Sunlight Flavor in Milk. II. Complex Formation between Milk Proteins and Riboflavin

Abstract

Spectral adsorption studies indicated milk proteins form a loosely bound complex with riboflavin. The complex was dependent upon the presence of tryptophan in the protein. When aqueous solutions of riboflavin and purified milk protein were frozen, then exposed to sunlight, a shift toward the red side of the spectrum was observed. Thus, the loosely bound complex absorbed light, undergoing an electronic transition to an excited state. Decreases in riboflavin and tryptophan concentrations indicated that complete electron transfer had occurred, followed by dissociation of the complex. In contrast, under anaerobic conditions the spectra of mixtures of riboflavin and purified milk protein were characteristic of riboflavin. No shift in color was observed when frozen samples were exposed to sunlight and a loss of tryptophan did not occur. These observations indicate the reaction is oxygen-dependent. A working scheme is proposed for the development of sunlight flavor. © 1964, American Dairy Science Association. All rights reserved.