Assessment of Heat Processing Effects on Cortisol Concentration in Dairy Milk Products

The presence of cortisol residue in processed dairy milk may be a good parameter for assessing the quality of dairy milk products and an alternative indicator of the overall welfare of dairy cattle. Thus, this study investigated the impact of heat processing on milk cortisol concentration (MCC). In total, 36 milk samples (50 mL) were collected from three Holstein dairy cattle at a research farm over two consecutive days. The samples were divided into experimental groups: unheated, heated at 65℃ for 30 min, and heated at 121℃ for 5 min. Additionally, 11 commercial dairy milk products were purchased under three heating conditions: low temperature, low time (LTLT), ultra-short time (UST), and ultra-high temperature (UHT). MCC was analyzed using an enzyme immunoassay. The average farm MCC (ng/mL) for the unheated milk, milk heated at 65℃, and milk heated at 121℃ were 0.88±0.16, 0.86±0.19, and 0.80±0.15, respectively. MCC was not significantly affected by the heating process. The average market MCC (ng/mL) in LTLT, UST, and UHT were 0.16±0.07, 0.15±0.08, and 0.15±0.07, respectively. Overall, cortisol levels in fresh farm milk were unaffected by the heating process. Monitoring cortisol levels in processed milk could offer a valuable alternative indicator for assessing product quality and animal welfare, particularly when access to raw milk is limited.