The origins of the organisms employed in food fermentations

For the longest time, the foodstuffs described in this book were prepared using endogenous microflora. Increasingly, however, and starting first with the isolation of pure strains of brewing yeast by Emil Christian Hansen in 1883, many of the products employ starter cultures in their production. The organisms conform to the criterion of being Generally Recognised as Safe (GRAS). They are selected for their advantageous properties in terms of process performance and impact on final product quality.

Many companies and academic laboratories are seeking newer, improved cultures. This can be achieved in what may be called 'serendipity mode' by screening a broad swathe of samples taken from multitudinous habitats, the screening employing growth media and cultivation conditions that are best suited to an organism with the desired characteristics. Alternatively, some narrowing of odds can be achieved by specifically looking in locales where certain types of organisms are known to thrive - for example, yeasts are plentiful on the surface of fruit. One extreme example of this approach might most reasonably be described as 'theft', with the pure culture of one company finding its way, through whatever mechanism, into the clutches of another corporation.

Table 1.5 Culture collections.

Collection

Organisms

Web page

American Type Culture

All types

http://www.atcc.org/

Collection (ATCC)

CABI Bioscience

Filamentous

http://www.cabi-bioscience.org/

fungi

Centraalbureau voor

Filamentous

http://www.cbs.knaw.nl/

Schimmelcultures

fungi and

yeasts

Collection Nationale de

All types

http://www.pasteur.fr/recherche/unites/Cncm/index-en.html

Cultures de

Microorganismes

Die Deutsche Sammlung

All types

http://www.dsmz.de/

von Mikroorganismen

und Zellkulturen

Herman J. Phaff Culture

Yeasts and

http://www.phaffcollection.org/

Collection

fungi

National Collection of

Bacteria

http://www.ncimb.co.uk/

Industrial and Marine

Bacteria

National Collection of

Yeasts

http://www.ifr.bbsrc.ac.uk/NCYC/

Yeast Cultures

A more honest approach is by purchasing samples of pure organisms of the desired character from culture collections (Table 1.5). Nowadays the cultures are likely to be in the form of vials frozen in liquid nitrogen (—196°C) or they may be lyophilised. For some industries, notably bread making and wine making, companies do not produce their own yeast but rather bring it into the production facility on a regular basis from a supplier company. This might be supplied frozen or merely refrigerated with cryoprotectants such as sucrose, glycerol or trehalose. The latest technology here is active dried yeast, with the organism cultured optimally to ensure its ability to survive drying in a state that will allow it to perform vigorously and representatively when re-hydrated. In other industries, notably beer brewing, companies tend to maintain their own strains of yeast and propagate these themselves. This is probably on account of the fact that beer-making is essentially the only industry described in this book where the surplus organism that grows in the process is re-used.

An overview of starter cultures is given in Table 1.6. A starting inoculum might typically be of the order of 1%. An example of how the volume can be scaled up from the pure 'slope' of the master culture to an amount to 'pitch' the most enormous of fermenters is given in Chapter 2.

There are various opportunities for enhancing the properties of the organisms that are already employed in food companies. Mutagenesis to eliminate undesirable traits has been employed. However, this is a challenge for eukary-otes as such cells tend to have multiple copies of each gene (polyploidy), and it is a formidable challenge to eliminate all the alleles of the undesirable gene. Classic recombination techniques (conjugation, transduction and transformation) have been pursued, but there is always the risk that an undesirable trait

Table 1.6 Starter cultures.

Organism

Type of organism

Foodstuff

Aspergillus oryzae

Mould

Miso, soy sauce

Brevibacterium linens

Bacterium

Cheese pigment and surface

growth

Lactobacillus casei

Bacterium

Cheese and other fermented

dairy products

Lactobacillus curvatus

Bacterium

Sausage

Lactobacillus delbrueckii ssp. bulgaricus

Bacterium

Cheese, yoghurt

Lactobacillus helveticus

Bacterium

Cheese and other fermented

dairy products

Lactobacillus lactis (various ssp.)

Bacterium

Cheese and other fermented

dairy products

Lactobacillus plantarum

Bacterium

Fermented vegetables,

sausage

Lactobacillus sakei

Bacterium

Sausage

Lactobacillus sanfranciscensis

Bacterium

Sourdough bread

Leuconostoc lactis

Bacterium

Cheese and other fermented

dairy products

Leuconostoc mesenteroides

Bacterium

Fermented vegetables,

cheese and other

fermented dairy products

Oenococcus oeni

Bacterium

Wine

Pediococcus acidilactici

Bacterium

Fermented vegetables,

sausage

Pediococcus halophilus

Bacterium

Soy sauce

Pediococcus pentosaceus

Bacterium

Sausage

Penicillium camemberti

Mould

Surface ripening of cheese

Penicillium chrysogenum

Mould

sausage

Penicillium roqueforti

Mould

Blue-veined cheeses

Propionibacterium freudenreichii

Bacterium

Eyes in Swiss cheese

Rhizopus microsporus

Mould

Tempeh

Saccharomyces cerevisiae

Fungus

Bread, ale, wine

Saccharomyces pastorianus

Fungus

Lager

Staphylococcus carnosus

Fungus

Meat

Streptococcus thermophilus

Bacterium

Cheese, yoghurt

will be introduced as an accompaniment to the trait of interest. Much more selectivity is afforded by modern genetic modification strategies. However, as noted earlier, this attracts far more emotion for organisms used in food production than it does in the production of, say, fuels or pharmaceuticals.

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