238 Chapter 10
further invade more bacterial cells, lysing
them in turn, and destroying culture activity.
Their attack can result in signifi cant eco-
nomic losses. Phages require Ca^ +^2 for their
growth; thus, sequestering Ca^ +^2 with phos-
phate in the growth medium inhibits phage
proliferation. Because phages are strain -
specifi c, rotating cultures is a practical way
to evade their attack. Cheese plants may
rotate as many as 10 cultures every day.
Other measures for phage control include
strict plant sanitation, use of phage - resistant
media and strains, direct - to - vat cultures, and
avoiding whey storage in the plant. Various
types of starters are available for selection in
a cheese plant.strains of the same organism. Table 10.4
shows the composition of various primary
starters used for cheese making.
A potential problem in cheese plants is
related to infection by bacteriophages; as
parasites, they depend on host bacteria for
their own life cycle. They are virus - like par-
ticles that destroy culture bacteria in 30 to 40
minutes of contact. A phage consists of a
head and a tail. The tail section attaches itself
to the bacterial cell wall, penetrates it, and
injects its DNA into bacteria. The bacteria
begin producing phage DNA and protein,
which form fresh phages. Eventually, the
bacterial cell explodes, releasing 50 to 100
new phages/bacterial cell. The new phages
Table 10.4. Microbial composition of starters used in the manufacture of major cheese varieties.
Two or more starters may be used in some cheeses.
Cheese varieties Microorganism
Cheddar, colby, Gouda, Edam, Monterrey Lactococcus lactis ssp. lactis
Lactococcus lactis ssp. cremoris
Cream, Neufchatel, cottage Lactococcus lactis ssp. lactis
Lactococcus lactis ssp. cremoris
Lactococcus lactis ssp. lactis biovar. diacetylactis
Leuconostoc mesentroides ssp. cremoris
Swiss, Emental, gruyere, Samso, fontina Leuconostoc lactis ssp. cremoris
Lactococcus lactis ssp. lactis biovar. diacetylactis
Leuconostoc lactis ssp. cremoris
Lactobacillus delbrueckii ssp. bulgaricus
Lactobacillus delbrueckii ssp. lactis
Lactobacillus casei ssp. casei
Lactobacillus helveticus
Streptococcus thermophilus
Propionibacterium freudenreichii
Propionibacterium shermanii
Italian cheeses: Mozzarella, provolone, romano Lactococcus lactis ssp. lactis
Streptococcus thermophilus
Lactobacillus delbrueckii ssp. bulgaricus
Lactobacillus delbrueckii ssp. lactis
Lactobacillus helveticus
Brick, Limburger, Muenster, Trappist, Port Salut,
St. Paulin, Bel Paese, tilsitStreptococcus thermophilus
Lactobacillus delbrueckii ssp. lactis
Blue - veined cheeses: Roquefort, bleu, Stilton, Gorgonzola Lactococcus lactis ssp. lactis
Lactococcus lactis ssp. cremoris
Penicillium roqueforti
Camembert, Brie Lactococcus lactis ssp. lactis
Lactococcus lactis ssp. cremoris
Streptococcus thermophilus
Penicillium candidum
Penicillium caseicolum
Penicillium camemberti