SHELF-LIFE MODELING OF SWEETENED CONDENSED MILK BASED ON KINETICS OF MAILLARD BROWNING

Nonenzymatic browning and related changes were monitored in commercial sweetened condensed milk stored at 7, 15, 30, 45 and 55C. Darkening of the color measured in terms of absorbance (100 - reflectance percent) followed zero-order kinetics, the apparent activation energy (E_a) being 45.2 kJ/mol at 7–30C and 139.9 kJ/mol at > 30–55C. Hydroxy-methyl-furfural (HMF) showed a first-order increase, the associated E_a values being smaller than those for absorbance. The pH exhibited a linear decline after a small initial rise at 30C and below. As browning progressed, the coffee whitening ability of the product decreased along zero-order kinetics. The Q₁₀ values for these variables ranged from 1.21 to 1.84 for temperatures up to 30C and were nearly 2–3 times higher above 30C. The sensory color score was negatively correlated with absorbance. The linear regression of color score on absorbance and the temperature dependence of the latter as expressed by Arrhenius relationship were combined into a mathematical model which could be useful in predicting the product's shelf-life.     

Whipping test for the determination of foaming capacity of protein: a collaborative study

A standard whipping test, which involved preparing a 0.5% protein dispersion, whipping the dispersion in a Kenwood Chef food mixer and measuring the foaming properties (foam expansion, FE; foam volume stability, FVS; foam liquid stability, FLS) was collaboratively evaluated. A total of sixty determinations was made involving six laboratories, each of which analysed five samples in duplicate. The repeatability coefficient of variation ( CV ₀) in the estimation of FE and FVS properties of proteins was 6.25%. The reproducibility coefficient of variation ( CV _X) for FE and FVS was 9.8%, excluding the FE value (i.e. 20%) for spray-dried albumen. The CV ₀ and CV _X values for FLS properties of proteins ranged from 7.4 to 13.4% and 17.2 to 24.6%, respectively. Thus, FE, FVS and FLS properties can be used for intralaboratory comparisons (e.g. to determine batch-to-batch variation in commercial protein products), whereas FE and FVS values are more reliable for inter-laboratory comparisons of the foaming properties of proteins.     

Anti-static properties of some cationic polymers used in hair care products

Anti-static properties of cationic polymers on hair have been measured by using an electrostatic voltmeter. Comparisons are made with conventional cationic surfactants. Behaviour of cationic polymers from a cationic base and an anionic base have been explained. Experiments are performed to arrive at the hypothesis that cationic polymers form a complex with anionic detergent and that this cation-anion complex solubilizes in excess of anionic detergent, but on dilution with water it forms a turbid solution.
Propriétés anti-statiques de certains polymères cationiques utilisés dans les produits de soins pour les cheveux     

Firing scheme for pulse-width controlled AC-DC converters

A novel firing scheme is proposed for the control of pulse-width modulation type AC-DC converters. The firing circuit is capable of providing control both for rectifying and regenerative operations of the converters, for continuous as well as discontinuous conduction.     

Electronic properties and charge density of Be x Zn1 − x Te alloys

Electronic band structure calculations are performed for the Be _x Zn_1???x Te (0≤x≤1 in steps of 0·2) alloys following the empirical pseudopotential method. The alloying effects are modelled through the modified virtual crystal approximation. Throughout the composition, valence band maximum resides at the Γ point. The conduction band minimum, however, shifts from Γ to X point of symmetry when x?= 0·27. The observed crossover from direct to indirect bandgap is well in accordance with the experimental observations. Effect of alloying on the density of states is also discussed. The charge density distribution along a few major planes is computed and discussed. The electronic band structure related parameters like bandwidths, bandgaps and ionicity are reported and compared with experimental data wherever available. We also give estimates of cohesive energy and bulk modulus for the alloys.     

ASSOCIATION OF DIVALENT IONS WITH PROTEINS OF THE YEAST PLASMA MEMBRANE

The plasma membrane of Saccharomyces carlsbergensis was isolated by lysis of protoplasts and purified by ultracentrifugation in a discontinuous sucrose gradient. Extraction of the purified membranes with buffer in the absence of Mg²+ released 80% of the membrane protein as macromolecular complexes. Solubilization of the membranes in sodium dodecyl sulfate (SDS) caused the majority of the membrane protein to be dissociated from the membrane phospholipid, but after gel filtration some material appeared consistently as an SDS-stable lipo-protein, which aggregated to visible particles if the solubilizing detergent was removed, was not associated with Mg²+-ATPase. Calcium appeared to be involved in the linkage of membrane phospholipid to protein while the reaction of magnesium was at the protein-protein level. Calcium had high affinity of binding to the membrane proteins compared to magnesium ions. Potassium was loosely associated with all membrane proteins. On separation of the membranes by SDS-polyacrylamide gel electrophoresis, 19 polypeptides were distinguished, with molecular weights from 185,000 to 14,000. At least 2 polypeptides with molecular weights of 17,000 and 14,000 were involved in the binding of divalent ions by the membrane.     

Heterocyclic methacrylates for clinical applications–further studies of water sorption

The room temperature polymerizing system comprising poly(ethyl methacrylate)-tetra hydrofurfuryl methacrylate (PEM/THFMA) has potential in orthopaedic and dental applications, and earlier work has shown it to have unusual water absorption characteristics. This aspect has been studied in further detail, by studying the water absorption behaviour from some biological solutions, and the effect of the addition of an antibiotic (gentamicin). For comparison purposes, a parallel system whereby tetrahydrofuryl methacrylate was replaced by hydroxyethyl methacrylate (PEM/HEMA), was studied. In the case of PEM/THFMA, water uptake was substantially reduced when absorption was carried out from solutions (from about 30% in water to about 1.5% in solutions of higher concentrations), and the corresponding diffusion coefficient increased (by a factor of several hundred). The addition of gentamicin increased uptake, but the extent of increase also decreased in solutions. It was concluded that uptake was related to the osmolarity of the external solution, and also on the presence of osmotic sites within the polymer; hence the uptake process appears to be governed by chemical potential considerations. At the higher uptakes, there was evidence of water clusters. In marked contrast, the uptake by the PEM/HEMA system was independent of the osmolarity of the external solutions, presumably due to the hydrophilic nature of HEMA.