Valorization of mulberry juice by-products: application of anthocyanin-rich flour in fermented plant-based beverage

Mulberry (Morus nigra L.) is a fruit rich in bioactive compounds, commonly processed into juices, pulps, and wines. These processes generate by-products rich in anthocyanins, accounting for 20% to 40% of the fruit’s weight, which are often discarded. Therefore, this study aimed to evaluate the effects of adding mulberry juice residue flour (MRF) to a commercial plant-based fermented beverage. The flour was obtained from ripe fruits, which were blended with water (1:1, m/v) and sieved. The retained solid residue was frozen at -80 °C and lyophilized at -40 °C under a pressure of 0.998 mbar for 48 hours. MRF was incorporated into the beverage at concentrations of 0%, 1%, 2%, 3%, and 4% (m/v), and the samples were evaluated for pH, soluble solids, total phenolic compounds, anthocyanins, color, and rheological behavior. The results showed that MRF addition reduced the beverage's pH, increased the concentration of soluble solids and phenolic compounds, and enhanced the anthocyanin content, especially in samples with higher MRF concentrations. Color analysis revealed a progressive darkening and an increase in reddish hue in the samples with higher MRF levels, suggesting that the flour may act as a natural dye. Furthermore, rheological analysis indicated that the beverage exhibited characteristics of a non-Newtonian pseudoplastic fluid (n<1), with increasing viscosity as MRF concentration rose. In conclusion, the addition of MRF is an effective strategy for enriching plant-based beverages, improving their bioactive properties, providing natural coloration, and contributing to sustainability by reusing fruit processing by-products.