RESUMEN
Lowfat milk and skim milk were fortified with either oil- or aqueous-based carrier blends of vitamins A and D, in 1-gal poly-ethylene containers, and illuminated up to 72 h with 1080 1× (100 ft-c) at 5°C in a commercial display case. Vitamin A measurments and sensory analyses showed that vitamin A was more stable in 2% lowfat milk than in skim milk regardless of the carrier. The aqueous-based carrier provided more stability in lowfat milk while the oil-based carrier gave more stability in skim milk. Skim milk fortified with the aqueous-based vitamin A had 69% loss, while the unexposed control exhibited only 15% loss of the vitamin. Off-flavors were evident after 6 h in light-exposed 2% lowfat milk with the oil-based vitamin A, but the same milk with aqueous-based vitamin A did not exhibit off-flavors until after 12 h. Both 2% lowfat and skim milk samples exposed to light received similar lowered preference scores compared to nonexposed control samples. When both fortified and nonfortified 2% lowfat and skim milk samples were tasted after exposure to light, the flavor was not significantly different, but were in the unacceptable range.
RESUMEN
Five 1-gal. retail containers were evaluated for their protection of homogenized milk against development of light-induced flavor and degradation of riboflavin. These were clear polycarbonate, tinted polycarbonate, high-density polyethylene, and glass returnable containers and an unprinted fiberboard non-returnable container. All containers were held in a commercial sliding door display case at 7 ± 1 C illuminated to 1076 lx with a fluorescent lamp up to 72 h. Sensory evaluation was conducted by a trained panel using hedonic 9-point scoring and magnitude estimation scale techniques. Riboflavin was determined by the fluorometric method. An evaluation of the containers demonstrated that there was a significant difference (P < .05) in preference and degree of light-induced flavor between the milk held in clear polycarbonate and glass compared to the control milk after 12 h of exposure. Milk held in high-density polyethylene was significantly different in preference from the unexposed control following 12 h when evaluated by the hedonic method; however, 24 h of exposure were needed to demonstrate a significant difference in the degree of light-induced flavor using the magnitude estimation technique. The tinted polycarbonate container, which is fabricated with a blocking agent that inhibits transmission of light at 380-480 nm, provided the milk with greatest protection of the returnable containers against development of the off-flavor. Milks exposed in fiberboard and also milks in the five containers held in the dark were not significantly different from the unexposed control. The milks held in glass demonstrated significant losses in riboflavin following exposure.