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 (T-g), alpha-relaxations, and relaxation time (tau) of amorphous poly (vinyl pyrrolidone) (PVP) and maltodextrin (MD) were studied at various a(w) and 25 degrees C. Water sorption behaviour of amorphous PVP and MD was M-wavg-dependent at a(w) <= 0.44, whereas the molecular size effects dominated the sorption process of MD at a(w) >= 0.56 and 25 degrees C. Fractional water sorption was confirmed in studied polymers/lactose mixtures at a(w) <= 0.44 in molecular scale, whilst collapsed structure of above mixtures were observed at a(w) >= 0.44 during storage up to 20 days at 25 degrees C. Despite of the calorimetric onset T-g of amorphous polymers/lactose mixtures showed a composition-independent at a(w) <= 0.44, T-g, alpha-relaxation, and tau 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 a(w) <= 0.44, whereas molecular size dominated the S of MD at 0.44 <= a(w) <= 0.76 due to water migration. The changes of a(w) and lactose addition significantly disturbed the S of studied polymers. Moreover, a combined use of water sorption isotherm and the relationship of S and a(w) gave a quantitative measurement of compositional effects and could be used to control the physicochemical properties of amorphous food polymers, such as collapse. (C) 2018 Elsevier Ltd. All rights reserved.