Physicochemical properties and soluble whey protein composition of local and imported commercial ultra-high-temperature milk in China

Ultra-high-temperature milk occupies a significant share of the Chinese dairy market, featuring various local and imported brands. This study examined the variations in physicochemical properties and whey proteomics among 10 local and imported milk brands available in China. The results showed that local brands exhibited a higher pH and a lower degree of protein structural denaturation compared with most imported brands. These characteristics indirectly contribute to the lower sedimentation levels observed in local brands. Proteomics analysis revealed that the conserved whey proteins across all brands play critical roles in biological functions such as immune system activities and molecular transport. Moreover, local brands exhibited higher levels of α-LA and β-LG compared with Oceania brands. In addition, local brands exhibited higher concentrations of serpin A3-1 and A3-3 compared with the majority of European and North American brands, while displaying reduced levels of cathelicidin-1, cathelicidin-2, and cathelicidin-4. Furthermore, local brands demonstrated a notable increase in the level of the endoplasmic reticulum chaperone BiP when compared with a European brand, although the level of vitamin D-binding protein was found to be lower. The variations in these specific proteins were mainly linked to biological functions associated with immunity and transport. These results contribute to a deeper understanding of the physicochemical and potential biological function disparities among milk from different origins, thereby offering consumers scientifically grounded and comprehensive information.