Comparison of storage stability and palatability in different UHT milks during 9 mon at ambient temperature

This study evaluated the storage stability and palatability of imported ultra-high temperature (UHT) milks during prolonged ambient storage (4–9 mon), compared with domestic high temperature short time (HTST) milk stored under refrigeration for 1 wk. HTST milk, produced within 7 d, was purchased from a local market and stored under refrigeration as a control. UHT milks produced 3 mon prior from Australia (UHT-A), Germany (UHT-G), and Poland (UHT-P) were stored at 25 ± 2℃ in a temperature-controlled incubator. All milks had a comparable amount of total solids, with fat (3.4–3.5 g/100 g), protein (3.0–3.3 g/100 g), and carbohydrate (4.7–5.0 g/100 g) contents. UHT milks consistently exhibited higher thiobarbituric acid reactive substances values than HTST milk throughout storage (p < 0.05), although all values remained below the safety threshold for consumption. Protein degradation was observed in all UHT milks during storage (p < 0.05), except for α_s-casein (p > 0.05). β-casein gradually decreased in UHT-A and UHT-G from 4 to 9 mon (p < 0.001), while κ-casein decreased in UHT-A and UHT-P over the same period (p < 0.001). Sensory evaluation by trained panelists showed that HTST milk had a stronger milky flavor than all UHT milks, regardless of the storage period (p < 0.001). In contrast, all UHT milks had greater cooked and cheesy flavors than HTST milk (p < 0.001), likely due to exposure to higher temperatures. Rancid aromatic flavor increased during storage in UHT-A and UHT-P milks (p < 0.001). In addition, all UHT milks showed higher viscosity and astringency scores than HTST milk throughout storage (p < 0.001). Overall, prolonged ambient storage of imported UHT milk induced persistent physicochemical changes, including lipid oxidation and protein degradation, ultimately leading to a gradual decline in palatability, a critical determinant of consumer acceptability.