Blackberry Juice Concentrated by Nanofiltration: Characterization, Stability and Application in a Fruit Juice

Blackberry (Rubus spp.) is a highly perishable fruit rich in bioactive compounds, particularly anthocyanins, which are associated with significant health benefits. This study investigated the application of nanofiltration using a pilot-scale spiral-wound module (DOW® NF90-2540) as a mild technology to concentrate phenolic compounds, especially anthocyanins, in blackberry juice. The process achieved concentration factors (CF) of 2.2 for monomeric anthocyanins and 1.9 for total phenolic content (TPC), reaching values of 54.3 mg C3G·100 mL−1 and 326.85 mg GAE·100 mL−1, respectively. The antioxidant capacity (ABTS+ and DPPH methods) also increased significantly in the concentrated fraction (CF 1.9 and 1.7, respectively). Stability of the concentrated juice was evaluated during 90 days of frozen storage, showing that low temperatures effectively preserved anthocyanin levels and visual quality, with only minor variations in color parameters (L*, a*, b*). Furthermore, the concentrated blackberry juice was successfully incorporated into apple–orange juice blends, generating formulations with progressively increased phenolic content, antioxidant activity, and red color intensity as the proportion of blackberry concentrate increased. Anthocyanin bioaccessibility in these juice blends was also evaluated and was not proportional to the increase in anthocyanin content. Strong correlations between anthocyanin concentration, antioxidant capacity, and CIELAB color parameters highlight the dual functional and technological role of blackberry compounds. In conclusion, this study demonstrates the feasibility of nanofiltration as a mild and efficient strategy for concentrating anthocyanins and phenolic compounds from blackberry juice while preserving physicochemical quality and color attributes.