Effect of Temperature and Water Content on the Physicochemical Properties of Crude Lecithin and Soybean Oil: A Response Surface Methodology Approach

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.