CONICET | Buscador de Institutos y Recursos Humanos

Salts may affect important properties of sugar systems (1). The kinetics of non-enzymatic browning (NEB), hydrolysis and crystallization were observed to be affected by several salts. The purpose of the present work was to analyze the effect of MgCl2 on chemical and physical properties of the non-reducing disaccharides, sucrose and trehalose. Solid systems consisted of freeze-dried solutions containing 20% D(+)sucrose or D(+)trehalose and 1% L-glycine. The systems were prepared in phosphate buffer, pH 5.0 and MgCl2 was added (5:1 sugar:salt molar ratio); controls without MgCl2 were also prepared. The freeze-dried systems were exposed to water activities 0.22 and 0.44 at 25°C for two weeks and then incubated at 70°C for adequate time intervals. Sugar hydrolysis was analyzed by measuring glucose released during the incubation time by means of an enzymatic method. The progress of NEB was followed by absorbance readings at 445 nm in the diluted samples, and pH was also measured. Thermal transitions were determined by differential scanning calorimetry. After humidification, all the samples with MgCl2 had a higher water content than those without salt. Consequently, the systems without salt showed higher Tg (glass transition temperature) values. During heat treatment, the presence of MgCl2 delayed sucrose and trehalose crystallization, and increased the rate of hydrolysis of both sugars. However, while in sucrose systems NEB was accelerated, in trehalose systems an inhibition of this reaction was observed. As a consequence of the enhanced Maillard reaction water content of sucrose systems increased and Tg values dramatically decreased. The formation of sugar-cation complexes depends on the tautomeric forms and spatial position of hydroxyl groups of the sugar (2). MgCl2 may thus interact with glucose (product of trehalose hydrolysis) in a higher extent than with fructose (product of sucrose hydrolysis (glucose + fructose)). Thus, in trehalose systems the inhibitory effect of the salt on NEB prevailed over the effect of increasing the concentration of reducing sugar due to disaccharide hydrolysis, and the overall rate of NEB decreased. The presence of MgCl2 in disaccharide systems delayed sugar crystallization, increased water retention and accelerated sugar hydrolysis, but while the effects on physical stability were of similar qualitative influence for both disacharides, chemical stability was dependent on specific sugar-salt interactions. Key words: MgCl2, disaccharide, hydrolysis, Maillard reaction, crystallization. (1) Mazzobre, M. F. & Buera, M. P. (1999). Combined effects of trehalose and cations on the thermal resistance of b-galactosidase in freeze-dried systems. Biochim.Biophys.Acta, 1473, 337-344. (2) Angyal, S. J. (1973). Complex formation between sugars and metal ions. Pure Appl. Chem., 35, 131-146. Acknowledgements: This work was supported by Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT), CONICET and Universidad de Buenos Aires.

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