Effect of Steam Explosion on the Morphological, Textural and Chemical Composition Characteristics of Betel Nut

Abstract

Abstract To reduce the adverse physical effects on the oral mucosa caused by excessive hardness of betel nut fibres, steam explosion was used to soften betel nuts. The effect of 3 operating parameters (pressure holding time, explosion pressure and initial moisture content) on the morphology, texture and chemical composition of the betel nuts was investigated. The fibre hardness and Shore hardness decreased by 56.17%-89.28% and 7.03%-34.29%, respectively, and the transverse tensile strength and fibre tensile strength also decreased by up to 60.72% and 24.62%, respectively. Moreover, the coefficient of friction and moisture content increased. After steam explosion, the betel nut increased in transverse diameter, became darker and more yellow‒red in colour, and showed a damaged microstructure. The contents of lignin, hemicellulose, free phenol, bound phenol and alkaloids decreased after steam treatment, with total phenols and alkaloids decreasing from 44.07 mg(GAE)/g and 7.84 mg/g to 30.61 mg(GAE)/g and 6.50 mg/g, respectively, after the A-50 s treatment condition. A slight increase in cellulose was observed when steam explosion conditions exceeded 80 s or 0.75 MPa. The steam explosion increased the quantity of phenols, alkaloids and soluble solids released from the betel nut under the same simulated release conditions. The research also showed that the explosion efficiency was positively correlated with the pressure holding time and explosion pressure, while the initial moisture content was reduced the explosion efficiency. Therefore, steam explosion is an effective pretreatment approach to soften betel nut and facilitate healthy development of the betel nut industry.