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Yoghurt Processing: Harum Fadhilatunnur, M.SC

Yoghurt is produced by fermenting milk with lactic acid bacteria. There are three main types - set, stirred, and drink yoghurt. The production of stirred yoghurt involves standardizing milk, homogenizing, heat treatment, inoculation with Streptococcus thermophilus and Lactobacillus delbrueckii ssp bulgaricus bacteria, fermentation at 31°C for 16-20 hours, cooling, mixing in fruits, packaging, and cold storage at 5-8°C. Fermentation produces lactic acid which causes the casein proteins to coagulate into a gel-like structure. Cooling slows fermentation while mixing rearranges the protein network. Shelf

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Harum Fadhilatunnur
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170 views17 pages

Yoghurt Processing: Harum Fadhilatunnur, M.SC

Yoghurt is produced by fermenting milk with lactic acid bacteria. There are three main types - set, stirred, and drink yoghurt. The production of stirred yoghurt involves standardizing milk, homogenizing, heat treatment, inoculation with Streptococcus thermophilus and Lactobacillus delbrueckii ssp bulgaricus bacteria, fermentation at 31°C for 16-20 hours, cooling, mixing in fruits, packaging, and cold storage at 5-8°C. Fermentation produces lactic acid which causes the casein proteins to coagulate into a gel-like structure. Cooling slows fermentation while mixing rearranges the protein network. Shelf

Uploaded by

Harum Fadhilatunnur
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We take content rights seriously. If you suspect this is your content, claim it here.
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YOGHURT PROCESSING

Harum Fadhilatunnur, M.Sc.


What is yoghurt?

• Fermented milk by Lactic Acid Bacteria (LAB)

Lactose  lactic acid

• Gel-like structure formed by protein (mainly casein) network


Gel formation

• Protruding hair of kappa casein prevents


aggregation  steric and electrostatic
repulsion
• At IEP, casein lost steric and electrostatic
repulsion  aggregation

casein micelle

IEP
Types of yoghurt

Set yoghurt Stirred yoghurt Drink yoghurt


Firm-gel Smooth, pourable, Smooth, thin liquid
viscous liquid
Stirred yoghurt production
Standardization

Homogenization

Heat treatment

Inoculation
0.5%
Fermentation (31°C)
16-20h
Cooling
Fruits
Mixing/stirring

Packaging

Cold storage 5-8oC


Stirred yoghurt production

Standardization

Homogenization
• Standardize the dry matters
Heat treatment - Protein
- Fat
Inoculation • Consistent texture/viscosity
0.5%
Fermentation (31°C)
16-20h
Cooling
Fruits
Mixing/stirring

Packaging

Cold storage 5-8oC


Stirred yoghurt production
Standardization

• Disruption of milk fat globules into


Homogenization
smaller ones
• 0.1-15 µm  <1 µm
Heat treatment

Inoculation High turbulence


0.5%  disruption
Fermentation (31°C) <50 ms
16-20h
Cooling
Fruits P
Mixing/stirring 10-20 MPa

Packaging

Cold storage 5-8oC


Homogenization

Unhomogenized Stage 1 Stage 2

casein

cluster

membrane - Fat globules act like


casein micelles
- Incorporated in the
protein network
Stirred yoghurt production
Standardization

Homogenization

Heat treatment

High Pasteurization (85oC, 20s)


Inoculation
• Kill most of bacteria
0.5%
• Inactivate anti-bacterial components
Fermentation (31°C) • Denature whey protein  aggregate
16-20h with casein micelles
Cooling
Fruits
Mixing/stirring

Packaging

Cold storage 5-8oC


Stirred yoghurt production
Standardization

Homogenization

Heat treatment

Inoculation
0.5%
Streptococcus thermophilus &
Fermentation (31°C) Lactobacillus delbrueckii ssp bulgaricus
16-20h
Cooling
Fruits
Mixing/stirring

Packaging

Cold storage 5-8oC


Characteristic of starter
S. thermophilus Lb. bulgaricus

Optimum pH growth 6.5 5.8


Optimum growth temp 40 40-45
Maximum growth temp 50 52
Homofermentative + +
Lactic acid prod (24 h opt) 0.9 (%) 2.5 (%)
- L-lactic acid + -
- D-lactic acid - +
Degradation of galactose - -
(majority of strains)
Proteolytic - +
Growth inhibition by pH at: 4.2 - 4.4 3.5 - 3.8
Fermentation process

Lactic
acid
lactic acid
formation

formation
growth
Amino acids
factors
Formic peptides
acid
stimulation
CO2
inhibition

S. thermophilus Lb. bulgaricus


Stirred yoghurt production

Standardization

Homogenization

Heat treatment

Inoculation
0.5%
• The lower the incubation
Fermentation (31°C) temperature, the longer it takes to
16-20h reach pH of aggregation, but the
Cooling firmer the gel is.
Fruits • Firmer gel  avoid syneresis
Mixing/stirring

Packaging

Cold storage 5-8oC


Stirred yoghurt production
Standardization

Homogenization

Heat treatment

Inoculation
0.5%
Fermentation (31°C) • Fermentation process (almost) done
16-20h • Slow down continuous fermentation
Cooling
Fruits
Mixing/ stirring

Packaging

Cold storage 5-8oC


Stirred yoghurt production
Standardization

Homogenization

Heat treatment

Inoculation
0.5%
Fermentation (31°C)
16-20h
Cooling
Fruits • Breaking down and rearrangement of
Mixing/ stirring
protein network

Packaging

Cold storage 5-8oC


Stirred yoghurt production
Standardization

Homogenization

Heat treatment

Inoculation
0.5%
Fermentation (31°C)
16-20h
Cooling • Shelf life is determined by sensory
Fruits defect, not by spoilage
Mixing/ stirring - cold storage
- low pH
Packaging - bacteria outnumbered by LAB

Cold storage 5-8oC

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