about dairy microbiology

1. HARAMAYA UNIVERSITY
COLLEGE OF AGRICULTURE AND ENVIRONMENTAL SCIENCES
SCHOOL OF ANIMAL AND RANGE SCIENCES
Course- Advanced Dairy Microbiology
By
Ewunetu Bekele
Instructor: Takele Wolkaro (PhD)

2. Presentation outlines
1.1 Production of starter cultures
1.2. Traditional starter cultures
1.3. Use of DVS cultures
1.4. Range of LAB used as starter cultures
1.5. Probiotic starter cultures

3. INTRODUCTION
 Starter culture is a concentrated preparation of live cells that is added
to a raw material to initiate fermentation rapidly.
 LAB occupies a central role in these fermentation processes.
 LAB widely distributed in nature and found naturally as indigenous
micro flora in raw milk are Gram positive (Hati, 2013).
 Probiotics cultures is live microorganisms influence the health of the
human or animal host (Tyler, 2006).

4. Application and Action of Lactic fermented Starter Cultures
All dairy fermentations use lactic acid bacteria for acidification and flavor production.
 lactic acid bacteria are genetically diverse, common characteristics of this group
include being:-
 Gram-positive
 Non–spore forming
 Nonpigmented and
 Growing anaerobically but being aerotolerant; and
 Obligately fermenting sugar with lactic acid as a major end product.
 A starter culture can produce particular characteristics in a more controlled and
predictable fermentation when added to milk.

5. Functions of starter cultures
Function Result
Acid production
 Expulsion (syneresis) of whey for texturing
 Preservation of milk
 Helps in the development of flavour
Flavour  Formation of flavour compounds like diacetyl
and acetaldehyde
Preservation  Lowering of pH and redox potential
 Production of lactic acid
 Production of antibiotics
 Production of H2O2
 Production of acetate

6. Gas formation  Eye formation in certain cheeses
 Production of open texture Ex. blue veined cheese
Stabilizer formation  Development of body and viscosity Ex.
Polysaccharide materials
Lactose utilization  Reduces off flavours
 Suitable for lactose intolerant people
Lowering of redox
potential
 Helps in preservation
 Helps in development of flavour
Proteolysis and lipolysis  Helpful in the ripening/maturation of cheeses
Continued…

7. Types of Starters
 Starters are grouped under different categories based on:-
 Composition of microflora
 Growth temperature
 Type of products
 Flavour production and
 Type of fermentation (Abdel, 2017).

8. Application of LAB in the production of some fermented food
Dairy products Genera of LAB1
Cheese (Mesophilic starter)  Lc. lactis ssp. lactis
 Lc. lactis ssp. cremoris
 Lc. lactis ssp. lactis var. diacetylactis
 Leuc. mesenteroides ssp. Cremoris
Cheese (Thermophilic starter)  S. thermoplillus
 Lb. delbrueckii ssp. bulgaricus
 Lb. helveticus
 Lb. delbrueckii ssp. Lactis
Cheese (Mixed starter)  Lc. lactis ssp. lactis
 Lc. lactis ssp. cremoris
 S. thermoplillus
Yogurt  Lb. delbrueckii ssp. bulgaricus,
 S. thermophilus
Acidophilus milk  Lb. acidophilus

9. Butter and buttermilk  Lc. lactis ssp. lactis,
 Lc. lactis ssp. lactis var. diacetylactis,
 Lc. lactis ssp. cremoris,
 Leuc. menesteroides ssp. cremoris
Kefir  Lb. kefir,
 Lb. kefiranofacies,
 Lb. brevis,
 Lb. plantarum,
 Lb. paracasei spp. paracasei,
 Lc. lactis spp. lactis, Leuc.
Mesenteroides
Continued….

10. Production of starter cultures
Stages of propagation
 The process may involve two or more stages. Cultures in various stages of
propagation are known by the following names:
Commercial culture, master culture – the original culture that the dairy buys
from the laboratory.
Mother culture
• prepared from master culture at the dairy.
• prepared daily and the origin of all cultures made at the dairy.
Intermediate culture – an intermediate step in the manufacture of large
volumes of bulk starter.
Bulk starter – the starter used in production (Gösta, 1995).

11. Stages in the process
 The process is essentially the same for production of mother culture,
intermediate culture and bulk starter .
 It comprises the following stages:
 Heat treatment of the medium - 90 – 95°C and held for 30 to 45
minutes.
 Cooling to inoculation temperature- 20 – 30°C for mesophilic types
of bacteria and 42 – 45°C for thermophilic types.
 Inoculation
Continued….

12.  Incubation
• The incubation time is determined by the types of bacteria in the
culture, the inoculation dosage
• can vary from 3 to 20 hours.
Cooling of the finished culture
• Cooling to 10 – 12°C is often practiced to be used within the next 6
hours.
• If more than 6 hours, it is advisable to cool it to about 5°C
 Storage of the culture
• The lower the temperature, the better the cultures keep.
• Freezing with liquid nitrogen to –160°C and storage at that
temperature preserve cultures very well.
Continued….

13. DVS cultures
 The concentrated culture is added directly to the vat, without need
for on - site starter propagation.
 DVI starters have become more accessible in recent times as the
technology for concentration and preservation has been improved.
 DVI can provide advantages, especially for factories that lack the
specialized facilities and trained personnel necessary for reliable
bulk starter preparation (Taylor & Francis, 2006).
Continued….

14.  DVS cultures need no activation or other treatment prior to use.
 Freeze-dried DVS cultures are water-soluble granules, 2-5 mm in
diameter
 Freeze dried DVS cultures should be stored at -18°C (0°F) or below.
 If freeze-dried cultures are stored correctly, the shelf life is at least 24
months.
 At +5°C (41°F) the shelf life is at least 6 weeks.
Continued….

15. Traditional starter cultures
 Traditionally, a starter is propagated by adding an amount of
grown culture to a small quantity of intensely heated skim
milk.
 These traditional methods are still practiced today for small-
to mid-scale production facilities, as well as in less developed
countries and in homemade-type products.
 Traditional methods are prone to slow or failed fermentations,
contamination, and inconsistent quality (Sonia, 2012).
Continued….
1. Traditional propagation of starter bulk culture.
2. Modern propagation using starter concentrate
3. Direct vat inoculation

16.  Lactic acid producing fermentation has been known for thousands
of years.
 Many different cultures used this method of food processing to
improve the storage quality, palatability, and nutritive value.
 Today lactic acid bacteria are mainly associated with a group of
dairy products such as cheese, yoghurt, kefir, and buttermilk.
 Lactic acid bacteria have been associated with beneficial health
effects (Hati, 2013).
Range of LAB used as starter cultures

17.  Lactic acid bacteria causes rapid acidification of the raw
materials through the production of organic acids, primarily lactic
acid.
 They also produce many important by-products such as:-
 Acetic acid
 Ethanol
 Aroma compounds
 Bacteriocins
 Exopolysaccharides and
 Several enzymes.
 These by-products enhance product shelf life, microbial safety,
improve texture, and ultimately contribute to the pleasant sensory
profile of the end product (Hati, 2013).
Continued….

18.  Probiotics are living microorganisms, when ingested
influence the health of the host by improving the
composition of intestinal microflora.
A prebiotic -a nondigestible food ingredient selectively
stimulating the growth and/or activity of bacteria in the colon.
Probiotic starter cultures

19. Types of probiotic Culture
Lactobacillus spp. Bifidobacterium spp. Other bacterial genera Probiotic yeasts
Continued….
1. L. acidophilus
2. L. casei
3. L. crispatus
4. L.fermentum
5. L. gasseri
6. L. johnsonii
7. L. paracasei
8. L. plantarum
9. L. reuteri
10. L. rhamnosus
11. L. helveticus
1. B. bifidum
2. B. breve
3. B. infantis
4. B. lactis
5. B. longum
6. B. adolescentis
7. B. essensis
1. E. francium
2. Entrococcus. faecium
3. E. faecalis
4. P. freudenrichii
5. L. lactis
6. Leunostoc mesenteroides
7. Pediococcus acidilactici
1. Saccharomyces
Cerevisiae
2. S. Boulardii
3. Kluyvermyces
marxianus

20. Health benefits of probiotic bacteria and mechanisms involved
Probiotic Strain Mechanism of Action
Lactic acid bacteria Ensures biodegradation of susceptible and potential
carcinogens, Boost the immune response system of the
host and inhibits pro cancerous enzymatic activity of
colonic microorganisms
Bifidobacterium bifidum Prevents and reduces diarrhea, inhibits invasive pathogens
by secretion of acids and increases antibacterial action of
the intestinal microflora
Bifidobacterium lactis, L.
bulgaricus, L. plantarum,
L. acidophilus
Alleviates symptoms of irritable bowel syndrome.,
Modulates and alters gastrointestinal microflora to offset
abnormal conditions.

21. Bifidobacterium breve Promotes and boosts the production of anti-rotavirus IgA
Oxalobacter formigenes
Lactobacillus and
Bifidobacterium species
Metabolic and mopping up action on toxic compounds.
Lactobacillus acidophilus
NCFM
Minimizes risks associated with type 2 diabetes mellitus
and enhances host metabolic system ensuring weight
management
Probiotic Strain Mechanism of Action
Lactobacillus,
Bifidobacterium
Epithelial and mucosal cells are competitively colonized.
Production of bacteriocins and organic acids to impede
action of the bacteria.
Continued….

22. Acidophilus milk
 Lactobacillus acidophilus is used as a starter culture.
 For the production, milk is heat processed at 95°C and goes through
homogenization. Then cooled to 37°C and inoculated with 2-5%
commercial L. acidophilus pure culture and left for incubation for 12-24
hours.
 After, milk is cooled to 5°C and kept under cold conditions.
 It is beneficial to people with diarrhea and intestinal gas problems.
Probiotic fermented milk products

23. Bifidus milk
 The first infant product produced with Bifidobacteria.
 In the process, milk is standardised and homogenised and kept at 80-120
°C for 5-10 minutes.
Then, 10% bifidobacteria starter culture (Bifidobacterium bifidum and
Bifidobacterium longum) is inoculated to milk and the milk is left for
incubation at 37°C until coagulation.
 Once it reaches to a pH value of 4.3-4.7, incubation is ended.
 Bifidus milk is easy to digest and is still used for the treatment of
gastrointestinal and liver diseases and for constipation
Continued….

24. Yakult product:
 Yakult is a probiotic milk product that is produced using L. casei Shirota
strain.
 This strain is resistant to gastric and duedonal acid, can populate and
form antimicrobial substances in small intestine and
 Has the ability to enhance the activity and quantity of macrophages.
 It is demonstrated to be beneficial for health and is on the market in 15
different countries including European countries.
Continued….

25.  There are currently 12 genera of lactic acid bacteria, of which :-
 Lactobacillus
 Streptococcus
 Lactococcus and
 Leuconostoc are commonly found in dairy starter
cultures.
 A fifth genus Enterococcus is occasionally found in
mixed-strain (undefined) starter cultures (Taylor &
Francis, 2006).
Taxonomy of LAB

26. Leuconostocs
 All Leuconostocs specie are capable of producing lactic acid, CO2 and
aromatic compounds (ethanol and acetic acid) from glucose.
 These organisms are normally used along with lactic acid bacteria
(LAB) in multiple or mixed strain cheese starter cultures, which produces
flavour compounds.
 Leuconostoc cremoris
 Leuconostoc citrovorum
 Leuconostoc dextranicum
 Leuconostoc spp. are distinguished from other lactic acid bacteria by being
mesophilic heterofermentative cocci (Abdel, 2017).
Identification of Lactic acid Bacteria

27.  The streptococcus is classified as a thermophile growing at 45°C, and
higher.
 widely used in the production of yoghurt and some types of cheese such
as Mozzarella cheese.
 Streptococcus thermophilus is the only species of this genus found in
starter cultures.
 It is a component, along with lactococci, in some DVI / DVS cultures in
which it produces acid rapidly during scalding.
 Streptococcus thermophilus is sensitive to low levels of salts and in
particular to sodium chloride concentrations of around 2% (Abdel, 2017).
Streptococcus
Continued….

28.  Lactobacillus genus is composed of a large group of:-
Gram positive
Rod-shaped bacteria.
Some species are homofermentative while others are
hetrofermentative.
 Lactobacillus delbrueckii subsp. bulgaricus is widely used
along with Streptococcus thermophilus as a starter in yoghurt
production (Abdel, 2017).
Lactobacillus
Continued….

29.  Lactobacillus acidophilus, typically present in the digestive
system, it is widely used as a probiotic.
 Lactobacilli are the most acid tolerant of the lactic acid bacteria,
preferring to initiate growth at acidic pH (5.5–6.2) and lowering
the pH of milk to below 4.0.
 Lactobacilli are slow to grow in milk in pure culture.
For this reason, they are generally used in combination with S.
thermophilus.
Continued….

30.  Major mesophilic microorganisms used for acid production in dairy
fermentations.
 Five species are recognized, only one, Lc. lactis, is of significance in dairy
fermentations.
The most perceived habitat for the lactococci is dairy products. They are:-
 Non- motile
 Coccu- shaped
 Homofermentative bacteria that
 Grow at 10 ° C but not at 45° C
 The utilization of lactococci is widespread and has the longest convention in
industrial starter culture technology.
 Strains of Lc. lactis produce nisin, which is a relatively wide range
bacteriocin (Abdel, 2017).
Lactococcus
Continued….

31. Common Genera of LAB and Their Characteristics (Tayler, 2019)
Continued….

32.  Starter culture is a concentrated preparation of live cells that
is added to a raw material to initiate fermentation rapidly.
 Starters are grouped under different categories based on:-
 Composition of microflora
 Growth temperature
 Flavor production and
 Type of fermentation
SUMMARY

33.  Stages in the process starter culture.
Continued….

34.  The probiotic is, as "A live microbial feed supplement which beneficially
affects the host animal by improving its intestinal balance".
 The most commonly used probiotics generally come from the genera
Lactobacillus and Bifidobacterium.
There are currently 12 genera of lactic acid bacteria, of which four-
 Lactobacillus
 Streptococcus
 Lactococcus
 Leuconostoc are commonly found in dairy starter cultures.
A fifth genus, Enterococcus, is occasionally found in mixed-strain
(undefined) starter cultures.
Continued….

35. Thank you
very much!!!!