Optimization of Partial Replacement of Wheat Flour with Black Plum Peel Powder and Citric Acid in Sponge Cake: Effects on Physicochemical, Sensory, and Antioxidant Properties

Black plum peel is a by-product of the processing of black plum and contains nutritional properties of black plum that can be utilized in the production of innovative food products. In this study, different percentages of black plum peel powder (5, 10, and 15%) and citric acid (0, 1 and 2%) were used in sponge cake formulation and physico-chemical properties (moisture content, acidity, pH), antioxidant capacity, cooking loss, texture characteristics (hardness, cohesiveness, gumminess, springiness, resilience and adhesiveness) and sensory attributes (hardness, adhesiveness, porosity, springiness and overall acceptance) were evaluated using Response Surface Methodology. Increasing the levels of black plum peel powder and citric acid resulted in higher moisture content, acidity, antioxidant capacity, cohesiveness, resilience and overall acceptance of the black plum peel cake, while the pH decreased. The linear effect of citric acid had the most significant influence on moisture content, acidity, antioxidant capacity, sensory hardness, adhesiveness and overall acceptance whereas pH, cohesiveness, and resilience were most influenced by the linear term of black plum peel powder. Porosity and springiness were impacted with quadratic parameter of citric acid and cooking loss was affected by the quadratic term of black plum peel powder. Response Surface Methodology proved to be an effective tool for optimizing the sponge cake formulation, with high model adequacy indicated by R2 values of 0.92–0.99, non-significant lack-of-fit (p > 0.05), and adequate precision > 10, identifying 2% citric acid and 11.56% black plum peel powder as the optimal concentrations. Compared to control cake, the optimized formulation showed slightly higher moisture content, significantly enhanced antioxidant capacity, and similar or improved overall acceptability, demonstrating its functional and sensory advantages. The black plum sponge cake is an economical, enriched cake with higher quality that utilizes a by-product of the plum industry.