Effect of Microwave Pretreatment of Sesame Seeds on the Flavor, Nutrition and Safety of Sesame Oil

The effect of microwave pretreatment of sesame seeds on the flavor, sensory quality, nutrition, and safety of sesame oil was systematically studied to provide a theoretical foundation for the application of microwave for aroma enhancement in sesame oil. Sesame oil samples were hydraulically pressed from sesame seeds microwaved at different powers (0, 180, 360, 540, 720 and 900 W) for 6 min. A total of 91 aroma active compounds were identified in sesame oil by solvent-assisted flavor evaporation and headspace solid-phase microextraction combined with gas chromatography-olfactometry-mass spectrometry. The total concentration of heterocyclic compounds including pyrazines, pyrroles, pyridines, thiazoles, thiophenes, and furans in sesame oil were positively correlated with microwave power, while the total concentration of carbonyl compounds including aldehydes, ketones, and esters increased initially and decreased later with an increase in microwave power. The intensities of roasted sesame-like, nutty, burnt and smoky aromas, and the bitter taste of sesame oil gradually increased, while the intensities of earthy, woody, and green odors decreased. The oil yield of microwave-pretreated sesame seeds (30.02%–31.93%), which was higher than that of raw sesame seeds (24.89%), was positively correlated with microwave power. Microwave pretreatment increased the nitrogen solubility index (NSI, from 11.7% to 18.07%) of sesame meal and the concentration of tocopherol in sesame oil (from 392.18 to 462.92 mg/kg). The highest NSI and tocopherol content appeared after 540 and 700 W microwave pretreatment, respectively. The concentrations of sesamin (13.01–15.78 mg/100 g), heterocyclic amines (HCAs, 33.19–143.88 ng/g), and polycyclic aromatic hydrocarbons (PAHs, 0.40–9.03 ng/g) in sesame oil were positively correlated with microwave power. The concentrations of PAHs and HCAs in sesame oil did not exceed the Chinese national standard limit. In summary, appropriate microwave pretreatment can provide sesame oil with a rich flavor, improve its nutritional value and oxidation stability, and increase the utilization value of sesame meal protein. Therefore, microwave pretreatment is highly advantageous and promising for application in aroma enhancement in sesame oil l and high-value utilization of sesame meal protein.