In order to improve the thermal stability of vitamin E (VE) in ultra-high temperature sterilized (UHT) milk, a complex of β-lactoglobulin (β-LG) with VE was prepared. Turbidity, particle size, zeta potential, scanning electron microscopy, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), infrared spectroscopy and fluorescence spectroscopy were used to explore whether β-LG combined with VE. The degree of binding was further analyzed by bio-layer interferometry. The contents of VE in common fortified milk (with VE) and complex fortified milk (with β-LG/VE complex) before and after ultra-high temperature sterilization were determined by high performance liquid chromatography (HPLC) and the loss rate of VE was calculated to determine the effect of β-LG on the thermal stability of VE. The results showed that β-LG combined with VE to form a complex through hydrogen bonds and hydrophobic interaction, and that binding to β-LG reduced the aggregation of VE in aqueous solution and increased its solubility. Bio-layer interferometry corroborated the binding between β-LG and VE, and the binding constant was 7.493 × 10^-2 mol/L. The loss rate of VE in complex fortified milk was significantly lower than that in common fortified milk, (4.01 ± 0.18)% versus (10.90 ± 0.17)% (P < 0.05). The above results showed that β-LG/VE could effectively improve the thermal stability of VE, which provides a theoretical basis for the development of vitamin fortified dairy products.

The differences in metabolites and related metabolism pathways in colostrum and mature milk from Saanen goats at different lactation stages were explored by untargeted metabolomics based on ultra-high performance liquid chromatography-quadrupole electrostatic field orbitrap mass spectrometry (UPLC-QE-orbitrap-MS). The results showed that a total of 118 differential metabolites were found between colostrum and mature milk, among which 62 had higher relative contents in colostrum than in mature milk and 56 had lower relative contents in colostrum than in mature milk. These metabolites were mainly lipids, amino acids, and nucleosides. Nine key metabolic pathways most associated with these metabolites were selected, which jointly regulated the lactation process of Saanen goats, and the citric acid cycle could act as a bridge connecting other metabolic pathways. The number of differential metabolites involved in these metabolic pathways was 12. The differential metabolites with relatively high contents in colostrum were taurine, hypotaurine, taurocholic acid, L-phenylalanine, L-tyrosine, succinic acid, isocitrate, D-maltose, α-lactose, 4-hydroxyphenylpyruvate and glycine. The differential metabolite with relatively high contents in mature milk was N¹-methyl-4-pyridone-3-carboxamide. They could be used as potential marker metabolites in the colostrum and mature milk of Saanen goats. Metabolomics technology can also be used for identifying differential metabolites in milk from other dairy species at different lactation stages.