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LECTURE PLAN

HISTORICAL CONSIDERATIONS

PRESENT SITUATION

Production data

I GENERAL CONSIDERATIONS ON YOGHURTS MANUFACTURE

II YOGHURTS QUALITY

III KEY POINTS ABOUT YOGHURTS

MANUFACTURE PROCESSES

III.1 - MIXES (CULTURE MEDIUM) PREPARATION

III.2 - FERMENTATION PROCESS

III.3 - COOLING – MECHANICAL TREATMENTS

III.4 - FROM PACKAGING TO COLD STORAGE

III.5 – CLEANING IN PLACE – PROCESS

AUTOMATION

IV CONCLUSIONS

-T 3

HISTORICAL CONSIDERATIONS

_____________________________________________

è APPARITION 8 000 TO 10 000 YEARS AGO (MESOPOTANIA, EGYPT, INDIA, NORTH-EAST OF AFRICA)

Ä LINKED TO ANIMALS DOMESTICATION

Ä A WAY OF MILK PRESERVATION

Ä IMPORTANT BENEFITS FOR HUMAN HEALTH

AND NUTRITION

è CENTURIES AND CENTURIES OF TRADITIONAL HANDICRAFT MANUFACTURE … ACCORDING TO PEOPLE'S TRADITIONS AND ENVIRONNE- MENTAL CONDITIONS

(MORE THAN 400 GENERIC NANES ;

NOT ONLY BASED ON LACTIC FERMENTATION)

è LARGE SPREADING OVER ALL THE WORLD

-T 4

PRESENT SITUATION

__________________________________________________

è INDUSTRIALISATION OF THE YOGHURT MANUFACTURE IS 30 TO 40 YEARS OLD

è LARGE MULTINATIONAL COMPAGNIES ARE INVOLVED

è A LOT OF YOGHURT TYPES AVAILABLE ACCORDING TO CONSUMERS DEMAND

è WELL ESTABLISHED MANUFACTURING

PROCESSES ð BETTER QUALITY CONTROL

ð PROCESS PRODUCTIVITY

IMPROVEMENT

è RESPECT OF THE REGULATIONS ESTABLISHED BY EACH DIFFERENT COUNTRY

-T 5

LACTIC ACID FERMENTATION

______________________________

LACTOSE

STARTER CULTURE

LACTIQUES

GALACTOSE

GLUCOSE

LACTIC ACID

AROMA

COMPOUNDS

TEXTURING

COMPOUNDS

Þ Symbiotic cultures : Streptococcus

thermophilus and Lactobacillus bulgaricus

Þ Galactose accumulation,

glucose utilisation

Þ The accumulation of the lactic

acid leads to an acidification of

the mix (pH decrease)

Þ Milk coagulation when pH ~ 5.2

Þ Production of aroma COMPOUNDS (acetaldehyde) and of texturing

compounds (E.P.S.)

-T 6

FRENCH YOGHURT DEFINITION

__________________________________________________

è THE FRENCH REGULATION FIXED THE CONCENTRATION OF :

ÄLACTIC ACID ³ 7.0 g/l

ÄALIVE THERMOPHILIC LACTIC BACTERIA ³ 10⁷b/g

(only Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus are allowed)

ÄADDITIVES £ 30% w/w

(fruits, sugar, flavouring agents)

è OTHERS INDICATIONS MUST BE GIVEN :

ÄFAT CONTENT

ÄMILK ORIGIN (ANIMAL)

ÄNATURE OF ALL THE ADDITIVES

Ä STORAGE TEMPERATURE

Ä MAXIMUM STORAGE TIME

è EXCEPT FOR SUGAR, ALL "MIXES" COMPONENTS MUST COME FROM MILK

-T 7

TYPES OF YOGHURTS AVAILABLE

________________________________

1) TEXTURE

ð SET TYPE YOGHURTS

ð STIRRED TYPE YOGHURTS

ð DRINKING YOGHURTS

2) FAT CONTENT

ð LOW FAT

ð MEDIUM FAT

ð FULL FAT

3) FLAVOR

ð PLAIN (NATURAL) YOGHURTS

ð FRUIT ADDITION

ð FLAVOURED YOGHURTS

4) DIVERSIFICATION IN PRODUCTS AND MANUFACTURING CONDITIONS

ð VEGETABLE OILS ADDITION

ð HEAT TREATMENT

ð VITAMIN FORTIFICATION

ð ENZYME HYDROLYSIS

-T 9

SIMPLIFIED YOGHURT MANUFACTURE

FLOW-SHEET

__________________________________________________

3 MAIN STEPS CAN BE DEFINED :

1) PREPARATION AND PHYSICAL

TREATMENTS OF THE MIXES

2) Ö INOCULATION OF THE MIX

Ö LACTIC ACID FERMENTATION

(INCUBATION IN CUPS OR IN TANKS)

3) COOLING, FILLING, PACKAGING*

AND COLD STORAGE

-----------------------------------------------------------------

*FOR SET YOGHURTS FILLING AND PACKAGING

ARE DONE BEFORE FERMENTATION.

THEIR INCUBATION IS DONE IN WARM ROOMS

T 10

MAIN YOGHURT QUALITY CRITERIA

___________________________________________

1) ORGANOLEPTIC EVALUATION

ð ACIDITY

CONSUMERS ARE SELECTING "NON ACID" YOGHURTS

ð TEXTURE

Ÿ KEY PARAMETRE (PIECES OF FRUIT

HOMOGENITY INTO THE BULK)

ŸON SPOON AND IN MOUTH APPRECIATION

ð FLAVOR

THE "YOGHURT TASTE" (BASED ON ACETALDEHYDE) IS VERY COMPLEX

2) OTHERS FACTORS

ð NO SYNERESIS

EXUDATION OF WHEY IS BADELY APPRECIATED BY

THE CONSUMERS

ð GEL HOMOGENITY

MICROSTRUCTURE, GRANULARITY

ð COLOUR

-T 11

METHODS FOR

YOGHURT QUALITY

DETERMINATION

______________________

ACIDITY

Ÿ pH

Ÿ LACTIC ACID CONTENT

ð MEASUREMENT AS A FUNCTION OF :

* FERMENTATION TIME,

* STORAGE TIME (POST-ACIDIFICATION)

ACIDIFICATION RATE (STARTER + PROCESS

PROPERTIES)

Ÿ THE CINAC SYSTEM

* pH = f (TIME)

* dpH/dt = f (TIME)

* KEY DESCRIPTORS :

- Vm : MAXIMUM ACIDIFICATION RATE

- Tm : TIME TO OBTAIN Vm

- pHm : pH CORRESPONDING TO Vm

- TpHi : TIME TO REACH A CERTAIN pHi

-T 12

METHODS FOR

YOGHURT QUALITY

DETERMINATION

_____________________

è A LOT OF MORE OR LESS EMPIRICAL METHODS

· POSTHUMUS FUNNEL

· BROOKFIELD (LARGE INDUSTRIAL UTILISATION)

· BOSTWICK CONSISTOMETER

è TEXTURE (FIRMNESS CARACTERISATION)

· PENETROMETRY

· ROPINESS ASSESSEMENT

è RHELOGICAL BEHAVIOUR

· OSCILLATORY MEASUREMENTS ON A CONE/PLATE INSTRUMENT

· OBTENTION OF THE CHANGE OF COMPLEX VISCOSITY VERSUS STRESS INCREASE

-T 13

METHODS FOR

YOGHURT QUALITY

DETERMINATION

_________________________________________

ANALYSIS OF FLAVOUR COMPOUNDS

· GAS CHROMATOGRAPHY

(+ MASS SPECTROMETRY)

· LIQUID CHROMATOGRAPHY

· COLORIMETRIC TESTS

è4 MAIN CATEGORIES OF COMPOUNDS :

· CARBONYL COMPOUNDS (ACETALDEHYDE, ACETON, ACETOÏN, DIACETYL)

· NON-VOLATILE ACIDS (LACTIC, PYRUVIC, OXALIC)

· VOLATILE ACIDS (FORMIC, ACETIC, PROPIONIC)

· SOME AMINO ACIDS

è ACETALDEHYDE IS THE KEY COMPOUND

(2 TO 75ppm)

· INCREASE IN MIXED CULTURES

· DECREASE DURING STORAGE

· MOST OF THE OTHER COMPOUNDS MUST BE PRESENT

-T 14

METHODS FOR

YOGHURT QUALITY

DETERMINATION

SOME OTHER QUALITY CRITERIA

è MICROBIOLOGICAL COMPOSITION

· GOOD AMOUNT OF ALIVE LACTIC BACTERIA

· AVOID CONTAMINANT FLORA

è COLOUR – COLORIMETRY

· WHITE COLOUR (NATURAL YOGHURTS)

· "FRUIT" COLOUR/FLAVOUR COLOUR

è GEL HOMOGENITY

· AVOID BUBLES AND GRANULAR COAGULUM

è SYNERESIS = VOLUME OF WHEY OBTAINED AFTER SOME DAYS

· LIMIT WHEY EXUDATION AND INCREASE WATER-BINDING CAPACITY

-T 15

METHODS FOR

YOGHURT QUALITY

DETERMINATION

SENSORY ANALYSIS

· EXPERTS TRAINED PANEL (10-20 PEOPLE)

· CONSUMERS TRAINED PANEL (100 PEOPLE)

è VERY TIME CONSUMING AND EXPANSIVE

è AGREEMENT AND TRAINING ON TEST METHODS AND SPECIFIC TERMINOLOGY (YOGHURT ATTRIBUTES)

è HOW TO SELECT ONLY A FEW NUMBER OF KEY ATTRIBUTES

-T 16

CULTURE MEDIUM (MIX) PREPARATION

___________________________________________

1) COMPOSITION OF THE MIXES

Ü GENERAL RULE

ð UTILISATION OF A MILK BASE

ð FAT CONTENT STANDARDISATION

ð PROTEIN ENRICHMENT

Ÿ MILK AND/OR CASEINE POWDER ADDITION

Ÿ CONCENTRATION (EVAPORATION, U.F.)

Ÿ NON-MILK PROTEINS ARE NOT ALLOWED

IN ALL COUNTRIES

Ü FRUIT/FLAVOURED YOGHURTS

ð ADDITION OF PIECES OF FRUIT

ð ADDITION OF SUGAR OR SWEETENING AGENTS

ð ADDITION OF FLAVOURING AGENTS

-T 17

CULTURE MEDIUM (MIX) PREPARATION

___________________________________________

Ü OTHER YOGHURTS

ð ADDITION OF OTHERS ADDITIVES (WITH POSSIBLE

RESTRICTIONS COUNTRY BY COUNTRY)

Ÿ STABILIZERS/EMULSIFIERS (POLYSACCHARIDES)

Ÿ VITAMINS (A, C ….)

Ÿ VEGETAL FAT, FATTY ACIDS

Ÿ PRESERVATIVES (SORBIC AND BENZOIC ACIDS,

SULFUR DIOXYDE)

Ÿ MINERAL CONTENT MODIFICATION (Mg²⁺, Fe²⁺, Ca⁺)

Ÿ FOOD COLOURANTS (10 - 15 COLOURANTS)

-T 18

CULTURE MEDIUM (MIX) PREPARATION

___________________________________________

2) PHYSICAL TREATMENTS OF THE MIXES

2.1 – HOMOGENISATION

ð TO OBTAIN A FAT-IN-WATER EMULSION

(NO FAT LAYER AT THE TOP OF THE YOGHURT)

CONDITIONS	CONSEQUENCES ON YOGHURT
	VISCOSITY	ARE IMPROVED
150 - 200 bars	SYNERESIS
60 - 70 °C	WHITE COLOUR
60 - 70 °C	MICRO STRUCTURE

T 19

CULTURE MEDIUM (MIX) PREPARATION

___________________________________________

2.2 – HEAT TREATMENT

ð "HIGH PASTEURISATION" (95°C – some minutes)

ð "LOW PASTEURISATION" (80°C <) AND UHT TREATMENT ARE LESS EFFICIENT

ð EFFECTS : Ÿ DESTRUCTION OF MICROORGANISMS

Ÿ WHEY PROTEINS DENATURATION

Ÿ INCREASE GEL CONSISTENCY AND

STABILITY

ð THE FERMENTATION TEMPERATURE (40-45°C) IS FIXED AT THE OUTSIDE OF THE HEAT EXCHANGER

T 19b

EFFECT OF HOMOGENISATION AND HEAT TREATMENT ON THE CONSISTENCY/VISCOSITY OF YOGHURT

Heat treatment of milk for 30 min at

Measurement of consistency/visco sity of yoghurt	70°C		78°C		86°C		95°C
Measurement of consistency/visco sity of yoghurt	H	NH	H	NH	H	NH	H	NH
Falling sphere ^a(depth, cm) Posthumus FUNNEL ^b (time, s)	3.0	>15.0	1.5	10.5	1.2	6.0	1.2	2.7
	9.0	5.0	14.0	7.5	17.0	8.5	18.7	9.0

a) Falling sphere : the deeper the sphere sinks into

the yoghurt, the thinner is the product.

b) Posthumus funnel : the longer the time required for

the yoghurt to pass through the funnel, the more viscous is the product.

h : HOMOGENISED MILD – NH : NON-HOMOGENISED MILK

(From TAMIME, 1999)

-T 21

FERMENTATION PROCESS

_______________________

3) MIXED CULTURES PROPERTIES

· IMMEDIATE ACIDIFICATION · IMPORTANT AND FAST BACTERIA GROWTH · RAPID AND LONG-TIME ACIDIFICATION		CONTROL OF FERMENTATION LENGTH

· SMALL (OR NONE) POST ACIDIFICATION (COOLING, PACKAGING, STORAGE) · SUITABLE TEXTURE AND VISCOSITY · GEL RESISTANCE TO MECHANICAL DESTRUCTURATION · APPROPRIATE FLAVOUR		CONTROL YOGHURT QUALITY

-T 22

FERMENTATION PROCESS

_______________________

B - FERMENTATION IMPROVEMENT

è MODIFICATION OF THE STRAINS INVOLVED IN THE STARTER

· INTRODUCTION OF NEW STRAINS WITH KNOWN PROPERTIES

· OTHER RATIO OF THE SAME STRAINS

è MODIFICATION OF THE STARTER PRESENTATION AND/OR INOCULATION AMOUNT

è OPTIMISATION OF THE YOGHURT MANUFACTURE CONDITIONS

-T 23

FERMENTATION PROCESS

_______________________

PROCESS MONITORING

è TEMPERATURE CONTROL IS QUITE IMPOSSIBLE :

· FIXED BY THE OUTSIDE TEMPERATURE OF HEAT TREATMENT

· A VERY "HEAT SENSIBLE" PROCESS

è pH AND ACIDIFICATION RATE ARE KEY PARAMETERS

· pH ON-line MEASUREMENT IS NOT AVAILABLE

· THE CONCEPT OF ACIDIFICATION RATE IS NOT YET POPULAR

è FERMENTATION END-TIME INITIATE THE COOLING STEP

· STRONG EFFECT ON YOGHURTS QUALITY

· DEFINED FROM pH MEASUREMENTS AFTER SAMPLING

-T 24

FERMENTATION PROCESS

FUTURE INNOVATIONS IN PROCESS MONITORING

1) INDIRECT pH MEASUREMENT

· pH CLASS PROBES ARE NOT ALLOWED

· ELECTRICAL CONDUCTIVITY METHOD

· THERMAL METHOD

2) PREDICTION OF FERMENTATION

END-TIME

· PREDICTION OF pH DECREASE VERSUS FERMENTATION TIME

3) OPTIMISATION OF YOGHURT QUALITY

SEE CONCLUSION

T 25

COOLING

_____________________________

è TWO TYPES OF PROCESSES FOR :

ÄSET YOGHURT

ÄSTIRRED YOGHURT

è SET YOGHURT

ÄSMALL UNITS : WATER BATH OR CABINETS

ÄLARGE UNITS : ROOMS INCUBATION TEMPERATURE,

AND TUNNELS (WARM AND CHILLED)

· AIR TEMPERATURE CONTROL, AIR CIRCULATING

CONDITIONS, AND COOLING CAPACITY ARE IMPORTANT

è STIRRED YOGHURT

ÄAGITATION IN TANK AND CONTINOUS COOLING

(HEAT EXCHANGERS)

· RAPID COOLING

IMPORTANT SHEAR STRESS

(MIXER, PIPES, PUMPS, EXCHANGER…)

COAGULUM

DESTRUCTURATION (LOSS OF VISCOSITY)

-T 26

PACKAGING

______________________________

1) MAIN FUNCTIONS OF PACKAGING :

ë PROVIDE PROTECTION

ë BRING A MESSAGE TO THE BUYER

ë FACILITATE THE HANDLING

2) TWO STAGES FOR PACKAGING :

ë SET YOGHURT : BEFORE FERMENTATION

(LOW VISCOSITY)

ë STIRRED YOGHURT : AFTER FERMENTA-

TION AND PRECOOLING (HIGH VISCOSITY)

-T 27

PACKAGING

___________________________

3) TWO KINDS OF PACKAGING EQUIPMENT :

ë FILL – SEAL TECHNIQUE (FS)

ë FORM – FILL – SEAL TECHNIQUE (FFS)

4) PACKAGING EQUIPMENT CHARACTERISTICS:

ë MECHANICALLY SOPHISTICATED

ë FULLY AUTOMATION

ë CLEAN, ULTRACLEAN OR ASEPTIC

MACHINES

ë VERSATILY (FLAVOR, SIZE, PRODUCT

PRESENTATION)

ë IMPORTANT INVESTMENT

-T 28

OVER PACKAGING – PALLETISATION –

COOLING – STORAGE

_____________________________________

è OPERATIONS FULLY AUTOMATED IN LARGE PLANTS

è FIVE STEPS :

· PLACEMENT OF YOGHURT CUPS IN CARDBOARD TRAYS

· PALLETISATION OF THE TRAYS

· COOLING OF THE PALLETISED YOGHURTS (CHILLED TUNNEL)

· PLASTIC OVERWRAPPING OF THE COOLED PALLETISED YOGHURTS

· COLD STORAGE (4°C) BEFORE DISTRIBUTION AND RETAILING

è THE LOW TEMPERATURE CHAIN MUST BY RESPECTED TO OBTAIN HIGH QUALITY AND SAVE YOGHURTS

-T 29

CLEANING – IN – PLACE (C.I.P.)

è GENERALISED PROCEDURE : MANUAL WASHING HAS DISAPPEARED

è PLANTS AND MACHINES ARE DESIGNED TO ALLOW C.I.P.

è MAIN AGENTS/ACTIONS

· HEAT TREATMENT (STEAM)

· CHEMICAL AGENTS (DETERGENTS, SURFACE ACTIVE, STERILISING…)

· MECHANICAL ACTION (PRESSURE, FLOW RATE)

· WATER (ONLY FOR RINCING).

-T 30

PROCESS AUTOMATION

è INDUSTRIAL PLANTS ARE LARGELY AUTOMATED

· CONTROL LOOPS (TEMPERATURE, FLOW RATE, WEIGHT…)

· SEQUENTIAL MONITORING (INCLUDING C.I.P.)

· PROCESS SUPERVISION WITH KEY DATA

è OPTIMAL QUALITY CONTROL DOES NOT EXIST : SOME STRATEGIC DECISIONS ARE ON THE OPERATOR RESPONSABILITY

BENEFITS	DRAWBACKS
ð SECURITY ð PRODUCT TRACEABILITY ð LABOR COST REDUCTION ð CENTRALISED INFORMATION	ð EXPENSIVE ð SPECIFICITY ð POOR FLEXIBILITY