Download Chr. Hansen Symposium: Microbial Ecology of Cheese

Dairy Foods Symposium: Chr. Hansen Symposium:
Microbial Ecology of Cheese
523 Dairy species from non-dairy sources: Their genomic
and metabolic diversity and potential applications in cheese. O.
McAuliffe*, Teagasc Food Research Centre, Fermoy, Cork, Ireland.
The widespread dissemination of species of the lactic acid bacteria
(LAB) group in different environments testifies to their extraordinary
niche adaptability. Members of the LAB are present on grass and other
plant material, in dairy products, on human skin, and in the gastrointestinal and reproductive tracts. The selective pressure imparted by these
specific environments is a key driver in the genomic diversity observed
between strains of the same species originating from different habitats.
Strains which are exploited in the dairy industry for the production of
fermented dairy products are often referred to as ‘domesticated’ strains.
These strains, which initially may have inhabited a non-dairy niche,
have become specialized for growth in the milk environment. In fact,
comparative genome analysis of multiple LAB species and strains has
revealed a central trend in LAB evolution: the loss of ancestral genes
and metabolic simplification toward adaptation to nutritionally-rich
environments. By contrast, ‘environmental’ strains, defined as those
from plants, animals and raw milk, exhibit diverse metabolic capabilities
and lifestyle characteristics when compared with their ‘domesticated’
counterparts. Owing to the limited number of established dairy strains
used in the production of fermented foods today, there is an increasing
demand for novel strains, with concerted efforts to mine the microbiota
of natural environments for strains of technological interest. Numerous
studies have focused on uncovering the genomic and metabolic potential
of these organisms, facilitating comparative genome analysis of strains
from different environments and providing insight into the natural diversity of the LAB, a group of organisms that is at the core of the dairy
industry. The natural biodiversity which exists in these environments
may be exploited in dairy fermentations to expand flavor profiles, to
produce natural ‘clean label’ ingredients or to develop safer products.
Key Words: niche adaptability, domesticated strains, environmental
strains
524 Development of secondary cultures for consistency and
control over cheese ripening. J. A. Hannon*, Chr. Hansen A/S,
Boge Alle, Hørsholm, Denmark.
Cheese ripening and flavor development is a dynamic process and for
mature cheeses the evolution of flavor and texture can often be slow. The
ripening of cheese is largely controlled by intricate biochemical reactions
mediated by several enzymes coming from milk, residual coagulant,
starter and secondary bacteria as well as the non-starter bacteria. The
flavor and texture characteristic of each cheese variety is a result of a
series of microbiological and biochemical reactions the extent of which
is dependent on the environmental conditions in the cheese – moisture,
pH and salt content. However, variations in milk quality, plant hygiene,
non-starter flora, moisture and salt levels can result in inconsistencies
and loss of control over the ripening of cheese at industrial scale. To
overcome some of these inconsistencies and achieve some control over
the development of flavor and texture of many cheese types, Chr-Hansen
has developed robotics assisted high throughput screening methods to
characterize strains of bacteria, better understand their needs and their
interactions to increase consistency and robustness of cultures. The
focus of this talk will be on the omics and automation methods used to
characterize individual strains for a range of phenotypes (acidification,
434
flavor and texture potential), compounding design to identify optimal
culture combinations, enhanced knowledge of their mode of action
to manage which bacterial components, and to what proportions, are
required for specific functionalities.
Key Words: cheese, ripening, methods
525 Interaction of starter cultures and nonstarter lactic acid
bacteria (NSLAB) in the cheese environment. G. LaPointe*, University of Guelph, Guelph, ON, Canada.
The microbiota of ripening cheese is dominated by lactic acid bacteria,
which are either added as starters and adjunct cultures, or originate from
the production and processing environments (non starter or NSLAB).
After curd formation and pressing, starters have reached high numbers,
but their viability then decreases due to lactose depletion, salt addition,
low pH and temperature. Starter autolysis releases cellular contents,
including nutrients and enzymes, into the cheese matrix. During ripening, NSLAB may attain cell densities up to 8 logs of colony-forming
units after 3–9 mo. Depending on the species and strains, their metabolic
activity may contribute to defects or inconsistency in cheese quality as
well as to the development of typical cheese flavor. Studies using qPCR
and RT-qPCR have shown that the starters survive and dominate the
cheese microbiota over 6 mo. The lowering costs of high throughput
sequencing have contributed to understanding the changing composition
of the cheese microbial community. The availability of gene and genome
sequences has enabled targeted detection of specific cheese microbes
and their gene expression over the ripening period. The application of
RT-qPCR has revealed how the expression of genes encoding peptide
transporters and peptidases of Lactobacillus paracasei is stimulated in
mixed culture compared with pure culture in cheese slurry. Integrated
systems biology is needed to combine the multiple perspectives of postgenomics technologies to elucidate the metabolic interactions among
microorganisms. Future research should delve into the variation in cell
physiology within the microbial populations, as spatial distribution
within the cheese matrix will lead to microenvironments that could
impact localized interactions of starters and NSLAB. Microbial community modeling can contribute to improving the efficiency and reduce
the cost of food processes such as cheese ripening.
Key Words: lactococci, lactobacilli, cheese
526 Interactions of production environment microbiota with
food and beverage fermentations: Lessons for cheese production.
D. A. Mills*, Department of Food Science & Technology, University
of California, Davis, CA.
Cheese production is a useful model to study food ecosystem dynamics
as these fermented products illustrate opposing roles of adventitious
microbes involved—as spoilage agents and as beneficial members of
the microbial consortium—both of which influence final product quality.
Recently, application of rRNA marker gene surveys to define the modes
of microbial transmission across space and time in cheese production has
provided unique insight into these important commercial fermentations.
Cheese fermentations are well known to be initiated by starter cultures,
however recent studies suggest that adventitious microbiota is influenced
by environmental factors thus potentially contributing to the “regional
J. Dairy Sci. Vol. 100, Suppl. 2
character” often attributed to specific products. Moreover, advances
in sensor technology now allows simultaneous monitoring of food
production facilities for various environmental parameters including:
temperature, relative humidity, volatile organic carbon, CO2, dust accumulation and human traffic. Integration of sensor data with microbiota
surveys provides unique insight into mechanisms of microbial dispersal
and persistence throughout seasonal or process-related environmental
changes. Elucidating microbial ecosystems and spatial characteristics
present in cheese production environments identifies the fundamental
drivers of microbial biogeography with practical implications for all
food production systems.
Key Words: cheese, microbiota, environment
527 Diversity and dynamics of surface-ripened cheese microbiomes: Implications for cheese quality and safety. B. E. Wolfe*,
Department of Biology, Tufts University, Medford, MA.
Despite the long history of producing and consuming surface-ripened
cheeses, we are just beginning to understand the diversity of microbes
J. Dairy Sci. Vol. 100, Suppl. 2
that negatively and positively affect the quality and safety of these
cheeses. I will explain the genomic and experimental approaches
that my research team is using to dissect microbiome diversity and
dynamics in the rinds of surface-ripened cheeses. Metagenomic and
genomic approaches demonstrate species and strain-level variation
that contributes to the diversity of cheese aesthetics and flavors and
highlight the widespread abundance of non-starter culture bacteria and
fungi in surface-ripened cheeses. Experimental approaches demonstrate
the dynamic interactions occurring within cheese rind microbial communities and highlight how these interactions can be managed to create
specific cheese communities. I will also describe our efforts to diagnose
the microbial origins of common cheese rind defects and how we are
collaborating with chemists to identify the sensory impacts of specific
cheese microbes. Ongoing work is uncovering the potential risks of
antibiotic resistance genes and opportunistic pathogens that can occur
in the rinds of some cheese varieties. Collectively, our work is uncovering a previously unknown diversity of microbes in cheese rinds and
providing key data on how to manage and manipulate these microbes
to improve the quality and safety of traditional cheeses.
435