Investigations into the use of the Lactoperoxidase/Thiocyanate/Hydrogen Peroxide Antimicrobial System for the Cold Pasteurisation of Liquid Egg

The antibacterial activity of the lactoperoxidase/thiocyanate/hydrogen peroxide (LP/SCN /H2O2) system against a number of milk spoilage organisms and several Gram-negative bacteria has been established by previous workers. In this study the antibacterial activity of the LP/SCN /H2O2 system against S. typhimurium (N.C.T.C.74) and S, senftenberg (N.C. T.C.9959) has been examined in liquid egg.
The lactoperoxidase and thiocyanate ion (SCN ) contents in egg products from five strains of hens were examined by immunodiffusion and gas chromatography respectively. Lactoperoxidase was not detected in egg products (limit of detection, of the method 7.8 μg/ml) and the levels of SCN detected ranged from 0.54 to 0.675 mg/Kg.
Feeding trials with Arbor Acre hens were conducted to determine whether the inclusion of 10% rapeseed meal in the diet could enhance the level of SCN in liquid egg, to a level required for an active LP/SCN /H2O2 system. Throughout the fifteen week feeding trials records were kept of egg productivity, egg weight, layers weight, yolk colour, egg taint and SCN content of the eggs. The levels of SCN reached 1.6mg/Kg in the eggs, from the rapeseed meal fed hens. The rapeseed meal was treated with myrosinase to ascertain the potentially available SCN .
The generation of H2O2 by glucose oxidase was investigated in a glucose-salts medium and conditions established for the production of adequate levels of H2O2, in liquid whole egg, using the glucose present in egg. Experiments were conducted with the Salmonellae organisms to ensure that the level of H2O2 generated was non-bactericidal.
The levels of LP and SCN required by the LP/SCN /H2O2 system for bactericidal activity against the salmonellae organisms were established in the glucose-salts medium. The LP/SCN /H2O2 system with similar concentrations of LP (1.8 U/ml), SCN’ (8 μg/ml) and H2O2 (ca. 35 μg/ml) was then applied to liquid egg products, where the system was inhibited. The inhibition against the LP/SCN /H2O2 system was also observed in dialysed egg suggesting that low molecular inhibitors were not responsible.
The influence of conalbumin (may complex with the iron atom in LP) and ovalbumin (contains free thiol (SH) groups) on the LP/SCN /H2O2 system were examined in the glucose- salts medium. Conalbumin had no effect. Ovalbumin was inhibitory whereas ovalbumin with blocked SH groups was non-inhibitory, indicating the involvement of SH groups of ovalbumin against the LP/SCN /H2O2 system.
The influence of thiamine (only present in yolk) on the LP/SCN /H2O2 system was also examined in the glucose- salts medium. Results indicated that levels of thiamine present in yolk were sufficient to inhibit the LP/SCN /H2O2 system under the conditions used in this study. The possible involvement of the colourless thiol (of thiamine) against the LP/SCN /H2O2 system has been proposed on the basis of the behaviour of thiamine in neutral aqueous media.
Due to the concerted effect of ovalbumin, thiamine and possibly other factors in egg products, the LP/SCN /H2O2 system seems to be inapplicable for the cold pasteurisation of liquid egg.