Optimization of pre-drying concentration and type of foaming agents to produce shelf-stable black mulberry juice powder using the foam mat drying technique

Abstract

In today's world, consumers increasingly demand shelf-stable products with longer shelf life and high levels of natural bioactive compounds. Mulberry (Morus nigra L.) juice powder is a cheap alternative at the industrial scale for the development of instant products with significant bioactive composition. This study explores the application of underutilized mulberry fruit juice through the foam mat drying process using plant-based and dairy-based alternatives. The carrier type and concentration of the foaming agents were optimized for the production of high-quality foam mat dried black mulberry juice powder. A whey protein isolate (WPI), soy protein isolate (SPI) and WPI:maltodextrin blend (WPI:M) were used for foam mat drying at concentrations of 2–10%. The effect of these carriers on the physicochemical properties, bioactive retention and subsequent powder functionality was determined. The results revealed that WPI-treated mulberry powder (8–10%) had higher solubility (68–71%), lower moisture content and improved flow properties. By contrast, lower concentrations of WPI-treated mulberry powder (2–4%) contributed to the preservation of antioxidant activity (65.3%), phenolics (180.6 mg GAE/100 g) and flavonoids (363.6 mg QE/100 g). For the blend of WPI:M, a 10% concentration offered a balanced formulation which had good solubility (64.9%) and anthocyanin stability (192.1 mg/100 g). FTIR spectroscopy confirmed the presence of phenols, proteins and anthocyanins in both T2 (WPI) and T6 (SPI). The WPI (T2)-treated powder demonstrated superior morphology and mineral distribution, along with stronger encapsulation, as compared to SPI (T6). Overall, powder quality was strongly dependent on the carrier type and concentration. WPI offered the most favorable functional attributes, SPI served as an effective plant-based alternative, and the WPI:M blend provided enhanced stability of the bioactive components. These insights allow formulation strategies to be tailored to specific industrial and nutritional requirements for the production of mulberry juice powder.