Milk fermentationMilk fermentation

Presented by:- T.Sekaran

IntroductionIntroductionThe main aim of milk fermentation is preserve the The main aim of milk fermentation is preserve the valuable nutrients in milk.valuable nutrients in milk.

It is initiated by the addition of starter culture of lactic It is initiated by the addition of starter culture of lactic acid bacteria to milk.acid bacteria to milk.

Since olden times people are using fermented products Since olden times people are using fermented products in their daily food consumption.in their daily food consumption.

There are many advantages of fermented foods such as There are many advantages of fermented foods such as they easily digestible and have improved flavour, texture they easily digestible and have improved flavour, texture and nutritive value. and nutritive value.

Some of the most commonly used milk fermented Some of the most commonly used milk fermented products are :-cheese, butter, yoghurt, kefir, sour cream, products are :-cheese, butter, yoghurt, kefir, sour cream, etc. etc.

Cont…Cont…With the advances made in microbiology and With the advances made in microbiology and biotechnology, food and beverage fermentation and biotechnology, food and beverage fermentation and production has become a major industry.production has become a major industry.

The food biotechnology has helped inThe food biotechnology has helped in

Improving the quality, Improving the quality,

nutrition value, nutrition value,

safety and safety and

preservationpreservation of foods of foods

which in turn has helped in making these foods available which in turn has helped in making these foods available through out the year.through out the year.

Cont…Cont…

LimitationsLimitations

2.2. ContaminationContamination

3.3. Slow acid formationSlow acid formation

4.4. Off flavour ariseOff flavour arise

5.5. Some time complete loss of productionSome time complete loss of production

Major problems in milk fermentation is Major problems in milk fermentation is slow acid slow acid formation.formation.

Intro…Intro…

Lactic acid bacteriaLactic acid bacteria

This bacteria is important to milk fermentation.This bacteria is important to milk fermentation.

The lactic acid bacteria are mesophiles:The lactic acid bacteria are mesophiles:

they generally grow over a temperature range of about 10 to they generally grow over a temperature range of about 10 to 4040ooC, C,

an optimum between 25 and 35an optimum between 25 and 35ooC. C.

Some can grow below 5 and as high as 45 Some can grow below 5 and as high as 45 ooC. C.

Most can grow in the pH range from 4 to 8. Though some as Most can grow in the pH range from 4 to 8. Though some as low as 3.2 and as high as 9.6.low as 3.2 and as high as 9.6.

Intro…Intro…

Starter culturesStarter culturesTraditionally the fermenting organisms came from the natural microflora or a portion of the previous fermentation.

In many cases the natural microflora is either inefficient, uncontrollable, and unpredictable, or is destroyed during preparation of the sample prior to fermentation (eg pasteurisation).

A starter culture can provide particular characteristics in a more controlled and predictable fermentation.

Cont…Cont…Lactic starters always include bacteria that convert Lactic starters always include bacteria that convert sugars to lactic acid, usually:sugars to lactic acid, usually:

Lactococcus lactis Lactococcus lactis subsp. subsp. lactislactis, ,

Lactococcus lactis Lactococcus lactis subsp. subsp. cremoris cremoris or or

Lactococccus lactis Lactococccus lactis subsp. lactis biovar diacetylactis.subsp. lactis biovar diacetylactis.

Where flavour and aroma compounds such as diacetyl Where flavour and aroma compounds such as diacetyl are desired the lactic acid starter will include are desired the lactic acid starter will include heterofermentative organisms such as:heterofermentative organisms such as:

Leuconostoc citrovorumLeuconostoc citrovorum or or

Leuconostoc dextranicumLeuconostoc dextranicum..

Cont…Cont…The primary function of lactic starters is the production of The primary function of lactic starters is the production of lactic acid from sugarslactic acid from sugars

Other functions of starter cultures may include the following: Other functions of starter cultures may include the following:

flavour, aroma, and alcohol production flavour, aroma, and alcohol production

proteolytic and lipolytic activitiesproteolytic and lipolytic activities

inhibition of undesirable organismsinhibition of undesirable organisms

Fermentation tankFermentation tank

Table Benefits of fermentation

BenefitRawmaterial

Fermentedfood

Preservation Milk(Most materials)

Yoghurt, cheese

Enhancement of safetyAcid productionAcid and alcohol production

Production of bacteriocinsRemoval of toxic components

FruitBarleyGrapesMeatCassavaSoybean

VinegarBeerWineSalamiGari, polviho azedoSoy sauce

Enhancement of nutritional valueImproved digestibilityRetention of micronutrientsIncreased fibre contentSynthesis of probiotic compounds

WheatLeafy veges.CoconutMilk

BreadKimchi, sauerkrautNata de cocoBifidus milk, Yakult, Acidophilus yoghurt

Improvement of flavour Coffee beansGrapes

CoffeeWine

how does milk ferment? how does milk ferment?

HistoryHistory

Fermentation of milk dates back thousands of years to Fermentation of milk dates back thousands of years to locations all over the world. This process was used as a locations all over the world. This process was used as a means of preserving a highly perishable product and to means of preserving a highly perishable product and to produce new flavors for an old food staple. In the early produce new flavors for an old food staple. In the early years of milk years of milk

fermentation, milk was simply allowed to be fermented fermentation, milk was simply allowed to be fermented by its normal microbiota, by its normal microbiota,

but the actual process was not completely understood. but the actual process was not completely understood. Cultures could be maintained by inoculating fresh milk Cultures could be maintained by inoculating fresh milk with fermented milk. Today, lactic acid-producing with fermented milk. Today, lactic acid-producing microorganisms are added to milk to decrease the pH of microorganisms are added to milk to decrease the pH of the milk and produce many different fermented milk the milk and produce many different fermented milk products.products.

PathwayPathway

The general pathway for fermentation of milk involves The general pathway for fermentation of milk involves the production of lactic acid from lactose in the milk. the production of lactic acid from lactose in the milk. This lowers the pH and results in a variety of products. This lowers the pH and results in a variety of products.

In this diagram, glucose can be replaced by many In this diagram, glucose can be replaced by many different sugars, including lactose, to produce the same different sugars, including lactose, to produce the same product.product.

Glucose Glucose 6-Phosphate

Fructose 6-Phosphate

Fructose 1,6-Bisphosphate

Glyceraldehyde 3-Phosphate

Pyruvate

Acetate Acetyl CoA

Citrate

α-Ketoglutarate

Succinate

Fumarate

Oxaloacetate

MalateIsocitrate

CO2+NADHFADH2

CO2+NADH

NADH

NADH

GTP

GDP+Pi

Phosphoenolpyruvate

Dihydroxyacetone phosphate

2-Phosphoglycerate

Glycolysis

TCA cycle

Lactate

Ethanol

Fermentation

Cont…Cont…The protein in milk that is responsible for curdling is The protein in milk that is responsible for curdling is casein. With the pH drop, casein molecules coagulate casein. With the pH drop, casein molecules coagulate in a structure similar to that shown below.in a structure similar to that shown below.

http://www.public.iastate.edu/~cfford/101Milk.htm

Products Products

1. Yogurt1. Yogurt

Yoghurt : semi-solid fermented milk.Yoghurt : semi-solid fermented milk.

Yogurt is produced from whole or skim milk.Yogurt is produced from whole or skim milk.

It is inoculated with a starter culture, which usually It is inoculated with a starter culture, which usually contains contains Lactobacillus bulgaricus Lactobacillus bulgaricus and and Streptococcus Streptococcus thermophilus. thermophilus.

These bacteria ferment the lactose in the milk to lactic These bacteria ferment the lactose in the milk to lactic acid, causing the milk to curdle and form yogurt. If the acid, causing the milk to curdle and form yogurt. If the product is not pasteurized, the result is yogurt with product is not pasteurized, the result is yogurt with “active cultures.” “active cultures.”

2. Sour Cream2. Sour Cream

Sour cream is produced in much the same way as yogurt. Sour cream is produced in much the same way as yogurt. However, light cream is used instead of whole or skim However, light cream is used instead of whole or skim milk. milk.

Streptococcus sppStreptococcus spp. and . and Lactobacillus spp Lactobacillus spp are used as are used as starter cultures to form lactic acid from lactose. starter cultures to form lactic acid from lactose.

The lowered pH causes the cream to coagulate, resulting The lowered pH causes the cream to coagulate, resulting in sour cream. in sour cream.

3. Kefir3. Kefir

Kefir is a fermented milk productKefir is a fermented milk product

That utilizes a wide variety of microorganisms to produce That utilizes a wide variety of microorganisms to produce a wide variety of products in addition to lactic acid a wide variety of products in addition to lactic acid including ethanol, free fatty acids, and acetaldehyde.including ethanol, free fatty acids, and acetaldehyde.

At the base of kefir production are kefir grains. At the base of kefir production are kefir grains.

These grains Contain many microorganisms including These grains Contain many microorganisms including bacteria such as bacteria such as Lactobacillus sppLactobacillus spp.. and non- pathogenic and non- pathogenic Streptococcus sppStreptococcus spp.., yeasts such as , yeasts such as Saccharomyces Saccharomyces delbruckidelbrucki and and S. cerevisiaeS. cerevisiae, as well as many other , as well as many other organisms that have yet to be classified. organisms that have yet to be classified.

4. Cheese4. Cheese

Cheese is yet another product of milk fermentationCheese is yet another product of milk fermentation

That requires factors in addition to the traditional That requires factors in addition to the traditional production of lactic acid.production of lactic acid.

The coagulation of casein due to lactic acid production The coagulation of casein due to lactic acid production and the subsequent drop in pH and the addition of and the subsequent drop in pH and the addition of rennet, an enzyme derived from the lining of the rennet, an enzyme derived from the lining of the stomachs of calves, form the curd of cheese Without stomachs of calves, form the curd of cheese Without rennet, a soft cheese such as cottage cheese or cream rennet, a soft cheese such as cottage cheese or cream cheese would result. cheese would result.

YeastsYeasts, , moldsmolds, and , and bacteriabacteria are all involved in the are all involved in the processes that produce different cheesesprocesses that produce different cheeses

The table below shows the bacteria involved in different cheeses:-The table below shows the bacteria involved in different cheeses:-

Species Major known

function Product

Propionibacterium shermanii Flavor & eye formation

Swiss cheese family

Lactobacillus bugaricusLactobacillus lactisLactobacillus helveticus

Acid and flavor Bulgarian buttermilk, yogurt, kefir, koumiss, Swiss, Emmental, and Italian cheeses

Lactobacillus acidophilus Acid Acidophilus, buttermilk

Streptococcus thermophilus Acid Emmental, Cheddar, and Italian cheeses, and yogurt

Streptococcus diacetilactis Acid Sour cream, ripe cream, butter, cheese, buttermilk and starter cultures.

Streptococcus lactisStreptococcus cremoris

Acid Cultured buttermilk, sour cream, cottage cheese, all types of foreign and domestic cheeses, and starter cultures.

Streptococcus duransStreptococcus faecalis

Acid and flavor Soft Italian, cheddar, and some Swiss cheeses.

Leuconostoc citrovorumLeuconostoc dextranicum

Flavor Cultured buttermilk, sour cream, cottage cheese, ripened cream butter, and starter cultures.

5. Buttermilk5. Buttermilk

Originally, buttermilk was the liquid left behind after Originally, buttermilk was the liquid left behind after churning butter out of cream. churning butter out of cream.

The variation of buttermilk which is a fermented dairy The variation of buttermilk which is a fermented dairy product, is produced from cow's milk, and with a product, is produced from cow's milk, and with a characteristically sour taste caused by lactic acid characteristically sour taste caused by lactic acid bacteria. bacteria.

The product is made in one of two ways: artificially made The product is made in one of two ways: artificially made buttermilk, also known as buttermilk, also known as cultured buttermilkcultured buttermilk, is made by , is made by adding adding lacticacid bacteria lacticacid bacteria calledcalled Streptococcus lactis Streptococcus lactis to to milk and so-called milk and so-called Bulgarian buttermilkBulgarian buttermilk is created with a is created with a different strain of bacteria called different strain of bacteria called Lactobacillus Lactobacillus bulgaricusbulgaricus, which creates more tartness., which creates more tartness.

Cont…Cont…

ProcedureProcedure

Traditionally, before cream was skimmed from whole Traditionally, before cream was skimmed from whole milk, It was left to sit for a period of time to allow the milk, It was left to sit for a period of time to allow the cream and milk to separate. cream and milk to separate.

During this time, the milk would naturally be fermented During this time, the milk would naturally be fermented by the lactic acid-producing bacteria in the milk. by the lactic acid-producing bacteria in the milk.

One reason this was done was to facilitate the butter One reason this was done was to facilitate the butter churning process since fat from cream with a lower pH churning process since fat from cream with a lower pH will coalesce more readily than that from fresh cream. will coalesce more readily than that from fresh cream.

The acidic environment helped prevent potentially The acidic environment helped prevent potentially harmful microorganisms from growing, thus the soured harmful microorganisms from growing, thus the soured liquid helped increase the shelf-life of the product.liquid helped increase the shelf-life of the product.

6. 6. KumisKumis

KumisKumis is a fermented dairy product traditionally made is a fermented dairy product traditionally made from from mare's milkmare's milk. It was also consumed by Hungarian . It was also consumed by Hungarian tribes.tribes.

Kumis is a is produced from a liquid starter culture, in Kumis is a is produced from a liquid starter culture, in contrast to the solid kefir "grains". Because mare's milk contrast to the solid kefir "grains". Because mare's milk contains more sugars than the cow's or goat's milk contains more sugars than the cow's or goat's milk fermented into kefir, kumis has a higher, though still mild, fermented into kefir, kumis has a higher, though still mild, alcohol content.alcohol content.

During the fermentation, During the fermentation, Lactobacilli bacteria Lactobacilli bacteria acidify the acidify the milk, and yeasts turn it into a carbonated and mildly milk, and yeasts turn it into a carbonated and mildly alcoholic drink.alcoholic drink.

ReferencesReferences

Kerr, TJ and BB McHale. Kerr, TJ and BB McHale. Applications in General Applications in General Microbiology: A Laboratory ManualMicrobiology: A Laboratory Manual. Winston-Salem: . Winston-Salem: Hunter Textbooks, 2001.Hunter Textbooks, 2001.

Wszolek, M, AY Tamimi, DD Muir, and MNI Barclay Wszolek, M, AY Tamimi, DD Muir, and MNI Barclay (2001). “Properties of kefir made in Scotland and Poland (2001). “Properties of kefir made in Scotland and Poland using bovine, caprine, and ovine milk with different using bovine, caprine, and ovine milk with different starter cultures.” starter cultures.” Lebensmittel-Wissenschaft und Lebensmittel-Wissenschaft und TechnologieTechnologie. 34: 251-261. 34: 251-261

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