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

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Abstract
Spectral absorption studies indicated that milk proteins form a loosely bound complex with riboflavin which depends upon the presence of tryptophan in the protein. When aqueous solutions of riboflavin and purified milk protein were frozen and then exposed to sunlight, there was a shift toward the red side of the spectrum. 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. Under anaerobic conditions, the spectra of mixtures of riboflavin and purified milk protein were characteristic of riboflavin. There was no shift in color or loss of tryptophan when frozen samples were exposed to sunlight. The reaction is O2-dependent. A working scheme is proposed for the development of sunlight flavor.

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