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The role of Pseudomonas and aerobe spore-formers in bacterial spoilage and safety of milk and dairy products

Valerie De Jonghe UGent (2010)
abstract
Bacteriological spoilage of milk and dairy products is an assumed cause of great economical losses for the dairy industry. This spoilage is for a large part caused by lipolytic and proteolytic enzymes that are mainly produced by pseudomonads and aerobe spore-formers (members of Bacillus sensu lato). Psychrotolerant Pseudomonas members can already grow out in the raw milk during cold storage. Even though they are easily inactivated by commercially applied heating processes to prolong the shelf life of the product, a large proportion of their heat-resistant spoilage enzymes persist even after the most intense processing conditions (e.g. UHT treatment). Aerobe spore-formers, on the other hand, are present in raw milk predominantly as dormant spores. This heat-resistant structure enables them to withstand commercial heating processes such as pasteurization which trigger germination of these spores. The resultant vegetative cells can then grow out and cause spoilage in the end product. This study aims to identify the most important spoilage microbiota present in raw milk using a polyphasic approach to attain an identification that is congruent with current taxonomical insights. In the first part of this thesis, the influence of farm practices and season of isolation on the aerobe spore-forming microbiota was assessed by comparing two extremes in dairy farm management (organic versus conventional farming) in two different seasons (summer/autumn versus winter). Toxinogenic and spoilage potential of the strains was determined, revealing that the predominant Bacillus species such as Bacillus licheniformis, Bacillus pumilus, the Bacillus cereus group, Bacillus subtilis and B. amyloliquefaciens may play an important role in spoilage and safety of dairy products. In the second part of this thesis, lab-scale simulations of the cold dairy chain were used to monitor the outgrowth of psychrotolerant Pseudomonas members in raw milk. Here also, the predominant Pseudomonas microbiota (identified as Pseudomonas gessardii-like, P. fluorescens-like, Pseudomonas lundensis and Pseudomonas fragi(-like)) proved to be the most vigorous milk spoilers. This study revealed the influence of certain practices in the dairy sector (from the primary production up to the dairy plant) on the population structure of the most important spoilage organisms, which may lead to advices for this industry to control bacterial spoilage and guarantee safe products.
Please use this url to cite or link to this publication:
author
promoter
UGent and Marc Heyndrickx
organization
alternative title
De rol van Pseudomonas en aërobe sporenvormers in bacterieel bederf en veiligheid van melk en melkproducten
year
type
dissertation (monograph)
subject
keyword
cytotoxicity, milk, Pseudomonas, Bacillus s.l., DGGE, polyphasic identification, farm management, spoilage
pages
IX, VIII, 218 pages
publisher
Ghent University. Faculty of Sciences
place of publication
Ghent, Belgium
defense location
Gent : Het Pand (zaal rector Blancquaert)
defense date
2010-05-03 17:00
ISBN
9789490695255
language
English
UGent publication?
yes
classification
D1
additional info
dissertation consists of copyrighted materials
copyright statement
I have transferred the copyright for this publication to the publisher
id
949646
handle
http://hdl.handle.net/1854/LU-949646
date created
2010-05-20 11:06:17
date last changed
2010-07-12 13:52:39
@phdthesis{949646,
  abstract     = {Bacteriological spoilage of milk and dairy products is an assumed cause of great economical losses for the dairy industry. This spoilage is for a large part caused by lipolytic and proteolytic enzymes that are mainly produced by pseudomonads and aerobe spore-formers (members of Bacillus sensu lato).
Psychrotolerant Pseudomonas members can already grow out in the raw milk during cold storage. Even though they are easily inactivated by commercially applied heating processes to prolong the shelf life of the product, a large proportion of their heat-resistant spoilage enzymes persist even after the most intense processing conditions (e.g. UHT treatment). Aerobe spore-formers, on the other hand, are present in raw milk predominantly as dormant spores. This heat-resistant structure enables them to withstand commercial heating processes such as pasteurization which trigger germination of these spores. The resultant vegetative cells can then grow out and cause spoilage in the end product. 
This study aims to identify the most important spoilage microbiota present in raw milk using a polyphasic approach to attain an identification that is congruent with current taxonomical insights. 
In the first part of this thesis, the influence of farm practices and season of isolation on the aerobe spore-forming microbiota was assessed by comparing two extremes in dairy farm management (organic versus conventional farming) in two different seasons (summer/autumn versus winter). Toxinogenic and spoilage potential of the strains was determined, revealing that the predominant Bacillus species such as Bacillus licheniformis, Bacillus pumilus, the Bacillus cereus group, Bacillus subtilis and B. amyloliquefaciens may play an important role in spoilage and safety of dairy products.
In the second part of this thesis, lab-scale simulations of the cold dairy chain were used to monitor the outgrowth of psychrotolerant Pseudomonas members in raw milk. Here also, the predominant Pseudomonas microbiota (identified as Pseudomonas gessardii-like, P. fluorescens-like, Pseudomonas lundensis and Pseudomonas fragi(-like)) proved to be the most vigorous milk spoilers. 
This study revealed the influence of certain practices in the dairy sector (from the primary production up to the dairy plant) on the population structure of the most important spoilage organisms, which may lead to advices for this industry to control bacterial spoilage and guarantee safe products.},
  author       = {De Jonghe, Valerie},
  isbn         = {9789490695255},
  keyword      = {cytotoxicity,milk,Pseudomonas,Bacillus s.l.,DGGE,polyphasic identification,farm management,spoilage},
  language     = {eng},
  pages        = {IX, VIII, 218},
  publisher    = {Ghent University. Faculty of Sciences},
  school       = {Ghent University},
  title        = {The role of Pseudomonas and aerobe spore-formers in bacterial spoilage and safety of milk and dairy products},
  year         = {2010},
}

Chicago
De Jonghe, Valerie. 2010. “The Role of Pseudomonas and Aerobe Spore-formers in Bacterial Spoilage and Safety of Milk and Dairy Products”. Ghent, Belgium: Ghent University. Faculty of Sciences.
APA
De Jonghe, V. (2010). The role of Pseudomonas and aerobe spore-formers in bacterial spoilage and safety of milk and dairy products. Ghent University. Faculty of Sciences, Ghent, Belgium.
Vancouver
1.
De Jonghe V. The role of Pseudomonas and aerobe spore-formers in bacterial spoilage and safety of milk and dairy products. [Ghent, Belgium]: Ghent University. Faculty of Sciences; 2010.
MLA
De Jonghe, Valerie. “The Role of Pseudomonas and Aerobe Spore-formers in Bacterial Spoilage and Safety of Milk and Dairy Products.” 2010 : n. pag. Print.