Abstract:
The aroma of milk has been often defined as bland and pleasant, yet characteristic.
Conventional thermal processing of milk can certainly extend shelf life, but
inevitably changes its flavor. High pressure processing has been suggested as an
alternative for milk pasteurization with improved fresh flavor retention. The
objective of this project was to study off-flavor volatile formation in milk subjected
to high hydrostatic pressure combined with moderate heating. Two sensitive and
accurate new techniques were developed for the analysis of off-flavor compounds.
Solid-phase microextraction/gas chromatography with flame ionization detection
was used for the analysis of aldehydes, ketones, and dimethyl sulfide. Solid-phase
microextraction/gas chromatography with pulsed flame photometric detection was
used for the selective analysis of trace sulfur compounds. Milk subjected to
different treatment combinations of pressure, temperature and time showed that
aldehydes formation is promoted during high pressure processing, while that of
methyl ketones and sulfur compounds is inhibited. It was also observed that at the
same temperature, off-flavor formation under high hydrostatic pressure differed
from that observed under atmospheric pressure. The formation of aldehydes under
high pressure followed first order reactions with rate constants increasing with
temperature and pressure. Methyl ketones and most sulfur compounds
concentrations showed no increase for all treatment combinations. Added food
antioxidants significantly inhibited the formation of aldehydes in high pressure
treated milk. This suggested that the aldehyde formation pathway under high
pressure is not different from that observed under atmospheric conditions. The
results obtained in this research work gave new insights on the flavor formation
under high hydrostatic pressure, while offering the possibility of designing high
pressure processes for milk with extended shelf life and improved flavor.
