E-Poster: Thermal and Rheological Analysis of phase transitions in model sugar systems, as a function of amorphous sugar’s ratio and fiber addition, and different water activities
Authors: Nikolaou, N. E., Nikolidaki, E., Karathanos, V. T, Papadakis, S.
Thermal and rheological measurements were performed for the evaluation of the impact of currant dominant sugars and fiber content in their standard mixtures, simulating natural dried fruit systems, on crystallization phenomena as affected by different water activities. Different mass ratios of sugars systems were prepared, with the predominance of G over F and vice versa (1:1, 1:1.2, 1:1.5, 1:2 F:G & G:F). Soluble (Pectin, P) and insoluble (Cellulose, C) fiber fraction (5%, 7%, 9%) was added in standard sugars mixture (1:1). In order to achieve an amorphous state, samples were freeze dried, and dried over P2O5, and relative humidity was equilibrated over different salts (LiCl, MgCl2, K2CO3, MgNO3, NaNO2, NaCl) with a known water activity . Thermal analysis was conducted with Differential Scanning Calorimetry, (DSC 6000, Perkin Elmer) and rheological properties were also evaluated with a Modular Compact Rheometer (MCR-102, Anton Paar). The increase in G concentration contributed in a significant increase in the ΔHm (J/g) of the mixture, possibly favoring crystallization phenomena, while the increase in F ratio resulted in the inhibition of crystallization. Apparent viscosity data suggested the same conclusion. Water activity close to the Aw of dried fruits (0.60-0.65) demonstrated higher ΔHm (J/g) for insoluble fiber, suggesting that cellulose possibly contributes, to a lesser degree than sugars, to the crystallization phenomenon. All sugar ratios show more viscous behavior than elastic (G″ ≫ G′) and G″ values are significantly increased for glucose predominance samples over fructose, in all studied water activities, that could be related with crystallization. The F/G ratio could be possibly used as an indicator and/or predictive tool for the crystallization tendency of dried fruits.
