Valorization of Black Plum Peel in Spread Formulation: Optimization of Physicochemical and Sensory Properties via RSM

Plum peel is a major by-product of plum processing and a rich source of nutrients and bioactive compounds. This study aimed to optimize a black plum peel spread formulated with apple puree (20–40%) and plum puree (10–30%) using response surface methodology (RSM). Increasing apple puree up to 30% reduced acidity, firmness, cohesiveness, and consistency while improving sourness and overall acceptability. At 40%, apple puree decreased total acceptability and sourness while slightly increasing texture parameters. Increasing plum puree up to 20% lowered acidity, firmness, consistency, cohesiveness, viscosity, and sourness, but further increases to 30% reversed these effects. Both apple and plum purees enhanced antioxidant capacity in a concentration-dependent manner. The interaction between apple and plum purees notably affected the viscosity of the spread. Overall, plum puree had the strongest influence on texture and color, while apple puree primarily affected sensory acceptance. The optimal formulation was 32.01% apple puree and 28.16% plum puree (R2 = 0.999). Developing a spread from black plum peel demonstrates a sustainable strategy for upcycling fruit-processing waste into nutritious, high-value products. This approach reduces environmental impact, supports circular food production, and creates new opportunities for functional spreads in the health-oriented food markets.