loss and affect consumer perception [21] [30] . Color is one aspect that consumers may use to determine the efficiency of fruit juice or pulp [31] . Figure 3 displays the findings on the impact of the sonication and pasteurization processes on the color values (L*, a*, and b*) of pineapple juice. Results showed that when pineapple juice was treated with ultrasound, there was a substantial (p < 0.05) decrease in a* value (Figure 3(a)) and b* value (Figure 3(b)) but slightly increase in L* value (Figure 3(c)). Juice that was ripe at the start was lighter than juice that was overripe. Whereas pasteurization and sonication jointly decreased L*, with pasteurization having an especially significant impact on the lowering of L* for overripe juice, sonication alone had a less significant impact on L* of ripe or overripe juice across all examined sonication durations (p < 0.05). According to Aadil et al. [21] , homogenizing by sonication raised L* due to inadequate precipitation of suspended particles, resulting in a high cloud value. A rise in temperature induced both enzymatic and nonenzymatic browning processes, which resulted in the decomposition of ascorbic acid and the caramelization of sugar, lowering L* [32] . Similar findings were reported by Bavisetty and Venkatachalam [20] who found that large reduction of L* value in ripe and overripe wax apple juice when processed by pasteurization and sonication. Cheng et al. [33] found the color shift in sonicated and carbonated guava juice, as well as significant changes in all color parameters, despite the fact that the naked eye was unable to identify these differences. Fonteles et al. [10] found that the breakdown of cell membranes during sonication results in the production of carotenoid-protein complexes, which produce a change in color.

Bioactive substances for example flavonoids, anthocyanins, phenolics, ascorbic acid, and other antioxidants, add nutritional value to fruit juices. In overripe and ripe pineapple juices, antioxidant activity, ascorbic acid levels, and total phenolic content levels were all influenced by ultrasonication and pasteurization.