Assessment of radio frequency heating on composition, microstructure, flowability and rehydration characteristics of milk powder

ABSTRACT

Abstract Radio frequency heating (RFH) provides higher efficiency and more uniform heating zone compared with conventional method. The aim of present work is to evaluate the effect of RFH (at 90 °C for 5 or 10 min) on the changes in composition (protein oxidation and fat distribution), microstructure, flow characteristic and rehydration property of infant milk powder. The results indicate that the concentration of protein dityrosine was slightly enhanced, more free fat appeared on powder surfaces (> 50% increase), and porosity in powder matrix as tested by SEM was increased after RFH treatment. For powder flowability, raw sample had low cohesiveness (specific energy = 4.39 mJ/g), and RFH provided better flowability and decreased compressibility. Moreover, RFH had some negative impacts on wettability and solubility of powder particles with contact angle increase at least 5% and solubility decrease of 2%~4%, indicating worse rehydration abilities. Guggenheim-Anderson-de Boer (GAB) model was applied to fit moisture vapor sorption isotherms, and longer RFH duration leading to higher c values (about 63% increase at 10 min). In addition, the RFH initiated browning reaction as CIE a* values increased from -1.8 to -1.3.