Black and Red Currant Pomaces as Raw Materials to Create Smoothies with In Vitro Health-Promoting Potential

Pomace is a by-product resulting from the pressing of fruits and vegetables into juices, and it is typically treated as waste. Interestingly, pomace contains minimal amounts of protein and fat but is characterized by its high polyphenol and dietary fiber contents, which may have health benefits for human physiology. Therefore, they are a potentially attractive raw material for the food industry, but to our knowledge, no smoothies with their addition have been prepared and described so far. Consequently, products derived from apple juice, incorporating different doses of fresh (6% and 12%) and dried (3% and 6%) black or red currant pomace, were formulated, and their physical properties, chemical composition, bioactive compound content, and health-promoting potential (in vitro antioxidant and antidiabetic activity) were evaluated. Additionally, the products underwent sensory assessment by consumers. The fortified beverages exhibited different physical characteristics and chemical compositions than apple juice. All smoothies were characterized by higher concentrations of anthocyanins, flavonols, and procyanidin polymers compared to the base product. Moreover, 75% of them exhibited a significantly elevated phenolic acid content as well as a higher concentration of flavan-3-ols. The majority of fresh smoothies exhibited significantly higher in vitro antioxidant capacities and increased in vitro α-amylase and α-glucosidase inhibitory effects compared to the base product. The highest ABTS activity was recorded in the variant with 6% dried black currant pomace. In turn, the smoothie with 3% dried red currant pomace had the most effective FRAP effect and, together with the product containing 12% fresh black currant pomace, ORAC antioxidant activity and α-glucosidase inhibition also. The introduction of 6% dried red currant pomace led to the creation of a beverage that most effectively inhibited α-glucosidase. The study showed that the application of various types of pomace, mainly that of black currant, into apple juice enables the development of new functional products with sensory attributes that are favorably evaluated by consumers.