Effect of steam pretreatment on the microstructure of tiger nuts (Cyperus esculents L.) and quality properties of its oil

Effect of steam pretreatment on the microstructure of tiger nut as well as the yield and quality properties of tiger nut oil (TNO) were investigated. Confocal laser scanning microscopy was used to demonstrate that steam pretreatment caused the cell structure of tiger nut to rupture and starch granules to aggregate, which resulted in 8.72%-18.85% increase in oil yield. Furthermore, steam pretreatment at 120 C for 60 min was found to significantly (P < 0.05) increase the induction time (3.47 vs. 1.10 h), total phenolic (88.85 vs. 48.58 mg/kg) and vitamin E (237.94 vs. 166.47 mg/kg), and decrease the levels of acid value (1.14 vs. 2.00 mg KOH/g) and carotenoids (5.12 vs. 6.09 mg/kg) in comparison to untreated TNO. The gas chromatography analysis indicated that steam pretreatment had no significant (P > 0.05) effect on the fatty acid composition of TNO. A total of 60 volatile compounds were detected in TNO samples, with aldehydes being the most abundant compounds in all samples, followed by esters and phenols. Steam pretreatment had a marked influence on the profiles of volatile compounds in TNO. In conclusion, steam pretreatment may be a feasible approach to enhance the oil yield and quality of TNO.