NZ713493B2 - Flash freezing for campylobacter reduction - Google Patents

Abstract

Disclosed is a process of reducing the number of viable microorganisms present on the surface of meat, comprising the steps of: a) providing an untreated meat item having a surface membrane and muscle tissue, said untreated meat item having viable microorganisms on the surface membrane, and an atmosphere surrounding the meat item; b) cooling the meat item by reducing the temperature of the atmosphere surrounding the meat item at a rate of between 0.5 °C/s and 5 °C/s, until the surface membrane reaches a first temperature as measured by a probe inserted within or just below the membrane of between -5 °C and 2 °C; c) allowing the surface membrane to warm to a second temperature higher than the first temperature to give a treated meat item; wherein the number of viable microorganisms present on the surface membrane is reduced, whilst the ß-hydroxyacyl-CoA dehydrogenase (HADH) activity of the muscle tissue is not increased by more than a factor of 2 in the treated meat item compared with the untreated meat item. sphere surrounding the meat item; b) cooling the meat item by reducing the temperature of the atmosphere surrounding the meat item at a rate of between 0.5 °C/s and 5 °C/s, until the surface membrane reaches a first temperature as measured by a probe inserted within or just below the membrane of between -5 °C and 2 °C; c) allowing the surface membrane to warm to a second temperature higher than the first temperature to give a treated meat item; wherein the number of viable microorganisms present on the surface membrane is reduced, whilst the ß-hydroxyacyl-CoA dehydrogenase (HADH) activity of the muscle tissue is not increased by more than a factor of 2 in the treated meat item compared with the untreated meat item.

Description

Flash freezing for campylobacter reduction Summary The invention relates to a process for reducing the number of viable rganisms present on the surface of meat, and to meat items so treated.

Introduction Food-borne ens represent a significant and serious threat to human and animal health. us s of microorganism reside naturally on many types of food, some of which are capable of causing diseases in man (and other animals) upon ingestion. Sensible precautions, such as thorough cooking at an appropriate temperature, observation of correct storage protocols for raw and cooked food, and adhering to proper hygiene standards when handling food, can all reduce but not eliminate incidence of such disease.

Amongst the disease-causing pathogens, Campylobacter is the most common bacterial cause of food poisoning. It is responsible for around 62,000 reported cases of s in the UK every year; however, the estimated number of actual incidences is much higher, of the order of 600,000, as it is believed that most individuals affected by the pathogen do not seek medical assistance. The total number of campylobacter cases across the European Union states is calculated at 9 n cases per annum. obacter ion is also extremely common in retail poultry. The ence of Campylobacter in chicken at retail in the UK was 65.2%, based on the results from both methods combined, for the 927 samples tested (Food Survey Information sheet 04/09, A UK survey of Campylobacter and Salmonella contamination of fresh chicken at retail sale, UK Food Standards Agency).

Campylobacter is ore one of the key organisms that health agencies are tackling in order to reduce levels of food-borne illness. Campylobacter can be found on meat, unpasteurised milk, and in untreated water; however there is strong evidence that poultry is the most common cause of illness.

Campy/abacter is naturally present in many poultry birds, and is often found in the cecum. Transfer to the skin is thought to occur when the birds are slaughtered and eviscerated. it would be very desirable to kill or remove Campylobacter (and other pathogens) from meat, in particular poultry and poultry ts, which are intended for human (or animal) consumption.

Brief Description of the Prior Art A known method of ecting y carcasses involves spraying or immersing the carcasses with water containing antimicrobial agents. However, in Europe, legislation specifies that potable water must be used to wash carcasses.

GB 2105570 (A) discloses a method of reducing “weepage” in fresh-pack poultry that includes the steps of first washing the carcasses with jets of unrefrigerated water to pre-cooi them and add p moisture, then tumbling the carcasses to equalize the amount of pick-up moisture carried by each carcass, to reduce the general level of pick-up moisture content somewhat, draining the carcasses by y to remove e moisture, and finally subjecting them to a supercold atmosphere, such as may be obtained by directing expanded liquid carbon e in rapidly moving currents over the carcasses for a time to freeze—crust the carcasses.

The “freeze-crusting" s the skin to squeeze out p moisture from the fatty fascia layer under the skin to reduce the pickup moisture level to the allowable amount of 8%, and to remove sufficient body heat that when a carcass is then allowed to temper to an even" temperature throughout, it will be below the freezing point of water, but above the —3.30 °C freezing point of the flesh, for a very short time.

The process is said to reduce seepage from the'poultry products so treated.

The method is said to inhibit bacterial growth, and thus prolong shelf life. There is no disclosure of the method having any icidal effect, however.

US 3637405 discloses a s for packaging and preserving meats to give long ‘35 shelf life and greater tenderness. The portioned or whole chicken is exposed to cold air at a temperature of -40 °C for 1 hour. The crust~frozen chicken is then held at 0 °C for at least 3 hours. The method is said to inhibit bacterial growth, and thus prolong shelf life. There is no disclosure of the method having any bactericidal effect, however.

WO 2004080189 discloses a method comprising rapidly cooling meat by exposure to a rapid cooling temperature of below about ~10 °C for sufficient time to provide a frozen crust on the meat and chilling the resultant crust-frozen meat by exposure of said crust-frozen meat to a chilling temperature greater than the rapid cooling temperature but no higher than about +10 °C to raise the temperature of the surface of the meat and to maintain said e at a temperature no higher than the freezing temperature of the meat for at least ient time to injure lethally and/or kill bacteria, is used to reduce the viability of bacteria on meat. The method is stated to have particular application in the processing of poultry meat to kiil bacteria comprising the Campylobacter and/or Salmonella species.

Although the method disclosed in WO 2004080189 apparently achieves the objective of reducing the count of Campylobacter (and other bacterial species), the poultry treated according to the process cannot be sold in the EU as ”fresh". The sale of poultry either as whole birds or ns is ted under the EC Poultrymeat ing Regulation 1906/90 (which has been incorporated into a combined EC ing Regulation 1234/2007). This tion categorizes poultry meat and only allows y to be ed as fresh, frozen or quickvfrozen. Fresh poultry is defined ‘iresh poultry meat' means poultry meat not which has not been stiffened at any time by the cooling process, prior to being kept at a temperature not below -2°C and not higher than +4°C. it is not ted to market chilled/fresh poultry which has been previously frozen and then thawed.

Studies have been conducted to determine rates of Campy/obacterjejunl inactivatioo on poultry d to different cooling and freezing temperatures (Reduction of C. jejunl on the Surface of Poultry by Low Temperature (J. Food Prot, 66, 4, 2003, 652— 655)). A mixture of three strains of C. jejuni originally isolated from poultry was inoculated onto chicken wings. Storage of wings at -20 and -30°C for 72 h reduced the population of C. jejuni on wings by 1.3 and 1.8 logic CFU/g, respectively. ols were developed to superchill chicken wings with liquid nitrogen at -80, -120, —160, and ~196 °C such that the internal portion of each wing guickly reached -3.3 °C but did not freeze. The study concluded that conditions used in the poultry industry to superchill poultry to a nonfrozen—state internal temperature are not likely to substantially reduce Campy/obacter tions on fresh products.

Summary of the Invention in a first aspect, the invention relates to a process for reducing the number of viable microorganisms present on the surface of» a meat item, comprising the steps a) providing an untreated meat item; to b) exposing the meat item to an atmosphere at a temperature T‘; c) rapidly ng the temperature of the atmosphere at a selected cooling rate to a temperature T2 below ~20 °C; d) optionally maintaining the atmosphere at temperature T2 for a selected period of time; e) allowing the meat item to warm, optionally at a ed slow warming rate, by ing the temperature of the atmOSphere to a temperature characterized in that selected temperatures T‘, T2 and T3, the selected g rate, selected period of time and selected warming rate are selected such that the number of viable microorganisms present on the surface is d, whilst the temperature of the meat item does not fall below -2 °C and remains unfrozen. in a second aspect, the invention es a process for reducing the number of viable microorganisms present on the surface of meat, comprising the steps a) providing an'untreated meat item having a surface membrane and muscle tissue, said ted meat item having viable microorganisms on the e ne; b) exposing the surface membrane to cooling at a selected cooling rate until the surface membrane reaches a selected first temperature; c) optionally maintaining the surface membrane at the selectedfirst temperature for a selected period of time; . d) allowing the surface membrane to warm to a selected second temperature higher than the first temperature to give a treated meat item; WO 68685 characterized in that the selected rate of cooling; the selected first ature, selected period of time and selected second temperature are selected such that the number of viable microorganisms present on the surface membrane is reduced, whilst the 13- yacyl-CoA dehydrogenase (HADH) activity of the muscle tissue is not significantly increased in the treated meat item compared with the ted meat item.

According to a third embodiment, there is provided a meat item prepared by the process of the invention.

Summary of the Figures Figure 1 is a graph showing the ature of the surface, or and atmosphere ot a turkey carcass d for 4 minutes Figure 2 is a graph graph showing the temperature of the surface, interior and atmosphere of a turkey carcass treated for 40 seconds.

Figure 3 is a graph graph showing the temperature of the e, interior and atmosphere of a turkey carcass treated for 1.5 minutes.

Figure 4 is a graph graph showing the temperature of the surface, interior and atmosphere of a turkey carcass treated for 2 minutes.

Figure 5 is a graph graph showing the temperature of the surface, interior and atmosphere at a turkey carcass treated for 1 minute. ' Figure 6 is a graph showing a summary of Campylobacter levels on ns — excluding warm bird data on day K+1.

Figure ’7 is a graph showing a y of Campylobacter levels on chickens - excluding warm bird data on day K+1.

Figure 8 is a graph showing a summary of' Campylobacter levels on chickens — ing warm bird data on day K+1 Figure 9 is a graphshowing a summary of Campylobacter levels on chickens — excluding warm bird data on day K+1 with 2 min treatment time.

Figure 10 is a graph showing a summary of Campylobacter levels on chickens — excluding warm bird data on day K+1 with 2.5 min treatment time.

Figure 11 is a graph showing a summary of Campylobacter levels on chickens ~ excluding warm bird data on day K+1 with 2.5 min treatment time.

Figure 12 is- a graph showing the temperature profile of a meat item subject to an embodiment of the inventive process.

Figure 13 is a graph graph showing the temperature of the surface, interior and here of a chicken carcass treated for 1 minute.

Detailed Description of the Preferred Embodiments The term “meat" as used herein refers to any form of edible (by human or animal) flesh, and includes, without limitation, pork, lamb, , veal, beef, venison, fish, shellfish, molluscs and poultry. The methods of the invention are, however, particularly appropriate for the treatment of poultry.

“Poultry" in this context includes edible birds of any type. Examples of poultry are n, turkey, pheasant, quail, duck, goose, guinea fowl and swan.

Chicken and turkey are preferred.

The term “meat item" encompasses whole animal carcasses, both entire and eviscerated, as well as ns of meat (cuts), which comprise at least a tion of muscle tissue. Examples of meat items are whole, eviscerated y carcasses, and poultry breasts, thighs, drumsticks, lower legs and wings.

The term “untreated meat item" refers to a meat item as hereinbefore defined, which has not been subjected to the'inventive process. it may (and ably will have) undergone a number of preceding steps ary in the preparation of meat, such as stunning, slaughter, evisceration, scalding, removal of head and legs, water or air chilling and jointing. _ defeathering, The term “microorganism” refers to any organism that is capable of g illness or disease in humans or other animals. Examples of microorganisms include bacteria, fungi, archaea, and protists. Preferred microorganisms which are controlled by the methods of the invention include Campy/obacter spp., Clostridium I perfringens, Escherichia coli, Salmonella spp., Bacillus cereus, Shigella spp., Staphylococcus aureus, Streptococcus, Listeria monocytogenes, Vibrio cholerae, Vibrio parahaemO/yticus, Vibrio vulnificus, Yersinia enterocolitica, Yersinla pseudotubercu/qsis, Coxiella ii, Bruce/Ia spp., bacterium ulcerans, and P/esiomonas shigeiloides. More preferred microorganisms are Campylobacter spp. ‘ and Salmonella spp. Highly red are gram negative bacteria, especially Campy/obacter species including Campy/obacter jejuni and Campy/obaoter coll, especially Campy/obacterjejuni. I The term “viable rganism” refers to a microorganism as hereinbefore defined, ~ which is capable of causing illness" or disease when ingested. it encompasses nonCUlturable bacteria that are in a state of very low lic activity and do not divide, but are alive and have the ability and become able once resuscitated, as well as culturable and reproducing microorganisms.

The term “membrane” refers to any biological layer which covers or adheres to the - e of the meat item to be treated, which is not muscle tissue. It includes, for e, skin (dermis and mis), as well as layers of fat or cartilage. It also includes the inner membrane of the body cavity of eviscerated poultry fowl.

The term “B-hydroxyacyl-CoA dehydrogenase (HADH) activity” refers to the activity muscle mitochondrial enzyme, B—hydroxyacyl-CoA-dehydrogenase, which is released into the intracellular fluid when the mitochondrial membranes are damaged during freezing and thawing.

B-hydroxyacyl-CoA dehydrogenase (HADH) activity is measured using the protocol described in “The Effect of Superchilling and Rapid ng on the HADH Assay for Chicken and Turkey”, J. Assoc. Publ. Analysts, 2010, 38, 13-23, a modification of the method described in “Verification of Labelling of Previously Frozen Meat and Poultry by Measurement of HADH Activity" Hargin, K., J. Assoc. Publ. Analysts, 1997‘, 33, '1- 46. These documents are incorporated herein by nce. The protocol is briefly summarised below.

A cuboid shaped portion of flesh with base dimensions of approximately 30x30mm and a height of 20mm is used for the HADH test. For the poultry cuboid it is necessary to have six out surfaces. 3O Preferably, the cuboid is taken from a predetermined 'depth below the surface of the surface membrane, such as between 1 and 10 mm below the surface.

Any excess e liquid on the sample is wiped off with a tissue. The meat juice is expressed from the sample and d with a phosphate buffer. Aliquots of EDTA, phosphate buffer and NADH are added to diluted press juice, followed by acetoacetyl~Coenzyme A solution, in a quartz spectrophotometer cuvette. USing a.

U.V. spectrophotometer the rate of conversion of NADH to NAD * is measured by the rate of decrease in the absorption of the solution. The extinction at 340mm is read.

The difference between the two gs AE is the decrease in absorption at 340mm.

HADH activity U/ml = V x AE / min x on factor of meat juice dexa Where V = volume of test mixture = 3ml C = extinction of co-efficient for NADH at 340nm = 6.3 d = light pathof cell = 1cm a = volume of diluted meat juice = 0.1ml T = time over which decrease in is measured in 7 absorption minutes AE / min = Extinction at start of reaction — extinction at T min The equation becomes:- HADH activity U/ml = 3 x AEJ/ min x dilution factor of meatjuice * 6.3 x 1 x 0.1 (* e.g. 200 for beef) The juice pressed from meat that has been frozen and thawed will therefore exhibit higher HADH activity than meat which has not been previously frozen. Since some HADH may be released when the meat is cut during sample preparation the method is a comparative one, where the HADH activity is determined on the untreated meat item as received (X0), and then determined after treatment (X1). The ratio of the HADH activities (X1/Xo) is ed to as the R value. if the R value is less than 1.2, ’ ably less than 1.1, more ably less than 1.05, then theHADH activity of 3O the meat or poultry is regarded as not significantly increased.

Cooling may be achieved by any oneof a number of "methods. Meat items may be placed in a chamber containing airlor other refrigerant gas) held at an riate ature to achieve the selected cooling rate. One or more gas circulation means (such as fans, blowers etc.) may be provided to increase the flow of cold air over the meat item, to increase the rate of cooling of the surface membrane. 2012/000499 Alternatively, and ably, the surface ne of the meat item may be cooled with a cryogen. Suitable cryogens include liquefied , such as liquid nitrogen, liquid air, liquid carbon dioxide and liquid argon, and solids, such as solid carbon dioxide (“dry ice", preferably in finely divided form), and combinations of these.

Liquid nitrogen is a preferred cryogen.

Cryogen may be applied to the surface membrane as a jet, spray or bath. It is preferred that cryogen is applied as a spray. Various types of spray nozzle, such as roses or spraybars may be utilised, depending on the size and shape of the meat item to be treated.

Preferably, the cryogen is d in combination with an impinging gas. lmpinging gas serves to convey the cryogen to the surface membrane of the meat item and thus increases the rate of cooling. Suitable impinging gasses include nitrogen, air, and carbon e, and mixtures of these. The pressure of the impinging gas, and the amount relative to the cryogen, are adjusted so as to achieve the selected cooling rate.

One embodiment of the process utilizes impingement type gas flow of cryogen, Such as carbon dioxide or nitrogen gas, in a straight pass-through COnfiguration. The meat item is loaded into one end of the apparatus, and is removed with the surface . membrane at a selected first temperature» at the opposite end. Conveyors or driven shackle lines may be used to convey the meat item through the cooling apparatus and process.

In certain ments, the meat item is conveyed tor stirtace cooling along a passage formed between a pair of impingement plates through which a g flow of a n, such as carbon dioxide or nitrogen gas, is circulated to cool the surface membrane. In an alternative embodiment, the impingement plates 'may be ed to one side, as opposed to being beneath the blower which circulates the cryogen. In embodiments where the meat item is a poultry carcass, the conveyer in these ments is a shackle conveyor.

In an alternative embodiment, a cryogenic food cabinet freezer is used.

A suitable ‘ device is the CRYOLINE® CF, supplied by LlNDE AG, Linde Gases Division, rstrasse 70 82049 Pullach, Germany. This embodiment is more appropriate for batch freezing and chilling ses where an in—line system is not appropriate.

In one embodiment, n is supplied to the interior of a meat item by means of a Spray nozzle connected to a cannula or probe. This embodiment is convenient for the internal sterilisation of the body cavity of eviscerated poultry carcasses, for example.

As used herein, the term “temperature of the meat item" refers to the average temperature throughout the item. in some ments, the temperature of the ‘ meat item does not fall below -2 °C at any point during the procedure. Preferably, no part of the meat item fails below -2 °C at any point during the ure. Preferably, no part of the meat item is frozen at any point during the inventive process.

As used herein, “surface temperature" refers to the average temperature of the whole or part of the surface of a meat item, as ed by a surface ature thermocouple probe.

As used herein, “interior temperature“ refers to the average temperature at a 4 predetermined depth below the surface of the meat item measured by a temperature probe. Preferably, the interior temperature is measured at a depth of at least 3mm below the surface, mere preferably at least 5mm. Preferably, the temperature of the interior does not fall below —2 °C at any point during the inventive process.

The temperature of the meat item may be (in the case of freshly slaughtered whole poultry ses, for instance), be around or just below body heat, such as between 25 and 37 °C. atively, the interior temperature may be around ambient ‘ ature, such as between 15 and 25 °C.

However, it has been found preferable that the temperature of the meat item is below ambient temperature, such as below 20 °C. More preferably, the interior temperature is below 15 °C. Still more preferably, interior temperature is below 10 °C. Still more preferably, the interior temperature is below 5 °C. When employing such l temperatures, good control of bacteria and consistency of results is achieved.

Preferably, the temperature of the meat item is above 0' °C. More preferably, the interiortemperature is above 1 .°C. Still more preferably, the or temperature is above 2 °C.

WO 68685 The untreated meat item is exposed to an atmosphere at an initial temperature T'.

The atmosphere may be air, nitrogen or any other suitable gas. Preferably, T1 is between -5 and 20’ °C. More preferably, T1 is between -3 and 10 °C.

As used herein, the term ted cooling rate” refers to the . average rate of g from initial temperature T1 to maintenance temperature T2. This is illustrated schematically in Figure 12, and is calculated as the ence between T,1 and T2 (referred to as AT‘) divided by the time taken to achieve this reduction (referred to as ' At‘), and is expressed in terms of °Cs". The d person will appreciate that it is not always practicable or desirable to provide a linear decrease in temperature.

The selected cooling rate is preferably between 0.1 and 10 °Cs", more preferably between 0.3 and 1.5 °Cs“.

Temperature T2 is preferably between -20 and -120 °C. Temperature T2 is more preferably between -20 and -100 °C. More preferably, temperature T2 is between —25 and -95 °C. More preferably, is between -40 and -90 °C. Still more preferably, T2 is between ~50 and -80 °C. in preferred embodiments, the here is maintained at the selected temperature T2. Some variation of e temperature may occur during this maintenance phase, as when g is periodically applied, Preferably,»such deviations from T2 are no more than i 20 °C, more preferably 1r 15 °C, still more preferably 1 10 °C. in preferred embodiments, the atmosphere is maintained at the selected temperature T2 for a selected period of time. The period of time is selected in order to optimise bacterial l in the l process, whilst avoiding freezing of the of any part of the meat item. it has been found in particular that the duration of the maintenance phase (Le. the selected period of time at which the atmosphere is maintained at T2) is a factor in determing, in certain embodiments, the warming rate in the subsequent process step.

Preferably, the atmosphere is maintained at the selected temperature T2 for a period of between 10 seconds and 10 minutes, more preferably between 30 seconds and 5 ‘ 35 minutes, still more preferably between 1 minute and 4 minutes.

In the third phase of some embodiments, the atmosphere is warmed at a selected warming rate to a temperature T3. Temperature T3 is above temperature T2, such as above -20 °C more preferably above -10 °C, more preferably above 0 °C. Preferably, Ta is between -1 and 4 °C.

Warming may be achieved by any conventional means, and is most conveniently achieved by simply ceasing the application of cooling. In this case, the latent heat stored in the interior of the meat item will permeate through to the surface of the meat.

Alternatively, the meat item can be transferred to a warmer environment, or warm air or other warm gas may be applied to the e of the meat. ln an alternative embodiment, the ambient temperature is gradually raised by passage of the meat item through an area having a temperature gradient, such as an in-line processing tunnel having a temperature which varies along its length.

- As used herein, the term “selected warming rate” refers to the average rate of warming from maintenance temperature T2 to final temperature T3. This is illustrated schematically in Figure 12, and is calculated as the difference betWeen T2 and T3 (referred to as ATZ) divided by the time taken to achieve this reduction (referred to as Ate), and is expressed in terms of °Cs". The skilled person ‘ will appreciate that it is _not always cable or desirable to e a linear increase in temperature. ably, the selected warming rate is less than 20 °Cs1 ,more preferably less than °Cs ,more preferably less than 5 °Cs“, more preferably less than 2 °Cs, more preferably less than 1 °Cs still more preferably less than 0 5 °Cs“, most preferably less than 0.1 °Cs singly, it has been'found that warming the meat item at a slower warming rate from maintenance temperature T2 to final temperature T3 leads to ed reduction of the number of viable microorganisms t on the surface of a meat item. This was contrary to the expectations of the inventors, and the reasons for this enon are not properly understood.

A number of factors affect the warming rate. These include the maintenance temperature T2, the ed period of time at which the meat item is held at this temperature, the initial temperature T‘, the mass of the meat item and its surface area to mass ratio. In ular, a slow warming rate which favours bacterial control is favoured by a low temperature T‘. in some embodiments, the surface membrane of the meat is exposed to cooling conditions until the surface membrane reaches the selected first temperature. The ed first temperature is chosen such that at least a proportion of the viable rganisms present on the surface become non-viable when allowed to warm to the selected second temperature.

The prior art indicates that in order to achieve successful control of microorganisms present on the surface of meat, rapid cooling to a temperature of less than -10 °C for sufficient time to provide a frozen crust on the meat, followed by subsequent warming, is necessary. singly, the inventors have found that an extremely ive antimicrobial effect can be achieved by rapid surface chilling to temperatures well above —10 °C. ln addition, the prior art indicates that a frozen crust is necessary to achieve the sterilisation effect. Surprisingly, the inventors have found that providing a frozen crust is not a requirement, and indeed superior results are obtained in certain instances when the e membrane remains unfrozen.

Preferably, the selected first ature is below 2 °C.~ More preferably, the selected first temperature is below 1 °C. More preferably, the selected first temperature is below 0.5 °C. Still more preferably, the selected first temperature is below 0 °C. Still more preferably, the selected first temperature is below —O.5 °C. ably, the selected first temperature is above -5 °C. More preferably, the selected first temperature is above 4 °C. Still more preferably, the selected first temperature is above -3.5 °C. Still more preferably, the selected first temperature is above —3 °C. Still more preferably, the selected first temperature is above -2.5 °C.

Most preferably, the selected first temperature is above -2 °C. Utilising a temperature above -2 °C has the age that meat treated according to the process fulfils the requirement that ‘fresh poultrymeat‘ is to be kept at a not below 2°C at any time Preferably, the selected first temperature being in the range of n -5 °C and 2 °C. More preferably, the selected first ature is n ~3 °C and 1 °C. Still more preferably, the selected first temperature is between -2 °C and 0.5 °C The selected first temperature and selected second temperature refer to temperature of the surface as measured by infrared meter or a probe inserted within or just below the membrane.

Prior to exposure of the surface membrane to the cooling step of the invention, the meat item may be at t temperature (for example, between 20 °C and 29 °C), or it may be (and preferably is) pre—chilled to below ambient temperature. In one embodiment, the meat item is pre~chilled to a ature below ambient temperature, such that the ature of the meat item is substantially uniform throughout the meat item, Preferably, the meat item is pre~chilled to below 15 °C, more preferably to below 10 °C, still more preferably to below 5 °C, still more preferably to below 2 °C. it may be more ient, however, to carry out the process of the invention on meat items which arrive from the preceding steps in the processing plant without a preliminary step of refrigeration.

The cooling rate is selected such that the d temperature ion of the surface membrane occurs sufficiently y that no substantial change in the temperature of the underlying muscle occurs. The skilled person will be able to determine a suitable g rate for each particular type of meat item. in a particularly preferred embodiment, the meat item is cooled by reducing the ambient temperature (i.e. the temperature of the atmosphere surrounding the meat item) at a rate of between 0.1 "Cs‘1 and 5 °C 5", more preferably at a rate of between 0.2 °C 5‘1 and 3 Ce", most preferably at a rate of between 0.5 °C 5‘1 and 3 °C 5".

Preferably, the ambient temperature of the atmosphere surrounding the meat is cooled to a ature of between ~10 °C'and 450 °C, more preferably between -20 °C and -100 °C, still more preferably between -30 °C and -90 °C.

Preferably, the meat item is exposed to the surface cooling conditions for as short a ' period of time as feasible. This ensures that the ature gradient through the , meat item is high, and a large differential between theftemperature of the surface membrane and the temperature of the underlying muscle is maintained.

Optionally, and ably, the surface membrane of the meat item is ined at the preselected temperature for a period of time. This period of time is selected such that insufficient heat is transferred from the muscle meat to cause a significant increase in the activity of HADH. ln one preferred embodiment, the cooling is achieved by use of a refrigerated tunnel having a predetermined temperature profile. The rate of passage of the meat items through the tunnel is adjusted so as to obtain the correct rate of g. This embodiment is ularly convenient when the process of the invention is part of the production line for the preparation of meat products.

Preferably, the surface membrane of the meat item is maintained at the selected first temperature for between 30 seconds and 20 minutes, preferably n 1 minute and 10 minutes, more preferably between 1.5 minutes and 7 minutes, most preferably between 2 and 6 minutes.

Alternatively, the meat item need not be maintained at the selected first temperature, but on reaching the ed first temperature may instead be warmed or allowed to warm to the selected second temperature.

The selected second temperature is higher than the selected first temperature. differential between the selected first and selected second temperature is selected such that the number of viable microorganisms is reduced, and also to fit efficiently with subsequent steps in the processing of the meat item. Preferably, the selected , second temperature is above -1 °C. Preferably, the selected second temperature is below 20 °C, more preferably below 15 °C, still more preferably below 10 °C, still more preferably below 5 °C, most preferably below 4 °C. Very preferably, the ed second temperature is between -1 °C and 4 °C. Maintaining the temperature not higher than +4°C at any time fulfils the requirement for fresh poultry ' meat under European ation.

Quantitative assessment of the number of viable microorganisms t on surface ne is carried out in accordance with riate protocols. For example, Campy/obacter is quantified according to lSOfTS 10272-2:2006(E) “Microbiology of food and animal feeding stuffs — Horizontal method for detection and enumeration of Campy/obacter spp. — Part 2: —count technique". Other microorganisms may- be quantified using ent techniques. The term '"number of viable ' microorganisms” will be understood by the skilled person as referring to the number of such rganisms present per unit surface area of surface tissue.

The rate of cooling, the selected first temperature and the selected second temperature are chosen such that the reduction in the number of viable microorganisms present on the surface of the meat observed is at least tically significant within the limits of the quantification method used. ably, at least a log (ten-fold) reduction in the number of microorganisms present is achieved. More preferably, at least a 2-log ed-fold) reduction in the number of rganisms present is achieved.

Preferably, the R, of the HADH activity in the treated item is less than 2, more preferably less than 1.5, more preferably less than 1.2, more preferably less than 1.1.

Because the muscle tissue s largely unaffected by the treatment of the skin (or other surface membrane) according to the present invention, the meat item retains the organoleptic and nutritional qualities of fresh meat.

Subsequent to treatment with the inventive process, the treated meat items may be subjected to any further processes customary for the treatment of fresh meat, such as jointing, chilling (air and water chilling are contemplated),-and packing or wrapping.

Preferably, the inventive process is one of- the last steps on the production line prior to packing to prevent the possibility cf recontamination of the treated meat item. in some embodiments, the presentfood hygiene s may be combined with additional foodphygiene treatments. Suitable additional treatments include chemical treatments (such as chlorine, chloramine, chlorite, chlorine dioxide, ozone, organic acids (such as citric and lactic acid), hydrogen peroxide and potassium permanganate. Other ents include gamma wave ation, treatment with steam, treatment with electrified water, and crust-freezing; The process mayalso include r process steps such as curing, g, salting, pickling, or cooking.

Examples The process involved using a CRYOLINE® CF unit which has a temperature control system with an ability to inject cryogenic gases into the unit for cooling purposes.

The cabinet has an inner chamber into which slaughtered y carcases were hung by their legs which allowed the neck skin to hang clear of the bird, and the body cavity entrance to be open.

The unit was set to a temperature that allowed rapid cooling of the skin of the bird and other outer or exposed membranes SUCh that a temperature of below -2 °C achieved, with no. parts going below ~ 3.8 °C. This was achieved via the use of cwogenic gas spray bar which introduced liquid nitrogen into the t, and a ation fan ablevto deliver impingement, or rapid temperature exchange, on the exposed membranes.

The flesh of the bird was not frozen, but the skin and membranes underwent rapid g. This was followed by removal from the unit, and the carcass was then allowed to rise backin temperature to the normal chilled holding range of -1 °C to +4 This process was designed to rapidly cool the surface membrane and campy/obacfer bacteria present upon the carcass es, and to render them into a cold tempered state, similar to that seen just before the product pasSes h the latent heat phase, thus ng full freezing of the poultry carcasses. The rapid cold shock administered to the bacteria on the bird renders them damaged such that during the ature rise back to normal chill temperatures the Campy/abacter bacteria severely damaged or killed, rendering them unable to create ion.

The birds were rapidly chilled in the cabinet and this was completed satisfactorily without the freezing of the muscle units of the birds, in times from around 30 seconds ,30 up to a dwell time of five minutes, depending upon carcass size and ingoing atures ‘ Example 1 The cabinet was set to a temperature of -80 °C (other temperatures delivered the same result but took more or less timer to deliver the cold tempered state). 2012/000499 In some cases the campylobacter bacteria were fully destroyed, and in all cases in excess of a two log ion was delivered. This damage and destruction of Campylobacter is delivered by faster and simpler means than any previous process.

Table 1 indicates the obacter count achieved after treatment of naturally infected chicken or turkey carcasses according to this protocol.

Figures 1 to 5 indicate the temperature profile of the surface of turkey carcasses exposed to rapid chilling conditions at i) the surface and ii) 5mm depth penetration of the wing and breast.

Table 1 Sample Temperature/ SURFACE SURFACE Campylobacter count No TEMP°C_IN °C cfu/g --80°C 2 mins 05°C 0.00E+00 .

°C~80°C 2 mins 1-1.5°C 05°C 0.00E+00 _—=m-1.5°C 0.00E+00 .0.00E+00 ~80°C 6 mins 1-1.5°C 0.3 0.00E+00 A ~80°C 6 mins 1-1.5°C 0.3 00 80°C 5 mins -o.2°c 0.00E+OO _,-80°C 5 mins 1~1.5°c -o.2°c 0.00E+OO ---m~80°05mms_ 1-1.5°C -1.1 0.00E+OO E~80°051mins 1-1.5°C -1.1 0.00E+00 ‘ to -1.9°C CONTROL _ 1.00E+02 E——12 -— 5.00E+01 III-- 3.00E+02 - “- 2.00E+01 1.00E+01 2.00E+02 lt- CONTROL 1.00E+01 IE- 1.00E+01 All birds were pre chilled to 4 °C es testing was completed externally. They were ' treated for between 30 seconds and for 2 minutes under the ions used for Example 1. The reduction in campylobacter count is shown in Table 2.

Table 2 2' 3.. an no t: c 3.. L 1: ‘- ‘O \- .<_> 3 mg or a m 3. 7:1 8- E» E u .5 ~ E. 2 0% “at? "’ “5% «I ‘- m 0 .0) u o m ° a- 0.3 ug Us 2 9 “52 “52 '52 :5 > > a u I“ >- o = e = a § = a 8 is g N 8 ‘V mummwai-a n Control 0 12,000,000 <10 Chicken Control 3,200,000 370 370 25,000,000 ' <10 Chicken Control 23,000,000 460 460 12,000,000 90 Chicken Control 1,900,000 2 10 210 16,000,000 <10 Chicken Control 140,000 60 , 60 13,000,000 <10 Chicken l 380,000 490 490 14,000,000 <10 Chicken l 350,000 830 830 16,000,000 340 Chicken Control 1,100,000 80 <10 21,000,000 <10 Chicken Treated 130,000 <10 <10 12,000,000 _ Chicken d 84,000 <10 <10 14,000,000 <10 Chicken Treated 660,000 <10 <10 16,000,000 <10 Chicken Treated 0 <10 <10 14,000,000 <10 Chicken Treated 0 <10 <10 12,000,000 <10 Chicken Treated 740,000 110 <10 ,000 <10 Chicken Treated 450,000 <10 <10 14,000,000 <10 , Chicken Treated 80,000 <10 <10 13,000,000 <10 Chicken Treated 75,000 <10 <10 13,000,000 <10 Chicken Treated 120,000 , <10 <10 14,000,000 <10 Turkey Control 26,000 50 <10 13,000,000 Turkey Control 58,000 300 60 16,000,000 50 Turkey Control 26,000 140 84 12,000,000 <10 Turkey Control 51,000 , 19,000,000 60 Turkey Treated 17,000 10 10 21,000,000 Turkey Treated 17,000 . <10 <10 23,000,000 '<10 Tu rkey Treated 15,000 20 20 16,000,000 <10 Turkey Treated 35,000 90 90 18,000,000 ,<10 Tu rkey d 9,900 50 30 20 , 19,000,000 Turkey Treated 52,000 23,000,000 Example 3 - 21 _ This example used only chickens. All birds were pre chilled to 4 °C. They were treated for between 1 minute and 2.5 minutes under the conditions used for Example 1. The redUction in campylobacter count is shown in Table 3.

Table3 Initial Bird Treatment ICount (log) Day Control Treated Difference Condition Campylobaoter Campylobacter Count (log) -—__ Example4 Chilled turkey ses (10 in total) at 4 ‘0 are treated under the conditions described in example 1 and held in the cryogenic cabinet for 2 minutes to an average surface temperature of -2 °C. All turkeys are allowed to warm to 4 °C. Five turkeys are allowed to warm over a period of 1 . The remaining turkeys are allowed to warm over a period of 10 minutes. Warming rates are varied by allowing ingress of ambient temperature air at differing rates. The carcasses allowed to warm more y ted lower counts of campylobacter compared with those d to warm‘ Over ' 1 minute; Example 5 d chicken carcasses (10 in total) at 4 °C were treated under the conditions described in example 1 and held in the cryogenic'cabinet for 1 minute or 45 Seconds with the atmospheric temperature at -80 °C. Some birds were removed from the cabinet immediately after treatment, and allowed to warm to 4 °C. A further set of birds were allowed to remain in the cabinet after the cessation of refrigeration, for a period of between 45 seconds and 2 minutes (referred to as "with dwell" birds). The ion in campylobacter count is shown in Table 4.

GEOMETFlIC LOG DIFFERENCE AVERAGE LOG” VALUES (compared to control) CONTROL ‘ '525 1:324 —_“ ‘15“ __“ Conclusions: 0 45 second treatment with no dwell in the cabinet produced almost exactly the same value as control. 0 45 second treatment plus dwell in the cabinet ed a small 0.1 log difference. 0 1 minute treatment looks even more effective than shorter residence times.

Claims (8)

What is claimed 1. is:

1. A process of reducing the number of viable rganisms present on the surface of meat, comprising the steps of: a) providing an untreated meat item having a e membrane and muscle tissue, said untreated meat item having viable microorganisms on the surface membrane, and an atmosphere surrounding the meat item; b) g the meat item by reducing the temperature of the atmosphere surrounding the meat item at a rate of between 0.5 °C/s and 5 °C/s, until the surface membrane reaches a first temperature as measured by a probe inserted within or just below the membrane of between -5 °C and 2 °C; c) allowing the surface ne to warm to a second temperature higher than the first temperature to give a treated meat item; wherein the number of viable microorganisms present on the surface membrane is reduced, whilst the oxyacyl-CoA dehydrogenase (HADH) activity of the muscle tissue is not sed by more than a factor of 2 in the treated meat item compared with the untreated meat item.

2. A process according to claim 1 wherein the temperature of the atmosphere surrounding the meat item in step b) is cooled at a rate of between 0.5 °C/s and 3 °C/s.

3. A s according to any one of the preceding claims wherein cooling step b) is achieved by passage of the meat item through a refrigerated tunnel.

4. A process according to any one of the preceding claims wherein the meat item is selected from a whole poultry carcass, optionally eviscerated.

5. A process according to any one of the preceding claims wherein the meat item is a poultry portion.

6. A process according to any one of the preceding claims wherein the selected second temperature is below 4 °C.

7. A s according to any one of the preceding claims wherein the microorganisms comprise at least Campylobacter species.

8. A s according to any one of the preceding claims comprising at least one further step of curing, smoking, salting, pickling, or cooking the treated meat item. -