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Refrigerated Milk Displays in Supermarket Dairy Cabinets

Refrigerated milk in supermarket cabinets can develop off-flavors and lose nutrients after four minutes of exposure to direct sunlight, and after four hours of exposure to fluorescent display case lighting.

Milk in glass or plastic containers are most vulnerable, but off-flavors will also develop when milk is packaged in paper cartons.

Promolux Safe Spectrum lamps emit lower levels of UV and visible spectrum radiation, thus reducing the rate of damaging chemical reactions in milk and dairy products.

For dairy science references and excerpts click here.

Lipid Oxidation of Milk in Grocery Store Milk Displays

When milk is exposed to sunlight or to the fluorescent lighting commonly found in refrigerated dairy display cases, the light initiates two chemical reactions which result in off-flavors and the loss of nutrients.

First, whey proteins, composed of amino acids containing sulfur, degrade and break down, producing “sunlight” flavors reminiscent of burnt feathers or burnt hair that can last for two to three days.

In the second reaction, the unsaturated fatty acids in milk lipids (milkfat triglycerides / triacylglycerols) become oxidized, producing malodorous carbonyl compounds that taste metallic or cardboardy and do not dissipate.

Various studies have found that these chemical reactions can occur in milk after four minutes of exposure to direct sunlight, and after four hours of exposure to fluorescent lighting, while the off-flavors were detected by trained tasters after milk was exposed to light for 15 to 30 minutes, and by consumers after milk was exposed to light for one to two hours.

In a Pennsylvania study, light-related off-flavors developed within 36 hours in almost half of 449 samples of milk in translucent plastic jugs. Another study found that off-flavors were present in approximately 80% of the blow-mold plastic milk containers exposed to fluorescent lighting in supermarket dairy display cases.

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Milk Nutrient Loss in Retail Milk Showcases

The following nutrients are lost from milk during lipid oxidation: Vitamin A (especially added Vitamin A), Vitamin D (especially added Vitamin D), riboflavin (Vitamin B2), Pyridoxine, Vitamin B12, and Vitamin C (ascorbic acid, present in small quantities in milk). Riboflavin is destroyed by ultraviolet light.

One study found that 90% of the added Vitamin A and 8% of the riboflavin was lost from milk in polyethylene containers after 24 hours of exposure to fluorescent lights, with increased loss of these nutrients as the fat content of the milk decreased.

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Flavor Changes of Milk in Commercial Milk Merchandisers

When milk is exposed to light, two chemical reactions occur that cause the milk to taste like burnt feathers, burnt hair, cardboard, or metal.

Factors that affect the rate of flavor change and nutrient loss in milk caused by exposure to display case lighting are the intensity of the light, the wavelengths present in the light, the distance between the fluorescent light bulb and the milk, the material of the container, the amount of surface area exposed to the light, the temperature of the milk, and the duration of light exposure. The higher the fat content, the more vulnerable the milk or cream is to the off-flavor effects of lipid oxidation.

Milk in light-transmissible containers such as transparent glass or plastic is most commonly affected but milk in paper cartons can also be affected when the cartons are exposed to intense light for long periods of time.

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Promolux True Color Definition Lamps

Promolux Safe Spectrum balanced full spectrum lamps emit lower levels of heat and ultraviolet radiation than regular supermarket fluorescent lamps, thus reducing the rate of damaging chemical reactions in milk and dairy products. Compared to other fluorescent lighting, Promolux lamps emit 86% lower UV B radiation, a shorter wavelength that penetrates and causes heating, and 52% lower UV A radiation, a longer wavelength that tends to affect surfaces.

Because Promolux lamps are designed for true color definition, they have a more balanced visible spectrum than other fluorescent lamps. The yellow and green wavelengths that are predominant in regular fluorescent lighting are the most damaging wavelengths in the visible spectrum. Promolux lamps emit a more balanced range of wavelengths, including more of the red and blue wavelengths and more moderate levels of the yellow and green wavelengths. It is impossible to create a natural light that does not have any yellow or green wavelengths, so light sources will always be damaging to some extent.

However, since Promolux lamps minimize the emission of damaging visible spectrum and UV wavelengths, using Promolux lamps will reduce shrinkage by 30 to 50 percent compared to the shrinkage caused by standard dairy display case lights. These savings will vary depending upon the duration of light exposure, which can vary from day to day and from hour to hour; the type of packaging; the fat content; and how the dairy product has been processed.