Download - Industrial Lecture 5
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BIO 425
Industrial Microbiology
Lecture 5
Cheese Making-2Fermented milks
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Content outline Lactic acid bacterias role
Lactate formation Texture and cheese
Fermented milks
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Functions of starter lactic acid
bacteria in cheese and other dairyproducts
Acidification
Texture and development
Flavor contribution
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Acidification Major attribute of lactic acid bacteria
Conversion of milk lactose into lactic acid
Low pH inhibits the pathogens.
Enhances the expulsion of whey from the
curd during cheese making-reduces
moisture levels,
and further promotes the preservative effect.
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Formation of lactate Lactose Glucose + Galactose
Glucose metabolism
Lactate
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Texture and development Texture: the result of a complex series of
interactions between:
a) milk constituents
b) milk coagulating enzymes
c) starter cultures
d) secondary flora activity e) cheese making process
f) environmental factors
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Texture and pH Final pH effects texture mostly.
E.g. cheeses with a high pH of 5.2-5.5
(Dutch varieties)
have a springy or plastic texture.
Protein aggregates are in a similar globular
form (10-15 nm in diameter).
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Texture and pH
Low pH such as 4.8(English territorial
varieties-Lancashire, Cheshire)
Texture is short, non-cohesive and crumbly.
Cheddar cheese: Varies between these
extremes
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Factors affecting flavor contribution
Milk composition
Milk heat treatments Lactic acid bacteria
Secondary flora
pH
Salt / moisture levels
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Factors affecting flavor contribution-
2
Milk enzymes e.g. Plasmin
Coagulating enzymes Cheese-making parameters
Cheese storage conditions
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Contribution of lactic acid bacteria
to flavor
1- By providing suitable environment for
enzymic and non-enzymic reactions to take
place:
includes the development of acidity and
redox potential within the cheese.
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Contribution of lactic acid bacteria
to flavor
2- By providing the flavor metabolites that
are produced directly from lactose and
citrate metabolism.
3- By breaking down the milk protein (and
fat) to release peptides, aminoacids and
volatile compounds.
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Examples for different flavors Mesophilic products: e.g sour cream,
fromage frais, fromage blanc, cottage
cheese, lactic butter.
Main flavor component: Diacetyl;
produced byLactobacillus lactis biovar.
diacetylactis.
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Examples for different flavors
Lactobacillus cremoris:
uses milk citrate as major flavor component.
In citrate metabolism: acetoin is formed.
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Examples for different flavors Thermophilic products (e.g. Cheese and
fermented milks)
Lactobacillus bulgaricus and Streptococcus
thermophilus : dominating flora.
Acetaldehyde: the major flavor compound.
Pyruvate Acetaldehyde
S.thermophilus
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Fermented milks Definition of International Dairy
Federation:
Fermented milk is a milk product prepared
from milk, skimmed or not with specific
cultures, the microflora is kept alive until
sale to the consumer and may not containany pathogenic germ.
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Historical background of fermented
milks
Metchnikoff (1907): pointed the presence ofLactobacillus
bulgaricus, cocci and yeast in yogurt.
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Traditional fermented milks
Methods for the production:
depends on the climatic and regional
circumstances in which the people lived.
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Types of fermented milks
(Based on the dominatingmicroflora)- (Marshall, 1984)
Type lt res sed amples
Mesophilic lactococciLeuconostoc spp
B ttermilk, lt red cream,o rmilk, candina ianttermilk, metanka
acto acill s strains B lgarian ttermilk, Yak lt
Thermophilic treptococciand acto acill s spp
Yog rt and yran
Mi ed pop lation ofdifferent lactic acid acteria& yeasts, sometimesmicrococci
Kefir, Ko mys
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Type 1s
cultured buttermilk Made from fresh pasteurized skimmed milk or
homogenized pasteurized low fat milk of
approximately 17% fat. After pasteurization cooled to 22 C and
inoculated with about 1% mesophilic startercontaining:
Lactococcus lactis sp. lactis, Lactococcus lactis sp. cremoris,
Leuconostoc mesenteroides sp. cremoris,
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Cultured cream Cultured cream (Sour cream): produced in a
similar manner to buttermilk.
Differs only in fat content (high even up to
18%)
Has typical flavor diacetyl.
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Scandinavian buttermilk E.g. Filmjolk, Lattfil, Langfil in Norway
and Sweden
Filmjolk and Lattfil:
fermented withLactococcus lactis sp. lactis
andLactococcus lactis sp. cremoris.
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Fortified withLeuconostoc mesenteroides
sp. cremoris,Lactococcus lactis sp. lactis
var. diacetylactis
Filmjolk: 3% fat
Lattfil: 0.5 % fat
produced as the same as cultured
buttermilk.
Scandinavian buttermilk-2
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Smetanka (Smetana) Mostly produced in Russia.
produced with viscous lactic acid bacteria,
Lactococcus andLeuconostoc spp.,
isolated from original fermented sourmilks
obtained from different regions of the
country.
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Smetanka (Smetana)-2
10% fat cream,
acidified to 0.63 % lactic acid, has a viscous consistency with a good
balanced flavor
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LITERATURE CITED Forsythe, S.J. The Microbiology of Safe
Food, Blackwell Science, Cambridge, 2000.
Wood, B. J. B., Microbiology of Fermented
Foods, Vol.1 and 2, Blackie Academic and
Professional, London, Second edition, 1998.