Microbiology & food safety of Yogurt
SUDHANSHU DHAWAN SHAMIM AHAMED KHAN FIREW AMSALU KARTHIKEYAN NANJAPPAN
ASHFAQ HUSSIAN GHULAM
Contents
1. 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.
Metabolism of LAB
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
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.
Two main types, divided by their optimum growth temperature: 1. Mesophilic starters :
Starter cultures (2)
growth in temperatures of 10-40C ; optimum: 30C used in the production of many cheese varieties, fermented milk products and ripened cream butter Examples for mesophilic starter organisms
Lactococcus Lactococcus Lactococcus Leuconostoc Leuconostoc
lactis spp. Lactis lactis spp. lactis var. diacetylactis lactis spp. Cremoris lactis cremoris
:
2.
Thermophilic starters
optimum growth temperature between 40C and 50C 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 (+115F) 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.
HACCP PLAN FOR YOGHURT PRODUCTION
Process step Raw material & other inputs Process step Q1. Is the hazard at unacceptable hazards and/or levels? potential impact Y/N Justification of process step on existing hazards B Similar Y pathogens from milk N handler, equipment, shed, pests Some pathogens expected in raw milk Personal, equipment and shed hygiene Water quality programme Pest management programme Q2. Control measure available?
Component
Hazards (B biological C chemical P physical) B Non-spore pathogens from cow, e.g. Salmonella, Listeria, E. coli, Mycobacterium bovis(TB)
1. Farm dairy collection (this may be included in the farm PSP)
Raw milk
See pasteurisation step for available control measures See supporting systems Microbiological tests (frequency?)
B Spore forming pathogens from cow, e.g. Clostridium perfringens, Clostridium botulinum
B Mycotoxins from cow
Some spores expected in raw milk
See steps for cheese processing for control, e.g. acidification, aerobic storage/temperature control
Diet controlled
Animal health program
contd...
Process step Raw material & other inputs Process step Q1. Is the hazard at unacceptable levels? hazards and/or potential impact of process step Y/N Justification on existing hazards Q2. Control measure available?
Component
Hazards (B biological C chemical P physical) C Chemical residues from cow, e.g. antibiotics, pesticides, heavy metals
1. Farm dairy collection (this may be included in the farm PSP)
Y N
Untested milk Tested milk minimal residue violations by national monitoring programme
On-farm tests Animal health programme See testing programme for chemical residues See supporting systems Farm Dairy PSP
C Chemical residues from cleaning: milk handler or equipment, environment; Pests P jewellery, nail polish, bristles, metal, rubber, plastic: milk handler, equipment, environment
Cleaning programme Chemical control Personal hygiene Pest management programme
Personal hygiene Maintenance programme
On line filter plus maintenance Supporting systems
LEGISLATION
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 g/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 g AFB1 per cow
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
THANK YOU
