| Abstract
| - Whole milk powder with an initial water content of 4.4% (w/w) and a water activity of 0.23 stored inhermetically sealed vials for up to 147 days below (37 and 45 °C) and above (55 °C) the glass transitiontemperature (Tg determined to have the value 48 °C) showed a strong temperature dependence forquality deterioration corresponding to energies of activation close to 200 kJ/mol for most deteriorativeprocesses. The glass transition was found not to cause any deviation from Arrhenius temperaturedependence. Lactose crystallization, which occurred as a gradual process as monitored by isothermalcalorimetry, is concluded to liberate bound water (aw increase to 0.46) with a modest time delay(approximately 2 days at 55 °C) and with concomitant surface browning as evidenced by an increasingHunter b-value. Browning and formation of bound hydroxymethyl-furfural determined by HPLC seemto be coupled, while formation of another Maillard reaction product, furosine, occurred gradually andwas initiated prior to crystallization. Initiation of lipid oxidation, as detected by lipid-derived radicals(high g-value ESR spectra), and progression of lipid oxidation, as detected by headspace GC, seemnot to be affected by lactose crystallization and browning, and no indication of browning productsacting as antioxidants could be determined. Keywords: Whole milk powder; lactose crystallization; lipid oxidation; Maillard reactions; nonenzymaticbrowning; ESR spectroscopy; furosine; HMF; radicals
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