Measurement of Fluorescent Materials in Milk and Milk Products

A number of workers in recent years have shown that various dehydrated food products and extracts thereof emit blue fluorescence when subjected to ultraviolet radiation.The intensity of fluorescence increases during storage of the products, and, in some cases, is correlated with loss of palatability, as Fryd and Hanson (8) found with dried eggs.Others, notably at the National Research Council of Canada (28,36,40,41,42,43), have demonstrated that heat treatment and storage of dried egg increase the blue fluorescence of a 10 per cent potassium chloride extract (26, 27) of the defatted powder.While Pearce (21) at first postulated that the active fluorescing materials fn such extracts are hydrolytic products of the proteins, it appears much more likely that they arise by interaction of the proteins with reducing sugars (1,13,20,25,33).Furthermore, although Pearce and Thistle (26) and Thistle et al. (35) concluded that loss of palatability of dried egg is correlated significantly with increase in fluorescence of the salt-soluble constituents, others (2, 7) have presented evidence indicating a much closer relation between flavor and fluorescence arising in the lipide fraction by reaction of lipide amines with aldehydes (5, 6).Fluorescence has been suggested as an index of storage deterioration of dehydrated pork, dried banana, dried parsnip, ration biscuits, and butter ( 22) and also for following development of rancidity in lard (10).Only very meager data are available on the fluorescence of milk, dairy products or milk constituents.It is well known that normal fresh milk emits greenish-yellow fluorescence when irradiated with ultraviolet light (3,30) and that this fluorescence is due principally to riboflavin (34,44).Gerngross and Schultz (9) observed that irradiation of milk causes an alteration in fluorescence from yellow to blue, perhaps by conversion of riboflavin to lumichrome (17), although Raoul's (31) data do not substantiate this explanation.Radley (29), finding that severe heat treatment and roller drying of milk shifted its fluorescence to the blue, attributed this change also to a breakdown of riboflavin.To date the only published quantitative data on the fluorescence of milk other than that due to riboflavin are those of Pearce (22,23), who studied the salt-soluble fluorescent compounds of defatted 2 dry whole milk.