Microbiology & food safety of Yogurt

SUDHANSHU DHAWAN

SHAMIM AHAMED KHAN

FIREW AMSALU

KARTHIKEYAN NANJAPPAN

ASHFAQ HUSSIAN GHULAM

Contents1. Definition

2. Metabolism of LAB

3. Interactions of LAB in yoghurt production

4. Starter cultures

5. Precautions during yoghurt production

6. HACCP plan for yoghurt production

7. Legislation

8. Economic aspects

Definition• Yoghurt:

– A fermented milk, obtained by a simultaneous operation of L. bulgaricus and S. thermophilus and in witch the two specific cultures remains active (= living) until consumption.

• contains other lactic acid bacteria for taste or health effects Lactobacillus acidophilus, L. casei

Bifidobacterium sp. • LAB are crucial to intense and rapid acidification of milk.

• Homolactic fermentation of glucose:– Embden-meyerhof pathway (Glycolysis)– Lactic acid as end-product– 2 moles of lactic acid – Net gain of 2 ATP/molecule glucose

• Heterolactic fermentation of glucose:– 6-phosphogluconate/phospho-ketolase pathway – other end products, in addition to lactic acid, such as

ethanol, acetate and CO2

– 1 mole of lactic acid, ethanol and CO2

– Net gain of 1 ATP/ molecule glucose

Metabolism of LAB

Metabolic characteristics of LAB (contd..)

• fastidious micro-organisms

• L. bulgaricus: – Break down of proteins into peptides and aminoacids– creates body– production of acetaldehyde

• S. thermophilus– production of pyruvic acid, formic acid and co2– weakly proteolytic

• production of polymers

• protocooperation of LAB - bacterial growth and - production of lactic acid and aroma compounds.

Interactions of LAB during yoghurt production

Starter cultures• Are bacteria, yeast and moulds or their combination.

• Initiate and carry out desired fermentation

• Cause specific changes in appearance, body , flavour and texture.

• Functions:

– flavour, aroma, and alcohol production – proteolytic and lipolytic activities – inhibition of undesirable organisms.

Starter cultures (2)• Two main types, divided by their optimum growth temperature:

1. Mesophilic starters :

– growth in temperatures of 10-40°C ; optimum: 30°C

– used in the production of many cheese varieties, fermented

milk products and ripened cream butter

– Examples for mesophilic starter organisms• Lactococcus lactis spp. Lactis• Lactococcus lactis spp. lactis var. diacetylactis• Lactococcus lactis spp. Cremoris• Leuconostoc lactis• Leuconostoc cremoris

2. Thermophilic starters :

– optimum growth temperature between 40°C and 50°C

– used for yogurt and for cheese varieties with high cooking

temperatures

Examples • Lactobacillus delbrueckii spp. bulgaricus • Streptococcus salivarius spp. thermophilus.

Precautions during yoghurt production Adding culture to very hot milk (+115°F) can kill bacteria

Too hot or too cold of an incubation temperature can slow down culture growth--Use a thermometer to carefully control temperature

If the starter culture is of poor quality then coagulation will be delayed--Use a fresh, recently purchased culture from the grocery store each time you make yogurt

If the starter culture is contaminated then the yoghurt will give odd smell--Obtain new culture for the next batch

Yogurt has over-set or incubated too long--Refrigerate yogurt immediately after a firm coagulum has formed. Overheating or boiling of the milk causes an off-flavor--Use a thermometer to carefully control temperature.

Process step

Raw material & other inputs Process step hazards and/or potential impact of process step on existing hazards

Q1. Is the hazard at unacceptable levels?

Q2. Control measure available?

Component Hazards(B – biologicalC – chemicalP – physical)

Y/N Justification

1. Farm dairycollection (thismay beincluded in thefarm PSP)

Raw milk B – Non-spore pathogens fromcow, e.g. Salmonella, Listeria,E. coli, Mycobacterium bovis(TB)

B – Similar pathogens from milkhandler, equipment, shed, pests

Y

N

Some pathogens expected in raw milkPersonal, equipment and shed hygieneWater quality programmePest management programme

See pasteurisation step for available control measuresSee supporting systemsMicrobiological tests (frequency?)

B – Spore forming pathogensfrom cow, e.g. Clostridiumperfringens, Clostridiumbotulinum

Y Some spores expected in raw milk

See steps for cheese processing for control, e.g. acidification, aerobicstorage/temperature control

B – Mycotoxins from cow

N Diet controlled Animal health program

HACCP PLAN FOR YOGHURT PRODUCTION

Process step

Raw material & other inputs Process step hazards and/or potential impact of process step on existing hazards

Q1. Is the hazard at unacceptable levels? Q2. Control measure available?

Component Hazards(B – biologicalC – chemicalP – physical)

Y/N Justification

1. Farm dairycollection (thismay beincluded in thefarm PSP)

C – Chemical residues fromcow, e.g. antibiotics, pesticides,heavy metals

YN

Untested milkTested milk – minimal residue violations by national monitoring programme

On-farm tests Animal health programmeSee testing programme for chemical residues

C – Chemical residues fromcleaning: milk handler orequipment, environment; Pests

N Cleaning programmeChemical controlPersonal hygienePest management programme

See supporting systemsFarm Dairy PSP

P – jewellery, nail polish, bristles,metal, rubber, plastic: milkhandler, equipment, environment

N Personal hygieneMaintenance programme

On line filter plus maintenanceSupporting systems

contd...

• Milking animals that ingest aflatoxin B1 (AFB1) by

contaminated diets, excrete the 4-deoxylated

metabolite aflatoxin M1 (AFM1) into milk with a

proportion of 1-3%

• The Commission set limit for AFB1 of 5 μg/kg for

supplementary feedstuffs for lactating dairy cattle (European

Commission, 1991)

tolerance level is difficult to be observed

• to produce bulk milk <50 ng AFM1 per kg = the daily

average individual intake in a herd is <40 μg AFB1 per cow

LEGISLATION

• Aflatoxins in milk are stable during heating treatments

i.e. pasteurization and sterilization

• Variation of pH during fermentation (yoghurts,

cheeses)cause coagulation of proteins that adsorb or

occlude the toxins

Economic aspects

• As the fat content cannot be fully differentiated correctly by all persons, it is better to prepare yoghurt with relatively low fat content yoghurt so that they can reduce the cost of the yoghurt

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