Industrial Lecture 5

8/4/2019 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.

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Industrial Lecture 5