The enzymatic hydrolysis of lactose to glucose and galactose gives rise to reactions that change the chemistry and quality of ambient-stored lactose-hydrolyzed ultra-high-temperature (UHT) milk. The aim of the present study was to investigate and compare chemical changes in lactose-hydrolyzed and conventional UHT milk during a 9 month ambient storage period. Several complementary analyses of volatiles, free amino acids, acetate, furosine, and level of free amino terminals were concluded. The analyses revealed an increased level of free amino acids and an increased formation rate of specific compounds such as furosine and 2-methylbutanal in lactose-hydrolyzed UHT milk compared to conventional UHT milk during storage. These observations indicate more favorable conditions for Maillard and subsequent reactions in lactose-hydrolyzed milk compared to conventional UHT milk stored at ambient temperature. Furthermore, it is postulated that proteolytic activity from the lactase-enzyme preparation may be responsible for the observed higher levels of free amino acids in lactose-hydrolyzed UHT milk.

In the present study, the ability of (1)H nuclear magnetic resonance (NMR) for metabolic profiling of human saliva samples was investigated. High-resolution (1)H NMR spectra were obtained, and signals were assigned to various metabolites mainly representing small organic acids and amino acids. In addition, the use of human saliva for metabolomic studies was evaluated, and multivariate data analysis revealed that the 92 morning and night samples from 46 subjects could be discriminated with a predictability of 85%. The diurnal effect on the salivary metabolite profile were ascribed to changes in intensities of several metabolites including trimethylamine oxide (TMAO), choline, propionate, alanine, methanol, and N-acetyl groups. No effects of gender and body mass index (BMI) on the salivary metabolite profile were detected. The relationships between the salivary metabolome and glycated hemoglobin, systolic and diastolic blood pressure were investigated; however, no significant correlations could be established.

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Proteolytic activity in milk may release bitter-tasting peptides and generate free amino terminals that react with carbohydrates, which initiate Maillard reaction. Ultrahigh temperature (UHT) heat treatment inactivates the majority of proteolytic enzymes in milk. In lactose-hydrolyzed milk a β-galactosidase preparation is applied to the milk after heat treatment, which has proteolytic side activities that may induce quality deterioration of long-term-stored milk. In the present study proteolysis, glycation, and volatile compound formation were investigated in conventional (100% lactose), filtered (60% lactose), and lactose-hydrolyzed (<1% lactose) UHT milk using reverse phase high-pressure liquid chromatography-mass spectrometry, proton nuclear magnetic resonance, and gas chromatography-mass spectrometry. Proteolysis was observed in all milk types. However, the degree of proteolysis was significantly higher in the lactose-hydrolyzed milk compared to the conventional and filtered milk. The proteins most prone to proteolysis were β-CN and αs1-CN, which were clearly hydrolyzed after approximately 90 days of storage in the lactose-hydrolyzed milk.

et al.. Volatile component profiles of conventional and lactose-hydrolyzed UHT milk-a dynamic headspace gas chromatographymass spectrometry study.Abstract Lactose-hydrolyzed milk gains still increasing market share, and understanding the chemical characteristics of lactose-hydrolyzed milk products is important for the dairy industry. The aim of the present study was to identify and compare volatile compounds of commercial lactose-hydrolyzed and conventional ultra-high temperature (UHT) milk. For this purpose, the volatile compounds of lactose-hydrolyzed (<1% lactose), conventional (100% lactose), and filtered (60% lactose) UHT-treated milk were extracted using dynamic headspace sampling and analyzed by gas chromatography-mass spectrometry (GC-MS). A total of 24 volatile compounds were identified including ketones, aldehydes, and sulfides. Overall, principal component analysis (PCA) showed grouping of the different milk types, with loadings indicating a higher concentration of ketones in conventional versus lactose-hydrolyzed UHT milk, but PCA also indicated a marked batch-to-batch variation. Elucidation of individual volatile compounds detected also revealed that the content of ketones in general was higher in conventional UHT milk than in lactose-hydrolyzed milk; however, no significant differences in the volatile compound profiles could be identified between the various milk types as a result of the batch-to-batch variation. The present study