| Summary: | Acetaldehyde is known to be responsible for the green
or yogurt-like flavor defect of lactic cultures. This study was undertaken
to extend the knowledge of acetaldehyde production and utilization
by microorganisms normally found in mixed-strain butter cultures.
It is anticipated that the resulting information will contribute
to a more thorough understanding of the development of a green
flavor defect; hence, to methods of avoiding and overcoming this
defect.
Acetaldehyde production by single-strain cultures of S. lactis,
S. cremoris, and S. diacetilactis was found to parallel the increase in
microbial population. S. lactis and S. cremoris were found to remove
some of the acetaldehyde produced on continued incubation at
21°C. S. diacetilactis did not remove any of the acetaldehyde produced.
The ratio of diacetyl to acetaldehyde in the strains of S.
diacetilactis studied was found to be unfavorable for a good culture flavor at all times up to 22-24 hr incubation. All of the cultures
studied produced a distinct green flavor when grown in milk media.
All of the lactic streptococci studied produced both ethanol
and acetone when grown in a boiled milk medium. No evidence of
acetone utilization by S. diacetilactis was observed. A tentative
mechanism for the formation of acetone from pyruvate via acetoacetate
was proposed.
Single-strain cultures of Leuconostoc dextranicum and Leuconostoc
mesenteroides were shown to be capable of utilizing added
acetaldehyde under a variety of culturing conditions. These two
organisms, along with L. citrovorum were combined into two-strain
mixtures with various lactic streptococci. The production and utilization
of acetaldehyde varied widely among different two-strain mixtures.
The ratio of different lactic organisms comprising the flora
of a desirably flavored commercial mixed-strain butter culture was
determined. The microbial shift occurring when this culture developed
a green flavor defect was found to be an overgrowth of the homo-fermentative
lactic streptococci by the S. diacetilactis population.
It was found that the concentration of acetaldehyde in a
ripened single-strain lactic culture could be significantly reduced by
adding a large inoculum of a culture of L. citrovorum and continuing
incubation at 21°C or by cooling and holding the culture at 5°C after
the addition of L. citrovorum. === Graduation date: 1966
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