Growth and Survival of microorganism during manufacturing and storage of condensed milk

1. GROWTH AND SURVIVAL OF
MICROORGANISMS DURING
MANUFACTURING & STORAGE
OF CONDENSED MILK
MICROBIOLOGY OF DAIRY
PRODUCTS(DM-2204)
SAHLA PARVIN MK
18-BDP-013

2. CONTENTS
❖ INTRODUCTION
❖ MICROBIOLOGICAL QUALITY OF CONDENSED MILK
❖ TYPES OF MICROFLORA
❖ FACTORS AFFECTING MICROBIOLOGICAL QUALITY OF
CONDENSED MILK
❖ PATHOGEN ; GROWTH & SURVIVAL
❖ MICROBIOLOGICAL DEFECTS IN CONDENSED MILK
❖ REFERENCE

3. INTRODUCTION
Concentrated milk is produced for direct sale to the consumer, but are
particularly important as food ingredients, providing a source of milk solids in
a variety of other products. The removal of water from fresh milk gives
advantages in terms of reduced storage and transport costs, convenience in
use, and, in some cases, a useful extension to shelf life. Concentrated milk is
intended to be reconstituted by the consumer, by dilution with water, to give a
similar composition to that of fresh milk. The keeping quality is limited
because it is not sterilised during or after processing

4. MICROBIOLOGICAL QUALITY OF SWEETENED CONDENSED MILK
➢ With modern processing, storage, and handling practices, spoilage
seldom is encountered
➢ If the bulk product is improperly handled or held for extended
periods before use, surface growth of yeasts or molds may occur
➢ The oxygen present in the headspace of incompletely filled or
poorly sealed containers may offer chances of proliferation of
organisms
➢ The presence of these microorganisms is indicative of unsanitary
post-pasteurization conditions

5. TYPES OF MICROFLORA
❏ Micrococci: M. varians, M. candidus, M. luteus, M. freudenreichii
❏ Staphylococci: S. aureus, S. epidermidis
❏ Coliforms: E. coli, Proteus sp., Enterobacter aerogenes (present in
low nos.)
❏ Aerobic spore-formers: B. subtilis, B. stearothermophilus, B.
mycoides, B. mesentericus
❏ Anaerobic sporeformers: C. butyricum, C. sporogenes, C. welchii
❏ Streptococci: S. faecalis, S. faecium
❏ Other groups: Pseudomonas sp., Serratia marcescens
❏ Yeasts and Molds: Saccharomyces, Candida, Torulopsis,
Rhodotorula, Aspergillus, Penicillium

6. FACTORS AFFECTING
MICROBIOLOGICAL QUALITY OF
CONDENSED MILK

7. Milk:
➢ The quality of raw milk determines the microflora in the finished product
➢ The raw milk used should usually be of manufacturing grade
Sugar:
➢ It should not contain osmophilic yeasts, mold spores and bacteria producing acid
and gas
➢ The standards for sugars should be total colony count (100), yeasts (nil) and
molds (10)
➢ Sugar should be stored at dry place free from dust, insects and rodent
contamination
1) QUALITY OF RAW MATERIALS

8. Skim Milk Powder:
➢ Skim milk powder is sometimes used for standardization of milk
before condensing operations
➢ Sometimes they may have some heat-resistant micrococci and
streptococci
➢ To reduce the counts, skim milk is subjected to high
temperatures

9. Pre heat treatment:
➢ The temperature used in pre-heat treatment kills all spoilage and
pathogenic microbes with exception of heat resistant proteases and
lipases as a result of growth of microorganisms
Holding in the hot-well:
➢ The development of viscosity of SCM subsequently during storage is
influenced by the time-temperature combination
➢ The surviving organisms would be mostly sporeformers as pre-heat
treatment has destroyed all heat-labile organisms
2) PROCESSING TIME & TEMPERATURE CONDITIONS

10. Addition of sugar
➢ Sugar should not be added to milk before preheating because it increases
the resistance of microorganisms
Super heating
➢ This process enables to obtain desired viscosity of the product
Condensing
➢ Milk and sugar mixture is subjected to vacuum operation in a vacuum pan at
52.7C at which it boils
➢ The vacuum pan may act as a source of contamination for the product
➢ The sticky nature of product increases the difficulty in cleaning and may also
become potential source of problem

11. Finishing and Seeding
➢ When the condensation is over, the vacuum in the pan is broken.This process
is called finishing
➢ Over-condensation can be done and adjust the composition by adding sterile
water or under-condensed milk
➢ Such a process is prone to post-contamination
➢ Seeding is the process of providing nuclei for the development of lactose
crystals
➢ It can be done either by adding sterilized lactose or good quality condensed
milk from a previous batch

12. Sterility of cans
➢ Cans used for filling should be sterilized before use
➢ The cans must be filled as possible to minimize head space, otherwise
if aerobic microorganisms if any present, may grow and cause defects
➢ Imperfect seals or can damage may permit the entry of microorganisms
Sterility of equipments
➢ The equipment used should be sterilized by use of chlorine, steam or
other sterilants
➢ The pipelines, filling machines should be washed, cleaned and
sterilized

13. Storage conditions
➢ The keeping quality of SCM is chiefly dependent upon the
concentration of sugar, total solids and the degree of destruction of
organisms
➢ The shelf-life of SCM is considerably longer even if allowed to stand
at open conditions
➢ SCM lacks sterility and micrococci, spore-formers and yeasts and
molds predominate

14. SPOILAGE IN CONDENSED MILK
★ Unsweetened condensed milks are not commercially sterile, and so,
are favourable media for microbial growth
★ Spoilage can be caused by heat-resistant organisms from raw milk,
for example Bacillus spp. and enterococci, or by post-process
contaminants, such as pseudomonads and members of the
Enterobacteriaceae
★ As long as the product is handled and stored correctly (<7 °C) only
thermoduric and thermophilic organisms will grow slowly

15. ★ Shelf-life varies from a few days to weeks, depending on the degree of
contamination, the severity of the heat treatment applied, and the
effectiveness of temperature control during cooling and storage
★ The pattern of spoilage is very similar to that described for pasteurised
fresh milk, although organisms adapted to slightly lower aw values may
have an advantage

16. SPOILAGE IN SWEETENED CONDENSED MILK
★ The low water activity (0.85) of sweetened condensed milks ensures that
only osmophilic and osmotolerant organisms are able to grow
★ Canned products may be spoiled by slow growth of osmophilic yeasts,
particularly Torulopsis spp., which enter the product after heating and may
produce sufficient gas to cause blown cans
★ If sufficient oxygen is present in the headspace, or the can has a small
pinhole leak, moulds such as Aspergillus and Penicillium spp. may grow as
'buttons' on the surface of the product

17. ★ Bulk products with lower sugar concentrations are more susceptible to
spoilage
★ Mould growth may occur on the surface of stored milk. Again,
Penicillium and Aspergillus are the main genera involved
★ Occasionally, bacterial spoilage by osmotolerant micrococci and Bacillus
spp. may occur in these products, causing thickening, and eventually,
lipolysis and proteolysis

18. PATHOGEN : GROWTH & SURVIVAL
➢ Concentrated milks are not normally regarded as high-risk
products, principally because of the relatively severe heat
treatments used in their manufacture
➢ As with other pasteurised and UHT processed milks, the main
concern for condensed and evaporated milk is post
heat-treatment contamination by pathogens

19. Listeria spp
➢ Listeria monocytogenes are present in condensed milk
➢ The organism declined during storage in sweetened condensed
milk at 21 °C, but the population remained stable at 7 °C

20. Clostridium spp
➢ A study of the incidence of clostridia in sweetened condensed milk
showed that about 40% of the samples contained >100 cfu/100 g
➢ These contaminants were identified mainly as Clostridium butyricum and
Clostridium perfringens
➢ However, the water activity of these products is too low to allow the
germination of spores and vegetative cell growth

21. Staphylococcus aureus
➢ Although there are no reported cases of foodborne disease associated with
canned sweetened condensed milk
➢ Its water activity (aw) of 0.85 is very close to the minimum value that
would allow Staphylococcus aureus to grow, although toxin production
would be inhibited
➢ However, bulk products with much lower sugar contents might be at risk if
they become contaminated
➢ Therefore, adequate hygiene is an important control

22. MICROBIOLOGICAL DEFECTS IN
CONDENSED MILK

23. GASSY FERMENTATION
SYMPTOMS
➢ Gas or bloat may develop suddenly in the product during storage after
10 days to few weeks
➢ The other signs are high acidity, lumpiness and darkening of internal
surface of containers as well as product in contact
CAUSATIVE ORGANISM
❏ Yeasts: Torulopsis lactis condensis ,Torulopsis globosa
❏ Bacteria: Coliforms, Bacillus cereus, Clostridium butyricum

24. BACTERIAL THICKENING
SYMPTOMS
➢ Progressive thickening either due to the action of microorganisms or
due to aging on storage at room temperature
➢ The defect is accompanied by high bacterial count, disagreeable
cheesy odour and taste and an increase in acidity
➢ When the thickened product is diluted with water and heated, the curd
separates
CAUSATIVE ORGANISM
❏ Bacteria: Micrococcus pyogenes, Stap. aureus, Bacillus subtilis

25. MOLD BUTTON FORMATION
SYMPTOMS
➢ Mold buttons are lumps of variable sizes, cheesy consistency,
disagreeable taste and whitish yellow to reddish brown colour
➢ Buttons are found on the surface or subsurface layers of
product
➢ Molds grow until the availability of oxygen in headspace is
exhausted
CAUSATIVE ORGANISM
❏ Bacteria: Aspergillus repens, A. glaucus, Penicillium sp.

26. REFERNCE
➢ http://courseware.cutm.ac.in/wp-content/uploads/2020/05/3.-Microbiology-
of-Condensed-and-Evaporated-Milk.pdf
➢ http://ssu.ac.ir/cms/fileadmin/user_upload/Daneshkadaha/dbehdasht/behd
asht_imani/book/Microbiology_Handbook__Dairy_Products.pdf

27. THANK YOU