Brendan T. O’Kennedy

Stable monomeric intermediate with exposed Cys-119 is formed during heat denaturation of β-lactoglobulin

The role of the free sulfhydryl group of beta-lactoglobulin in the formation of a stable non-native monomer during heat-treatment of beta-lactoglobulin solutions was investigated. Two concomitant events occurred at the earlier stage of heating: unfolding of native globular monomer and intramolecular sulfhydryl/disulfide exchange reaction. Thus, two denatured monomeric species were formed: a non-native monomer with exposed Cys-121 (Mcys121) which became reversible after cooling, and a stable non-native monomer with exposed Cys-119 (Mcys119) which exhibited both a larger hydrodynamic conformation than native monomer and low solubility at pH 4.7. The results also show that the formation of these monomeric species throughout heat-induced denaturation of native beta-lg monomers is faster than their subsequent aggregation. A mechanism describing the behavior of beta-lg denaturation/aggregation during heat-treatment under selected conditions (5.8 mg/ml, low ionic strength, pH 6.6, 85 degrees C) is presented.

Influence of κ-casein genetic variant on rennet gel microstructure, Cheddar cheesemaking properties and casein micelle size

Cheddar cheese was manufactured on three separate occasions over a two week period from milk collected from two mid-lactation, spring-calving, Holstein–Friesian herds (n=11) containing similar casein levels, having phenotype AA or BB for κ-casein genetic variant. κ-Casein variant did not significantly (P>0.05) influence the casein content or gross composition of milk. κ-Cas ein BB milk had significantly smaller average casein micelle diameter and superior rennet coagulation properties than that of the AA milk. Pilot-scale Cheddar cheesemaking studies showed that the κ-casein BB milk resulted in significantly higher fat recoveries into cheese and higher actual and moisture-adjusted cheese yields. Cheese produced from κ-casein BB variant milk had higher concen trations of fat and lower protein levels than that produced from the AA variant. κ-Casein variant had no significant effect on prote olysis or on the acceptability scores awarded to the cheeses.

Effects of sodium caseinate concentration and storage conditions on the oxidative stability of oil-in-water emulsions.

The oxidative stability of various oils (sunflower, camelina and fish) and 20% oil-in-water (O/W) emulsions, were examined. The mean particle size decreased from 1179 to 325 nm as sodium caseinate (emulsifier) concentration was increased from 0.25% to 3% in O/W emulsions (P<0.05). Increasing the microfluidisation pressure from 21 to 138 MPa, resulted in a particle size decrease from 289 to 194 nm (P<0.05). Emulsified oils had lower detectable lipid hydroperoxide and p-Anisidine values than their corresponding bulk oils (P<0.05). The lipid hydroperoxide and p-Anisidine values of emulsions generally decreased as sodium caseinate concentration increased, and similarly decreased as microfluidisation pressure increased (P<0.05). Increasing storage temperature of the emulsions from 5 to 60°C, resulted in lower detectable lipid oxidation products during storage (P<0.05).

Oxidative stability of water/oil mixtures as influenced by the addition of free Cu2+ or Cu–alginate gel beads

The formation of Cu-alginate complexes and the impact of free or bound copper on the oxidative stability of model water/oil mixtures containing edible sunflower or corn oil were examined. Equilibrium dialysis showed that copper binding capacity of alginate increased proportionally with copper concentration and the binding was rapid. The results indicated that 25mM CuCl2 was necessary in obtaining beads of spherical shape and adequate mechanical strength (0.45N at 80% compression) to avoid rupture during mixing, whereas lower CuCl2 concentrations resulted in weak gel beads (0.34N) of irregular shape. When Cu-alginate beads were dispersed in the aqueous phase to give 0.5mM copper, the peroxide value of water/corn oil mixtures was 3.7mEq peroxide/kg oil after 7days. Corn oil-containing mixtures with 0.5mM free Cu2+ in the aqueous phase had a peroxide value ∼3 times higher (P<0.001) after the same storage time. However, copper binding by alginate did not significantly reduce the peroxide values of the water/sunflower oil mixtures. Results indicated that the binding of pro-oxidant minerals, such as copper, in alginate beads can reduce the levels of oxidation in water/oil mixtures.