Effect of edible oils and oil emulsions on the perception of basic tastes.

The intensity of sweet, bitter or astringent tastes is reduced by consumption of edible oil or oil emulsions immediately before the ingestion of test solutions. The basic taste substances were dissolved in 30% aqueous ethanol, flavoured with plant extracts. The time-intensity dependence was influenced similarly. The sensitivity of taste receptors returned to the original value within 15-20 min. Intensities of acidic or salty tastes were not affected.

Interactions of oxidized lipids with protein. Part XVI. Interactions of oxidized ethyl linoleate with collagen.

The reaction of ethyl linoleate with collagen proceeded at 60 degrees C following the first order kinetics but during the hydroperoxide decomposition the rate constant of the first order decomposition was substantially lower than that of the second order decomposition. Contrary to cellulose, collagen catalyzed the hydroperoxide decomposition. The amount of total oxidation products rose rapidly at the stage of rapid hydroperoxide formation, and slowly afterwards. The browning reaction was fasted in the stage of maximum hydroperoxide content, and both ether-insoluble and ether-soluble pigments were formed, the latter low in nitrogen. The amount of lipid oligomers increased mainly in the reaction stage following the hydroperoxide maximum. Soluble collagen was converted into insoluble forms by the reaction with oxidized lipids. Basic amino acids were blocked by reaction with oxidized lipids but the bonds formed became resistant to acid hydrolysis only in the stage following the hydroperoxide maximum. Changes of sensory profiles could be explained by reactions of flavour-active carbonylic oxidation products with protein.

Reactions of oxidized lipids with protein. Part 15. Mechanism of lipoprotein formation from interactions of oxidized ethyl linoleate with egg albumin.

During the reaction of oxidized ethyl linoleate with egg albumin in dry medium at 60 degrees C, hydroperoxides were rapidly decomposed almost completely, while carbonylic anisidine-active and thiobarbituric-acid-active substances were decomposed rapidly in the beginning and only slowly afterwards. Both hydroperoxides and carbonylic oxidation products were substantially more stable in mixtures with cellulose than with albumin. Hydrogen-bonded lipoproteins were rapidly formed, passed through a maximum, and remained nearly constant in the last reaction stage. Covalently bonded lipids in lipoproteins were mainly formed in the stage following the rapid decomposition of hydroperoxides and carbonylic compounds, and immediately following the decrease of hydrogen-bonded lipoproteins. The binding of oxidized lipids into lipoproteins was accompanied by the formation of protein oligomers and by the loss of available lysine.

Modified determination of 2-thiobarbituric acid value in fats and oils.

Several methods for the determination of TBA-value were compared with a new direct modification (omitting the previous distillation), using 1-butanol as the sole solvent. The absorbance is measured at 530 nm after heating to 95 degrees C for 120 min, and cooling. The effect of variables was tested by the Youdens ruggedness test (reaction time, temperature, cooling, concentration of sample, thiobarbituric acid, water, heavy metals, antioxidants, chelating agents, bubbling with oxygen or nitrogen). The Lambert-Beers law is valid in the absorbance range between 0.05 and 0.8. The repeatability is better than that of the Dzikowskis procedure and comparable with those of more complicated distillation methods. The standard deviation is in a linear relation with the absorbance (range 0.1-1.0). The method was found satisfactory for evaluating lard, cooking fat, soybean, sunflower, and rapeseed oils in the stage of beginning rancidity.