Increasing the Content of Bioactive Compounds in Apple Juice Through Direct Ultrasound-Assisted Extraction from Bilberry Pomace

The increasing trend of diet-related chronic diseases has stimulated research into developing new food products and beverages with health-promoting potential. At the same time, new resources, including plant by-products, are currently being investigated as a sustainable source of bioactive compounds. In this context, the present study focused on the enrichment of apple juice with anthocyanins and other phenolic compounds by direct ultrasound-assisted extraction (UAE) from bilberry pomace. Response surface methodology combined with a Box-Behnken design was used to find the optimal extraction conditions for maximizing the total anthocyanin content (TAC), total phenolic content (TPC) and DPPH radical scavenging activity (RSA) in the enriched apple juices and to characterize their phenolic profile as influenced by the extraction temperature. UAE from 15% bilberry pomace during 15 min in apple juice at 80 °C resulted in the highest TAC (262.73 mg CGE/L), TPC (1700.91 mg GAE/L) and RSA (8.93 mmol Trolox/L) of the enriched apple juice. The chromatographic polyphenolic profile of the control and enriched juices showed that, besides anthocyanins, phenolic acids (chlorogenic, gallic, caffeic, 3-hydroxybenzoic, p-coumaric, ellagic and protocatechuic acids) and flavonoids (epigallocatechin and catechin) were extracted from the bilberry pomace directly in the apple juice, while the extraction temperature differently impacted the content of individual phenolic compounds.