Optimization strategies for black soybean oil development: Investigating the effects of different processing and storage methods on nutritional value and oxidative stability

This study aims to propose an optimized strategy for developing black soybean oil as a novel edible oil by evaluating its oxidative stability and nutritional composition. A commercially refined soybean oil and three Taiwanese soybean varieties, including Tainan No. 10 (TN10), Tainan No. 5 (TN5), and Tainan No. 3 (TN3) were used to prepare nine oil samples via solvent extraction (SE), screw pressing (SP), and hydraulic pressing (HP). The oil yields across different soybean varieties and extraction methods were similar, ranging from 11.53 % to 13.80 %. SP oils exhibited the lowest acid (0.49–1.37 mg KOH/g oil) and peroxide values (2.11–3.88 mEq O₂/kg oil). The fatty acid composition of SP oils was similar to that of SE oils, while HP oils contained a lower proportion of essential fatty acids. SP oils retained the highest chlorophyll (158.76 ± 1.51 mg/kg) and carotenoid (122.53 ± 3.55 mg/kg) levels, particularly in TN3 oil. SP TN3 oil also exhibited the highest vitamin E content (1616.74 ± 43.90 μg/g), significantly exceeding that of HP and SE oils (p < 0.05). The phytosterol content in SP oils ranged from 417.54 to 495.54 mg/100 g, with no significant differences between TN5 and TN3 oils. Under both light and dark storage conditions, the oxidative stability of the oils followed the order of TN3 ≌ TN5 > TN10, which related to antioxidant contents. Based on these results, TN3 black soybean oil produced via SP and stored under light-protected conditions demonstrated the highest nutritional value and oxidative stability.