Optimization of Processing Methods for Enhancing the Oxidative Stability and Nutritional Properties of Pressed Black Soybean Oil

This study investigated the impact of roasting conditions and acid degumming on the properties of pressed black soybean oil (PBSO) extracted from Tainan No. 3 black soybeans. Unroasted and roasted soybeans at 90°C, 120°C, and 150°C were screw-pressed to produce PBSOs (URB, 90RB, 120RB, and 150RB). Their fatty acid composition, nutritional profiles, and oxidative stability were analyzed. Roasting increased the contents of total phenols, carotenoids, and chlorophylls, with 150°C roasting yielding the highest total phytosterol and vitamin E contents. Oxidative stability, as determined by induction period, was highest in 150RB, attributed to elevated levels of phenolic compounds and vitamin E. Degumming 150RB using citric acid removed 96% of phospholipids, increased acid value, phytosterol content, and smoke point, while preserving carotenoids, chlorophylls, and fatty acid profiles. Shelf-life predictions extended from 355 to 425 days post-degumming. These findings establish 150°C roasting followed by degumming as the optimal processing conditions for PBSO with improved nutritional value and storage stability.