|Abstract or Summary
- Deterioration of the flavor of sterilized concentrated milk (SCM)
is recognized as the principal limiting factor to commercial acceptance
of this product. Although a number of volatile compounds have
been identified in SCM, quantitative information on these compounds
is lacking. It is therefore difficult to ascertain the significance of
these compounds. The purpose of this investigation was to determine
the identity of additional flavor compounds of stored SCM and to
determine the concentrations of the major flavor compounds.
Vacuum steam distillation was utilized to recover volatile
flavor compounds from samples of SCM. The distillates were
extracted with ethyl ether, and components of the ethereal flavor concentrates
were separated by gas-liquid chromatography (GLC).
Major components whose identity was unknown were collected from
the GLC effluent, and were analyzed by capillary column GLC and
mass spectrometry. A system for transferring trapped components directly onto a capillary GLC column was developed.
2-Furfural, which had not previously been identified in SCM,
and 2-furfurol, which had not been identified as a component of any
stored milk product, were identified in stored SCM.
Commercial samples of SCM were placed in controlled storage,
and subjected to flavor panel evaluation and a number of quantitative
determinations at selected intervals of storage. The concentration
of the odd-numbered n-methyl ketones, C₃-C₁₁, and of o-aminoacetophenone
were determined by measuring the absorbance of their
respective 2, 4-dinitrophenylhydrazone derivatives. The concentration
of 2-furfurol was determined by a gas entrainment, on-column
trapping GLC technique. Acid degree values were obtained by titration
of SCM milk fat. Hydroxymethylfurfural (HMF) values were
determined by measuring the absorbance of the HMF thiobarbituric
acid reaction product.
The methyl ketones and o-aminoacetophenone were found to
exceed their flavor threshold concentrations after 13 weeks storage
of SCM at 27°C. The concentration of 2-furfurol exceeded its
threshold concentration after 26 weeks at 27°C, but not after 13
weeks. Acid degree values increased slowly, but did not reach significant
levels through 26 weeks at 27°C. Hydroxymethylfurfural
values increased slowly through the first 13 weeks at 27°C storage,
followed by a marked increase during the second 13 weeks.
Heat degradation of thiamine was studied as a possible source
of volatile flavor compounds. Heating of thiamine solutions in
phosphate buffer at pH 6.7 resulted in the production of volatile components
of potential flavor significance. The identity of these components
was studied by gas entrainment, on-column trapping GLC,
collection of components, and capillary column GLC in conjunction
with mass spectrometry. The system developed for the transfer of
trapped components directly onto the capillary GLC column was
Hydrogen sulfide, 2-methyl furan, 2-methyl thiophene and a
compound which appeared to be a dihydro-2-methyl thiophene were
identified as volatile heat degradation products of thiamine.