Typical dairy display cases use fluorescent lighting, which can have an oxidizing effect on the nutrient riboflavin found in milk. This reaction causes a negative flavor change and can also reduce the nutritional content of milk.
Sensory evaluation methods and results
The objective of the study was to determine the effects of fluorescent and LED lighting under retail storage conditions on consumer acceptance of milk products. The majority of the participants asked to test different 2% milk samples said they drank milk two or more times a week and roughly half (48%) consumed 2% more frequently than other varieties.
Participants were asked to assess the flavor of light-protected control milk products as well as milk samples that were exposed to LED lighting and milk exposed to fluorescent lighting.
What researchers observed was that HDPE and PET packaging under LED lighting functioned well with no significant differences of overall acceptability for milk after four hours of light exposure. Mean scores were above or close to 6.5 (between “like slightly” and “like moderately”) on the 9-point hedonic scale.
According to the study, typical overall acceptance ratings for most food products on the market range from 5.5 and 7.5. Milk exposed to fluorescent lighting received an average rating of less than 5 on the hedonic scale, researchers reported.
“A telling contrast, however, is the significant decrease in overall acceptability of milk packaged in translucent HDPE and clear PET exposed to fluorescent light. Overall acceptability fell to just above ‘like slightly,’ suggesting that consumers would prefer milk in light-protective packages and that low level LED light was less detrimental over short time exposure,” the study said.
Exposure to certain types of light such as conventional fluorescent lights can result in a stale and cardboard-like flavor profile of milk, according to the Virginia Tech researchers carrying out the study.
"We want to help figure out ways to return to the fresh taste of milk that our grandparents experienced when it came straight from the dairy," Susan Duncan, a professor of food science and technology in the Virginia Tech College of Agriculture and Life Sciences, said.
Flavor factors into repeat purchase behavior, and the findings of this study could help boost declining milk sales, which dropped 5.2% in 2015 partly due to the increasing competition of plant-based milk alternatives.
Packaging plays a role
The majority of milk is packaged in HDPE but, according to this study, HDPE packages provide insufficient protection against light exposure and allow for extensive light-induced oxidation to occur in milk.
If traditional HDPE translucent jug containers are used, milk is more likely to undergo oxidation as well as flavor and nutrient degradation. However, Duncan’s tests shows that when light-blocking pigments in HDPE or plastic PET containers were used, the flavor did not undergo as dramatic a change, and consumers thought the milk tasted fresh.
Though improved packaging costs more than the traditional jugs, Duncan said the cost is worth for milk manufacturers who want to maintain flavor quality.
"The research that is being done around this new lighting gives us momentum to explore other ways that we can preserve the natural taste of milk," Duncan said.
Source: Journal of Dairy Science
Published online ahead of print, doi: 10.3168/jds.2016-11673
“Retail lighting and packaging influence consumer acceptance of fluid milk”
Authors: H. L. Potts; K. N. Amin; S. E. Duncan