A study to evaluate the effects of LED light on the perceived quality of milk shows that exposure to LEDs for even a few hours degrades the perceived quality of milk even more than the microbial content that naturally accumulates over time. The study indicates that fluid milk should be protected from all sources of light exposure from processing plant to consumer. Current milk packaging allows for varying degrees of light exposure. Researchers from Cornell University sourced fluid milk samples from three processing facilities with varying microbial postprocessing contamination patterns. They tested the effects of light exposure, microbiological content, age and fat content across 23 samples, using direct consumption, descriptive sensory perception and instrumental analyses. They found that exposure to LED sources impaired the perceived quality of fluid milk more so than microbiological contamination exceeding 20,000 cfu/mL. The quality of milk remained high for two weeks when shielded from LED exposure; and consumers preferred older milk over fresh milk stored in a typical container that had been exposed to LED light for as little as four hours. Milk contains several photosensitive components, including riboflavin, porphyrin and chlorophyll. When the components are activated by natural or artificial light, the underlying photonic energy is transferred into the milk itself, initiating a chain reaction whereby free-radical compounds and singlet oxygen are formed within the milk, inducing further chemical changes in neighboring molecules. Chemical changes may include the generation of unwanted aromatic compounds, which can have a negative effect on the perceived quality and consumer acceptance of milk. The resulting taste is commonly described as that of cardboard or plastic. "For most consumers the idea of freshness is in inverse relationship to the expiration date on the package. This study shows that light exposure is a much greater factor explaining deteriorating milk quality than even age," said Nicole Martin, supervisor of Cornell's Milk Quality Improvement Program laboratory. Additional effects of LED light exposure may include degradation of the milk’s nutritional properties and even an alteration in its visual characteristics. The emission peak in LEDs is near the narrow band where riboflavin absorbs light, a factor that may cause this nutrient to be selectively destroyed by LEDs. The study provides new information that can be used to further improve the quality of milk, for example through light-shielding packaging. Previous research in this area has focused on the effects of fluorescent light. The research was published in the Journal of Dairy Science (doi: 10.3168/jds.2015-9603).