Ultrasound and freezing pretreatment as effective solutions for convective drying of BRS vitória grape

Drying is a well-known food preservation technique. However, it is imperative to develop new techniques to reduce drying time by maintaining its quality characteristics. This study evaluated the effect of freezing and ultrasound combined on the microstructure of BRS Vitória grape during drying and on its quality parameters and antioxidant activity. BRS Vitória grapes were subjected to six treatments including control, freezing, US275, US550, FUS275, and FUS550. Samples were dried using an incubator with airflow (1 m/s) at 60 °C. Samples analysis included microstructure, quality parameters, total phenolic content (TPC), and antioxidant activity. Results revealed that the combination of freezing and ultrasound pretreatment accelerated drying by 61 %, significantly improved texture and colour (ΔE values of 8-11), reduced hardness (from 53 N in US275 to 27 N in FUS550), and preserved phenolic content (TPC retention of up to 864 mg gallic acid/100 g d.m.) and antioxidant activity (DPPH activity of 58 %). Our findings indicate that freezing+ultrasound combined generate a change in the grape waxy layer and can be used as a pretreatment for drying to improve the appearance and quality of BRS Vitória grape.