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introduction to refrigeration and therma一 processing Of meat and meat products

1, Introduction to refrigeration and therma一 processlng of

meat and meat products

1,1 1NFLUENcE OF TEMPERATURE oN QUALITY AND SAFETY

The American Food and Drug Administration (FDA) estimates - `conseNatively', according tO

one o仰ciai - that there may be anywhere between 24 and 81 m掴on cases and 10,000 ･neediess

deaths'from food ●poisonlng in the US every year･ In Eng一and and Wa一es reported cases of food

poisoning have increased near一y ¶ve-fo一d over the 一ast decade. in addition tO the human cost the

economIC loss ln terms Ot WOrking days and medical treatment ln the US is between $5 bIIIl0n and $6

biiiiOn･ A study of one outbreak of Salmonella ententidis in the UK calcuiated that it cost the country

between f224 and f321 miliiOn･ Even a superficia一 examinat10n °f the prob一em reveals that

temperature contro一 is the叩me factor that determines the safe distribution 一ife of many foods inCiudlng

meat･ Temperature contr°I a一so determines the u一timate eating qua一ity and economic yie一d of the

product.

Temperature is one of the maior向ctors a鵬cting microbiOiogICai groMh MiCrObiOlogiCal

growth iS described in terms Of the 一ag phase and the generation time･ When a microorganism lS

血roduced to a pamcular environment there IS a time (the 一ag phase) in Which n° Increase ln numbers

is apparent foiiowed by a period when growth occurs一　丁he generation time IS a measure Of rate of

growth ln the latter stage･ McroorganISmS have an optimum growth temperature at which a partlCularstrain grows most rapid一y,一･e･ the 一ag phase and genera的n time are both at a minimum･ They a一so

have a maximum growth temperature above which groMh no 一onger occurs- Above this temperature,

one or more of the enzymes essentiaiわr growth are inactIVated and the ceii iS Considered to be heat-

injured However･ in genera一, un一ess the temperature iS raised to a point SubstantiaIIy above the

maximum growth temperature then the巾ury iS not iethai and growth wiii recommence as the

temperature iS reduced･ Atta面ng temperatures substantialiy above the maximum growth temperature

are therefore critica一 during cookmg and re-heating Operations.

Of most concem during Storage. distribution and retai一 disp一ay of meat and meat products iS a

third temperature･ the minimum grOMh temperature for a miCrOOrganiSm･ As the temperature of an

organism is reduced be一ow that for optimum growth then the 一ag phase and generation time bo机

inCreaSe･ The m面mum growth temperature can be considered to be the highest temperature at which

either of the growth criteria･ i･e･ 一ag phase and generation ume, becomes inmitely 一ong. The minimum

groMh temperature iS not On一y a function Of the pahiCuiar organism but a一so the type of food or groMh

media that is used for the inCubatIOn･ A一though some pathogens can grow at OoC一〇r even sIIghtiy

一ower, from a practica一 point of view the risks to ねod safety are considerab一y reduced if meat iS

maintained be一ow 50C

Meat may a一so become miCrObiOiogicaily unacceptab一e as a resu一t of the groMh of spoi一age

microorganisms Their growth can produce unacceptab一e changes jn the sensory qua一ity Of many

ねods and their rate Of growth is a一so very temperature dependent･ The deve一opment of o惰odours iS

usuaiiy the mst sign Of putre向ct一〇n ln meat and occurs when bacteria一 ieveis reach approxlmateiy 107

per cm2 of su鳴ce area When bacteria一 Ievels have increased a fuhher 10 fo一d s一ime begins to appear

on the suぬce and meat received in this COndlti°n iS uSuaiiy condemned out of hand. At OoC beef with

average imtIai contamination ieveis can be kept for at 一east 15 days bebre any o備odours can be

detected Every 5oC rise in the storage temperature above O｡C wili approxlmateiy ha一f the storage

time that can be achieVed･ So from a spoi一age point Of view, and the underly-ng economic

consequences of extended storageldistributiOn 一ife, temperature iS again a Very lmpOhant向ctor in food

production.

Meat exhibits Other pahiCuiar quailty advantages as a resu一t of rapid cooiing･ ln meat the pH

starts to fall Immediately aner slaughter and proteln denaturation beglnS. The result of this

denaturatiOn is a pink proteinaCeOuS帥d, common一y caiied idrip', ○鵬n seen in prepackaged joints.

The rate of denaturatI°n is direCuy re一ated to temperature and it therefore foliows that me faster the

chiiiing rate the 一ess the drip lnvestigatiOnS using pork and beef musc一es have shown that rapid rates

of ch鞘ng can ha一ve the amount of drip 一oss,

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◎ 2008, University of BriStOi (FRPERC)

introduction to refrigeratiOn and therma一 processing Of meat and meat products

A flnaI･ but important, quality and economlC advantage of temperature control IS a reductIOn in

weight ioss･ which resu一ts m a higher yleid of saieabie materiai･ Meat has a high water content and the

rate of evaporation depends on the vapour pressure at the su鳴ce･ Vapour pressure increases With

temperature and thus any reduction in the su向ce temperature wiii reduce the rate of evaporation.

The use of very rapid ch冊g systems for pork carcasses has been shown to reduce weight by at 一east

1 % when compared with conventIOnai systems.

in a wor一d where consumers require `sa俺f°°d'of high quality Without additives and

preseNatives then temperature iS the cntI∞i contro一 factor･ Most of the previous discussion has

centred around chiIIed foods, but to provide 一onger sa向sheif iIVeS than can be produced by ch冊9,

temperature contro一 in the form of打eezing IS again the answer.

1,2 OVERVIEW oF THE CoLD CHAIN

The co一d chain 一inks temperature changing Operations, such as ch冊g'打eezing, thawing,

hand一ing and cooking, and temperature maintenance operations, Such as chliled and百〇zen storage,

transpo鴫tiOn and diSpiay･ in genera一 as meat moves a一ong the c｡id chain lt becomes inCreaSIngiy

dmcult to control and maintain its temperature･ Temperatures of bulk packs of meat and meat

products ln 一arge storerooms are向r 一ess sensitive to smaii heat Inputs than sing一e consumer packs ln

transpoH or open diSPiay cases.

1･2･1 Primary chiIIingnreezing

After slaughter meat carcasses are at a temperature which lS Close to the optlmum growth

temperature for many microorganisms and ch細ng IS required before the meat can be processed or

dIStributed･ The血st stage in the co一d chain W用therebre be a coo一ing OperatiOn tO reduce the

temperature of the meat to a va一ue tha川mltS mICrObioiogiCal and qua一ity changes. If the meat iS tO be

distributed in a Chiiied form then this Vaiue will be above the i南al freezing point and ln the range -1 to

+15cc･ If a frozen food lS requlred then tJle value wlll typically be between -12 and -30oC

l･2･2　Seconda町proceSSIng

Any meat that is processed a船r its initia一 primary Ch輔ng or freezing operation is iikeiy to gain

heat and consequent一y rise in temperature･ This rise can range from a few degrees in a Packing

operation to Over 100 degrees ln COOking To maintain product qua一ity it lS Ohen impO鳴nt to remove

this added heat･ Industriai cooking processes CamOt be guaranteed t｡ eiimlnate ai一 pathogemc

organisms and if coo冊g rates are s一ow miCrObial spores that suNiVe the cooking process wiii

germinate and grow一 Systems that produce a rap-d reduction in the temperature of the meat wiII retard

microblaI growth and consequent一y extend shelf life･ This iS eSPeCiaiiy -mportant when chIIIlng cooked

products that wiii eventuaiiy be consumed co一d or in a warm reheated state.

1･2･3　Storage and transpoh

A範r the temperature of the meat has been reduced to a desired va一ue it iS iikeiy to remain at

that tempe｢ature for a period which may range什om a few hours, for chliied products, to a mmber of

years in the case offrozen fo｡ds･ During mat pe面d it may remain in a slngie store or be transpohed

around the wor一d The°retiCally･ there shou一d be few prob一ems in the storage and transpoh of either

c間ed o而ozen f｡ods･ if the meat iS at the corred temperature when lt is 一oaded into the storage

room or transpoh vehic一e then a旧he refrigeration IS required to do is to insu一ate the meat from sources

of heat･ Most of the time me main SOurCe WIii be a s一ow movement of heat from the outside ambient

through the waIIs･ wh-ch can be easily cateredねr Coping with door openings and peop一e moving

around lnSIde the refrigerated chamber iS more d珊cult However, if the standard of management is

good, and the meat bu一k s一acked, then temperature rise in the meat wiil be smaii and restricted to

exposed sur向ces.

in practice there are many prob一ems in meat Storage and transpoh because the meat and

meat products are not at the correct temperature when they are ioaded･ if the temperature of the meat

iS too high when i白S wrapped and bu一k packaged then it b∞0mes very d櫛cult to reduce that

temperature within the storage or transpoh compahment･ Since these systems are not designed to

extract heat then the average room temperature ca-se together with that of any other foods a一ready

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@ 2008, Universlty Of Bristol (FRPERC)

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introduction lo refrigeration and therma一 processing Of meat and meat products

stored･ Fai一ure to remove the required heat before 一oading Can be due to a number of causes:川

InSumClent tlme allowed. [2l InSumCient refrigeratIOn CaPaClty tO Cater for hlgh Initial product load, [3I

over一oading, 【4i variabi一ity in size Of products, or t5日ncorrect environmenta一 conditions

l･2･4　Retail disp一ay

Chiiied meat products spend periods ranging from a few minutes tO a Week in retaii disp一ay

and in extreme Cases With五〇zen products a few months During that time there iS a COn耶d between

the need to protect the food什Om extraneous heat sources and those to disp一ay it to Its best

advanぬge･ Retai一 disp一ay cabinets Can have integra一 or remote remgeration units, air movement can

be gravlty Or forced air and the dlSPlays can be single-tier, multi-tler Or Well.

1･2･5　Domestic transpoh and storage

Even if food producers and retai一ers maintain aCCep由bie product temperatures during the

dIStrlbutiOn Chain they 一ose contro一 when the product 一eaves the retai一 store. Aner the meat is removed

from a disp一ay cabinet it spends a period outside a remgerated environment Whlist lt is carried around

the store and then transported home- Temperatures of ねods, especiaIIy thin siiCed products, can rise

considerab一y during these journeys.

Consumers have considerab一e faith ln the temperature maintenance prOpehIeS Of domestic

re請gerators However, measurements taken at 5 positions a1 5 mimte inteNais over an average of 6

days in remgerators ln 250 homes have revea一ed considerab一e variation in peHormance･ The highest

recorded mean temperature was ll･37cc and the 一owest -0･89cc, produc活g a range in mean

temperatures of 12･3cc･ The overall mean air temperature for ai一 the refrigerators in the suNey was

6-04oC･ Consequent一y, over hair operated at mean temperatures that wou一d suppoh the groMh of

saimoneIIa.

1,3 TEMPERATURE LEGISLATION

The past俺w years has seen a considerab一e growth in ai一 types of legisiatIOn re一ating to the

contro一 of food temperatures throughout the coin chai∩一　丁he recommended reading Section for this

course inc一udes references to most of the current impohant bod temperature iegiSIation. However,

temperature iegiSiation iS Constant一y changing and there may weii be other legISiatIOn re一ating tO the

spec緬c food of interest °r i°caiity･ it IS therebre impo鴫nt to check with the appropriate O怖cial body

in the pamcuiar country of interest what iS the regu一atory position at a pa巾cuiar time.

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◎ 2008, UniVerSity of Bristo一 (FRPERC)