The quality of meat and meat products is defined by the following criteria:
- palatability (typical texture and consistency, juiciness, good flavour);
- proportion of lean meat to fat;
- freshness and adequate conservability of the products;
- absence of harmful micro-organisms or substances; and
- appropriate (preferably minimal) use of additives and meat extenders.
The different criteria need different methods of quality control, such as:
- organoleptic evaluation
- physical test methods
- chemical analysis
- microbiological examination
According to the accuracy needed, the control method applied can besimple or more complicated and different auxiliary technical devices mustbe used.
In order to inform consumers and meat processors about the quality ofmeat and meat products, simple and fast control methods are best suited inmany cases, although exact details on residues, toxins and special foodcomponents can only be obtained through specialized laboratories.
Basic methods for quality control must involve little or no equipment andobviously sensory evaluation will be most important. Some physical tests,however, can easily be performed using simple instruments such as thermometers, manometers, scales, etc.
By contrast, chemical and microbiological tests are more complicated.These methods not only require standard equipment but also skilled andexperienced personnel to do the tests and to interpret the results.
The following mainly refers to the basic methods of quality control usedin connection with the handling and processing of meat. These controlmethods can easily be applied for meat products processed with simple meatpreservation techniques.
ORGANOLEPTIC EVALUATION
Organoleptic evaluation consists in describing the attributes of food, in thisspecial case of meat and meat products, that can be perceived by the senseorgans. The attributes to be evaluated are appearance, colour, texture andconsistency, smell and taste.
Appearance
The way meat looks, either as a carcass or as boneless meat cuts, has animportant impact on its objective or subjective evaluation. Grading is anobjective evaluation method in this context. Traditional methods of carcassgrading after slaughter involve the aspect of beef or pork sides, poultrycarcasses, etc. Skilled graders are able to classify different carcasses bychecking the size, the volume of muscular tissue, fat layers, etc. Althoughin modern grading procedures more and more technical equipment has beenincorporated, visual methods are still in use. They can be of special valuein most developing countries where no extremely sophisticated methods areneeded.
The way the consumers or the processors check the appearance of meat issubjective. Differences will be registered in the relation of lean meat and fatincluding the degree of marbling or in the relation of bones and lean meat.Furthermore, unfavourable influences can be detected such as unclean meatsurfaces, surfaces too wet or too dry, or unattractive blood splashes onmuscle tissue.
Processed meat, on the other hand, can roughly be evaluated by itsappearance according to the different raw materials of which the product iscomposed and where the use of some components is exaggerated (forinstance too many particles of visible fat or connective tissue, etc.). Specialproduct treatments (for instance chilling, freezing, cooking, curing, smoking, drying) or the kind and quality of portioning and packaging (casings,plastic bags, cans) will be recognized by evaluating the appearance.
Colour
Under normal circ*mstances the colour of meat is in the range of red andmay differ from dark red, bright red to slightly red; but also pink, grey andbrown colours may occur. In many cases the colour indicates the type andstage of the treatment to which the meat has been subjected, as well as thestage of freshness.
In judging meat colour, some experience is needed to be able to distinguishbetween the colour which is typical for a specific treatment or which istypical for specific freshness. Furthermore, meat deriving from differentspecies of animals may have rather different colours, as can easily be seenwhen comparing beef, pork and poultry meat.
The natural colour of fresh meat, except poultry meat, is dark red, causedby the muscle pigment, myoglobine. Fresh meat surfaces which have beenin contact with the air for only a short period turn into a bright red colourbecause of the influence of the oxygen in the air. Oxygen is easily aggregatedto the myoglobine and drastically changes the colour of the meat surfacesexposed to it. On the other hand, in the absence of oxygen, for example inmeat cuts packaged in impermeable plastic bags, meat surfaces remain orbecome dark red again. The same conditions generally prevail in the interiorof meat cuts which are not reached by oxygen. Changes from dark red tobright red are therefore typical and are normal reactions of fresh meat.
Meat which is in the process of losing its freshness, however, no longershows a bright red colour, even when intensively exposed to the air, becauseof the partial destruction of the red meat pigment which results in a grey,brown or greenish colour. Once these conditions occur the consumer has todecide, after carefully checking the appearance, together with testing smelland taste, whether the meat has to be discarded as a whole or whether usecan be made of some parts which so far have not been altered.
Remarkable changes in the meat colour occur when fresh meat has beenboiled or cooked. It loses its red colour almost entirely and turns to grey orbrown. The reason for this is the destruction of the myoglobine through heattreatment. On the other hand, it has long been known that after pickling(curing) fresh meat with curing ingredients (nitrite), the meat colourremains red during longer storage periods, after ripening, drying and evenafter intensive heat treatment. Obviously the original meat colour has notbeen conserved, but a chemical reaction has taken place during the curingprocess transforming the unstable pigment of the fresh meat into a stable redpigment. This is the typical colour shown in sausages of all types, raw andcooked hams, corned beef, etc.
It should also be noted that cured products have a longer shelf-life thanfresh meat because of the conserving effect of the curing salt. However,cured products will also deteriorate under unfavourable conditions, cookedcured products sooner than raw cured products. Cured products with adecreasing keeping quality can be recognized when the red colour becomespale or changes to grey or green.
Texture and consistency (tenderness and juiciness)
Meat prepared for the consumer should be tender and juicy. Meat tendernessdepends on the animal species from which the meat originates. Lamb, porkand poultry meat are sufficiently tender after slaughter, but beef requires acertain period of maturation to achieve optimal eating quality.
Texture and consistency, including juiciness, are an important criterion,still neglected by many consumers, for the eating quality of meat. Oftenconsumers do not know that the eating quality of meat can be upgraded byripening, especially in the case of beef and similar meats. There is also agreat deal of consumer negligence in how to prepare meat. It should becooked to become sufficiently tender, but cooking should not be too intenseotherwise the meat becomes dry, hard and with no juiciness.
The simple way to check the consistency of foods is by chewing. Althoughthis test seems easy, in practice it is rather complicated. Taste panelists needexperience, particularly when the different samples have to be ranked, forexample which sample is the toughest, the second toughest or the mosttender.
The texture is of less importance in meat products, such as cured or cannedproducts, sausages, etc., because they are either made of comminuted meatand/or meat which has undergone heat treatment or long maturation periodsand will therefore generally be tender. On the other hand, inadequateprocessing methods (too intensive cooking, curing, comminuting) maycause losses in the desired consistency and juiciness, and the best way tocheck this is by chewing.
Smell and taste (aroma and flavour)
These characteristics are related to each other to a certain extent becausethey have to be evaluated together for the reliable determination of aproduct's flavour. The smell of fresh meat should be slightly acidic,increasing in relation to the duration of the ripening period because of theformation of acids such as lactic acid. On the other hand, meat in decomposition generates an increasingly unpleasant odour owing to substancesoriginating from the bacterial degradation of the meat proteins, such assulphur compounds, mercaptane, etc.
The freshness of meat is generally indicated by its smell together with itsappearance and colour. Sorting out deteriorated meat is mandatory from thepoint of view of the product's palatability. It is also important because of thefact that high bacterial contamination of meat in decomposition could beaccompanied by food-poisoning bacteria(pathogens), which have a deleterious impact on consumers' health. On the other hand, the best fresh meatcan also be heavily contaminated with food-poisoning bacteria becausethese micro-organisms do not cause organoleptic alterations by destructionof meat proteins. Food poisoning can therefore only be avoided by properhygienic meat handling. The flavour of fresh meat can also be checked byputting small samples (approx. 10 pieces of 1 cm3 each) in preheated waterof 80°C for about five minutes (boiling test). The odour of the cooking brothand the taste of the warm meat samples will indicate whether the meat wasfresh or in deterioration or subject to undesired influences, for instancerancidity of the meat fat, any a typical meat flavour due to the feed and thesex (boar taint) of the animal or treatment with veterinary drugs shortlybefore slaughter.
When processing the meat, the smell and taste of the meat products candiffer a great deal owing to heat treatment and the use of salt, spices and foodadditives. Every meat product has its typical smell and taste, and the testperson should know about it. Changes in these qualities indicate the use ofimproper raw materials or a deterioration of the meat product duringstorage.
Experience is required to become acquainted with the typical flavour(smell and taste) of foods. Only four basic taste components--sweet, sour,bitter and salty--will be perceived by the taste buds. These receptors aresmall papillae located in certain areas of the tongue. However, the overallflavour consists of smell and taste produced by the meat components andinfluenced and covered by spices and those compounds produced byripening or heat treatment. Flavour test panelists should be aware of thesespecial cases. Panelists should not smoke or eat spicy meals before startingthe test and should rinse their mouth frequently with warm water during thetest.
Sensory evaluation plays an important role in the examination of meat andmeat products. Not only does scientific sensory evaluation with skilledpanelists using special test programmes and point systems give reliableresults, but useful results can also be obtained in a simple way at theconsumer level. For the average consumer sensory evaluation is the onlyway to decide whether or not he or she should buy or eat a certain product.
In developing countries consumers do not receive sufficient informationand training on this point, although it is often the only means available forquality control. Sensory evaluation is easy to understand and to perform.What is needed is a basic knowledge of the composition of foods and theirtypical texture, colour and flavour.
PHYSICAL TEST METHODS
Physical test methods focus either on the actual condition of meat and meatproducts, or on the conditions around the product, for example in storagerooms, packages, etc. Equipment will be needed for all these tests which iseasily applicable and resistant to utilization under the conditions of practicalmeat handling and processing.
Temperature
Storage of meat and meat products requires low temperatures to make surethat the growth of micro-organisms will be retarded (chilling between-1 to+4°C) or inhibited (freezing preferably in the range of -18 to -30°C).
Cooking of meat requires high temperatures (starting from a temperatureof about 55°C needed for denaturation, but generally higher temperaturesare applied, up to 100°C).
Canning of meat requires temperatures above 100°C, and for sterilizedproducts where all micro-organisms are inactivated, at least 121°C.
These examples demonstrate the importance of different temperatures fordifferent purposes and the necessity of exact temperature measurementsusing thermometers or temperature recorders.
Glass thermometers should not be used in direct contact with meat becausethey may break, leaving undesired fragments in the meat, but they are usefulwhen permanently fixed to walls of chillers or production rooms or tocooking equipment or autoclaves for easy checking of the relevant temperatures.
Mechanical bimetal-thermometers, utilizing the extension or contractionof a bimetal spiral under various temperatures, are not very accurate and notsufficiently shock-resistant for practical work in meat industries. Nevertheless, they are widely used and can serve for rough estimates.
Electrical thermometers (Fig. 33), consisting of a sensor and a battery-powered electronic instrument, are well suited for meat industries. Thesensor functions as a semiconductor. Under different temperatures, differences in the electric conductibility of the sensor are produced. The temperature which the sensor takes up by contact to the surrounding media (water,air, meat, etc.) produces a certain voltage in the electric system. This voltageis registered and displayed as a digital reading of the actual temperature onthe instrument.
Advantages of modern electronic thermometers are:
- no glass or other parts that can easily break;
- the sensor can be easily pushed deep into the meat, as well as into frozenmeat, and is also heat-resistant under sterilization temperatures;
- display of the correct temperature within seconds;
- no frequent calibration necessary;
- a wide range of temperatures can be covered using one instrument (thetemperature range of the instruments recommended for use in meatindustries should be between +140°C and -40°C); and
- accurate temperature measurement, also in decimals.
Humidity
In some special field of meat processing and storage, air humidity is ofimportance.
In cutting rooms the humidity of the air should be below the level whichwould cause vapour condensation on the surfaces of the meat being debonedand cut. Vapour condensation may enhance bacterial growth.
Storage chillers for fresh meat require a balanced air humidity that does notcause wet surfaces on the meat with resulting accelerated bacterial growth,but on the other hand keeps evaporation losses low. The relative humidityrecommended for this special purpose lies in the range of 70 percent.
Chambers for the maturation of raw hams or dry sausages of the salamitype require controlled air humidity, starting from 90–95 percent and aftera certain period finalizing the process at 70–75 percent relative humidity.This procedure is important for the balanced drying and ripening of theproducts. Suitable instruments (hygrometers) for the exact measurement ofrelative humidity are therefore needed.
In simple but less accurate hygrometers a hair or special synthetic fibre isconnected with a pointer and, according to the contraction of the hair or fibreunder dry conditions and its extension under wet conditions, the pointerindicates the actual relative humidity on an appropriate scale.
A more accurate way for humidity control is the psychrometric system.These instruments use a dry and a wet sensor to define the ambientaltemperature. The temperature indicated by the wet sensor will always belower, in this case, because of evaporative cooling. The drier the air, themore intensive evaporative cooling will be. Using both temperature values(dry and wet temperature), the value of the relative humidity is determinedin practical work using a table for easy calculation.
A modernized psychrometric system which uses electronic devices isavailable. In this case the humid sensor has not actually to be kept wet, butconsists of hygroscopic material with altering electrical resistance. Therelative humidity calculated from the temperatures delivered by the sensorsby means of a micro-processor is directly displayed on the instrument (Fig.34).
Water activity (aw)
Water activity is the free water available for microbial growth in a foodproduct. Free water is that part of the water content that can be eliminatedfrom the product in the form of water vapour. Hence, the term “wateractivity” is defined as the ratio of the water vapour pressure measured in theproduct and the pressure of a saturated water vapour atmosphere at the sametemperature. This physical definition is used in connection with a numberof meat products whose keeping quality depends on their water content.Micro-organisms need a certain degree of moisture to be able to grow onfoods. The minimum moisture content necessary for microbial growthvaries with the single species of micro-organisms and can be expressed interms of minimum water activity required.
The lowest aw-values permitting growth of spoilage organisms are:
- normal bacteria 0.91
- normal yeasts 0.88
- normal moulds 0.80
- halophilic (NaCl-tolerant) bacteria 0.77.
The keeping quality of dried meats and meat products without refrigeration depends on their water activity. Dried meat such as biltong, charque,etc. reaches a sufficiently low water activity to be shelf-stable. However,water activity should decrease as fast as possible as slow drying could causedeterioration in a prolonged phase of the process with a still high wateractivity. The situation is more complicated in the case of products whichcannot be dried too intensively such as dry sausages or raw hams. The wateractivity of these products is relatively low but would still allow the growthof some undesired micro-organisms. Under these circ*mstances an appropriate shelf-life has to be ensured by the combination of several inhibitingfactors, i.e. water activity, content of salt and curing ingredients and theacidity of the product.
Information on the water activity of certain products can be important forfurther handling, packaging and storage. Simple methods for the determination of water activity are therefore useful.
As water activity refers only to the water available for microbial growthin a product, the chemical analysis of the total moisture content is of limitedvalue since it would also include the water bound by the proteins. The properway to determine water activity is to measure the humidity of the remainingair in a hermetically closed small cabinet which is to a certain extent filledwith the product sample. After a short time a hygroscopic equilibriumbetween the sample and the surrounding air will be reached. Thus, thehumidity determined in the air is equivalent to the humidity available in theproduct and water activity can be calculated.
For the measurement of air humidity under these conditions, the sameprinciples apply as previously described. Simple devices utilize the extension or contraction of hairs or synthetic fibres, and more sophisticated andmore expensive systems use electronic devices.
The sample is placed in the bottom part of the tin and then the lid of thetin that contains the device to measure the humidity is hermetically screwedon. After two hours, hygroscopic equilibrium is reached in the can and thereading of the instrument corresponds to the actual water activity of theproduct, provided the test has been carried out at a temperature of exactly25°C. If this temperature cannot be maintained, corrective calculations willbe necessary.
Some examples for values of water activity (aw) of different products areshown:
| fresh raw meat | 0.99–0.98 |
| cooked ham | 0.98–0.96 |
| frankfurter-type sausages | 0.98–0.93 |
| liver sausage | 0.97–0.95 |
| raw cured ham | 0.96–0.80 |
| dry sausage (salami type) | 0.96–0.70 |
| dry meat | 0.75–0.50 |
A certain number of micro-organisms are inhibited at aw 0.95, but otherspecies are still able to grow. At aw 0.92 all bacteria groups are inhibited, butthe growth of moulds and yeasts is still possible.
Airtight closure of cans
For shelf-stable canned meat products two aspects are important from themicrobiological standpoint. During sterilization, micro-organisms andtheir spores have to be inactivated and the can must be hermetically sealedto avoid further contamination of the product after sterilization.
Invisible small perforations of the tinplate or small defects after the closureof the lid will inevitably lead to a recontamination by penetrating bacteriaand after a short time spoilage of the canned product will occur. Cans shouldtherefore be checked from time to time for these defects.
A simple method is available for this purpose. Using an air-pump with aspecial device to penetrate the tinplate, the air is pumped into a closed butempty can (Fig. 35). The internal pressure built up in the can can becontrolled by a manometer connected with the air pump. When dipping theinflated can into water it can easily be seen whether the can is hermeticallysealed and if not where the cause for the permeability is, either in theprefabricated body (side wall and bottom) of the can or in the area of the lidseam. In the latter case the function of the can-closing equipment in theprocessing plant has to be thoroughly checked.
Weight differences
The high water content of meat (approx. 70 percent) and meat products(which varies from 70 percent to 10 percent) causes weight differencesowing to evaporation losses or drip losses that occur during handling,processing or storage.
Unpackaged meat and meat products are especially subject to considerableevaporation losses. During chilling of warm carcasses evaporation losses of1 to 2 percent cannot be avoided but further evaporation losses of chilled orfrozen meat should not occur when suitable storage conditions (not too dry)or suitable packaging (plastic bags, containers, boxes) are employed.However, some drip losses of packaged meat cannot be avoided.
During meat processing weight losses of meat by cooking, frying or otherheat treatment can be registered and reach high values (up to 30 to 35percent). These losses are unavoidable.
On the other hand, some meat products require weight losses by evaporation to reach their specific keeping quality, for example raw hams, drysausages or dried meat. In this case, water activity as previously describedplays an important role.
Information on weight losses in meat handling and processing is importantfrom the economic and technological point of view. Weight losses can easilybe determined using scales of different types, such as suspension scales forcarcasses or batches of products and horizontal scales for packages orportions.
Salt concentration in brines
In addition to dry curing methods (dry salt and curing ingredients on themeat), brines are also used for pickling and curing the meat. Brines containsalt and in most cases also sugar and nitrite dissolved in water. With thiscuring process, meat is either immersed into a brine or the brine is injectedinto the meat with special devices. In both cases salt is a limiting factor forthe sensory quality of the products; in other words salt is needed but shouldnot exceed 2.5 to 3 percent in cooked cured products and 4.5 to 5 percent inraw cured and dried products.
To comply with these requirements, simple methods for testing saltconcentration in brines are necessary. For this purpose salimeters haveproved to be a useful piece of equipment. Salimeters are densimeters, thegraduation showing salt concentrations. Salimeters are dipped into the brineand according to a lower or higher salt content they sink deeper or less deepinto the brine. The reading of the salimeters at surface level indicates the saltconcentration of the brine. The various technologies of meat curing usebrines with NaCI-concentrations in the range of 8 to 22 percent.
FIG. 35.
Mechanical instrument to prove airtight closure of cans.
OTHER PHYSICAL TEST METHODS
The physical test methods which have been described can easily beperformed since the use of the technical equipment necessary is not toocomplicated. Other physical test methods exist too, for example, lightintensity measurement, colour measurement or texture and consistencymeasurements of meat and meat products. These tests require rathercomplicated and expensive instruments and skilled technical personnel. Forroutine work, criteria such as light, colour, texture and consistency can beevaluated in a satisfactory way by using the corresponding sensory testmethods.
Chemical analysis
Chemical characteristics of foods are related to the product itself and referprimarily to the content of specific substances, which are important from thepoint of view of keeping quality, flavour, nutritional value, etc., or whichmay also represent harmful residues.
The test methods necessary are generally complicated and need sophisticatedequipment. However, there are also some simple and quick methodsfor chemical testing with sufficient accuracy which can be applied in thedaily routine work such as pH-measurement, moisture/fat/protein determination and various screening methods utilizing test paper strips.
pH-measurement
The pH-value or acidity of meat is important in relation to the meat'smicrobiological and keeping quality. In the live animal the pH-value of themuscular tissue is about 7.0 to 7.1. Very soon after slaughter a drop in thepH-value is observed and after several hours (24 hours or less) the pH-valuereaches its lowest level of about 5.6 to 5.8. The increasing acidity is becauseof the post-mortem formation of lactic acid from glycogen, a sugar-likesubstance stored in the live animal's muscles for energy supply.
In meat lactic acid causes a decrease in pH-value which is favourable forkeeping quality (low pH inhibits bacterial growth) and for flavour (acidityis one of the components of meat flavour). However, the pH of meat is notuniform either in different carcasses or in different muscles of one carcass.Physiological oscillations do not greatly harm meat quality but abnormalreactions in meat are of great economic, hygienic and technological impact.
There are two types of abnormal reaction with regard to the pH in meat.First the pH-value may drop too fast and second it may not reach the normallow level several hours after slaughter, but remain in the range of 7.
Both abnormalities can easily be detected by pH-measurement in the meat.A too fast pH-value decrease is evident, when one hour after slaughter lowpH-values in the range of 5.6 to 5.8 are already reached. This phenomenonoccurs only in pigs and the meat remains pale, soft and exudative (PSE).Because of its paleness and wetness (low water-holding capacity), this meatshould not be used for ham and sausage manufacture (gives dry, tastelessproducts).
An insufficient decrease of the pH-value, which occurs both in pork andbeef, is of hygienic significance because of the lack of building up a certaindegree of acidity and suppressing microbiological growth. This meat alsoremains close to pH-value 7 after several hours, and is dark, firm and dry(DFD). It should not be used for meat and meat products which have to bestored over a longer period, such as vacuum-packed meat cuts, dry sausagesof the salami-type or cured raw hams. However, it is well suited for cookedmeat products because of its extremely good water-holding capacity.
It can be seen from this that the pH-measurement is of particular importancefor the selection of the raw material for meat processing purposes.Hence, portable electric pH-meters are widely distributed and utilized in themeat industry (Fig. 36).
The pH is measured on meat surfaces or in the meat itself, in the latter caseby pushing the sensor into the muscle or by means of an incision using aknife. The sensor consists of a glass electrode filled with an electrolyte(solution of KC1) and a sensitive glass membrane attached at the top.
Through the membrane the difference in the hydrogen-ion concentration,which corresponds to the acidity of the meat, is detected and digitallydisplayed on the attached instrument.
pH-measurement on meat can easily be performed but the following pointsmust be considered:
- the electrode sensor must be completely filled with the electrolyte;
- the instrument must be adjusted daily (calibrated) using two buffersolutions with pH-values 4 and 7;
- after each measurement the electrode must be cleaned using distilledwater;
- before each measurement the temperature of the meat, meat product,etc. must be checked and the instrument adjusted accordingly.
Moisture/fat/protein determination
Information about the moisture, fat and protein content is essential for theevaluation of the quality of different meats and meat products. Determinationmethods have changed a great deal in this field in recent years.Revolutionary techniques were introduced using X-rays, infra-red radiationor microwaves in automatic equipment for quick analyses of moisture, fatand protein. These modern methods are time-saving, the results are deliveredwithin minutes or seconds and high numbers of samples can be tested.However, the equipment is expensive and therefore not suitable for smallindustries. For routine controls, where not necessarily highly accurate butreliable results on moisture, fat, protein and anorganic components (ash) areneeded, cheaper and less complicated methods can be applied. A speciallydesigned laboratory scale, together with some other devices, is required.After hom*ogenizing and weighing the sample, it is fast dried using an infraredbeam (or a microwave oven if available). The weight difference isequivalent to the product's water (moisture) content. The fat is thendissolved using a fat-extracting liquid and removed together with the liquid.The solvent is evaporated. The weight of the residue represents the fatcontent of the sample. Finally, the sample is charred in a muffle furnace andthe weight of the residue is the ash content. Since the sum of the percentagesof moisture, fat, ash and protein must be 100, and since the percentage ofmoisture, fat and ash is known, the protein content in percent is calculatedas follows: 100% minus the percent of moisture, fat and ash. This methodis not precise, but it is fast, provides useful results about the composition ofmeat and meat products and can be applied without high costs.
For chemical evaluations a number of screening methods are also availableusing different test papers. The results are indicated by changes of the colourof certain areas on the paper strips. These test papers are used for pH-measurement, screening of the nitrite content and even for the screening ofsome harmful residues such as antibiotics. pH-measurements on meat withtest strips are negatively influenced by the meat pigment making the colourdetermination often difficult and the pH-determination not very accurate.
MICROBIOLOGICAL EXAMINATION
These control methods cannot be carried out without laboratory equipment,because they require sample preparation under sterile conditions, incubation of the samples under constant temperatures and sufficient microbiological knowledge on the part of the personnel involved to interpret theresults. However, the application of microbiological methods is the onlyway to obtain information about the hygienic status of places, equipmentand foods. It is true that unclean conditions will always indicate highmicrobiological contamination and one could argue that a thorough cleaning-up rather than a further microbiological analysis would be needed inthose cases. But there could also be the need of detecting the source ofpermanent contamination (for example through the water, movement ofpersonnel, raw material delivered, etc.) or of food poisoning bacteria. Underthese circ*mstances microbiological examinations can often be very helpfuland solve immediate problems.
Some methods suitable for routine work should be mentioned.
Trigger methods
Microbiological culture media in special small moulds are lightly pressedagainst walls, equipment (knives, machines), meat surfaces or hands ofpersonnel. The micro-organisms adherent to these objects are absorbed bythe surface of the culture media, and after adequate incubation (one to twodays at 30 to 37°C), microbial colonies can be identified and counted on themedia. Each one of the colonies grown during incubation corresponds to onemicro-organism which was on the object tested.
Instead of culture media a special sterile strip of cellotape together with atrigger can be used for taking samples from surfaces (Fig. 37). After that thecellotape is laid on a culture media for incubation. This procedure allows theutilization of one culture medium for the incubation of different samples atthe same time (Fig. 38). However, there is one disadvantage with the triggersystem. In the case of high bacterial contamination of the surfaces, testedbacterial colonies will grow very densely together and can no longer becounted.
Swab method
Surface contamination related to a certain area can be sampled using a sterileswab. After rubbing the swab gently along the surface to be tested (Fig. 39),it is suspended on the surface of a culture media. In contrast with the triggermethod, bacterial contamination can be spread over the whole surface (Fig.40) which is important in the case of high contamination. Thus the samplescan always be evaluated since the single colonies are not grown together(Fig. 41). However, the method lacks some accuracy since bacteria mayremain in the swab.
FIG. 37.
Trigger and sterile cellotape for microbiological sampling of the meat surface.
FIG. 40.
Transfer of the sample taken with swab on to the surface of the culture medium.
FAO TECHNICAL PAPERS
FAO ANIMAL PRODUCTION AND HEALTH PAPERS:
1. Animal breeding: selected articles from World Animal Review, 1977 (C* E*F* S *)
2. Eradication of hog cholera and African swine fever, 1976 (E * F * S *)
3. Insecticides and application equipment for tsetse control, 1977 (E * F *)
4. New feed resources, 1977 (E/F/S *)
5. Bibliography of the criollo cattle of the Americas, 1977 (E/S *)
6. Mediterranean cattle and sheep in crossbreeding, 1977 (E * F *)
7. Environmental impact of tsetse chemical control, 1977 (E * F *)
7 Rev. Environmental impact of tsetse chemical control, 1980 (E * F *)
8. Declining breeds of Mediterranean sheep, 1978 (E * F *)
9. Slaughterhouse and slaughterslab design and construction, 1978 (E * F * S *)
10. Treating straw for animal feeding, 1978 (C *, E *, F *, S *)
11. Packaging, storage and distribution of processed milk, 1978 (E *)
12. Ruminant nutrition: selected articles from World Animal Review, 1978 (C * E * F * S *)
13. Buffalo reproduction and artificial insemination, 1979 (E **)
14. The African tripanosomiases, 1979 (E * F *)
15. Establishment of dairy training centres, 1979 (E *)
16. Open yard housing for young cattle, 1981 (E * F * S)
17. Prolific tropical sheep, 1980 (E * F * S *)
18. Feed from animal wastes: state of knowledge, 1980 (E *)
19. East Coast fever and related tick-borne diseases, 1980 (E * S *)
20/1. Trypanotolerant livestock in West and Central Africa, 1980Vol. 1 - General study (E * F *)
20/2. Trypanotolerant livestock in West and Central Africa, 1980
Vol. 2 - Country studies (E * F *)
20/3. Le bétail trypanotolérant en Afrique occidentale et centrale
Vol. 3 - Bilan d'une décennie, 1988 (F *)
21. Guidelines for dairy accounting, 1980 (E *)
22. Recursos genéticos animales en América Latina, 1981 (S *)
23. Disease control in sem*n and embryos, 1982 (E * F * S *)
24. Animal genetic resources - conservation and management, 1981 (E *)
25. Reproductive efficiency in cattle, 1982 (E * F * S *)
26. Camels and camel milk, 1982 (E *)
27. Deer farming, 1982 (E *)
28. Feed from animal wastes: feeding manual, 1982 (E *)
29. Echinococcosis/hydatidosis surveillance, prevention and control: FAO/UNEP/WHO guidelines, 1982 (E *)
30. Sheep and goat breeds of India, 1982 (E *)
31. Hormones in animal production, 1982 (E *)
32. Crop residues and agro-industrial by-products in animal feeding, 1982 (E/F *)
33. Haemorrhagic septicaemia, 1982 (E * F *)
34. Breeding plans for ruminant livestock in the tropics, 1982 (E * F * S *)
35. Off-tastes in raw and reconstituted milk, 1983 (E * F * S *)
36. Ticks and tick-borne diseases: selected articles from World Animal Review, 1983 (E * F * S *)
37. African animal trypanosomiasis: selected articles from World Animal Review, 1983 (E * F *)
38. Diagnosis and vaccination for the control of brucellosis in the Near East, 1983 (Ar * E *)
39. Solar energy in small-scale milk collection and processing, 1983 (E * F *)
40. Intensive sheep production in Near East, 1983 (E * Ar *)
41. Integrating crops and livestock in West Agrica, 1983 (E * F *)
42. Animal energy in agriculture in Africa and Asia, 1984 (E/F *)
43. Olive by-products for animal feed, 1985 (Ar * E * F * S *)
44/1. Animal genetic resources conservation by management, data banks and training, 1984 (E *)
44/2. Animal genetic resources: cryogenic storage of germplasm and molecular engineering, 1984 (E *)
45. Maintenance systems for the dairy plant, 1984 (E *)
46. Livestock breeds of China, 1985 (E *)
47. Réfrigération du lait à la ferme et organisation des transports, 1985 (F *)
48. La fromagerie et les variétés de fromages du bassin méditerranéen, 1985 (F *)
49. Manual for the slaughter of small ruminants in developing countries, 1985 (E *)
50. Better utilization of crop residues and by-products in animal feeding: research guidelines - 1. State of knowledge, 1985 (E *)
50/2. Better utilization of crop residues and by-products in animal feeding: research guidelines - 2. A pracital manual for researchworkers, 1986 (E *)
51. Dried salted meats: charque and carne-de-sol, 1985 (E *)
52. Small-scale sausage production, 1985 (E *)
53. Slaughterhouse cleaning and sanitation, 1985 (E *)
54. Small ruminants in the Near East: Vol.I 1986 (E *)
Selected papers presented at Tunis Expert Consultation
55. Small ruminants in the Near East: Vol II 1986 (Ar * E *)
Selected papers from World Animal Review
56. Sheep and goats in Pakistan, 1985 (E *)
57. Awassi sheep, 1985 (E *)
58. Small ruminant production in the developing countries, 1986 (E *)
59/1. Animal genetic resources data banks, 1986 (E *)
1 - Computer systems study for regional data banks
59/2. Animal genetic resources data banks, 1986 (E *)
2 - Descriptor lists for cattle, buffalo, pigs, sheep and goats
59/3. Animal genetic resources data banks, 1986 (E *)
3 - Descriptor lists for poultry
60. Sheep and goats in Turkey, 1986 (E *)
61. The Przewalski horse and restoration to its natural habitat in Mongolia, 1986 (E *)
62. Milk and dairy products: production and processing costs, 1988 (E * F * S *)
63. Proceedings of the FAO expert consultation on the substitution of imported concentrate feed in animal production systemsin developing countries, 1987 (E *)
64. Poultry management and diseases in the Near East, 1987 (Ar *)
Availability Janurary 1990
Ar - Arabic
C - Chinese
E - English
F - French
S - Spanish
* Available
** Out of print
*** In preparation
The FAO Technical Papers are available through the authorized FAO Sales Agents or directly from Distribution and Sales Section, FAO,Viale delle Terme di Caracalla, 00100 Rome, Italy.
