Blackcurrant Pomace as a Rich Source of Anthocyanins: Ultrasound-Assisted Extraction under Different Parameters

The industry is currently trying to manage the waste generated during juice pressing. Berry pomace is an especially rich source of many bioactive compounds. Blackcurrant pomace is particularly valuable because of the large amount of extractable anthocyanins remaining in the fruit skin. The aim of the study was to evaluate the effect of ultrasound-assisted extraction (UAE) parameters on the content of anthocyanins and color parameters of blackcurrant pomace extracts. The pomace used for the study was very rich in anthocyanins—an average content of 853.2 mg/100 g fresh weight. The effect of temperature (25, 35, 45 °C), time (15, 30, 60 min) and material/solvent ratio (1:20 or 1:7) on extraction yield was analyzed. The extracts were obtained using two solvents: water–ethanol acidified with HCl and water acidified with citric acid. Either solvent type, as well as the other parameters of the extraction process, have an impact on the level of anthocyanins in the extracts. The lowest range of extraction yield (63–68%) was obtained for a 1:7 ratio with water–citric acid solvent. The highest range of extraction yield (74–93%) was obtained for a 1:7 ratio with water–ethanol solvent. The most efficient method was extraction in a water–ethanol solvent (50/50 v/v) acidified with HCl, at a 1:7 material/solvent ratio, at 35 °C, for 15 min, providing 93% process efficiency. A strong relationship (r > 0.991) was also found between anthocyanin content and color saturation (C*) or hue (h°) in the obtained extracts. Based on the E1% coloring strength results, all the extracts obtained can be considered strong colorants, especially those obtained with the water–citric acid solvent. Ultrasonic extraction can be successfully applied to extract pigments from blackcurrant pomace and obtain, for example, food coloring.