Process Optimization and Quality Research of Oil Extraction from Tiger Nut (Cyperus esculentus L.) Using Ultrasonic-assisted Extraction

In order to improve the yield and quality of tiger nut oil, the strategy of ultrasonic-assisted n-hexane was studied by response surface methodology. In this study, the total phenolic content, total flavonoid content, free radical scavenging rate, fatty acid composition, and 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) clearance rate in oil samples were investigated at three temperatures including 25 ℃ (room temperature), 47 ℃ (optimal temperature for ultrasound assisted extraction), and 60 ℃ (high temperature). The results showed that a high tiger nut oil extraction yield of 25.01%±0.03% was obtained at a solid-liquid ratio of 1:15 (g/mL), ultrasonic time of 20 min, ultrasonic temperature of 47 ℃, and particle size of 70 mesh. The obtained oil sample was yellow-orange and slightly turbid with a unique aroma of beans. Besides, tiger nut oil had a certain scavenging effect on DPPH free radicals. Ultrasound could better dissolve the nutrients in tiger nut, but it had a large destruction effect on tiger nut flavonoids, while the content of phenolic acids significantly (P<0.05) decreased at high temperatures. Ultrasonic treatment and temperature showed slight effect on the types and contents of fatty acids between 25 ℃ and 60 ℃, and the highest content of oleic acid (C18:1) was about 73.81%~74.00%. These results provide a theoretical basis for the development and utilization of oil from tiger nut.