Homogenized milk packaged in three conventional half-gallon containers, unprinted fiberboard, blown mold plastic, and clear flint glass, was held in a sliding door display case with fluorescent light exposure of 100 ft-c for 144 hr. The fiberboard container afforded protection from the light activated flavor up to 48 hr, whereas milk in plastic and glass containers developed the off-flavor following only 12 hr of exposure. No differences in organoleptic response could be demonstrated between milk held in glass and plastic half gallon containers. Similarly riboflavin destruction in plastic and glass was not significantly different and amounted to approximately 10–17% loss following 72 hr of exposure. No significant loss in riboflavin could be demonstrated in milk held in fiberboard as compared to the control. Ascorbic acid losses were evident in all milk samples independent of container material, however losses of this vitamin in milk held in plastic and glass were much more rapid than in milk held in fiberboard, decreasing to a minimum level after 48 hr exposure. The TBA values did not parallel the organoleptic response demonstrating that the activated flavor associated with light exposure is differentiated from flavors caused by lipid oxidation.
Exposure of milk in all three containers tested to light had no effect on the amino acid composition as compared to the control milk held in the dark. These studies reinforce present thinking that protection of milk from light during marketing is necessary to assure flavor quality and to a lesser extent nutrient value.
1Authorized for publication on February 2, 1973 as Paper No. 4386 in the journal series of the Pennsylvania Agricultural Experiment Station.