Fundamental Food Microbiology, Third Edition - Fuad Fathir

174 FUNDAMENTAL FOOD MICROBIOLOGY
production of butter and cheese, respectively. 2 This process was found to give better
products than those produced through natural fermentation of the raw materials.
These starters were mixtures of unknown bacteria. Processing plants started maintaining
a good starter by daily transfer (mother starter) and produced product inoculum
from these. However, the bacteriological makeup of these starters (types and
proportion of the desirable as well as undesirable bacteria) during successive transfers
was continually susceptible to changes as a result of strain dominance among
those present initially, as well as from the contaminants during handling. This
introduced difficulties in producing products of consistent quality and from product
failure due to bacteriophage attack of starter bacteria. Some private companies started
supplying mixed cultures of unknown bacterial composition for cheese manufacture
both in the U.S. and in Europe. Subsequently, the individual strains were purified
and examined for their characteristics, and starter cultures with pure strains were
produced by these commercial companies. Initially, such starter cultures were developed
to produce cheeses. Currently, starter cultures for many types of fermented
dairy products, fermented meat products, some fermented vegetables, fermented
baking products, for alcohol fermentation, and for other purposes (especially with
genetically modified organisms, GMOs) are commercially available. In this chapter,
a brief discussion on the history, current status, bacteriophage problems, and production
of concentrated cultures is presented.
II. HISTORY
Initial development of starter cultures resulted from the need and changes in the
cheese industry. Before the 1950s, small producers were producing limited amounts
of cheese to satisfy local consumers. A plant used to maintain a bottle of mother
culture by daily transfer, which it received from a culture producer or another
neighboring processor. From the mother culture, the plant used to make bulk culture
through several transfers to meet the inoculation volume (to meet the need of 1 to
2% of the volume of milk to be processed for cheese). These starters were a mixture
of undefined strains of bacteria, and it was difficult to produce a product of consistent
quality. There were also problems with starter failure from bacteriophage attack. To
overcome the problem of quality, the single-strain starter (a desired strain isolated
from a mixture) was introduced. Good sanitation and newly designed processing
equipment were introduced to overcome phage problems. 1,2
Since the 1950s, large cheese operations have replaced the small producers. They
needed products of consistent quality and could not afford to have too many starter
failures from phage attack. Starter-culture producers developed single-strain cultures
and supplied these in dried form to the cheese processors, who, in turn, used them
to produce mother cultures and bulk cultures. To overcome phage problems, rotation
of strains (such as using different strains each day) to prevent the buildup of a
particular phage, as well as multiple-strain cultures (if one strain is killed by a
specific phage, another will work), were practiced. Later, defined media to produce
bulk cultures that reduced phage attack were introduced. Even then, daily production
of large amounts of bulk cultures (some cheese processors were handling more than