Comparing quality and emotional responses as related to acceptability of light-induced oxidation flavor in milk

• High-quality milk creates a positive emotional experience for consumers.
• Lighting in retail dairy cases affect milk quality if milk is not properly packaged.
• Consumers dislike light-exposed milk flavor, using the emotional term “disgust.”
• Automated facial expression analysis illustrates consumers' unique response.

Off-flavors in fluid milk often result from light exposure during retail display if milk packaging does not provide light-blocking protection. There is no direct evidence that light-induced oxidation affects milk acceptability. In this 2-part study, effects of fluorescent light exposure (375 lx at the package) on fluid 2% milk packaged in HDPE without and with a (foil) light-blocking overwrap for periods of 8, 72, and 168 h (4 °C) were determined. Study 1 evaluated oxidative stability of milk, as well as consumer acceptability (hedonic 9-pt scale) and explicit emotional response (check-all-that-apply terminology selection) at 8 and 168 h (n = 41). Oxidative stability was measured by riboflavin (Rb) and thiobarbituric reactive substances (TBARS) assays. Rb, a photo-initiator of the oxidation reaction, decreased significantly, with 71% loss by 168 h. TBARS assays showed significant increases in oxidative by-products by 168 h. Within 8 h of light exposure, acceptability decreased significantly from 7.20 (“like moderately”) to 5.85 (below “like slightly”) and decreased further to 3.46 (between “dislike moderately” to “dislike slightly”) by 168 h. Light-protected milk (control) maintained a score of 7.0 over 168 h. Emotion term selection reflected acceptability response; the term disgust was used more frequently for both the 8 h (17.1%) and 168 h (46.3%; p < 0.05) light-exposed milk compared to both light-protected milks (2.4% 8 h; 12.2% 168 h). Light-protected milk had higher frequency of positive emotion term selection (content, calm, good, happy, and pleased) than did light-exposed milk (168 h). In study 2, automated facial expression analysis was completed (n = 12) at 72 h light exposure. Automated facial expression analysis provided evidence for great variety of unique responses from individuals. Light-induced reactions in fluid milk affect emotional response and flavor acceptability of milk, which may be contributing to the reduction in fluid milk sales and decreased milk consumption.