UHT Theory LTH

Tetra PakUHT technology Seminar

LTH

PSD.TPD&B.BP.1.01, AA10

Presented by Andrzej Holanowski, PhDSenior Dairy Technologist

Tetra Pak Dairy & Beverage Systems AB

Lund, Sweden


Aseptic processing

Aseptic environment

SterilisationSterilisation

Filling &sealing

Aseptically packagedproduct

Conta

inerProduct


SterilisationA process applied to a product with the object of destroying all micro-organisms (by heat treatment at a temperature exceeding 100C)SterileCondition in which living cells are absent or killedSteriliserEquipment used for sterilisation: autoclave, hydrostatic steriliser or aseptic processing plantCommercial sterilityProduct which is free from micro-organisms that can grow and contribute to its deterioration (Not absolutely sterile)

UHT definitions

AsepticConditions to prevent bacteriological contamination


High-acid pH 4.5milk products, tea, coffee, liquid food products containing vegetables

Long-life products


UHT what do we need to achieve ?


In low acid foods (specifically milk):Required bacteriological effect expressed as:- Reduction of Clostridium botulinum spores to the level of 10-12

or 1 of initial 1012 survives - public health requirement (12D reduction or Fo= 3 process)

- Reduction of thermophilic spores by minimum 9D (B*>1) guarantying commercially sterile product

Minimised chemical changes expressed as:- Decomposition of thamin (vit. B1) less than 3% (C*

UHT what do we need to achieve ?


In low acid foods (specifically milk):Biochemical stability expressed as:- Maximal reduction of enzymatic activities in the heat treated

product

Physical and chemical stability:- No phase separation (fat, proteins, serum)

- No sedimentation

Raw milk quality

for processability:pH 6.65-6.80alcohol stability >75%total Count of bacteriafor sterility level:limit of heat resistant spores


Classification of bacteria by temperature preference

Psychrophilic

Thermophilic

Mesophilic

Psychrotrophic

45 C

20 C

7 C


Bacterial formation of spores

No. TP70:68, 9311BM

1

2

3

4

5

6

1 Viable bacterium2 Nuclear content gathered

(at bad growing conditions)3 A thick wall is formed around

the nucleus (the spore)4 The cell decomposes and the

spore is liberated5 The spore is free6 At favourable conditions the

membrane of the spore bursts and a new cell will be formed

The commercially sterile product must: Keep without deterioration, stable and

good commercial value during storage Free from micro-organisms and toxins

harmful to the health of consumers Free from any micro-organisms liable to

proliferate during storage

Commercial sterility


UHTUHT

Heat treatment>135C and >1 s

(Council directive 92/46/EEC)--------------------Lactulose*50 mg/l

(*IDF and ECC suggestions)

SterileSterile

Lactulose*>600 mg/l or

-Lactoglobulin*

PretreatmentThermisation 6365C/15 sec Preliminary heatingPasteurisation 63C/30 min Pasteur's method

rare today (batch pasteurisation)

Heat treatments definitions

Heat treatment Chilled distributed productsHTST pasteurisation 7275C/15 sec MilkHTST pasteurisation 8590C/25 sec CreamHTST pasteurisation 90120C/25 sec Fermented productsUltra pasteurisation 125138C/24 sec Cold storageAmbient distributed productsUHT 135150C/415 sec Ambient storageConventional sterilisation approx. 116C/20 min Ambient storage

HTST = high temperature short time, UHT = ultra high temperature PSD.TPD&B.BP.2.06, AA10

Definition of D-valueD-value (decimal reduction time) is the time at a specific temperature necessary to reduce the number of micro-organisms to 1/10 of the original value

Micro-organismsD121 C

B. cereus 2.3 sec.Cl. botulinum. 12.25 sec.B. stearothermophilus 408 sec.

N

D

time, t

104

103

102

101

100

10-1

105

10-2

temperature = constant

N

u

m

b

e

r

o

f

m

i

c

r

o

-

o

r

g

a

n

i

s

m

s


Type of micro-organismvegetative bacteria (high) viruses (medium) endospores (law)Medium surrounding micro-organismspH, water activity (aw), concentration and type of food components i.e.(simple carbohydrates, fats, chemical ions, type of acid and )

Rate of thermal death of micro-organisms at high temperatures depends on:


Absolute sterility not possible

Logarithmic destructionTime/temperature would be

too drasticNot possible to prove

by random testingNot possible to prove sterility

(prove absence)

B

a

c

t

e

r

i

a

Timet

N


Definition of z-valuez-value is the increase in temperature, necessary to obtain thesame lethal action or the same effect in 1/10 of time

Temperature dependancez-value [C]

B. stearothermophilus 10.5Colour changes 29.0Losses of vitamin B1 31.2Losses of lysine 30.9

time, t [s]

temperature

103

102

101

100

10-1

z


Definition of F-value

t = heating time, secondsT = heating temperature, Cz = the increase in temperature necessary

to obtain the same effect in one tenth of the time.

(T 121.1)

Fo = 10t

60. z

Fo = 1 when heatedone minute at 121.1C PSD.TPD&B.BP.2.11, AA10

Definition of B*-value

Assumption:Commercial sterility is achieved at B* = 1(heat treatment at 135 C for 10.1 sec., z = 10.5)= reduction of thermophilic spores = 109

B* = 10t10.1.

(T 135)

10.5


Definition of C*-value

C* = 1 = heat treatment at 135C for

30.5 sec. and z = 31.4C= 3% destruction of thiamine

C* = 10t30.5.

(T 135)

31.4


UHT treatmentTime-temperature combinations needed for destruction of spores

Temperature oC

Heating time or equivalent heating time, S Region of in-container sterilisation

A

B

2000

1000

1

400

200

100

4

40

2

110 120 130 140 150

10

20Mesophilic spores 30oC

Thermophilic spores 55oC

1% Destruction of lysine

90% Ps- Lipase de-activationno discolouration

UHTregion

3% Destruction of thiamine

90% Ps-protease inactivation


Bacteriological destruction

Chemical destruction

Enzyme inactivation

Temp, C110 120 130

10 3

104

10 5

10 6

Decimal reductiontime, sec

Heat effects

No. TP70:38, 9305BM

Heat effects

Temperature Fo Time C*C minutes(z=10C)

seconds seconds(z=31.4 C)

121 6.0 360 4.23130 6.0 45 1.02135 6.0 14 0.46140 6.0 5 0.24141 8.3 5 0.25


PSD.TPD&B.PEH.6.09, AA10

Batch sterilisation in containerContinuous processes

Time Minutes

Temp C Temp FTemp

Time Seconds

Temp F

DirectUHT

Indirect UHT

Pasteurisation

Continuous processes

150

100

50

300

200

100


UHT Ultra High Temperature processes

Shelf-life of milk

Subjective criteria: Taste Sedimentation Colour Fat separation Smell Viscosity Gelation

The time the product can be stored before the quality falls below an acceptable and minimum level


Factors influencing shelf-lifeQuality of raw product (chemical and microbiological)Pretreatment processType of aseptic processing system usedHomogenisation/deaerationPost heat treatment contaminationnon-sterileAseptic packagingBarrier properties of packaging material



Main factors affecting the flavour of UHT milkMilk qualityType and severity of heat treatmentPackaging materialStorage temperature and time

SulfurCooked

MetalStale

Rancid/Bitter

No. TP70:61, 9311BM

SulfurCooked

MetalStale

Rancid/Bitter

Optimum

Optimum

Off flavour

Sensoric changes in UHT milkDuration of storage (week)

5 C

25 C

Source: Blanc

2 4 6 8 10 12 14

No. TP XX:XXX, JF06

Sensory Quality of UHT MilkHeated Flavour - four notesCooked, Sulfurous, Cabbagey

Various sulfur compoundsRich, Heated,UHT, Keton-like

Products of Maillard reactionCaramelized, Sterilized

Non-enzimatic browningScorched, Burned

Burn-on heating suffaces

No. TP XX:XXX, JF06

Sensory Quality of UHT MilkHeated Flavour

The cooked flavour appears immediately after UHT treatment and is reduced during storage with rate dependant on availability of oxygen an temperature of storage.

No. TP XX:XXX, JF06

Sensory Quality of UHT MilkStale and Oxidized flavour

Stale Aldehydes from autooxidation of fat

Oxidized, Flat Ketons, PropanalBland N-PentanalChalky N-HexanalCardbordy Brownning reactions

No. TP XX:XXX, JF06

Sensory Quality of UHT MilkStale and Oxidized flavourStale and oxidized flavour develops during storage while the cooked flavour is disappearing.

It depends on a large number of different compounds.Aldehydes and ketons play the major role.

Formation of oxidised flavour is accelerated by high storage temperature.

No. TP XX:XXX, JF06

Sensory Quality of UHT MilkOther off-flavours

Bitter flavour Proteolitic activities of plasmin and bacterial thermoresistant proteases.

Rancidity Lipolitic activities of native and bacterial lipases.

Lactose and heat effectsLactulose

AcetaldehydeFormaldehydeFormic acidAcetic acidLactic acidTartaric acid

Maillard reactions productsbrown colourantioxydents

No. TP70:49, 9309BM

pH drop


Loss of vitamins in UHT milk

VitaminAscorbic acid

Folic acid

B12B6B2 (riboflavine)

Thiamine

A

D

E

UHT treatment

080

1020

030

020

Documents

UHT Theory LTH