Minimizing photooxidation in pasteurized milk by optimizing light transmission properties of green polyethylene films.

The effect of different amounts of transmitted green light on photooxidation in pasteurized milk was studied. Five different green films produced with combinations of pigments and additives to minimize exposure to harmful wavelengths with regard to photosensitizers (400-450 and 600-650 nm) were evaluated. In addition, a non-colored transparent film and an orange film were compared with 1 selected green film. Pasteurized milk (3.9% fat) was packed in an air atmosphere and exposed to light for 14, 20, 26, and 32 h at 4 °C under the different films. Samples stored in the dark were control samples. The results showed that the most-effective green film had low overall light transmission, and also almost completely blocked light wavelengths shorter than 450 nm and wavelengths longer than 600 nm, which prevented photooxidation of riboflavin and chlorophyllic compounds. Chlorophyll degradation was highly correlated with sensory properties (coefficient of determination = 0.80-0.94). To preserve milk quality, total blocking of all visible light would be preferable. If total blocking is not feasible, then light transmission for wavelength below 450 nm and above 650 nm should be minimized (e.g., less than 5%). The newly developed green film can be used as a prototype for protection of dairy products to reduce the degradation of photosensitizers.

Effect of different colored filters on photooxidation in pasteurized milk.

The effect of different colored filters and atmospheres on photooxidation and quality in milk was studied. Pasteurized bovine milk (3.9% fat) was packed in 2 different atmospheres (air and N(2)) and exposed to light for 20 h at 4 degrees C under 8 transparent filters with different light transmission properties. The following transparent, noncolored, and colored filters based on polyethylene terephthalate (PET) were used: noncolored (PET), noncolored with 2 different UV-block regions, yellow, green, amber, orange, and red. Control samples were stored in darkness and in a carton. Sensory evaluation showed off flavors significantly increased in milk stored under all filters compared with the control samples. Variation in atmosphere resulted in significant differences in formation of rancid flavor in milk stored under different filters. Milk samples stored in N(2) underwent the most sensory deterioration under orange and red filters, whereas milk samples stored in air were most deteriorated under noncolored filters. According to the oxidation compounds measured by gas chromatography, milk samples stored under noncolored and orange filters were highly oxidized, whereas red, green, and amber filters offered better protection against photooxidation. Fluorescence spectroscopy was used to examine the degradation of photosensitizers (riboflavin, protoporphyrin, and chlorophyllic compounds) in the milk samples. Degradation of protoporphyrin and chlorophyllic compounds in N(2) correlated well with sensory properties related to photooxidation (R(2)=0.75-0.95). The study indicates that protoporphyrin and chlorophyllic compounds were effective photosensitizers in milk. To avoid photooxidation in milk, it is therefore important to protect it against light from the UV spectrum as well as light from the entire visible region.