Phase separation, antiplasticization and moisture sorption in ternary systems containing polysaccharides and polyols
Sman, R.G.M. van der - \ 2019
Food Hydrocolloids 87 (2019). - ISSN 0268-005X - p. 360 - 370.
Antiplasticization - phase separation - Sorption isotherm - Starch - Thermodynamics
In this paper, we investigate whether the Flory-Huggins-Free-Volume (FHFV) theory can describe the rich thermodynamics of the ternary mixtures of starch, polyol, and water. These systems exhibit 1) non-monotonic moisture sorption with increasing plasticizer concentration, 2) phase separation, and 3) antiplasticization. After extending the FHFV theory with 1) the proper formulation of the chemical potential of water and polyol, and 2) the proper composition dependency of the interaction parameter between starch and water, the theory is well able to describe the above described complex thermodynamic behavior, showing good agreement with experimental data. Furthermore, our analysis shows that phase separation can already occur when the ternary mixture is still in the glassy state. Overall, the phase separation happens after the antiplasticization/plasticization transition, which can be linked to the minimum in moisture sorption, when increasing the polyol concentration at equal water activity. We think that the extended theory will become an important tool for analysis and design of complex food materials, pharmaceutical systems, and biopolymeric films having carbohydrates as plasticizers.
Modeling the equilibrium moisture content of desorption and adsorption of yam (Dente)
Amankwah, E.A. ; Dsizi, K.A. ; Straten, G. van; Boxtel, A.J.B. van - \ 2018
Agricultural Engineering International 20 (2018)1. - ISSN 1682-1130 - p. 184 - 192.
Equilibrium moisture content - GAB - Sorption isotherm - Yam
The experimental equilibrium moisture content of yam (Dioscorea rotundata; cultivar: Dente) at temperatures of 25°C and 50°C were determined at relative humidity from 0% to 95% employing the dynamic vapor sorption analyzer. Wet yam samples with about 68% initial moisture content were used, first for desorption and subsequently for sorption. Water activity decreased with increased temperature at constant equilibrium moisture content. The desorption and adsorption isotherms were fitted by the Guggenheim-Anderson-de Boer (GAB), Henderson, Halsey, Oswin, Smith, Brunauer-Emmett-Teller (BET) and Peleg models. On the basis of the fit the Peleg, GAB and Oswin models were most suitable for describing the observed data. When the focus is on drying, the GAB (3 parameters) and empirical Peleg model (4 parameters) performed best. Of these, GAB is preferable because it has fewer parameters, which, moreover, have a physical meaning.