yogurt preparation with milk by using Lactobacillus bulgaricus and Streptococcus thermophillus

1. Preparation of
yoghurt
Bangaru. karthik
Dept .of microbiology

2. Introduction
• Fermented milk product
• Word yoghurt comes from turkish word
“jugurt”

3. Mostly made from……
• Normal milk
• Skimmed milk
• Fortified milk

4. Milk source
• Mostly from cow
• Rarely from goat and sheep
• Limitation: milk should be free from
antimicrobial substance

5. Milk used in preparation
• Whole milk
• Partially defatted milk
• Condensed skimmed milk
• Cream
• Non fat dry milk
• Milk is condensed by removing 15-20% of
water in vaccum pan
• Milk fat levels are 1-3.25%

6. Limitation of milk
• Infected milk is not used

7. Additives permitted
• Nutritive carbohydrate sweetners
• Coloring agents
• Stabilizers
• Fruit preparation for flavouring yoghurt

8. Starter culture
• Lactobacillus bulgaricus
• Streptococcus thermophillus

9. Sweeteners
• Majorly used : Sucrose
• Others : corn sweetners and honey
• The level of sucrose effects preparation
– Production of lactic acid
– Flavour of yoghurt

10. Sucrose…..
• It can be added either in
– wet form
– dry form
– Granulated from
– Free flowing form
– Crystalline or liquid form
– 67% of sucrose can be added

11. Other sweeteners
• Non- nutritive sweetners eg: ca-saccharin
• Lactose, glucose & galactose is also
suggested
• Commercial yoghurt have
– 4.06% lactose
– 1.85% galactose
– 0.05% glucose
– pH = 4.1

12. Stabilizers
• Main function :
• Smoothness in body and texture
• To impart gel structure
• To reduce wheying off
• Increase the shelf life
• Provides a degree of uniformity

13. Charecters of a good stabilizer
• Should never effect flavour
• Should be effective at low pH
• Should be easily dispersed

14. Different stabilizers
• Gelatin
• Sea weed gums
• Algin & sodium alginate
• carrageenan

15. Fruit preparations in yoghurt
• Different fruit preparation are blended to
satisfy market requirement
• Generally 15-20% of low levels of fruit are
present
• Depending on their usage yoghurt is
classified into three types

16. Different types of yoghurt
• Eastern sundae style
• Western sundae style
• Swiss style yoghurt

17. Eastern sundae style
• Also called fruit on bottom
• 59ml of fruit preserves at bottom followed
by 177ml of inoculated yoghurt mix
• No flavour or sweetners are added

18. Western sundae style
• Fruit preserves or special fruit preparations
forms the bottom layer
• Top layer has yoghurt containing sweetners
with the flovour and color
• It is identical to eastern sundae style
• Flavor level is usually 2-4% in the top layers

19. Swiss style yoghurt
• Also known as continental style or french
style or stirred yoghurt
• Fruit preparation is thoroughly blended in
yoghurt

20. Fruits used are….
• Strawberry
• Raspberry
• Bluberry
• Apples, peaches, orange, lemon

21. Starter culture
• Important in preparation
• Should be…
• Free from contaminants
• Vigorous growth in yoghurt mix
• Good flavour
• Body and texture production
• Resonable resistance to pahges and antibiotics

22. Starter cultures used are….
• Lactobacillus bulgaricus
• Streptococcus thermophilus

23. • Starter culture
– Gives flavor and texture production

24. • The lactobacilli grows first and liberate the amino
acid glycine and histidine
• This stimulate the growth of streptococci
• Formation of lactic acid, acetaldehyde, acetic
acid and diacetyl decides the flavour of yoghurt
• Sterptococci lowers the pH to 5.5
• Then lactobacilli reduces pH still 3.8 – 4.4

25. • Homogenization and high fat content gives
smooth texture
• Gassiness in yoghurt is due to
contamination by some bacilli

26. Types of yoghurt
• Plain yoghurt
– Set type
– Stirred type
• Fruit flavored yoghurt
– Eastern sundae style
– Western sundae style

27. Set type yoghurt
Low fat milk, skim milk,
non fat dry milk
Standardized yoghurt
Milk fat – 1-2%
MSNF – 12.5%
Pasteurize at 95°C
For 30 min
Homogenize at 60°C
Mix in holding VAT
43°C
Bulk starter
Packing container
Incubate container
At 43°C pH 4.5
Cool & store plain
Yoghurt at 5°C upto
3-4weeks
Cool to
43°C

28. Low fat milk, skim milk,
non fat dry milk
Standardized yoghurt
Milk fat – 1-2%
MSNF – 10.5%
Stabilizers – 0.7%
Pasteurize at 95°C
For 30 min
Homogenize at 60°C
Mix in holding VAT
43°C, pH 4.5
Bulk starter
Packing container
Cool & store plain
Yoghurt at 5°C upto
3-4weeks
Cool to
43°C
Cool to 25 °C
Stirred type of yoghurt

29. Low fat milk, skim milk,
non fat dry milk
Standardized yoghurt
Milk fat – 1-2%
MSNF – 10 -12.5%
Pasteurize at 95°C
For 30 min
Homogenize at 60°C
Mix in holding VAT
43°C
Bulk starter, fruit syrup
And color for western style
Packing container, 1 part fruit
& 3-4 parts yoghurt
Incubate container
At 43°C pH 4.5
Cool & store plain
Yoghurt at 5°C upto
3-4weeks
Cool to
43°C
Sundae style

30. Low fat milk, skim milk,
non fat dry milk
Standardized yoghurt
Milk fat – 1-2%
MSNF – 10.5%
Stabilizers – 0.7%
Pasteurize at 95°C
For 30 min
Homogenize at 60°C
Mix in holding VAT
43°C, pH 4.5
Bulk starter
Packing container
Cool & store plain
Yoghurt at 5°C upto
3-4weeks
Cool to
43°C
Swiss style
Cool to 25 °C
Yoghurt fruit is added