Thermal vs Non-Thermal

8/9/2019 Thermal vs Non-Thermal

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Food Microbiology 1

Unit 5

Thermal and Non-ThermalPreservation


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Thermal

Pasteurization

Commercial SterilizationNon-thermal

o! Tem"erature

#rradiation

Chemical

Micro $iltration

%igh Pressure

Pulsed electric $ield


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Thermal &%igh Tem"erature' Processing

ogarithmic (eath) Microbial destruction byheat occurs in a logarithmic $ashion allo!ing

us to "redict the death o$ a "o"ulation o$

organisms

The theory o$ logarithmic death is based on a

single hit or one event e*uals death


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Pasteurization

(erives its name $rom the mild heat

treatments develo"ed by ouis Pasteur to"revent or delay s"oilage o$ !ine and beer

Today it re$ers to a heat "rocess that results

in destruction o$ all vegetative cells &non-

s"ore $ormers' o$ "athogens e+"ected in that

$ood


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Pasteurization

The "rocess o$ "asteurization is based on

$ood sa$ety and not on $ood "reservation

alone#t ,ills target "athogens

+tends shel$ li$e & shel$-li$e re$ers to the

amount o$ time $rom "ac,aging o$ the $ood"roduct to the time o$ s"oilage under a""ro"riat

storage conditions'.

(oes not inactivate all microbes "resentPasteurized $ood usually re*uires additional

control measures &such as re$rigeration/ lo! a!/

lo! "%' to "revent ra"id s"oilage


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Pasteurized Foods

The most common "asteurized $ood is mil,

0riginally designed to eliminate

Mycobacterium tuberculosisand Coxiella

burnetti

Fruit uice

S"oilage yeast and bacteria/ E. coli

0152)%2

3eer

S"oilage bacteria and yeast


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Pasteurized Foods

i*uid egg

Salmonellaand s"oilage bacteria

%oney

S"oilage yeast

Meat sur$aces &steam/ hot !ater'

E. coli0152) %2/ Salmonella,

Campylobacter


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Mil, Pasteurization

Time4Tem"erature Combinations

%igh Tem"erature Short Time &%TST' 15 sec

26oC

o! Tem"erature ong Time &TT' 78 min at

97o

CThese "asteurization time4tem"eratures are

considered to be e*uivalent.

%eat treatments are established on the

basis o$ sa$ety $irst &elimination o$

"athogens' and s"oilage &e+tension o$ shel$

li$e' second.


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:""lying high tem"eratures over a shorttime "reserves the sensory and nutritional

*uality o$ mil,

0ther combinations may result in a sensory

*uality not acce"ted by consumers

Can e$$ect the *uality o$ "roducts derived

$rom treated mil, &e.g. cheese'


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Commercial Sterilization

Some mil, is sold in cans &eva"orated or

s!eetened condensed mil,' or in bo+es thatremain at room tem"erature

The bo+ed mil, is ,no!n as Ultra %igh

Tem"erature mil, &U%T' mil,U%T mil, has undergone commercial

sterilizationand so can be stored at room

tem"erature

U%T treatment is 6 sec 1;8-158oC


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Sterilization)#nactivation o$ all

microorganisms

Essential in clinical settings (surgical

instruments)

Commercial Sterilization)< : "roduct is not

necessarily $ree o$ all microorganisms/ but

those that survive the sterilization "rocessare unli,ely to gro! during storage and

cause s"oilage=


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: "roduct that has undergone commercial

sterilization is $ree o$ vegetative and s"ore-

$orming "athogens and s"oilage

microorganisms that are ca"able o$ gro!ing

in that $ood under ty"ical non-re$rigeratedstorage conditions

Most common commercially sterilized $oodsare canned "roducts


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Primary 0bective)

(estroy the most heat resistance

"athogenic s"ore-$orming organisms-

Clostridium botulinum

Secondary 0bective)

(estroy vegetative and s"ore-$orming

microorganisms that cause s"oilage.S"oilage s"ore-$ormers are usually more

heat resistant than "athogenic s"ore $ormers


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Thermal (estruction Curves

Thermal destruction curves "rovide an

em"irical model to calculate time4tem"eraturerelationshi"s used in "rocessing

( value

> value

F value


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( -value

(-value- (ecimal ?eduction Time)#s the time

needed to reduce a "o"ulation o$ microorganisms

by @8A &1 log cycle' at a s"eci$ied tem"erature

and in a s"eci$ied medium

#$ the initial "o"ulation !as 188 CFU4ml

18 CFU4ml !ould remain a$ter a 1 log cyclereduction


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( -value

Time &s' 161oC

D-value10

5

104


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( Bvalue Formula

(Talue D t6-t14 &log N8-log N1'

TD tem"erature

t1D initial time

t6D $inal time

N8D initial "o"ulation

N1D $inal "o"ulation

From previous example:

(161D ;5-7845-;

D 1541D 15 sec


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>- alue

>-value)is the change in tem"erature re*uired

to "roduce a 18-$old change &1 log' in (-value.

>-values are calculated $rom the slo"e o$ the

curve o$ (-value vs tem"erature

>- valueis the measurement o$ the sensitivity

o$ an organism to changes in tem"erature

> l


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>- alue

>(-value

> l F l


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> D T6 B T14 log a- log b

T6D Final tem"erature

T1D #nitial tem"erature

a D u""er (-valueb D lo!er (-value

From previous figure:

>D 6;8-6684log 188- log 18

>D 6846-1

>D 68o

F

>- alue Formula

i


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+ercise

Time &min' og18

viable count

&c$u4g'

8.6 2.1

8.5 9.5

1.8 9

( value determination $or E. coli0152)%2 in bee$ at

98oC) Calculate the ( value o$ the organism under these

conditions


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Tem"erature &oC' og18( value &min'

55

98

8.25

-8.2

Calculate the > value o$ the organism

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Thermal vs Non-Thermal