NANOFILTRATION APPLIED TO THE CONCENTRATION AND STABILITY OF ANTHOCYANINS FROM BLACKBERRY PULP

Blackberry (Rubus spp.) is widely recognized for its high content of bioactive compounds with antioxidant and anti-inflammatory properties. However, its elevated moisture content and low mechanical resistance contribute to its high perishability, making processing into juice and derivatives a viable strategy to reduce post-harvest losses and add value to the product. This study aimed to evaluate the concentration and chemical stability of blackberry juice obtained by nanofiltration using membranes with different configurations. Three nanofiltration membrane modules were evaluated: (i) tubular ceramic (1 kDa, 0.0165 m²), (ii) spiral-wound polyamide (0.01 µm, 2 m²), and (iii) plate-and-frame polyester (0.001 µm, 0.36 m²). The concentrated juices were analyzed for pH, titratable acidity, soluble solids (°Brix), total anthocyanins (differential pH method), total phenolic compounds (Folin-Ciocalteu), and antioxidant activity (ABTS and DPPH assays). The spiral-wound membrane demonstrated the best performance, with a concentration factor (CF) of 2.91. Anthocyanin content increased from 26.8 ± 1.93 to 54.3 ± 2.67 mg cyanidin-3-O-glucoside equivalents (C3G) per 100 mL (102% increase), and total phenolic compounds from 143.69 to 326.85 mg gallic acid equivalents (GAE) per 100 g. (127% increase) indicating a selective concentration of these bioactive compounds beyond the mere volumetric reduction. Antioxidant activity improved significantly (ABTS: +61%, from 11.21 to 18.04 µmol/g; DPPH: +79%, from 4.50 to 8.05 µmol/g). Soluble solids and titratable acidity also increased, indicating effective concentration. The chemical stability of the juice concentrated with the spiral-wound membrane was evaluated during frozen storage at –18 °C over 90 days. After homogenization, the juice was aliquoted into sterilized amber glass bottles, and analyzed on days 0, 15, 30, 45 and 90. Anthocyanin content remained stable throughout the period (72.71 ± 1.78 mg C3G/100 mL to 71.15 ± 2.04 mg C3G/100 mL), as did total phenolic compounds content (375.62 to 369.84 mg GAE/100 mL). Antioxidant activity remained consistent as well, ranging from 16.5 ± 1.52 to 15.48 ± 1.24 µm/mL equivalent (ABTS), and from 11.21 ± 0.13 to 11.02 ± 0.21 µmol Trolox/mL equivalent (DPPH), demonstrating chemical stability over time. Overall, the spiral-wound polyamide membrane was the most effective configuration for concentrating bioactive compounds from blackberry pulp.  The concentrated juice maintained its functional properties under frozen storage, highlighting its potential for application in the development of antioxidant-rich functional ingredients.