Impact of ultrasounds on the extraction of polyphenols during winemaking of red grapes cultivars from southern Italy

Effectiveness of ultrasounds (US) on polyphenols extraction during winemaking of three red grapes cultivars grown in southern Italy (Primitivo, Nero di Troia and Aglianico) was investigated. Innovative stainless steel horizontal rotary wine fermenters were developed for the study. The US protocol was tested on the first harvested cultivar (Primitivo), and efficacy was ascertained (+ 15% of flavonoids, + 10% of total polyphenols and + 100% of proanthocyanidins), even though the delivery system reached only 30% of maximum power. It was due to the "scree" effect caused by skins around the US transducer. In order to overcome this problem, the other two cultivars were processed after diluting the grapes with previously extracted juice (1:1 w/v). This modification allowed power to increase to 60%. Extraction of polyphenols was improved in Aglianico (+ 20% of flavonoids, + 15% of total polyphenols, + 12% antioxidant activity, + 20% colour intensity), whereas little effect was observed for Nero di Troia. It was concluded that impact of ultrasounds varies, depending on the cultivar. Under our conditions, the treatment could be useful in winemaking of Primitivo and Aglianico. Industrial relevance The use of ultrasounds in winemaking could increase the extraction of polyphenols from grapes, improving the sensory characteristics and health benefits of wine due to higher content of nutraceuticals. The ultrasound generator and transducer can easily be included in the traditional winemaking process as an "add on" technology, without distorting the processing lines. This innovation could reduce the environmental impact of winemaking, involving lower energy consumption and reduced processing times.