Chemistry Reference
In-Depth Information
suggested that Strecker degradation of phenylalanine and methylglyoxal
might contribute to the formation of acetophenone in UHT and sterilized
milks.
Metabolic products of dairy cultures have attracted attention because
of their possible reactivity in Maillard reactions. Kowalewska et al. (1985)
showed that the Maillard products, 2,5-dimethyl-4-hydroxy-3[2H]-furanone
and pyrrolidine, could be produced from metabolic products of Lactobacillus
helveticus. Griffith and Hammond (1989) attempted to model flavour gen-
eration in Swiss cheese by reacting carbonyl products known to be produced
by Lactobacillus delbruechii subsp. bulgaricus with amino acids. The Strecker
aldehydes, isovaleraldehyde, 2-methylbutanal, isobutanal, phenylacetalde-
hyde and methional, derived from leucine, isoleucine, valine, phenylalanine
and methionine, respectively, were shown to be formed in reaction systems
containing methylglyoxal. In addition, volatile Maillard reaction products of
lysine and proline with various carbonyls, such as glyoxal, methylglyoxal and
dihydroxyacetone, were detected. These included pyrrolidines, pyrrolizines,
pyridines and pyrazines. The results suggested that the final stages of flavour
formation in Swiss cheese are dominated by Maillard reactions rather than by
enzymatic or microbiological processes. Scanlan et al. (1968) reported the
presence of furfural, phenylacetaldehyde, maltol, acetophenone and diacetyl
in milk heated at 1468C for 4 s. Presumably, the phenylacetaldehyde was
derived from the Strecker degradation of phenylalanine.
Extraction of spray-dried skim milk powder using a Likens-Nickerson
apparatus and ether as solvent resulted in 196 individual GC peaks
(Shiratsuchi et al., 1994). Surprisingly, however, no Strecker aldehydes were
detected. The Maillard reaction products, furfural and furfuryl alcohol, were
the only furans detected. Shiratsuchi et al. (1994) suggested that furfural and
furfuryl alcohol could be important flavour molecules in condensed milk but
concentrations in skim milk powder were probably too low to be important.
Ferretti and Flanagan (1971) detected many potential products of the
Maillard reaction in a lactose-casein mixture allowed to brown for 11 d
(75% RH; 758C): acrolein, 5-hydroxymethyl-2-furaldehyde, 2-furaldehyde,
3-hydroxy-2-butanone, acetol, acetol acetate, 2-furfuryl formate,
2,2'-bifuran, 1-(2'-furyl)'-2-butanone, 1-(2'-furyl)'-3-butanone, maltol,
methyl-2-thiofuroate, 5-methyl-2-propionylfuran, 2-furfuryl vinylacrylate,
methylethylpyrazine, C-4-alkylpyrazine, tetramethyl pyrazine, trimethylpyr-
azine, N-methyl-2-formyl pyrrole and N-methyl-2-acetylpyrrole. The forma-
tion of several furanones which were probably products of Maillard reactions
was also reported. The volatiles present at high concentrations included
several Maillard reaction products: acetic acid, acetol, 2-acetylfuran,
5-methyl-2-furaldehyde, furfuryl acetate, furfuryl alcohol and maltol. Many
potential Maillard products were also detected in a 2-year-old skim milk
