Comparative Studies of Brown Discoloration and Ammonia Liberation from the Milk Proteins by Ultraviolet Light Irradiation

Abstract

Investigations were undertaken on α-, β-casein, β-lactoglobulin and β-lactalbumin isolated from fresh milk to ascertain the development of color and ammonia liberation when exposed to ultraviolet light.
Experimental data showed that α-, β-casein equally contributed to cause considerable brown discoloration, followed by α-lactalbumin, while β-lactoglobulin remained almost colorless. Furthermore, additional evidence in a model system suggested that the participation of tryptophan is very important in such a discoloration.
On the other hand, some discussion is offered together with the suggestion that the liberation of ammonia might initiate from histidine residue without hydrolysis of linkage of peptide in protein.