Nonenzymic browning. XI. Effect of free amino groups on browning reactions in lipid-protein mixtures.

The course of browning was more rapid in mixtures of polyunsaturated fatty acid esters with casein that in those of the same lipids with formaldehyde-treated casein or with an inert inorganic substrate (barium sulphate or sodium sulphate). On the contrary, the content of oxidation products (peroxides and aldehydes) was much higher in lipids mixed with formaldehydetreated casein or with inorganic substrates. The results obtained with albumin were similar. The ratio of red to yellow pigments was higher in mixtures with non-treated casein than in the other two investigated reaction mistures. Brown pigments contained only low per centages of nitrogen.