The Relationship of Ascorbic Acid to the Development of Oxidized Flavor in Market Milk

Abstract

Summary The addition of ascorbic acid to milk at the rate of 1.5 g. to 100 lb. resulted in a three-fold increase in ascorbic acid content of the milk. Non-fortified milk lost more than one-fifth of its ascorbic acid during the first day of refrigerated storage in the dark, about half by the second day, three-fourths by the third day, and better than 90 per cent by the fifth day. Milk fortified with ascorbic acid lost less than one-tenth during the first day, slightly more than one-fifth the second day, about one-third by the third day, and about one-half after 5 days of storage. After 5 days the fortified samples contained about one-half more ascorbic acid than the control milk did originally. No oxidized flavors developed in the fortified milk in 5- or 7-day storage periods, while the control samples began to develop oxidized flavors after 2 days of storage and became increasingly worse as storage time extended. Milk fortified with ascorbic acid rapidly lost its ascorbic acid when exposed to light, the rate depending upon the intensity of light and the time exposed. When exposed to direct sunlight for 40 minutes, all measurable ascorbic acid was destroyed. Stored samples in which ascorbic acid was destroyed partially developed an oxidized flavor. Rapid destruction of all measurable ascorbic acid in milk either by exposure to direct sunlight or through the addition of 30 per cent hydrogen peroxide resulted in no oxidized flavors over a 5-day storage period, indicating that ascorbic acid is a contributing factor in the development of this off flavor. Milk in which the ascorbic acid was destroyed by the addition of hydrogen peroxide did not develop oxidized flavor when exposed to sunlight. A study on the destruction of ascorbic acid and the development of oxidized flavor in milk under commercial conditions showed that about one-sixth of the ascorbic acid was lost from a fortified sample (30 mg. per 1.) after 24 hours of storage. The same milk lost only a slight amount of ascorbic acid when carried in a case in a covered milk truck from 5 to 8 a.m. When this milk then was exposed to daylight in the shade for 30 minutes it lost about one-third of the remaining ascorbic acid. Another trial with non-fortified milk showed no loss of ascorbic acid while carried in a case on a covered milk truck for 2.5 hours. About one-half of the ascorbic acid was lost, however, when this milk was exposed to daylight in the shade for 1 hour at noontime. Exposure of the milk to direct sunlight for 15 minutes at noon destroyed all measurable quantities of the ascorbic acid. These results indicate that most of the destruction of ascorbic acid occurs after the milk leaves the truck.