Effect of LED and fluorescent light on protein oxidation in pasteurized milk during shelf storage

Aim: Photooxidation phenomena may occur in pasteurized milk during shelf storage, primarily involving lipids, proteins and vitamins and leading to off-flavor development, thereby compromising both the nutritional value and sensory quality of the product. This study investigated the influence of various factors– including the type of light source (fluorescent or LED), and the fat and riboflavin contents – on protein photooxidation in pasteurized milk under retail storage conditions. Methods: Pasteurized and microfiltered pasteurized milk samples, both whole and semi-skimmed, were exposed to either LED (4000K) or fluorescent light (4000K) with an intensity of approximately 5000 and 4000 lux, respectively. Samples were stored in transparent PET bottles at 5 ± 1 °C for up to 14 days and maintained under continuous illumination to simulate typical retail display conditions. Protein photooxidation was evaluated by monitoring the formation of the protein crosslink di-tyrosine (di-Tyr) using a direct HPLC method with fluorescence detection. Results: The results indicated that di-Tyr levels increased during light exposure, with a more pronounced effect observed under LED lighting compared to fluorescent illumination. The maximum concentration of di-Tyr was reached after 14 days of light exposure, with a concentration of 18 µmol/L. The microfiltration process did not exert a significant effect, whereas increased riboflavin concentration significantly promoted the formation of di-Tyr and the fat content had the opposite effect. Conclusion: LED lighting systems are increasingly replacing traditional lighting solution due to their superior energy efficiency, extended lifespan, and operational stability. While these characteristics align with the principles of sustainable development, our study demostrated that LED illumination induces a greater extent of milk protein photooxidation compared to fluorescent lighting. Although the mechanisms of milk protein photooxidation are highly complex – given the potential role of various milk components as either pro-oxidants or antioxidants – storage conditions should be carefully optimized. In particular, the choice of lighting systems and packaging materials plays a crucial role in preserving the quality of high-value products such as pasteurized milk.