processing of poultry || utilisation of turkey meat in further-processed products

9

Utilisation of Turkey Meat in Further-processed Products

R. I. RICHARDSON

Agricultural and Food Research Council, Institute of Food Research, Bristol Laboratory, Langford, Bristol, UK

1. INTRODUCTION

World turkey meat production has continued to increase over the last few years, with the United States of America still producing half the total output. Surveys of consumer attitudes would suggest that there are three main reasons for this popularity. Turkey meat is relatively cheap (and therefore seen as value for money), it has a healthy image (from a perception of low fat and saturated fatty acid content), and it is now available in more varied and interesting forms (i.e. further processed). The importance of this last view is well illustrated by production figures for the United Kingdom shown in Fig. 1. Total bird production has risen, mainly due to an increase in the numbers being further processed. Whole-bird consumption is virtually static and highly seasonable, with over 60% being sold in the Christmas and New Year period. A similar pattern has been seen in the USA (Fig. 2). In the 10 year period, 1975-85, the amount of turkey meat being further processed in the USA increased from 29% to 46% of total production. Production and consumption data for the European Economic Community, USA and Israel are shown in Table 1. It is noticeable that countries with high consumption have a large proportion of their production in further-processed products. In Italy, for instance, turkey meat has always been sold as cut-portions, in direct competition with veal and pork; latterly, a small proportion (6%) has been used for other further-processed lines.

The term 'further processing' encompasses such processes as portioning, deboning, size reduction, tumbling, massaging, reforming, emulsifying, breading, battering, marinading, cooking or smoking.

283 G. C. Mead (ed.), Processing of Poultry© Chapman & Hall 1995

284

U) "E li '0 t/) c: ~ I "S a. "S 0

20

10

R. I. Richardson

76 77 78 79 80 81 82 83 84 85 86

Year

FIG. 1. Number of turkeys produced in the UK and used either as whole birds (-0-), for catering (--<>--) or for further processing (-6-) in the period

1976-1986.

U) Q) c: c:

1500

.9 1000 o o e. c: o :u ::J 500 e

Cl.

61 66 71 76 81 86

Year

FIG. 2. Turkey meat output in the USA during the period 1962-86 and used either whole (-0-), further-processed whole or further-processed cut -up (--+-), further-processed as cut-up (--<>--) or as cut-up portions (-0-). From 1974 further-processed whole and further-processed cut-up were treated as separate categories by the US Department of Agriculture. (Data from US

Dept of Agriculture.)

Turkey Meat in Further-processed Products 285

TABLE 1 PRODUCfION AND CONSUMPTION OF TURKEY MEAT

Belgium/Luxembourg Denmark Eire France Greece Italy Netherlands UK West Germany Portugal Spain Israel USA

Production ('000 tonnes) 1975 1986

6·0 4·4 1·7 4·0

NA 16·0 93·0 289·0 NA 3·0 NA 234·0 14·6 22·0 85·0 155·6 17·0 73-0 19·0 20·0 NA 19·0 NA 43·0

981·8 1790·0

~~-~-~~--- ---

Consumption Proportion cut-up or (kg/head) further-processed

1986 (%) 1986

1·5 31 0·4 3 4·4 NA 4·5 87 0·3 NA 4·1 95 1·3 10 3·0 55 1·9 73 2·0 NA 0·4 NA 9·5 95 6·1 76

- --- -------

Data from US Department of Agriculture (1987) and Anon. (1987b). NA, no data available.

Whole carcasses which undergo any of these processes may also be referred to as 'further processed'. Further processing leads to a better utilisation of carcass meats, can up-grade off-cuts or poorer cuts, offer portion control, convenience, variety and relatively consistent product quality. Turkey meat is now used for making many traditional products previously made from red meats, as well as a variety of recently developed turkey products. These now include cut-portions, reformed roasts, rolls, escalopes, grillsteaks, burgers, turkey hams, nuggets, sausages, frankfurters, salamis, bolognas, etc. More recently, ready-prepared meals have utilised an increasing amount of turkey meat (Anon., 1987a). The distribution between fresh and frozen sectors for the entire further-processed poultry market in the UK is seen in Fig. 3.

Turkeys are very efficient feed-converters compared with red-meat species, and the modern, large, fast-growing strains have very good lean-meat to bone ratios. What is more important is the fact that, as the large birds bred for processing reach their optimum weight. the more favoured parts of the carcass, i.e. the breast and thigh meats,

286 R. I. Richardson

OTHERS

R CIPE DISHES

TURKEY ROLLS ROASTS -----:7"'-- -\--7

FRESH FROZEN

CCO<ED

CHICKEN

OTHERS

FIG. 3. UK poultry meat retail sales divided into product type groupings and fresh versus frozen. Total retail sales for the year March 1986-March 1987

were £344 million. (Data derived from Anon. (1987a».

increase as a proportion of the total carcass weight, whereas the less favoured parts decrease (Leeson & Summers, 1980; Peng et al., 1985). Indeed, Larsen et al., (1986b) concluded that, since the breast meat is the most valuable part of the bird and it increases both in terms of absolute weight and as a proportion of the whole carcass, turkeys could probably be grown larger and older than is currently the practice in the USA, without too much sacrifice of feed-conversion efficiency or increased fatness. It is more efficient for a processor to debone larger carcasses, but handling procedures should be monitored to avoid the increased damage to these larger birds that has been seen in some plants.

2. FUNCTIONAL PROPERTIES OF TURKEY MEAT

2.1. Structure of Turkey Meat The structure of turkey meat is similar to that of other meats, and has been reviewed by Jones (1980) and Dutson & Carter (1985). Each


muscle contains large numbers of elongated muscle cells (fibres) which, in turn, contain numerous filaments (myofibrils). Associated with these elements are membranous structures, and the fibres are bathed in inter- and intracellullar fluids. Muscle proteins are conveniently sub-divided on the basis of their localisation within the muscle; this division also approximates to their sub-division on the basis of solubility.

The sarcoplasmic proteins are in solution in the intracellular fluid, and are soluble at low ionic strength (11 < 0·05) and neutral pH. This fraction contains many of the soluble enzymes of the cell, along with myoglobin, and makes up some 30% of the total protein in chicken and turkey muscle (Khan, 1962; Scharpf & Marion, 1964).

The myofibrillar proteins are an integral part of the muscle fibre and contain the contractile and regulatory proteins responsible for musculature contraction in the living bird. They are extracted at ionic strengths between 0·225 and 1·500 11. They make up some 55% of the total muscle protein, the most important for meat restructuring being actin and myosin. The many individual proteins found in this fraction are dealt with in reviews by Asghar et al. (1985) and King & Macfarlane (1987).

The stromal proteins are generally regarded as those not allocated to the sarcoplasmic or myofibrillar fractions. They are mainly the connective tissue proteins (collagens) that surround the whole muscle (epimysium), fibre bundles (perimysium) and individual fibres (endomysium). Collagen is insoluble in neutral aqueous solutions. In meat, it contributes to background toughness, the extent of which depends upon the amount present, the type, and the temperature to which the meat has been heated. In well-cooked meat, collagen toughness is reduced.

Myofibrillar proteins can also contribute to meat toughness. This depends upon the contractile state of the muscle, but is not seen until the cooking temperature rises above 60°C.

2.2. Meat Functionality The functional properties of meat systems are mainly conferred by the meat proteins. The functional properties of the proteins are, in turn, conferred by their physico-chemical properties. In a food system, the important functional properties are those which contribute to the behaviour of the food during preparation and storage, and which determine the eating quality of the product. Wilding et al. (1984) have


listed the functional properties of proteins in food systems as being:

Colour Solubility Turbidity Flavour Water holding Stabilisation Texture Gelling Viscosity Smoothness Adhesion Syneresis Chewiness Emulsification Elasticity Grittiness Foaming Extrudability Fibre formation

These are all perceived attributes and cannot be easily related to physical or chemical properties of the protein in question; neither do all the attributes apply to all protein systems. Some of the relevant physico-chemical properties are: surface charge, association/ dissociation behaviour, molecular weight, shape, hydrophobicity and thermal stability, which are conferred by the primary, secondary, tertiary and quaternary structure of the proteins. Kinsella (1982) discussed the factors which can determine or modify the functional properties of proteins.

2.3. Methods of Assessing Functionality Most methods for measuring functionality are based on model systems, or involve systems that differ from those which might be used for product manufacture. Care should be taken, therefore, if these results are to be used to predict the behaviour of meats during product manufacture, especially for products which contain larger meat particles as opposed to comminutes.

Protein extractability is usually measured in a system where the meat is either minced or highly comminuted in salt solutions, with high solution to meat ratios. Samples are centrifuged and the protein content of the supernatant measured (Carpenter & Saffle, 1964; Acton, 1972b; Porteus, 1979).

Bind and gelation have been measured in a number of ways, using whole-meat systems, mixtures of salt-extractable proteins or purified indiyidual proteins. In whole-meat systems, such as restructured steaks, puncture probes or breaking bars are pushed down through samples suspended on a base (e.g. Pepper & Schmidt, 1975). Alternatively, slices of cooked product are held in pneumatic jaws or


glued to support stubs, and pulled apart in an instrument such as the Instron Universal Materials Testing Machine, thus measuring the adhesive or tensile strength of the product (e.g. Purslow et al., 1987).

Trautman (1964) introduced the concept of 'least concentration end-point', a measure of the least concentration of isolated protein required to form a gel, which would remain in a test-tube upon inversion. More sophisticated methods of measuring gel strength or rigidity have since been developed. Reviews by Acton et al. (1983) and Asghar et al. (1985) should be consulted for details. Other methods have included differential scanning calorimetry (Wright et al., 1977) and changes in the optical density of dilute protein solutions during heating (Deng et al., 1976).

Objective measurements for predicting water holding in meat systems are many and varied. Methods used can be divided into those intended for raw samples and those for cooked. In the filter-paper press method of Grau & Hamm (1957), meat samples are placed on filter-paper and pressed between two plexiglass plates. The area of the ring of expressed juice absorbed by the filter paper is calculated as a percentage of the area of the meat sample. Other methods use force applied by centrifugation, and measure either the amount of free water expressed, or the amount of added solution (usually a salt solution) that is retained (Swift & Berman, 1959; Wierbicki et al., 1962; McMahon & Dawson, 1976; Regenstein & Rank Stamm, 1979; Porteus & Wood, 1983). Similar methods are used for cooked samples, and often involve equipment similar to that devised by Wierbicki et al. (1957). Other methods, giving a more detailed insight into the behaviour of water in the system, have included nuclear magnetic resonance (NMR) (Hazelwood et al., 1969; Wilding et al., 1984), or the examination of isolated fractions of meat samples under the phase contrast microscope, when subjected to differing conditions of salt concentration and pH (Offer & Trinick, 1983).

Measurements of emulsification capacity (EC) have attempted to predict the ability of different meat sources to bind fat in comminuted products. Most methods are based upon that developed by Swift et al. (1961). Meat is comminuted with salt solution and the resultant slurry is centrifuged. The supernatant is removed and placed in an apparatus to which melted fat or oil is added at a constant rate, whilst undergoing high shear from an impeller blade. Addition is continued until the emulsion breaks. The amount of fat/oil added at the time the emulsion collapses, divided by the amount of protein in the extract, is


defined as the Ee. Halling (1981) and Acton et al. (1983) have reviewed methods for measuring EC and the many factors which affect it. The major criticism of attempting to measure EC of meats has been that the methods employed have not been standardised, and that the amount of fat emulsified in such systems is far greater than that used in meat products. However, EC values for different types of meat, when adjusted to take account of both the amount of salt-extractable protein and the total protein content of the meat, have been used as 'bind constants' (Saffle, 1968) by the meat industry.

More recently described functionality tests, such as those for surface hydrophobicity, protein solubility or sulphydryl content, may be more precise in relation to emulsion systems (Li-Chan et al., 1984,1985).

2.4. Protein Extractability and Product Bind Protein extractability is perhaps the most important property, since many of the other properties depend upon it. However, in a meat system, solubility does not necessarily mean that the proteins are extracted or solubilised into an external solution. For binding in reformed products, proteins are extracted onto the surface environment of the meat particles, whilst in a comminuted product a greater degree of extraction and/or solubilisation occurs.

Studies on poultry meat have been conducted mainly with emulsions or comminuted meat systems, and results extrapolated to systems containing chunks or large pieces of muscle. Turkey breast meat has a higher protein content than leg meat, and more of it is extractable by salt solutions (McCready & Cunningham, 1971; Prusa & Bowers, 1984). In a highly comminuted system, with solution to meat ratio of 20: 1, protein extraction was affected by both pH and salt concentration (Richardson & Jones, 1987). The main effect of pH was in the range pH 5·0-5·7, but extraction continued to rise with increasing salt concentration in the range 0·15-1·20M (Fig. 4). Once isolated, the proteins appear to have similar solubility properties in the pH range 5·0-7·0, and salt concentrations of 0·25 and 0·50M (Foegeding, 1987). In a study of turkeys aged from 10 to 22 weeks, protein extractability was more dependent upon the ultimate pH of the meat than upon the age of the birds (Richardson, in preparation). Taste preference dictates that salt concentrations used in product manufacture are lower than those which give optimum protein extraction. However, in the initial mixing of salt and meat, the concentration of salt at the meat surface will be higher than at equilibrium in the final product. The


1; Q)

E 60

~ .§. "t) Q) 40

~ )( Q)

c: 20 'iii

'0 ... Q.

0.0 0.3 0.6 0.9 1.2

Salt concentratration (M)

FIG. 4. The effect of salt concentration upon protein extraction from turkey breast (-D-), thigh (-0-) and drumstick (-0-) meat.

importance of salt-extracted proteins for bind was demonstrated by Acton & McCaskill (1972). Cubes of broiler meat, which had been previously washed in either water or salt solution (0·6 M NaCl), were subsequently tumbled in salt, pressed into pans and cooked. Prior washing with water had little effect on subsequent bind strength, but bind was less between cubes which had been washed in salt solution.

Extractability is greater with smaller meat particles (Acton, 1972a) and at low temperatures. In a patent for making a reformed poultry-meat product, a temperature of -2 to -1°C was recommended for optimum protein extraction (Hansen et al., 1966). Polyphosphates enhance the effect of salt on protein extraction, normally acting through their effect on pH and ionic strength (Trout & Schmidt, 1986). They may also have a role in removing sarcoplasmic proteins, which have been precipitated onto the myofibrillar proteins in muscles with rapid rates of post-mortem glycolysis, such as pale, soft, exudative (PSE) pork, thus making them more available for extraction (Lewis et al., 1986). The latter study also showed that polyphosphates have a reduced effect in meats with a pH value above 5·9. Some poultry breast meat is in the pH range 5·8-6·0, with leg meats often having a higher pH. Whether this has an effect on the role of polyphosphates in poultry meat requires further study. In contrast, a lower, early post-mortem extractibility of protein was noted for


meats from turkeys which had been anaesthetised and had exhibited a slower rate of post-mortem glycolysis than control birds (Landes et aI., 1971).

Binding of meat pieces was improved for turkey breast muscles when the pieces were tumbled in the presence of both salt and polyphosphate, with a combination of sodium tripolyphosphate and sodium hexametaphosphate giving higher protein extractability than other phosphates, either alone, or in combination (Froning & Sackett, 1985).

2.5. Protein Gelation When extracted proteins involved in meat binding are heated, they interact both within themselves and with the surface of the intact meat pieces to form a cohesive joint. This interaction is known as 'gelation'. Gelation is a heat-induced protein-protein interaction, which leads to coagulation and formation of a well-ordered matrix. Heating induces a certain degree of unfolding of the proteins, which then reassociate into strands. Further heating coagulates the proteins, leading to a stable gel matrix with properties of cohesiveness, rigidity and plasticity, which contribute to the texture and bind of a product.

Acton & Dick (1986) have shown differences in the behaviour of chicken breast and thigh meat actomyosins upon heating. Heatinduced protein-protein aggregations began at 30-31°C for breast actomyosin, but at 42-44°C for that from thigh. Further thermal transitions were found for breast-meat actomyosin at 49·2 and 6O·2°C, and for thigh actomyosin at 52·6 and 57·9°C. It was suggested that, since the differences between these two thermal transition temperatures were half as much in thigh as in breast actomyosin, less thermal energy is required for aggregation of thigh actomyosin. Reasons for the differences in thermal behaviour should be interpreted with caution. The ratio of actin to myosin in these experiments was different for the breast and thigh actomyosin, although this does not exclude differences in amino acid composition and hence in the properties of the two actomyosins. Studies involving differential scanning calorimetry have shown that the thermal denaturation pattern of chicken breast meat (five peaks) was more complex than that of chicken thigh meat (three peaks). The thigh-muscle pattern was similar to that for red meats (Xiong et at., 1987).

Foegeding (1987) reported that the greatest gel strength and stability of the salt-soluble proteins of turkey breast and thigh meat were

Turkey Meal in Furlher-processed Producls 293

developed with a pH value of 6·0 and salt concentration of 0·5 M. The salt-soluble proteins from breast formed more stable gels than those from thigh at pH 7·0. However, chicken white muscle (M. pectoralis profundus) myosin gave a greater gel strength than red (M. gastrocnemius) muscle myosin at pH 6·0, when protein concentration, ionic strength and temperature conditions were kept constant (Asghar et al., 1984). It was also noted that under-feeding of broilers had no effect on the gel strength of white-muscle myosin, but reduced the gel strength of myosin from the red (M. gastrocnemius) muscle. In contrast, Angel & Weinberg (1981) reported that salt-soluble proteins of turkey thigh meat would form gels at lower concentrations than those of breast meat, and that gels formed at lower protein concentrations at pH 5·8 than at pH 6·6. Thigh meat usually has a higher ultimate pH value than breast meat. These differences in thermal behaviour and gel strength may be reflected in the differences in behaviour of heat-processed products made from breast and thigh tissues. Breast-meat loaves have higher cohesive strength and give lower cooking losses than thigh-meat loaves (Froning & Norman, 1966; Maesso et al., 1970; Schnell et al., 1970) and dark-meat emulsion products give greater cooking losses than breast-meat products (Hargusetal.,1970).

Montejano et al. (1984) have compared gel development in surimi, pork, beef and turkey pastes in a model system. Temperature was increased at 0·5°C/min and gelation monitored in a thermal scanning rigidity monitor. Final rigidity of the turkey gels was about the same as surimi, but twice that of beef and pork. Final energy loss (damping) in the turkey gels was the lowest of the gels tested, indicating that they had a near-perfect elastic character. The greater strength and deformability of the turkey gels may indicate a better protein functionality than for those from beef or pork. Electron microscopy of the turkey gels showed that they had a higher proportion of strands and interconnections than the gels of beef or pork.

2.6. Water Holding Water holding in meat has been reviewed by Hamm (19"/5). It is generally held that water holding is lower for breast than thigh meat, but results from experimental studies have not always shown this. Thus, in the absence of salt, cooked chicken breast had lower cooking losses than thigh meat (Froning & Norman, 1966; van den Berg et al., 1964a,b), whilst other studies have shown that raw chicken meat lost a


similar amount of natural juices upon centrifugation (Jauregi et ai., 1981), but retained more added water in the absence of salt (Froning & Norman, 1966; Vadehra et al., 1970), whilst retaining less added water in the presence of salt (Vadehra et al., 1973). A recent study (Richardson & Jones, 1987) has shown how water uptake and retention by finely comminuted turkey meat are affected by the concentration of salt, the pH value, the type of meat and by cooking. These results are summarised in Figs 5 and 6. At higher salt concentrations, raw breast meat retained more salt solution than leg meat, especially at higher pH values. Upon heating, breast meat retained more salt solution than leg meat at all salt concentrations. Similar results were obtained for raw meat by Prusa & Bowers (1984). Salt and polyphosphates improve the water retention of products by reducing cooking losses (Froning & Sackett, 1985). However, an unexpected result was found when the action of salt and polyphosphate on hand (HDTM) and mechanically (MDTM) deboned turkey meat were compared. A synergistic effect for the improvement of water holding capacity (WHC) and water binding capacity (WBC) by salt and polyphosphate was seen for the HDTM but polyphosphate improved the WHC and WBC of MDTM more than either salt or salt and polyphosphate (McMahon & Dawson, 1976).

Qj ::

500

400

III 300 IIJ en ra ~

c ~ 200 L IIJ a..

°5~0~--~5~5~--~6~0~----~6~5----~70 Adjusted pH

FIG. 5. The effect of pH upon the percentage swell of turkey breast (-.-, -0-), thigh (-.&-, -6-) and drumstick (__.._, --0-) meat in the presence of 0·5 (-___ , -.&-, __.._) or 1·0 (-0-, -6-,

--0-) M salt.

..J

..J W

240

200

~ 160 en

!II

120

Turkey Meat in Further-processed Products

80 _"'--__ "--__ ---'L--__ ---' ___ --1

o 0.3 0.6 0.9 1.2 SALT CONCENTRATION 1M)

295

FIG. 6. The effect of salt concentration upon the percentage swell of turkey breast (--O-,~) and thigh (-6-,-.-) meat adjusted to pH6·0. Open symbols are for raw meat (water binding potential) and closed for cooked meat (water holding capacity). Values are the means for five turkeys. Standard errors are represented by vertical bars. (Courtesy of Richardson &

Jones (1987), International Journal of Food Science and Technology.)

Mast et al. (1982), in a study of mechanically deboned chicken meat (MDCM) produced by four different deboning machines, reported that cooking losses in patties made from the MDCM were affected by the type of machine, more so in the presence of salt than in its absence. Salt was more able to reduce cooking losses in patties derived from meat deboned in a Protecon machine than it did in patties derived from Yieldmaster deboned meat. This may have been related to the varying structural integrity of the meat, or the amount of protein denatured during the deboning process. Some machines raise the temperature of the meat more than others during deboning.


2.7. Emulsification The values for emulsification (EC) derived by Hudspeth & May (1967, 1969) for various meat types from different poultry species are often quoted. A higher EC value was found for leg meat than breast meat, despite the former having a lower protein extractability. Similar results were obtained by Maurer et al. (1969), and a comparable trend, but without significant difference, was found by McCready & Cunningham (1971). In none of these studies was the protein concentration of the extracts equalised. This can produce misleading results, since EC is reduced with increasing protein concentration in model systems (Saffle, 1968). Pre-rigor turkey muscle had a higher EC than post-rigor muscle (Froning & Neelakantan, 1971) due, probably, to its higher pH value (Froning & Janky, 1971). Salt improved the EC of HDTM and MDTM, the EC of HDTM being greater than that of MDTM (McMahon & Dawson, 1976). In these experiments, the amount of salt-soluble protein was also higher in the HDTM, and was increased to a greater degree than for the MDTM with the addition of polyphosphate. The results for protein extraction by polyphosphate alone were not given, but it was stated that the types of meat reacted differently. An unexpected result was that, whilst polyphosphate showed a synergistic effect with salt in improving the EC of MDTM, polyphosphate alone gave a higher EC for MDTM than did salt or salt and polyphosphate together.

3. PRODUCT MANUFACTURE

In some countries a high proportion of turkey meat is sold as cut-up portions. The factors in primary processing that determine the eating quality of such products will be the same as those for whole carcasses, and are described in the chapter by Jones & Grey. The time necessary for 'ageing' the carcass, prior to boning, is important for most further-processed products.

Some of the cut-up products currently available may be coated in a batter, breading or flavour-glaze and sold either cooked or uncooked. Most further-processed turkey products are reformed in one way or another.

3.1. Reforming Technology Technologies used for product manufacture range from reforming of large or whole-muscle chunks, through size reduction, such as minc-


ing, for burgers, or flaking for grillsteaks, to emulsion technologies used in making traditional European-type sausages or frankfurters.

Many early products had little resemblance to cooked, whole meat since they were made from minced meat, which was mixed with cures, stuffed into casings and cooked. When large, deboned, red and white turkey meat pieces were stuffed into casings and cooked, they fell apart upon slicing. Early patents claimed the use of mechanical action, with or without the addition of salts, or the inclusion of salted emulsions of skin and meat-trim, to bind large muscle pieces in reformed products. These products were more like whole muscle in appearance and texture (Torr, 1965; Aref & Tape, 1966; Hansen et al., 1966; Schlamb, 1970).

It is now well documented that salt and mechanical action are necessary to extract protein from meat pieces which, upon heating, will bind the pieces together in poultry (Schnell et al., 1970; Acton, 1972b), pork or beef (Theno et al., 1976,1977; Siegel et al., 1978). Whole turkey breast muscles can be tumbled or massaged in brine and stuffed into casings or moulds. Some size-reduction, or the addition of a matrix of smaller particles, may be employed to provide material which will fill spaces in the product. Poor bind can result from insufficient protein extraction, but may also be due to interference from fat (which is non-wettable) or collagenous sheaths (which restrict access of the salts to the meat proteins). Thigh meat is composed of a number of smaller muscles, each with its own collagenous sheath. Blade tenderisation can be employed to slit this sheath and improve bind (McGowan, 1970). Other turkey meats, such as drum or outer-wing sections, are less easy to debone as whole pieces. Mincing them would destroy the fibre structure, but still leave the collagen intact. Flaking is a more recent technique for particle-size reduction which also reduces the size, and hence the toughness, of the collagen. The temperature chosen for flaking must be correct; if too low a temperature, then the meat shatters into smaller particles; if too high, the meat comes out in strands like mince (Koberna, 1986; Jolley et al., 1986). Discrete flakes of meat of various sizes can be obtained by using different sizes of flaking head. A combination of flake sizes can be used. Larger flakes add to the texture, whilst smaller flakes are used as the bind matrix. Flaked meat is used in several types of product, including grillsteaks, which are growing in popularity. Grillsteaks have eating qualities that are closer to those of whole meats than minced products, such as burgers. A processing technique designed to use


large flakes of meat and align the particles in the product, so as to improve the texture and eating quality, has been patented (Bradshaw & Hughes, 1985). Finely comminuted skin or trim is often added to such products to improve juiciness.

White turkey meat is in greater demand than the corresponding red meat, but a manufacturer must balance his production to use all edible parts of the carcass. Cook-out and eating quality of dark meats can be improved by restructuring techniques, such as flaking (Graham & Marriott, 1986), and by correct blends of salt and polyphosphates or other additives, such as egg white (King et al., 1986). Because of its higher myoglobin content, dark meat has been used successfully in cured products, such as turkey ham (Baker & Oarfier, 1981). Turkey meat is permitted as a substitute for other meats in some products and, because of its low flavour profile, will readily blend in. Brennand & Mendenhall (1981) produced extruded steaks from turkey meat which contained 15% of added fat. The fat was from either beef, pork, lamb or turkey. All steaks were found to be acceptable by a trained taste panel, with the lamb-fat samples scoring slightly lower than the rest. However, the majority of the steaks were considered by the panel to have been made from pork.

Attempts have also been made to develop washing procedures to reduce the colour of dark meats, either from MOTM (Hernandez et al., 1986) or strips of chicken thigh meat (Ball & Montejano, 1984; Acton et al., 1985). Using calcium caseinate instead of sodium caseinate lightens the colour of chicken nuggets (Hendrickx, 1987).

Emulsion technology is used for producing continental-type sausages and frankfurters from finely comminuted meat, which may be trim, but more usually MOTM (see Section 4).

3.2. Product Formulation Product formulation differs around the world, depending upon local custom and taste. Many formulations will, of course, be company secrets, but it is possible to give a guide to general formulation which may prove useful to those wishing to manufacture products on a small scale. Mountney (1976) and Long et al. (1982) may be consulted for many established early recipes. Cordray and Huffman also run a series on pOUltry-product recipes in Meat and Poultry magazine. Ingredient suppliers in many countries are useful sources of basic recipes and processing techniques. Below are generalised recipes for turkey roasts, hams, grillsteaks, burgers and British-style sausages.

Turkey Meat in Further-processed Products

Reformed Turkey Roast

Components Deboned turkey whole-muscle Water Salt Polyphosphate

kg 100-0 10-0 1-0 0-25

299

Roasts can be made from breast or thigh meat, and it is better to process the muscles intact, so as to retain the eating attributes of whole muscle_ Protein extraction and absorption, and distribution of the salts, are facilitated, especially for thigh meat, if the muscle and muscle-collagen sheaths are first slit by use of a blade tenderiser.

The meat should be tumbled or massaged under vacuum for 45 min; alternatively it can be processed for 15 min, 'rested' for 30 min and processed again for 15 min. At the end of this time, a sticky exudate of extracted proteins should have formed; if not, the meat can be processed for a further period of time. The meat should then be stuffed into moulds or casings. The use of a rotary-vane vacuum stuffer will reduce the size of the muscles, and this, in conjunction with their soft, pliable nature, will ensure that few air pockets are included. The product can be frozen or cooked_ Frozen logs can be cleaved into roasts or into thinner burgers, which can be battered and breaded, if required. Since breast roasts tend to be dry, a fat emulsion can be added to the mix to impart succulence. However, this may cause discoloration in seams of the cooked product. As an alternative, the roast can be injected with oil and thus become self-basting. Protein extraction that is sufficient to give a good bind takes longer for thigh meat, and the meat has a higher cooking loss than that of breast-meat roasts. Lactose, soy proteins, potato starch and milk proteins have all been used to improve yield.

Pre-cooked Turkey Roll Components kg

Breast meat 65-0 White-meat trim 25-0 Skin 10-0 Water 12-0 Salt 1·5 Dextrose 1·5 Polyphosphate 0-5


The breast meat is reduced by passing it through a kidney plate. It is then mixed with half the salt, phosphate and water. Meanwhile, the skin and trim are chopped with the rest of the water (as ice), salt, phosphate and dextrose to yield a fine emulsion. The emulsion is added to the breast meat and mixed for a short period before the product is stuffed into casings and cooked to a centre temperature of noe.

The use of a higher proportion of breast meat and less trim gives a product of greater monetary value.

Turkey Ham

Components Turkey dark meat Water Salt Polyphosphate Sodium nitrite Sodium ascorbate

kg 100·0 12·0 1·2 0·5

156 ppm maximum 0·05

Up to 1·0 kg of sugar may also be added for a sweet cure. The dry ingredients can be dissolved in the water and ~umped into the meat, which may then be left to soak overnight. The ham roasts are made up in the same manner as before. As an alternative to cooking and smoking in a smoke-house, smoke extract may be incorporated in the formulation. An alternative type of presentation is to slice the turkey ham into thin burgers, insert a slice of cheese between two burgers and then cover with batter and breading.

Turkey Grillsteak This is a useful product to make from trim, or the leg and wing meats, which contain the most connective tissue. To add succulence to the product, or for a cheaper product, an emulsion of turkey skin, MDTM, milk proteins and fat-trim can be incorporated. Untrimmed leg meats give a very acceptable product without these additions. The meats should be frozen and tempered to - 3°C. A one-third portion of the meat is flaked through a small flake-head (e.g. size 180), before mixing for 0·5 min in a high-shear mixer with water, salt and polyphosphate (2·0%, 0·75% and 0·25% respectively by weight of the final product weight). This matrix is then added to the rest of the meat, which has been flaked through a larger flaking head (e.g. size


1600). The components are mixed together for 4·5 min in a paddle- or ribbon-mixer. The resultant mix can be pressed into moulds or stuffed into casings and frozen. The frozen block can then be sawn or cleaved into steaklettes. Alternatively, the mix can be tempered and put through a former.

Turkey Nuggets Turkey nuggets can be made from a combination of meats, e.g. breast, thigh, trim and MDTM. The amounts of each will, to some extent, determine the ultimate quality of the product. Not more than ca 15% MDTM should be used. The poorer quality meats are minced through a 2-3 mm plate, the better quality ones through a 20 mm plate. To the mixed meats are added 0·75% (w/w) salt and 0·25% (w/w) polyphosphate. These ingredients are mixed for 5 min to extract protein. In a commercial operation, the temperature of the mix would be reduced by adding CO2 snow, and then the meat would be formed into nuggets, battered, breaded and flash-fried.

Turkey Sausage

Components Turkey dark meat Pork fat Cooked turkey skin Water Rusk Salt Seasoning

kg 100 20 10 40 (as ice) 6 3 2

The type of seasoning will vary, depending upon taste or even regional preference; nutmeg, pepper and mace being the commonest spices, sage the commonest herb.

The meat and fat should be minced through a 5 mm plate, and the skin through a 2-3 mm plate. Then, both are transferred to a bowl chopper with the seasoning and half the required amount of water, and chopped for a few turns. The rusk and remainder of the water are added and chopping continued until the desired texture and stiffness are reached. The mixture is stuffed into casings and tied.

Because of the comminuted nature of the meat used in some of these products, it may be necessary to incorporate an anti-oxidant, such as sodium ascorbate, at levels up to 500 ppm, especially for those products containing leg meats or being stored frozen for long periods.


3.3. Some Problems of Turkey-meat Products

Colour In the past, a number of colour problems associated with turkey breast meat have occurred. A pink colouration found after cooking, that gives the impression of under-cooking, is sometimes seen in whole turkey breasts or breast rolls. Nitrite from curing procedures used in other areas of the processing plant, or in the water-supply, have sometimes been implicated. Other causes have been leakage of refrigerant gases (Everson, 1984), inhalation of gases during transportation of the birds (Froning, 1983), gases from cooking ovens (Poole, 1956), spray-dried albumin used as an additive (Froning et al., 1968a), different concentrations of muscle myoglobin (Froning et al., 1968b), and pre-slaughter stress leading to higher levels of cytochromes in muscle (Babji et aI., 1982; Ngoka & Froning, 1982). Cornforth et al. (1986), have shown that pinkness may also be caused by reduced, denatured haemochromes rather than nitrosyl pigments. This reducing effect is probably caused by nicotinamide already present in the meat. Production of pinkness will then depend upon the redox potential of the meat. Factors affecting the redox potential are still to be determined, although addition of salt or phosphate has been shown to reduce the redox potential of raw meat (Ahn & Maurer, 1987).

Sodium erythorbate (or sodium ascorbate) is sometimes added to products to reduce the colour-fading due to oxidation reactions. However, this compound has been implicated in a greening defect, slices of turkey breast and thigh meat having increased greening upon cooking, as the concentration of sodium erythorbate solution in which they were soaked was increased. It was postulated that greening was due to the effect of cooking in increasing the surface concentration of sodium erythorbate, and exposure of the meat to air (Janky & Froning, 1971). Thigh meat was more susceptible than breast meat to this problem.

The use of fibre optic spectrophotometry has shown that the darker areas seen at junctions between meat pieces in reformed rolls were not due to a chromophore (Swatland, 1987).

Rancidity and 'Warmed-over' Flavour Turkey meat is more prone to oxidative rancidity than broiler meat due to its higher phospholipid content and lower level of natural tocopherols (Moerck & Ball, 1974; Dawson & Gartner, 1983). Hence,


turkeys require higher levels of tocopherols in their diet than broilers to improve meat stability (Marusich et al., 1975). With minced turkey thigh, breast and skin samples held at 4°C, only the thigh samples developed significantly higher thiobarbituric acid (TBA) values during storage for 8 days (Whang & Peng, 1987). The polyunsaturated fatty acid, arachidonic acid, from the polar lipid fraction, also decreased in both the thigh and breast samples. During frozen storage, the arachidonic acid decreased significantly, but the TBA values did not rise. The oxidation of polyunsaturated fatty acids of meat phospholipids have been shown to cause 'warmed-over' flavour (see e.g. Wilson et al., 1976). The greater susceptibility of thigh meat to oxidation than breast meat may be due to its higher myoglobin and iron content.

Conalbumin extracted from egg white has been shown to reduce the rate of increase in TBA values for minced turkey thigh-meat, during refrigerated storage, and probably acts through metal-ion chelation (Froning et al., 1986). An extract of rosemary oleoresin has also been shown to have anti-oxidant properties, and these were comparable to those of a commercial anti-oxidant mixture, when used in a sausage formulation (Barbut et al., 1985b).

Rancidity can also be a problem in reformed roasts, particularly those made from dark meats, since they develop rancidity during storage at a faster rate than meat stored in the form of a whole carcass. Processing probably causes disruption of the cell membranes, thus exposing phospholipids, which are more prone to oxidation, and diluting the natural anti-oxidants of the cell membranes within the product.

3.4. New Developments in Meat Binding To date, reformed meat products have been made by means of heat-set gels of meat proteins, extracted by using mechanical action in the presence of salts to bind meat pieces together. Hence, they must be sold either pre-cooked or frozen in a natural or synthetic casing. Some products are now sold fresh, e.g. burgers or escalopes, where the breading or other coating helps to hold the product together, and flash-frying results in some surface-setting of the meat pieces.

Meat proteins produce a better bind than other non-meat additives (Siegel et al., 1979). Milk proteins, already used as additives, enhance colour, flavour and juiciness. A new milk protein has been introduced, and this is composed of a mixture of casein and whey proteins (Anon.,


1986). An emulsion of the derivative recommended for poultry products (Alacen TMP 1350, Alaco Food Ingredients, Wellington, New Zealand) is claimed to produce a good cooked bind in the absence of salt, when added to whole-muscle pieces with skin, fat and trimmings. It also lightens the colour of products made from finely comminuted, dark, thigh meat.

Two recent developments have introduced the concept of chemically rather than thermally induced gels for developing bind in raw, fresh products without salt or polyphosphates. The enzyme transglutaminase is reponsible for blood-clotting, and has been shown to form crosslinks between myosin molecules and between myosin and soya protein, casein or gluten at temperatures and pH values found in meat systems (Kurth, 1983; Kurth & Rogers, 1984). The use of this enzyme, along with fibrinogen and thrombin, as a method for binding pieces of meat has been patented by the Netherlands Centre for Meat Technology (Paardekooper & Wijngaards, 1987). After these components have been mixed with the meat pieces, the mixture is put in a mould and allowed to stand overnight at chill temperature, by which time a sliceable, coherent mass is obtained (Paardekooper, 1987).

Another patented process, from Colorado State University, uses the seaweed polysaccharide, sodium alginate as a binder (Schmidt & Means, 1986). Trimmed meat is reduced in size and placed in a mixer; alginate is added, followed by an insoluble calcium salt, such as calcium carbonate, and a slow-release acidulant, such as glucono-blactone. The acidulant neutralises the salt, releasing the calcium, which causes the alginate to gel. The whole mass is placed in a mould or stuffed into a casing and allowed to set. Initial reports on the system suggested good raw-bind development, good but variable cookedbind, good storage stability but reduced palatability scores when compared with a salt/polyphosphate system (Means & Schmidt, 1986; Means et ai., 1987). The system is being developed in the USA and also in the UK at the Institute of Food Research-Bristol Laboratory, where improvements have been made in raw and cooked bind, palatability and colour stability through formulation changes, and the means by which the ingredients are added.

3.5. Electrical Stimulation and Hot-deboning Electrical stimulation (ES) is used in the red-meat industry to allow hot stripping of carcasses, earlier processing and to reduce energy costs for cooling (Cuthbertson, 1980). It would obviously be an


advantage to the poultry industry if carcasses used for further processing could be deboned without long holding times for 'ageing' and tenderisation. ES of poultry meat has been mentioned in the chapter by Jones & Grey. Few studies have been carried out on the ES of turkey carcasses to be used for stripping, but high voltage (800 V, 340 rnA) stimulation of turkeys resulted in more tender meat after overnight 'ageing' (Maki & Froning, 1987). With broilers, low voltage ES (45 V) produced more tender hot-stripped meat, but the meat was still tougher than that 'aged' conventionally. High voltage ES (up to 820 V) had no effect (Thompson et al., 1987). Turkey rolls made from hot-deboned meat were tougher than conventional rolls (Nixon & Miller, 1967). The use of salt and polyphosphates, adequate tumbling and a 3-day 'ageing' period for the prepared rolls, did, however, yield a product rated by a trained panel as being indistinguishable from conventionally prepared rolls (Kardouche & Stadelman, 1978). Salting and mixing alone were inadequate to tenderise hot-deboned turkey meat (Furumoto & Stadelman, 1980).

In our own studies (Richardson et al., in preparation), hot-deboned turkey breast or thigh meat tumbled in salt and polyphosphates and made into rolls, which subsequently were not 'aged', were significantly tougher than rolls made from cold-de boned meat. Thigh rolls also had greater cooking losses and shrinkage. Low-voltage electrical stimulation failed to significantly improve rolls made from hot-deboned breast or thigh meat. Hot-deboning also produced less tender breast fillets, whether or not the carcass had been electrically stimulated.

4. MECHANICALLY DEBONED MEAT

4.1. Production and Properties With increased numbers of turkeys being cut-up and deboned for further processing, a large number of carcass shells and bones, with meat still adhering, are produced. Machines were adapted from the fish industry to recover a high proportion of this meat. The development of these deboning machines is described in the chapter by Parry. The properties of mechanically de boned meat, and its use for product manufacture, has been one of the most intensively studied areas of poultry-meat science. Reviews by Cunningham & Froning (1972), Froning (1976), Randall (1977) and Froning (1981), should be consulted for earlier references.


TABLE 2 PROXIMATE ANALYSES OF MECHANICALLY DEBONED TURKEY MEAT

Source Protein Fat Moisture Reference (%) (%) (%)

Frame 12·8 14·4 70·7 1 Frame 12·8 12·7 73·7 3 Frame 15·5 13·5 70·6 6 Frame 16·3 15·8 65·9 8 Frame 13·9 13·1 79·0 11 Frame, machine A 11·8 18·4 68·8 2 Frame, machine B 13-5 11·5 73·3 2

Range of 10 samples of frames in Protecon 12·7-15·7 4·1-8·4 72·6-79·3 12

Breast cage 15·4 10·2 71·3 7 Back, some skin 13·0 21·7 65·9 7 Rack, some skin 13·4 17-0 67·9 7 Racks 14·5 14·7 63·7 11 Backs 13·5 16·0 68·9 9 Backs and necks 16·2 15·6 67·8 5 Necks 12·4 4·5 81·7 12 Necks 15·7 5·2 79·0 12

US turkey plant no. 1 16·0 12·0 70·8 4

2 14·8 15·2 69·5 4 3 16·2 15·6 67·5 4 4 17·4 10·0 72-5 4

Typical hand-deboned meat Breast 23·6 1·2 74·2 10 Thigh 19·6 8·6 70·8 10 Drum 20·5 6·8 71·9 10

References: 1. Froning et al. (1971). 2. Froning & Janky (1971). 3. Grunden et al. (1972). 4. Dawson (1975). 5. McMahon & Dawson (1976). 6. Essary (1979). 7. MacNeil et al. (1979). 8. Babji et al. (1980). 9. Hamm & Young (1983). 10. Grey et al. (1983). II. Barbut et al. (1984). 12. Meech & Kirk (1986).

Table 2 shows the variability in chemical composition of MDTM from different sources. The composition of this product is affected by the type of machine used and its settings, the types of bones used, the amount of meat left on the bones and the amount of skin (for references, see Table 2). Skin does not contribute to an increased


collagen content, since it tends to stay with the bones, but will add considerably to the fat content (Satterlee et al., 1971) and to the microbial load. The protein recovered is of similar amino-acid composition to hand-de boned meat (Essary & Ritchie, 1968) and is of good nutritional quality (Hsu et al., 1978; Babji et al., 1980). Any bone particles found are smaller in size than in hand deboned meat (Froning, 1979), but the overall calcium content is higher. It has been suggested that this may be beneficial in the diet of many individuals (Froning, 1981).

The very nature of the deboning process means that much of the normal structure of the meat is lost and the product is very pasty, although less so with modern machine design. However, yield can be sacrificed for the retention of some myofibrillar structure. Screen size will determine residual structure (Schnell et al., 1974), and the functional properties of the protein may be changed if operating temperatures are too high. Long bones contribute bone marrow, resulting in a darker colour, due to the presence of increased haemoglobin (Froning & Johnson, 1973). Fat, haem, metal ions, increased temperature, the highly comminuted nature of MDTM and the incorporation of oxygen all contribute to a relatively high susceptibility to microbial spoilage and oxidative rancidity. It has been suggested that MDTM should not be stored for more than 6 days at 3-4°C (Dimick et al., 1972; Moerck & Ball, 1974), or 10 weeks in a frozen condition (Johnson et al., 1974). Smith (1987) has shown that TBA values for frozen MDTM increase rapidly during the first 7 weeks of storage, but this was prevented by the inclusion of an anti-oxidant mixture. However, the mixture was unable to prevent the change in protein functionality. After 26 weeks of frozen storage, gels made from isolated myofibrils were less able to retain water, and the gel microstructure had changed from a continuous, filamentous matrix to a globular one.

Froning & Johnson (1973) have advocated centrifugation of MDTM to reduce the fat and haem content, but it has been claimed that this is ineffective (Dhillon & Maurer, 1975). Cooling MDTM by the application of CO2 snow would appear to be acceptable, but use of this method for freezing is not recommended, since it can lead to increased rancidity as measured by TBA and peroxide values (Uebersax et al .. 1977, 1978; Mast et al., 1979). Liquid-nitrogen tunnels, plate- or blast-freezers give rapid rates of freezing, without such a problem. MDTM used in comminuted products can be tempered, reduced in


size by flaking and added to the mixer in the frozen state. This would reduce oxidation and microbial proliferation during thawing, and preclude the need to add ice during mixing. In the USA, MDTM is often distributed after pre-blending with the correct level of salt and half the desired amount of nitrite.

4.2. Use of MecbanicaUy Deboned Turkey Meat MDTM is used in the manufacture of soups, meat balls or patties but, because of its highly comminuted nature, it is best suited to emulsiontype products, such as bolognas, salamis, frankfurters and other sausages. Even so, a further emulsification step is required to give a satisfactory texture in frankfurters (Dockerty et al., 1986). Mechanically deboned poultry meat (MDPM) can be incorporated in sausages of other meat types, up to a level of 15%, but by far the greatest production in the USA is in 100% poultry frankfurters. By 1980, poultry frankfurters had captured market shares of 15-25% in some areas (Marsden, 1981). Froning (1981) has reviewed the functional characteristics of MDPM for use in frankfurter production. The major differences between the preparation of poultry frankfurters and those from red meat are that poultry frankfurters need less added water, due to the high moisture-content of MDPM, end-point chopping temperatures are lower at around 12°C, because of the lower melting point of poultry fat (Froning, 1970), and cooking at a higher humidity helps to avoid a tough external skin caused by the higher protein content (Marsden, 1981). Smoke-houses can also be dispensed with, if liquid smoke is added during preparation (Schneck, 1981).

The use of fresh, as opposed to frozen MDPM, does not appear to confer any advantages, although the de boned meat from frozen necks gave mushier frankfurters than that from fresh necks or fresh or frozen MDPM from backs and necks mixed in a 5: 1 ratio (Baker & Kline, 1986). The use of MDPM in other products is limited by its lack of texture, although it can be used in small proportions in emulsions added to reformed products to provide succulence. Acton (1973) texturised the deboned meat by cooking 4 mm diameter strands at 100°C. Lampilla et al. (1985) used such strands, cut into chunks, to add texture to roasts made with MDTM or HDTM. Roasts with up to 50% texturised MDTM showed no increase in product shear-values but had a higher degree of visible fibrosity. Similarly, texturised MDTM was used in the production of summer sausages (a fermented and smoked sausage product). Formulations using one-third HDTM, one-third


MDTM and one-third turkey heart meat, or substituting texturised MDTM for HDTM, resulted in very acceptable products. These were further improved by darkening the product colour with the addition of beetroot-juice extract (Barbut et al., 1984). Morphology and texture were rated good with this formulation, and were as acceptable as traditional sausages made with beef, but at half the cost (Barbut et al., 1985a). MDTM has also been used successfully in 'sloppy toms' (a meat in gravy sandwich filling), again at half the price of the traditional beef product (Laughren & Maurer, 1985).

High-temperature short-time (HTST) extrusion cooking may be another way to reform MDTM for use in products, but HTST of mechanically deboned chicken meat (MDCM) failed to produce bind in the absence of other additives, such as wheat flour or pre-gelatinised corn starch (Megard et aI., 1985).

5. PRODUCT PRESERVATION AND PRESENTATION

The cutting, deboning, handling, mixing and packaging of turkey meat increase the likelihood of microbial contamination or proliferation. Studies of various poultry plants have shown that bacterial numbers increase during further processing (Brant & Guion, 1972; Denton & Gardner, 1981).

The rate of increase in bacterial numbers in mechanically deboned meat is no greater than in minced meat (Maxcy et al., 1973), since both processes cause cellular disruption and provide an ideal medium for bacterial growth. The action of mechanical de boning machines also breaks up clumps of microbes and thus spreads them throughout the meat.

Commercial cooking destroys most vegetative bacteria (Denton & Gardner, 1981). For pre-cooked products, there is a conflict between ensuring that cooking temperatures are high enough to kill vegetative, pathogenic bacteria, yet not so high as to cause unnecessary cooking losses. If 80-85°C is attained, all vegetative pathogens are destroyed. At lower temperatures, there is a greater chance of bacterial survival, but cook-losses are reduced. If final cooking temperatures are below 70°C, then the time needed to kill the organisms is longer. This problem, with respect to Salmonella, is considered by Simonsen et al. (1987) and Roberts & Gibson (1988).


5.1. Salting, Curing and Smoking Salting, curing and smoking are traditional methods for preserving meat products, but reduced levels of cure and smoke are now used with poultry meat to provide milder flavours. Consumer desire for reduced levels of salt and nitrite is balanced by a requirement for greater safety and diversification in product appearance and flavour. Acceptable colour and flavour for smoked turkeys can be produced with only 25% of the level of nitrite (156 ppm) permitted by the US Department of Agriculture, provided good cure distribution is obtained by the use of multi-needle injection (Sheldon et at., 1982). These cure levels are inadequate to allow unrefrigerated storage (Mast, 1978; Wisniewski & Maurer, 1979) or extended refrigerated storage (Oblinger et ai., 1978). Thigh meat needs higher levels of nitrite than breast to prevent microbial proliferation, due to its higher iron content (Bushway et al., 1982).

Sofos (1981) has reviewed studies aimed at reducing the levels of salts and nitrite in frankfurters, whilst retaining microbiological stability. One treatment is to use sorbic acid as a partial replacement for salt and/or nitrite. However, sorbic acid lightens the colour of products (Larsen et al., 1986a) and concern has been expressed about the use of reduced cure levels in new poultry products for nonrefrigerated distribution. Cooking during the processing of these products will destroy bacteria, as outlined above, but does not destroy spores of pathogens such as Clostridium botulinum and CI. perfringens, which will grow if temperatures rise above lO°e. Nitrites are traditionally used in cured products to prevent spore growth in products designed to be stored above chill temperatures, such as canned frankfurters. Whilst the effect of reducing the levels of individual components of a cure-mix on spore development is readily assessed, the interactions between the components are more complex, and merit further study before reduced levels of cure are used in new poultry products (Roberts & Gibson, 1986, 1988). The microbiology of poultry products is discussed in two recent reviews (Bacus, 1986; Tompkin, 1986).

5.2. Packaging Packaging helps to protect the product from damage, contamination and loss of moisture. It improves the presentation and can aid in extending the shelf-life of fresh meat. The use of new packaging materials and printing techniques has allowed improved product


presentation and visibility, added information and consumer appeal. Red-meat packaging has been reviewed by Taylor (1985); similar principles have been applied to poultry meat (Dawson, 1987).

Vacuum Packaging The introduction of vacuum packaging for the transport of large primal joints from slaughterer to processor has been one of the greatest innovations in the red-meat industry in the last 20 years. The use of gas-impermeable plastics reduces evaporative losses, prevents further microbial contamination and reduces proliferation of aerobic microbes already present, due to the natural production of carbon dioxide as a result of tissue respiration. Because of vertical integration in the turkey industry, there has not, as yet, been the same demand for this process, although it is used in Europe for the distribution of cut-portions to stores and butchers. It can be used for fresh retail display, but the pressure exerted during vacuum packing can distort the product and squeeze out meat juices. The method is used also for pre-cooked, pre-sliced products.

Over-wrapping Over-wrapping is carried out on rigid or expanded plastic trays, with a clear film of material which has a high oxygen and a low water-vapour permeability. It is still the most popular method, but relies upon good refrigeration, efficient distribution chains and quick turnover. Jones et al. (1982) compared the storage of turkey breast fillets or drumsticks in oxygen-impermeable, vacuum packs and oxygen-permeable, polyethylene over-wrap at 1°C. The results of this work are discussed in the chapter by Jones & Grey.

Gas Packaging In gas packs, the initial gaseous atmosphere in the pack is controlled by the packer, but the atmosphere will also change due to meat respiration. Much higher levels of CO2 (e.g. 30%) are possible than in vacuum packs. This type of pack is becoming more popular for cut-up, diced or minced meat. For red meats, a high concentration of oxygen (e.g. 80%) is included in the pack to retain the natural, bright redness of the meat. For poultry white meats, this is not necessary or even desirable, since it can result in undue pinkness of the meat and some undesirable 'off' odours. Mead et al. (1983) compared vacuum-packed


breast fillets with gas-packed breast fillets. This work is summarised in the chapter by Jones & Grey.

A combination of packaging has also been advocated. Bulk-packs of meat portions can be flushed with CO2 for preservation during storage and distribution. Alternatively, individual-product packs can be overwrapped in a gas-permeable film and boxed in a container lined with a gas-impermeable bag (see chapter by Baker & Bruce).

5.3. Breadings, Batters and Coatings Breadings and coatings were the subject of a recent symposium held in the UK (Anon., 1987c) and developments in enrobed products is the subject of the chapter by Cunningham. Coatings enhance product appearance (Zwiercon, 1974; Elston, 1975) and add to the pleasure of eating (Vickers & Bourne, 1976). Flavourings in a coating or a glaze serve to extend the product range, whilst breadings act as a moisture barrier, improve yield and reduce unit costs. The Japanese crumb has a crisper, lighter bite and will allow longer cooking times, but has a finish with a lighter colour than traditional fish breadings. It was developed because of a desire by the poultry industry to differentiate its products from those of the fish industry. Wholemeal crumbs and potato-based crumbs have followed, and the incorporation of gums, modified starches and other additives help to stabilise batters, alter crumb-texture and reduce frying-oil uptake. The comparatively cheap costs of crumbing, and the acceptability of these products to consumers have stimulated an increase in the variety of value-added items available. In the UK, there has been a rapid increase in the development of such products, especially in the fresh sector of the market (Anon., 1987a).

5.4. Irradiation Recent reviews on the irradiation of poultry meat include Mead & Roberts (1986) and Faw & Chang-Mei (1987). Irradiation will reduce bacterial levels and thus extend shelf-life, and is already permitted in some countries.

Radicidation with doses of 250-500 krad (2·5-5·0 kGy) is designed to reduce the levels of any viable, non-sporing pathogens to undetectable levels. The dose can be increased to 750 krad for frozen poultry because, in the frozen state, a larger dose is needed to obtain the same order of kill. Radurisation uses doses up to 250 krad and is designed to


reduce the numbers of organisms responsible for spoilage of chillstored products. It will also markedly reduce the number of salmonella-contaminated items.

At these low doses, the formation of radio lytic products, or the loss of vitamins, such as thiamine, is no greater than that associated with other processing methods. However, some changes in meat colour and odour occur.

Irradiation of turkey fillets under chill conditions at 250 krad produced a pinker meat with a distinct odour, but these effects were minimised by cooking (Mead & Roberts, 1986). The choice of packaging material was also important. Vacuum packs of oxygenimpermeable material produced fillets of a more intense red colour, and with a more obvious radiation odour, when first opened, when compared with fillets in oxygen-permeable, polyethylene packs.

In principle, the greatest advantage of irradiation would be to eliminate bacteria associated with food-borne illness, e.g. Salmonella, Campy/obacter, Listeria, Escherichia coli, the absence of which cannot be guaranteed by any other method (World Health Organisation, 1986).

REFERENCES

ACTON, J. C. (1972a) The effect of meat particle size on extractable protein, cooking loss and binding strength in chicken loaves. Journal of Food Science, 37, 240-243.

ACTON, J. C. (1972b) Effect of heat processing on extractability of salt-soluble protein, tissue binding strength and cooking losses in poultry loaves. Journal of Food Science, 37, 244-246.

ACTON, J. C. (1973) Composition and properties of extruded, texturized poultry meat. Journal of Food Science, 38,571-574.

ACTON, J. C. & DICK, R. L. (1986) Thermal transitions of natural actomyosin from poultry breast and thigh tissues. Poultry Science, 65,2051-2055.

ACTON, J. C. & MCCASKILL, L. H. (1972) Effect of partial protein removal from muscle cubes on properties of poultry meat loaves. Journal of Milk and Food Technology, 35,571-573.

ACTON, J. c., ZIEGLER, G. R. & BURGE, D. L. (1983) Functionality of muscle constituents in the processing of comminuted meat products. CRC Critical Reviews in Food Science and Nutrition, 18, 99-121.

ACTON, J. c., BOWIE, B. M. & DICK, R. L. (1985) Alteration of meat color. Proceedings of the Twenty Seventh Annual Meat Science Institute (Ed. J. A. Carpenter), University of Georgia, Athens, Georgia, USA, pp. 48-58.


AHN, D. V. & MAURER, A. J. (1987) Effect of added pigment, phosphate and dextrose on color, extractable pigment, total pigment, and oxidationreduction potential in turkey breast meat. Poultry Science, 66, Supplement 1,53.

ANGEL, S. & WEINBERG, Z. G. (1981) Gelation property of salt soluble protein of turkey muscle as related to pH. Journal of Food Technology, 16, 549-552.

ANON. (1986) New binder for restructured meat products. National Provisioner, 8 November, p. 17.

ANON, (1987a) The Further-Processed Poultry Report. lain Smyth Associates for Sun Valley Poultry Ltd, London.

ANON. (1987b) EEC facts and forecasts 1987. Poultry World, September, pp. 11-22.

ANON. (1987c) Savoury Coatings (Eds R. Parry and D. B. Fuller), Elsevier Applied Science Publishers, London.

AREF, M. & TAPE, N. W. (1966) Method for producing a composite body of poultry meat. Canadian Patent, 864,447.

ASGHAR, A., MORITA, J., SAMEJIMA, K. & YASUI, T. (1984) Biochemical and functional properties of myosin from red and white muscles of chicken as influenced by nutritional stress. Journal of Agricultural and Biological Chemistry, 49,2217-2224.

ASGHAR, A., SAMEJIMA, K. & YASUJ, T. (1985) Functionality of muscle proteins in gelation mechanisms of structured meat products. CRC Critical Reviews in Food Science and Nutrition, 22, 27-106.

BABJI, A. S., FRONING, G. W. & SATrERLEE, L. D. (1980) The protein nutritional quality of mechanically deboned poultry meat as described by C-PER assay. Journal of Food Science, 45,441-443.

BABJI, A. S., FRONING, G. W. & NGOKA, D. A. (1982) The effect of preslaughter environmental temperature in the presence of electrolyte treatment on turkey meat quality. Poultry Science, 61,2385-2389.

BACUS, J. N. (1986) Fermented meat and poultry products. In Advances in Meat Research, Vol. 2, Meat and Poultry Microbiology (Eds A. M. Pearson and T. R. Dutson), Van Nostrand Reinhold Co., New York, pp. 123-164.

BAKER, R. C. & DARFLER, J. M. (1981) The development of a poultry ham product. Poultry Science, 60, 1429-1435.

BAKER, R. C. & KLINE, D. S. (1986) Acceptability of frankfurters made from mechanically deboned poultry meat as affected by carcass part, condition of meat and days of storage. Pouliry Science, 63,274-278.

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processing of poultry || utilisation of turkey meat in further-processed products

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