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Photolysis of Riboflavin in Milk^*

Departments of Agricultural Chemistry and Dairy Husbandry, Idaho Agricultural Experiment Station, Moscow, Idaho

ABSTRACT

Riboflavin is one of the important vitamins and probably is a limiting factor in the average diet. Since milk is probably the most regularly relied upon source of riboflavin for children as well as most adults, precautions should be taken to prevent photolysis of riboflavin before milk is consumed.

The results of this study show that direct sunlight exposure of milk is very detrimental to the riboflavin content. It is a common practice to deliver milk bottles on doorsteps where they stand fully exposed for long periods. A shady place or lightproof box or cabinet should be provided unless protective types of containers are adopted.

The results of this work show that as much as 40 per cent of the riboflavin in milk was destroyed after two hours' exposure to direct sunlight in clear quart bottles even though the milk was quite cool. Good shade, brown glass bottles or paper containers gave very good protection. One type paper container was less efficient in this respect than three other types.

After milk was exposed to sunlight and subsequently stored in the dark in a refrigerator, there was no further loss of riboflavin for the 20 hours investigated.

Temperature is an important factor, and the photolysis of riboflavin at near freezing temperature was low as compared to near boiling temperature. The photolysis of riboflavin in raw milk was generally greater than in pasteurized milk and least in homogenized milk.

Milk kept in a store showcase close to a window lost some riboflavin, but there was practically no loss in milk stored in a showcase where most of the light came from low intensity electric lights.

As much as 11–12 per cent of the riboflavin was lost due to daylight when milk was allowed to simmer for 30 minutes in covered glass pan or uncovered aluminum pan in a bright room, but there was practically no loss when a covered aluminum pan was used.

^* Published with the approval of the Director of the Idaho Agricultural Experiment Station as Eeseareh Paper No. 234.