Particle size of yam flour and its effects on physicochemical properties and bioactive compounds

Abstract

Chinese yam (Rhizoma Dioscoreas Oppositae) has been recorded in Traditional Chinese Medicine and is utilized as a common food delicacy in China. This study was carried out to evaluate effects of superfine grinding at variable mesh sizes on physicochemical, thermal, microstructural attributes, bioactive compounds and radical scavenging activities (RSA’s) of yam flour powders (YFP). Physical, color, hydration, total phenolic, flavonoid contents, RSA’s and absorption characteristics were significantly influenced by exhibiting increasing trends with reduction of YFP particle sizes. YFP fraction obtained at M400 size showed obviously improved specific surface area as compared to M60 fraction. Generally, it may be implied from the results that free-form phenolic compounds exhibited increasing trends whereas cell-wall bound phenolic compounds showed particle size-dependent decreases with corresponding increases in mesh size. ESEM micrographs endorsed the finding of reduction of YFP particle sizes with corresponding increases in sieve mesh sizes. ESEM analysis evidently showed that mechanical shear significantly led to enhancement of surface area. Differential scanning calorimetry showed that melting temperature of YFP with reduced particle size were lower. Conclusively, it may be implied that YFP superfine powders might be utilized in food formulations with improved functional properties and uniformity.