Occurrence, growth and survival of yeasts in matured cheddar
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Date
1999-03
Authors
Laubscher, Petrus Johannes
Journal Title
Journal ISSN
Volume Title
Publisher
University of the Free State
Abstract
Yeasts play an important role in dairy products causing spoilage or contribute
positively to the ripening of some cheeses due to their lipolytic and proteolytic
activities and the ability to grow at low temperatures, pH and water activity, and
high salt concentrations. Despite various factors affecting the survival and growth
of yeasts in cheese, the food commodity is considered as a potential habitat of
yeasts. Cheese renders an ideal medium for the survival and progression of
yeasts due to the availability of the necessary nutrients. A historical review of the
incidence of yeasts, their interaction with bacteria and their properties, during the
manufacturing and ripening of matured Cheddar cheese is given in Chapter 1.
The history of Cheddar cheese making, the fermentation of milk during cheese
making, different starter cultures and methods of application and occurrence of
yeasts are highlighted. In Chapter 2 a survey was undertaken with the objective of identifying the
predominant yeast contaminants associated with matured Cheddar cheese
production. A total of 168 yeasts strains, representing 12 different species,
isolated from matured Cheddar cheese and the immediate environment were
isolated. Once the identity of the yeast flora associated with the cheese had been
established, the survey was extended to determine the sources of yeast infection
during the processing of the matured Cheddar cheese. The results obtained,
showed that yeasts contributed substantially to the deterioration as well as the
ripening of the matured cheese, especially when stored under environmental
conditions exhibiting, low temperature, water activity and pH values and high salt
concentrations. In Chapter 3 seven of the most dominant yeasts frequently associated with dairy
products are screened for their resistance against nine commercial cleaning
compounds and sanitizers commonly used in the dairy industry. None of the
compounds used, however, were able to sufficiently kill the yeasts, within 60
minutes.
In Chapter 4 the influence of temperature and NaCI on the dominant yeasts
isolated in a cheese factory, during the manufacturing and ripening of matured
Cheddar cheese was examined. Relevant yeast species were screened for
lipolytic and proteolytic activities, and their ability to ferment lactose. The
chemical and physical characterition including pH, fat content, water activity, salt
and moisture were determined and its relevance to the growth and survival of
yeasts studied.
The interaction between yeasts, coliforms and total bacteria during the
manufacturing and ripening of matured Cheddar cheese, by using DVI- and
Mass- starters was studied in Chapter 5. Results obtained indicate that yeast
contaminants have to be controlled during the salting process to prevent
overgrowth of the starter cultures. During the salting stage, the curd is prone to
yeast contamination and may result in excessive loads due to the competitive
growth advantage of the species and the simultaneous bacterial inhibition. This
may contribute to product spoilage or stimulate the growth of the starters adding
to the formation of aroma components.
Description
Keywords
Diary processing, Yeast, Food spoilage, Food -- Microbiology, Dissertation (M.Sc. (Microbiology and Biochemistry))--University of the Free State, 1999