In industrial soybean lecithin production, process variables such as temperature, water content, agitation, and processing time play a critical role in determining the final product quality. Despite their importance, the combined effects of these parameters under industrial-scale conditions have not been sufficiently quantified. Therefore, this study systematically evaluated the influence of processing temperature (70–80 °C) and water content (1.5–3% w/w of oil) on key quality attributes, including lecithin moisture content, purity, acidy number, and peroxide value, as well as soybean oil acidity and insoluble fine substances. A response surface methodology (RSM) approach was applied to model the relationships between variables and to identify optimal processing conditions. The results indicate that an increasing temperature reduces lecithin moisture content, likely due to enhanced water evaporation and improved phase separation, while simultaneously increasing peroxide value and oil acidity (p < 0.05), possibly because of accelerated lipid oxidation and hydrolysis. Lecithin purity improved up to 75 °C, indicating more efficient separation, but decreased at higher temperatures, suggesting thermal degradation or emulsification effects. Similarly, increasing water content led to higher moisture, peroxide value, and acidy numberin lecithin, as well as increased acidity and insoluble fine substances in soybean oil (p < 0.05), which can be attributed to excessive hydration promoting emulsion stability and entrainment of oil-phase impurities into the lecithin fraction. Process optimization indicated that a water content of 1.5% and a temperature of 73.93 °C yielded the highest overall product quality, with a desirability value of 0.874.

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.