Kinetics of galactose and tagatose formation during heat-treatment of milk

The kinetics of the formation of galactose and tagatose during the heating of milk at various temperatures (115–135°C) was studied. A first-order kinetic model was satisfactorily used to describe the formation of both carbohydrates. The Arrhenius plot enabled calculation of the activation energies to be made (113 kJ/mol for galactose and 115 kJ/mol for tagatose). The formation of tagatose in appreciable amounts takes place only under sterilization conditions, and its presence in commercial milks may be an indication of the severity of the heat-treatment.Peer reviewe

Changes in free monosaccharides during storage of dried milk

Changes in furosine, free monosaccharides and P-lactoglobulin of dried milk products (atomised skim milk and instant skim milk product) stored under several conditions of temperature and water activity were studied. The main changes observed were attributable to Maillard reaction. Furosine content increased during storage, mainly at the most severe conditions (30 degrees C 0.44 a(w)). Values up to 400 mg/100 g and 200 mg/100 g were obtained in atomised skim milk and instant skim milk product, respectively. In both products, a substantial decrease was observed at 30 degrees C 0.44 a(w) during the first 30 days and during all storage period in galactose and glucose levels, respectively. Myo-inositol was found in all the samples analysed and no changes were observed during the storage period. Although substantial modifications in the shape of the peaks were found, no variations in undenatured beta-lactoglobulin content were detected during the storage of the dried milk products at 0.33 a(w) 20 and 30 degrees C.Peer reviewe

Isomerization of lactose over natural sepiolite

Sepiolite (a hydrated magnesium silicate) was investigated as a catalyst for the isomerization of lactose. Factors such as temperature, concentration and time were studied. The main reaction product was lactulose; small amounts of epilactose, galactose, tagatose and 3-deoxypentulose were also formed. Product distribution indicated that the reaction routes were isomerization of the disaccharide followed by degradation of lactulose.Peer reviewe

Isolation and characterization of 3-deoxypentulose and its determination in heated milk

The presence of 3-deoxypentulose in heated milk is reported. This compound has been isolated from alkaline solutions of lactose and characterized by spectroscopic and Chromatographie techniques. Gas Chromatographic analysis of free monosaccharides of milk revealed two peaks corresponding to 3-deoxypentulose in commercial sterilized milk samples, in a concentration range of 30–50 mg/1. Its concentration increased with temperature and length of time of processing.This work was supported by Comision Interministerial de Ciencia y Tecnologia (Projects ALI88-0158-C02-02 and ALI91-0540).Peer reviewe

Gas chromatographic analysis of free monosaccharides in milk

Three silylation methods for the gas chromatographic analysis of ketohexoses have been compared for yield and tautomeric composition of trimethylsilyl ethers. One of them has been applied to the analysis of milk monosaccharides and evaluated for precision and accuracy. Of the different stationary phases employed, OV-215 and AT-1000 were the best suited to resolve the TMS ethers of the studied sugars.Peer reviewe