Rk 52

The prepared samples were placed in the water bath with a controlled temperature, where the extraction was carried out at different temperatures (40, 50, and 60 °C) and durations (60 and 120 min) as indicated in Table 1. For further extraction, samples were transferred to the ultrasonic (Bandelin, RK 52) and sonicated for 15 or 30 min at 35 kHz (as indicated in Table 1) to determine the optimal duration of the ultrasonic-assisted extraction. After sonication, samples were centrifuged at 4500 rpm for 5 min in a Z206A laboratory centrifuge (Hermle, Germany). After centrifugation, the supernatant was collected and used for total anthocyanins (TA), total phenolic content (TPC), colour parameters determination, and high-performance liquid chromatography (HPLC) analysis. The extraction and all tests were carried out in triplicate. Before the HPLC measurement, the supernatant was filtered through a 0.45 µm membrane filter before injecting 10 µL into the HPLC system.

Ultrasonic extraction was performed directly and indirectly using, respectively:

a sonicator with an operating frequency of 26 kH, effective output of 200 watts, equipped with a titanium (7 mm i.d.) sonotrode (Hielscher Ultrasonics UP200 St, Teltow, Germany); and

an ultrasonic bath (BandelinSonorex RK52, Berlin, Germany) with 35 kHz frequency, maximum power of 240 watts, and internal dimension of 150 × 140 × 100 mm.

Process conditions of the UAEs were determined using already published results [23 (link),24 (link)] after several preliminary trials to adapt them. The details are reported in Table 4.
The results were compared with a conventional extraction using a conventional water bath. The conventional extraction was performed by soaking 3.0 g of wet pomegranate marc with the same amount of water used for the green extraction (40 mL of deionized water) under steady stirring while maintaining a constant temperature of 50 °C for 10 min.