Pulsed electric field, ultrasound, and thermal pretreatments for better phenolic extraction during red fermentation

The moderate thermal (MT), ultrasound (US), and pulsed electric field (PEF) pretreatments are studied to enhance the phenolics extraction from Cabernet Franc (CF) grapes. The next pretreatment conditions are investigated: MT (50 A degrees C, 15 min, 125 kJ/kg), US1 (24 kHz, 5 min, 121 kJ/kg), US2 (24 kHz, 10 min, 242 kJ/kg), US3 (24 kHz, 15 min, 363 kJ/kg), PEF1 (0.8 kV/cm, 100 ms, 42 kJ/kg), and PEF2 (5 kV/cm, 1 ms, 53 kJ/kg). The qualitative parameters of extracts (pH, A degrees Brix, and color intensity), their total polyphenols content, anthocyanins, tannins, and free radical scavenging activity were determined during the whole period of alcoholic fermentation. The results show that all studied pretreatments improve phenolics extraction (anthocyanins and tannins content), color intensity, and scavenging activity of the samples during red fermentation. However, the moderate (0.8 kV/cm) and high (5 kV/cm) PEF were the most effective pretreatments and increased the phenolics extraction yield, respectively, on 51 and 62 %, while the MT and US3 pretreatments increased the phenolics extraction yield, respectively, on 20 and 7 %. The anthocyanin and tannins were also better extracted, and the color intensity was highest after the PEF pretreatments in comparison with the MT and US pretreatments.