Physicochemical properties and relaxation time in strength analysis of amorphous poly (vinyl-pyrrolidone) and maltodextrin: Effects of water, molecular weight, and lactose addition

Fundamental knowledge of physicochemical properties of polymeric food materials is of practical importance in food and pharmaceutical industry. Effects of water, molecular weight, and lactose addition on glass transition temperature (Tg), α-relaxations, and relaxation time (τ) of amorphous poly (vinyl pyrrolidone) (PVP) and maltodextrin (MD) were studied at various aw and 25 °C. Water sorption behaviour of amorphous PVP and MD was Mwavg–dependent at aw ≤ 0.44, whereas the molecular size effects dominated the sorption process of MD at aw ≥ 0.56 and 25 °C. Fractional water sorption was confirmed in studied polymers/lactose mixtures at aw ≤ 0.44 in molecular scale, whilst collapsed structure of above mixtures were observed at aw ≥ 0.44 during storage up to 20 days at 25 °C. Despite of the calorimetric onset Tg of amorphous polymers/lactose mixtures showed a composition-independent at aw ≤ 0.44, Tg, α-relaxation, and τ of PVP and MD were disturbed by water, molecular weight and size, and adding lactose. Structural strength (S) of PVP was determined by its molecular weight at aw ≤ 0.44, whereas molecular size dominated the S of MD at 0.44 ≤ aw ≤ 0.76 due to water migration. The changes of aw and lactose addition significantly disturbed the S of studied polymers. Moreover, a combined use of water sorption isotherm and the relationship of S and aw gave a quantitative measurement of compositional effects and could be used to control the physicochemical properties of amorphous food polymers, such as collapse.