- In an attempt to investigate the probable roles of lactic starter
flora in the development of fruitiness and slit-openness in Cheddar
cheese, several experimental lots of cheese were made with different
commercial lyophilized starters until the defect could be consistently
duplicated. From many such trials, two cultures, B and C, which repeatedly
provided the defect, and one, designated as A, tiat yielded
high-grade product, were selected for further experiments. With
starter culture as the only variable, "defective" and "normal" cheeses
were made under uniform operating conditions in adjacent vats from
portions of the same bulk milk to compare the microbiological and
chemical changes occurring within the respective cheeses.
Attempts to correlate differences between "normal" and "defective"
starters in the rates of cheese - sugar and -protein degradation
to the development of fruity flavor and slit-openness in cheeses
were unsuccessful; no significant differences were noted in this regard between starters A, B, and C. Distinct differences throughout the
ripening period, however, were observed in the starter population
trends in the cheeses made with the "normal" and the "defective"
cultures. Starter A exhibited a rapid decline in numbers of the starter
population; cultures B and C persisted at very high population levels
for prolonged periods. As a result, the progressive replacement of
starter flora by succeeding lactobacilli, considered necessary for
normal flavor development, was considerably delayed in the "defective"
cheeses. In the "normal" cheeses, replacement occurred within
six to eight weeks.
Taxonomic studies on starters A, B, and C showed that the "normal"
culture was almost entirely made up of S. cremoris strains, and
the "defective" starters contained S. lactis and S. diacetilactis strains
in addition to S. cremoris strains. Of these, the S. lactis and S.
diacetilactis strains were generally found to produce greater concentrations
of carbonyl compounds in milk cultures than S. cremoris
strains, and as such the carbonyl concentrations in milk cultures of
B and C were considerably greater than in A. Similar trends were
observed when known strains of S. cremoris, S. lactis, and S. diacetilactis
were compared for total carbonyl production in milk cultures.
No striking differences in the types or numbers of carbonyl compounds
were found in milk cultures of starters A and C. However, in a given amount of culture, the latter had higher concentrations of
formaldehyde, acetaldehyde, diacetyl, and possibly pyruvic acid.
The effect of the "defective" starter strains on the final flavor of
Cheddar cheese was, therefore, reasoned to be two-fold. One was
indirect and concerned with the sequential predominance of different
microbial flora that occurred within the ripening cheese. The other
was direct and related to the starter metabolic activity, and the accumulation
within the cheese of certain carbonyl compounds important
in flavor impairment.