180 Modern Food Microbiology
rods, with L. mesenteroides being the single most abundant species, followed by E. faecalis. The
leavening action of idli is produced by L. mesenteroides. This is the only known instance of a lactic
acid bacterium having this role in a naturally fermented bread.
46 The latter authors confirmed the
work of others in finding the urd beans to be a more important source of lactic acid bacteria than
rice. L. mesenteroides reaches its peak at around 24 hours, with E. faecalis becoming active only after
about 20 hours. Other probable fermenters include L. delbrueckii subsp. delbrueckii, L. fermentum,
and Bacillus spp.
69 Only after idli has fermented for more than 30 hours does P. cerevisiae become
active. The product is not fermented generally beyond 24 hours because maximum leavening action
occurs at this time and decreases with longer incubations. When idli is allowed to ferment longer,
more acidity is produced. It has been found that total acidity (expressed as grams of lactic acid per
gram of dry grains) increased from 2.71% after 24 hours to 3.70% after 71 hours, whereas the pH
decreased from 4.55 to 4.10 over the same period.
65 (A review of idli fermentation has been made by
Reddy et al.
65 )
PLANT PRODUCTS
Sauerkraut
Sauerkraut is a fermentation product of fresh cabbage. The starter for sauerkraut production is
usually the normal mixed biota of cabbage. The addition of 2.25–2.5% salt restricts the activities of
Gram-negative bacteria, while the lactic acid rods and cocci are favored. Leuconostoc mesenteroides,
Lactobacillus plantarum, and Leuconostoc fallax are the three most dominant lactics in sauerkraut
production, with the two Leuconostoc spp. having the shorter generation time and the shorter life span.
The activities of the cocci usually cease when acid content increases to 0.7–1.0%. The final stages of
kraut production are effected by L. plantarum and L. brevis. P. cerevisiae and E. faecalis may also
contribute to product development. The final total acidity is generally 1.6–1.8%, with lactic acid at
1.0–1.3% and pH in the range of 3.1 to 3.7.
The microbial spoilage of sauerkraut generally falls into the following categories: soft kraut, slimy
kraut, rotted kraut, and pink kraut. Soft kraut results when bacteria that normally do not initiate growth
until the late stages of kraut production actually grow earlier. Slimy kraut is caused by the rapid growth
of Lactobacillus cucumeris and L. plantarum, especially at elevated temperatures. Rotted sauerkraut
may be caused by bacteria, molds, and/or yeasts, whereas pink kraut is caused by the surface growth
of Torula spp., especially T. glutinis. Due to the high acidity, finished kraut is generally spoiled by
molds growing on the surface. The growth of these organisms effects an increase in pH to levels
where a large number of bacteria can grow which were previously inhibited by conditions of high
acidity.
Olives
Olives to be fermented (Spanish, Greek, or Sicilian) are done so by the natural biota of green olives,
which consists of a variety of bacteria, yeasts, and molds. The olive fermentation is quite similar to
that of sauerkraut except that it is slower, involves a lye treatment, and may require the addition of
starters. The lactic acid bacteria become prominent during the intermediate stage of fermentation.
L. mesenteroides and P. cerevisiae are the first lactics to become prominent, and these are followed by
lactobacilli, with L. plantarum and L. brevis being the most important.
87
rods, with L. mesenteroides being the single most abundant species, followed by E. faecalis. The
leavening action of idli is produced by L. mesenteroides. This is the only known instance of a lactic
acid bacterium having this role in a naturally fermented bread.
46 The latter authors confirmed the
work of others in finding the urd beans to be a more important source of lactic acid bacteria than
rice. L. mesenteroides reaches its peak at around 24 hours, with E. faecalis becoming active only after
about 20 hours. Other probable fermenters include L. delbrueckii subsp. delbrueckii, L. fermentum,
and Bacillus spp.
69 Only after idli has fermented for more than 30 hours does P. cerevisiae become
active. The product is not fermented generally beyond 24 hours because maximum leavening action
occurs at this time and decreases with longer incubations. When idli is allowed to ferment longer,
more acidity is produced. It has been found that total acidity (expressed as grams of lactic acid per
gram of dry grains) increased from 2.71% after 24 hours to 3.70% after 71 hours, whereas the pH
decreased from 4.55 to 4.10 over the same period.
65 (A review of idli fermentation has been made by
Reddy et al.
65 )
PLANT PRODUCTS
Sauerkraut
Sauerkraut is a fermentation product of fresh cabbage. The starter for sauerkraut production is
usually the normal mixed biota of cabbage. The addition of 2.25–2.5% salt restricts the activities of
Gram-negative bacteria, while the lactic acid rods and cocci are favored. Leuconostoc mesenteroides,
Lactobacillus plantarum, and Leuconostoc fallax are the three most dominant lactics in sauerkraut
production, with the two Leuconostoc spp. having the shorter generation time and the shorter life span.
The activities of the cocci usually cease when acid content increases to 0.7–1.0%. The final stages of
kraut production are effected by L. plantarum and L. brevis. P. cerevisiae and E. faecalis may also
contribute to product development. The final total acidity is generally 1.6–1.8%, with lactic acid at
1.0–1.3% and pH in the range of 3.1 to 3.7.
The microbial spoilage of sauerkraut generally falls into the following categories: soft kraut, slimy
kraut, rotted kraut, and pink kraut. Soft kraut results when bacteria that normally do not initiate growth
until the late stages of kraut production actually grow earlier. Slimy kraut is caused by the rapid growth
of Lactobacillus cucumeris and L. plantarum, especially at elevated temperatures. Rotted sauerkraut
may be caused by bacteria, molds, and/or yeasts, whereas pink kraut is caused by the surface growth
of Torula spp., especially T. glutinis. Due to the high acidity, finished kraut is generally spoiled by
molds growing on the surface. The growth of these organisms effects an increase in pH to levels
where a large number of bacteria can grow which were previously inhibited by conditions of high
acidity.
Olives
Olives to be fermented (Spanish, Greek, or Sicilian) are done so by the natural biota of green olives,
which consists of a variety of bacteria, yeasts, and molds. The olive fermentation is quite similar to
that of sauerkraut except that it is slower, involves a lye treatment, and may require the addition of
starters. The lactic acid bacteria become prominent during the intermediate stage of fermentation.
L. mesenteroides and P. cerevisiae are the first lactics to become prominent, and these are followed by
lactobacilli, with L. plantarum and L. brevis being the most important.
87