Abstract:
Many volatile compounds generated during the thermal
processing of milk have been associated with
cooked, stale, and sulfurous notes in milk and are considered
as off-flavor by most consumers. A headspace
solid-phase microextraction (HS-SPME)/gas chromatographic
technique for the quantitative analysis of thermally
derived off-flavor compounds was developed in
this study. The extraction temperature, time, and sample
amount were optimized using a randomized 23 central
composite rotatable design with 2 central replicates
and 2 replicates in each factorial point along with response
surface methodology. Calibration curves were
constructed in milk using the standard addition technique,
and then used to quantify 20 off-flavor compounds
in raw, pasteurized, and UHT milk samples
with various fat contents. The concentrations of these
volatiles in raw and pasteurized milk samples were
not significantly different. However, dimethyl sulfide,
2-hexanone, 2-heptanone, 2-nonanone, 2-undecanone,
2-methylpropanal, 3-methylbutanal, heptanal, and decanal
were found at higher concentrations in UHT milk
as compared with raw and pasteurized milk samples.
In addition, the concentration of methyl ketones was
greater in UHT milk with higher fat content. The calculated
odor activity values suggested that 2,3-butanedione,
2-heptanone, 2-nonanone, 2-methylpropanal,
3-methylbutanal, nonanal, decanal, and dimethyl sulfide
could be important contributors to the off-flavor of
UHT milk. The HS-SPME technique developed in this
study is accurate and relatively simple, and can be used
for the quantification of thermally derived off-flavor
compounds in milk
