Mechanisms underlying quality modulation of pasteurized milk under a nitrogen-sparging-induced hypoxic environment: Insights from volatile metabolomics and microbial community succession

Dissolved oxygen (DO) and aerobic psychrotrophs accelerate off-odor development in refrigerated HTST-pasteurized milk. This study evaluated pilot-scale in-line nitrogen sparging deoxygenation (NSD) prior to HTST to mitigate volatile deterioration. Control and deoxygenated milks were stored at 4 °C (0-21 d) and analyzed via HS-GC-IMS and 16S rRNA sequencing. NSD reduced packaged milk DO from 8.84 ± 0.32 to 0.97 ± 0.05 mg/L. Volatile differences were most pronounced at 7-10 d. Notably, the oxidation marker hexanal remained significantly lower in deoxygenated milk at day 21 (0.385 ± 0.029 vs. 0.804 ± 0.083). Furthermore, hypoxia constrained aerobic psychrotrophic spoilage taxa (Pseudomonas, Acinetobacter), decreasing predicted lipid catabolism and altering mid-storage methyl ketone accumulation. Upstream DO control via NSD represents a practical strategy to improve pasteurized milk flavor stability without increasing thermal load, potentially extending its sensory shelf life.