Non-enzymatic browning may be inhibited or accelerated by MgCl2 according to the level of water availability

SANTAGAPITA, PATRICIO R.; MATIACEVICH, SILVIA B.; BUERA, M. PILAR

Bangkok, Tailandia

Simposio; International Symposium on Properties of Water (ISOPOW 10); 2007

International Symposium on Properties of Water Organization

The kinetics of non-enzymatic browning (NEB), which is severely affected by water, is one of the variables that determine product quality in food and pharmaceutical areas. The addition of salts may affect important properties of sugar systems. The purpose of the present work was to analyze the effect of MgCl2 on non-enzymatic browning as related to water interactions, measured by NMR. Liquid/supercooled systems consisted in 50-70% w/v saccharide (glucose or trehalose) and 0.5% w/v L-glycine. Being trehalose a non-reducing sugar its participation in NEB reaction occurred after hydrolysis. The systems were prepared in 0.1M phosphate buffer pH 5 and 0.14M MgCl2 was added; controls without MgCl2 were also prepared. All systems were incubated at 70°C, in order to accelerate NEB reaction. The progress of NEB was followed by absorbance at 445nm, by fluorescence (excitation at 340/emission 492nm) and pH changes. Transversal relaxation times (T2) were measured by 1H-NMR using CPMG method. The presence of MgCl2 showed a great ability to inhibit NEB in glucose systems but in trehalose systems the reaction was accelerated. Fluorescence emission spectra showed that the presence of salt does not affect the type of fluorophore obtained in both sugar systems. Two sets of T2 values were obtained, one of them ranged between 140-500 ms and the other between 800-1200 ms. The presence of MgCl2 had different effect on T2 values in both systems: while in systems containing glucose the T2 values were slightly affected (water-glucose interaction was unmodified by salt), in trehalose systems T2 values were between 6 and 14 % lower in the presence of salt. These lower values reflect that salt imposed a certain local order to water molecules, reducing their mobility. Consequently, the relative effect of MgCl2 on browning rate depends on the rate disaccharide hydrolysis and on the inhibitory effect of water, which on time depends on the interactions of the cation with water and of the complexation of cation with sugar.