This paper suggests that dairy products have natural contents of porphyrins and chlorins, and that these light sensitive compounds play an important role in photo-oxidation of cheese. Samples of the Gouda-like Norvegia cheese were exposed to light through plastic films of different colors. In addition, some samples were stored under transparent films and some in the dark. Sensory evaluation showed that cheese stored under transparent, violet and blue films were severely oxidized, while those stored under green, yellow. orange and red were less, but still significantly oxidized. Fluorescence analysis indicated that the photo degradation of porphyrins and chlorins correlated closely (R > 0.90) with the sensory attributes oxidized odor, sun flavor and acidic flavor. The corresponding degradation of riboflavin correlated well with oxidized odor, but significantly less with the two other attributes (R = 0.65-0.69). Fluorescence analysis indicated that the naturally present compounds in the cheese are protoporphyrin, hematoporphyrin, chlorophyll a and chlorophyll b. It is suggested that photo-induced breakdown of these compounds provides a significant contribution to photo-oxidation in cheese, and other dairy products. (C) 2004 Elsevier Ltd. All rights reserved.
