Quality and flavor evolution of infant formula during simulated secondary shelf-life storage: Focus on volatile compounds at different storage temperatures

The increasing prevalence of early breastfeeding cessation has increased dependence on infant formula (IF). However, IF is usually not consumed in a timely manner after opening. The manufacturer-specified secondary shelf-life for IF is usually 28 d, and milk powder undergoes quality and flavor deterioration during storage. Therefore, the appropriate selection of storage duration and temperature is critical for preserving IF quality. This study investigated the quality and flavor changes in IF during simulated secondary shelf-life storage at various temperatures. Significant alterations in lipid oxidation, protein oxidation, flavor, and volatile substance content of IF occur during storage. Gas chromatography-ion mobility spectrometry (GC-IMS) identified 34 volatile organic compounds (VOCs), and Orthogonal Partial Least Squares Discriminant Analysis (OPLS-DA) identified key volatile compounds associated with storage progression, namely 1-Hexanal-M (pungent), 1-Hexanal-D (pungent), 2-Methylpropanoic acid (yogurt), 4,5-Dihydro-3(2H)-thiophenone (garlic), cyclopentanone-M (pleasant), and 1-Pentanol-D (alcohol). The concentrations of these compounds increased in a temperature-dependent manner during storage. These compounds, which originate from lipid oxidation and Maillard reactions during IF storage, contribute to undesirable off-flavors, including acidity, bitterness, and astringency. Therefore, storage temperature and duration must be optimized to preserve the sensory quality of IF. This study provides theoretical guidance for IF development and storage and offers valuable insights for manufacturers and consumers.