Physicochemical properties of fluid milk with different heat treatments and HS-GC-IMS identification of volatile organic compounds

Abstract

To improve understanding of the effects of industrial heating processes on its physiochemical and flavour properties, fluid milk was evaluated for protein denaturation and flavour volatiles after high-temperature short-time (HTST), indirect ultra-high temperature (IND-UHT) and direct ultra-high temperature with direct steam infusion (INF-dUHT) treatments. Protein denaturation was evaluated by particle size, free sulphydryl content, fluorescence spectra, native whey protein retention rate and microstructure. Volatile organic compounds (VOCs) were compared by headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS). HTST treatment exerted the lowest negative effect on the aggregation and denaturation of native whey proteins including α-lactalbumin, β-lactoglobulin and lactoferrin, followed by INF-dUHT. IND-UHT caused the most severe denaturation of native whey proteins. HTST-treated milk was characterised by a high level of low molecular weight ketones and INF-dUHT milk possessed the greatest abundance of aldehydes, whereas IND-UHT milk exhibited the highest contents of high molecular weight methyl ketones, which contributed to an unpleasant aroma.