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ABSTRACT
Crystallization of lactose in a co-lyophilized amorphous polysaccharide matrix was investigated under various hydration conditions to test the possible relation between the ability of the polymer to raise the glass transition temperature (Tg) of the lactose-pullulan blend, relative to pure lactose, and the crystallization kinetics. Both calorimetric (DSC) non-isothermal measurements and x-ray diffraction analysis of samples stored at a constant temperature revealed a marked retardation in lactose crystallization in the presence of pullulan; i.e., the rate constant values, as determined by the Avrami analysis, declined and the ‘half-time’ (t1/2c) for lactose crystallization increased with decreasing ratio of lactose/pullulan. The inhibitory action of pullulan on crystallization of lactose could not be solely attributed to Tg-related effects on molecular mobility of the composite systems. At a pullulan weight fraction range of 0.25–0.33 (w/w of total solids) the influence of the polymeric additive on Tg was marginal over the entire water content range examined, although crystallization was delayed as compared with pure lactose. Modeling of the temperature-dependence of t1/2c for the combined lactose-pullulan systems with the Williams-Landel-Ferry (WLF) equation was feasible only when the coefficients C1 and C2 were allowed to vary instead of assuming their ‘universal’ values.
ACKNOWLEDGMENTS
This work has been carried out in part with the financial support from the Commission of the European Communities, Agriculture and Fisheries (FAIR) specific RTD programme CT96-1085 “Enhancement of Quality of Food and Related Systems by Control of Molecular Mobility”. It does not necessarily reflect its views and in no way anticipates the Commission's future policy in this area.