ASSESSMENT OF HAM QUALITY

Gariépy1 C., Riendeau2 L. and Pettigrew3 D.

1 Agriculture and Agri-Food Canada, Food Research and Development Centre, 3600, Casavant Blvd. West, St.Hyacinthe, Quebec J2S 8E3
2 Consultech Alimentation, 14 Des Pélicans, Saint-Basile-le-Grand, Québec J3N 1L1
3 Centre de développement du porc du Québec, 2795, boulevard Laurier, suite 340, Sainte-Foy, Québec G1V 4M7

INTRODUCTION

Ham is the largest primal cut of the pork carcass. Its main use is for the fabrication of cooked cured ham, a product category which is known and produced all over the world. However, important variation in its processing and hence final composition and quality can be encountered depending on market characteristics and regulations in different countries (DMV International, 1995).

Over the years, the merchandising of the traditional primal cut has evolved from one­ to three­piece-ham (inside, outside, knuckle) up to separate muscles that are now being sold in order to keep with the introduction of new functional ingredients, along with faster and more efficient technologies for brine addition, tumbling, cooking and packaging. These are all aimed at improving the uniformity and cooking yield of the product, and reducing the length of the process.

However, in spite of the use of adjuncts and improved processing technologies, the quality of the final product is still mainly dependant on the technological quality of the raw material.

DETERMINANTS OF PORK TECHNOLOGICAL QUALITY

As the basic reason for the increased number of faults in meat today is genetically determined, the situation can only be improved in the long run by further changes in breeding (Wirth, 1986). According to Sellier and Monin (1994), pork technological quality refers to a complex set of compositional and physicochemical properties such as water holding capacity, intensity and homogeneity of colour, softness, shelf life, processing yield, slicing yield, etc.

Physicochemical factors

Most of the above properties are influenced by the rate and extent of the postmortem pH fall through its direct influence on water holding capacity of the muscle. The effects of muscle acidification on quality categories are well known and are summarized in Figure 1. Physicochemical relationships between quality attributes of the fresh meat were recently reviewed by Murray (1995). The curing aptitude of the meat is also dependant on the muscular postmortem events. In normal muscle, the pH drop from 7.2 to an ultimate value varying in between 5.5­5.8 is accompanied by a reduction of approximately 40% of the volume of the myofibre, due to the ultimate pH value approaching the isoelectric point of the proteins and the formation of actomyosin (Monin, 1988). This change in volume is caused by the release of water, outside the muscle. The resulting open structure is now more permissive for salt absorption which is responsible for the solubilisation of myofibrillar proteins. These structural proteins play a decisive role in structure building and meat juice retention during heat processing and determine to a large extent the coherence hence sliceability of the final product (DMV International, 1995).

Effects of PSE and DFD meats on curing ability

The very rapid production of lactic acid in PSE meat results in an important protein denaturation with excessive water liberation. The much more open meat structure accelerates salt absorption which often leads to a saltier taste. In addition, the remaining functional proteins cannot support a good cooking yield and the colour and texture of the final product are still altered. In the opposite case where ultimate pH remains high due to insufficient glycogen content at slaughter, DFD meats will result in powerful swelling of the muscle fibres (close structure) which will reduce salt penetration and hence flavour and colour development. Shelf life of the resulting product will also be impeded because of high pH in spite of good cooking yield (Wirth, 1986).

Genetic factors

In pigs, large variation in the rate and extent of pH fall causing severe quality defects have been associated to two major genes, the halothane gene (Hal) and the RN gene.

The Hal gen 6 (Harbitz et al., 1993) and can now be detected by the PCR technique (Houde and Pommier, 1993). It is responsible for the larger than normal rate of acidification of the muscle which, at body temperature, increases protein denaturation leading to the severe loss of water and paler colour of the PSE condition, as mentioned earlier. In addition to the saltier taste of cooked cured product, the cooking yield is reduced by 2­3% in comparison with normal meat (Sellier and Monin, 1994). Moreover, hams from Halothane positive pigs frequently show the two-toning conditions. White muscles develop PSE traits due to the fast postmortem pH fall, whereas the higher ultimate pH prevents this occurring in red muscles. Therefore, the loin and the outer muscles of the ham appear as PSE, whereas the inner muscles appear as normal or even DFD (Monin and Ouali, 1991). Cohesiveness and slicing yield may also be reduced depending on the severity of the conditions and the processing technologies employed.

Contrary to the halothane gene, the RN gene is dominant and its effect has been demonstrated by the low Napole yield carried out on muscle samples from composite Hampshire lines (Naveau et al. 1985). The Napole yield is determined by curing and cooking a 100 g meat sample from the semimembranosus muscle (Naveau et al., 1985). The RN gene increases the glycogen content by 70% in the white or glycolytic muscles (Fernandez and Monin, 1994), as the magnitude of this effect decreases when the oxidative capacity of the muscle increases (Marinova et al., 1992). Therefore, the rate of postmortem pH fall is normal, but the extent is larger than normal in the ham muscles (Fernandez and Monin, 1994). From another composition point of view, water content is minimally affected or none (Sellier and Monin, 1994), but protein content decreases by 5 to 7%. The fresh meat has a pale appearance which is somewhat wet, although much less exudative than PSE meat. However, upon cooking of cooked cured Paris ham, there is a decrease of 5­6% in technological yield in comparison with normal meat but which is twice as much loss than that caused by PSE (Sellier and Monin, 1994). According to Fernandez and Monin (1994), from the 5­6% lower cooking yield, 2% would be explained by the low ultimate pH, while the low protein content would probably contribute to the other part. Contrary to PSE- prone pigs, RN gene, where all muscles appear pale will not conduct to the two-toning phenomenon (Monin and Ouali, 1991). However, the low cooking yield induces a low slicing yield (ITP, 1996), and this effect would be more pronounced in ham from Hampshire breed. According to Alviset et al. (1995) for ultimate pH value < 5,5 in the semimembranosus, slicing yield was reduced by 50% in hams from Hampshire in comparison to 16% and 14% respectively for Pietrain and Large White x Pietrain in the same pH class. In this study, slicing yield increased with cooking yield.

Compositional factors

The effect of RN gene on technological or cooking yield of ham has shown, in addition to the effects of physicochemical factors, the importance of the compositional aspect of muscles aimed at further processing. In terms of meat quality, composition aspects have been mainly linked to the eating quality of pork with respect principally to the effect of marbling fat on sensory properties. However, according to Barton-Gade (1985), meat for processing should have, in addition to a good water holding capacity, a high protein content, a low marbling fat and a good pigment content to give the best possible colour in the finished product. Among these factors, protein is of extreme importance as a decrease of only 0.25% in its content is approximately equal to 1% less yield in cooked cured USA ham as shown in Table 1. This aspect is of prime importance for processors since many regulations are now based on either minimal amount of meat proteins or maximum amount of non-meat proteins or on the water to protein ratio which will have to be met to access export markets. Apart from its indirect influence on protein content, the amount of intramuscular fat is also of importance for the quality of cooked cured products since high levels of marbling will have detrimental effect on the appearance of such products (Barton-Gade, 1985). From the preceding information, a summary of the important quality factors for cooked cured ham from the processors to the consumers is as follow:

- good curing ability
- good cooking yield
- good slice cohesiveness
- good shelf life
- good homogeneity of colour
- low marbling fat.

HERITABILITIES

Except for the amount of intramuscular fat, the above quality factors are all pH dependent. Heritability estimates for technological quality traits including pH and intramuscular fat are presented in Table 2. It can be seen that traits referring to the technological quality of meat are lowly to moderately heritable and, therefore, their measurements could be used for selection purpose. On the other hand, intramuscular fat content appears as highly heritable. However, in the review by Hovenier et al. (1993), there is no report of estimates for the effects of heterosis on the amount of intramuscular fat. According to these authors, breed crosses should be more or less intermediate to parental breeds for this trait, and reported one conclusion where additive inheritance was assumed. For Sellier and Monin (1994) however, an heterosis effect close to zero can be expected in crosses involving breeds differing in eating quality due to large differences in intramuscular fat content. On this basis, this trait could be easily modified by within-breed selection (Sellier and Monin, 1994). Variations in heritability estimates of Table 2 can be attributable to a large extent to the methods used for the measurement of a given trait and their repeatabilities.

HAM QUALITY ASSESSMENT

Context

The literature does not contain much information on raw ham quality. For years, the loin has been the focus of research scientists for both eating and technological quality evaluation through measurements of pH and estimates of water holding capacity, among others. However, technological parameters measured on the longissimus muscle provide only a simplified view of the real situation. Ham is a much more complex cut composed of different muscles varying in fibre type composition. To these differences in metabolic and contractile equipment are juxtaposed variations in location of the muscles on the carcass which lead to variation in kinetics of temperature changes, and variations in the stress applied on the muscles before and during the slaughter process, which are in turn related to both the function and location of the muscles. According to Monin and Ouali (1991), the interactions between these factors make it difficult to clearly establish their respective importance in practical situations.

Another consideration for the lack of information is that in ham processing, technologies and functional ingredients can be used to produce a cooked cured product with up to 80% of brine added, and over, in some cases. In such a context, ham improvement can be more easily passed over to processors. However, with the advent of globalization, regulations will likely become more stringent and better yield will probably have to rely more on the quality of the raw material.

The French situation

In spite of improved processing technologies, France has maintained a traditional high quality cooked cured ham product called Paris ham. This ham is produced with a low level of brine addition (below 15%) with no phosphate added or other ingredients in order to increase the water holding capacity of the meat. ption (Fernandez and Monin, 1994). It is therefore not surprising that France is the only country which has documented the assessment of ham quality for the purpose of genetic evaluation of market pigs.

The technological yield of Paris ham processing which is defined below has been, for more than 20 years, the key factor of pork quality in France (Gueblez et al., 1990a).

Its measurement, however, is expensive and time consuming. Therefore, prediction equations have been established from selected quality indicators. These were measured on line (45­60 min) or at 24 h postmortem on different muscles from either the entire carcass (halves) or the ham itself, in order to represent different working conditions. Quality indicators were pH values, surface and internal reflectance, electrical conductivity, imbibition time and subjective colour score. All the variables were submitted to a step by step regression analysis. The following prediction equations were obtained from different experiments since 1969.

< 19831
MQI = 2,1466 (pH24) AF - 0,0088 (ref) GS or BF + 0,0071 (WHC) BF r = ---
19841
MQI = 53.63 + 5.9019 (pH24) AF + 0.1734 (WHC) BF - 0.0092 (ref) BF r = 0.72
19902
MQI = 34 + 11.04 (pH24) SM + 0.105 (WHC) GS - 0.231 (ref) GS r = 0.74


1 Jacquet el al. (1984). Journées Rech. Porcine en France, 16:49.
2 Anonyme. 1995 Techni-Proc, 18.4.95: 15-31.

It is a possibility that this interpretation on the respective effects of ultimate pH and protein content on technological yield be based on the results of Barton-Gade (1988).

The meat quality index (MQI) represents the best possible predictor of technological yield as used in test station on 24 h postmortem hams since 1970. Other valid equations are available for either on line or 24 h measurements on the entire carcass (Gueblez et al. 1990a; Jacquet et al., 1984). Simple correlations are also presented. All these equations have multiple correlations values varying in between 0.63 to 0.76 (Gueblez et al., 1990a). In addition, they should lead to an improved quality of fresh meat since a negative correlation value (r = ­0.42) exists between drip loss in the loin and ultimate pH value of the semimembranosus as it is now currently measured for the prediction of technological yield (Gueblez et al., 1990b). Nevertheless, additional specific traits for loin quality are now being measured in the French program. According to Monin et al. (1984), the effect of ultimate pH is much more influential on technological yield than on fresh meat characteristics such as colour and imbibition time which are more sensitive to the rate of pH fall. Results of Jacquet et al. (1984) and Gueblez et al. (1990a) have both confirmed that among all the variables measured, correlations with technological yield were always higher with ultimate values obtained at 24 h postmortem than with initial values measured on line (45­60 min). In addition, ultimate pH was superior to any other variables and the best site for its measurement was the semimembranosus (Gueblez et al., 1990a).

Although satisfying, these equations are not exceptional in comparison with predictive equations for carcass yield which have multiple correlation values beyond 0.90 (Jacquet et al., 1984). It is therefore easier to predict meat quantity than meat quality. According to the 1990 MQI, more than 45% (r2) of the technological yield would remain unexplained.

However, if we consider the importance of compositional factors on technological yield as shown by Barton-Gade (1988) (Table 1) along with the much more influential effect of low protein content in comparison with the slight ultimate pH effect caused by the RN gene as presented by Fernandez and Monin (1994), it seems quite likely that measurement of compositional factors could significantly improve the predictive value of the French MQI equations. Although equations with more than three variables could only be conceivable in a research context where more precision is needed (Jacquet et al. 1984), new technologies for composition analysis which are rapid and accurate are now available and should certainly be considered in such a context.

Finally, it should be realized that the technological yield is very appropriate under French processing conditions where a low level of brine without phosphate is used. Such products are not common in North America where hams contain on average 25­50% brine addition (DMV International, 1995). It is therefore legitimate to wonder how would behave meat from RN gene, as an example, under a high injection rate and added phosphate or other functional ingredients? Although no compromise should be made on the quality of the raw material aimed at further processing, any attempt to establish a systematic evaluation of ham quality should streamline the criteria of importance for processors under specific market conditions.

CONCLUSION

The overall processing ability of the ham depends on both tissue composition and technological quality of the meat (Monin and Sellier, 1985). A systematic approach for the evaluation of technological quality has been developed in France in order to predict the technological yield of high quality cooked cured ham product. However, compositional factors were not included in their prediction equations. Therefore, such a combined approach could be adapted to the North American processing context and lead to improvement of pork technological quality. This proposition certainly merits further investigation.

However, it must be realized that compositional factors such as intramuscular fat content which is positively linked to eating quality of fresh pork, is negatively associated with the processing aptitude as presented earlier and, therefore, would rule out the possibility for an all purpose crossbreed, according to Barton-Gade (1988). Nevertheless, to our knowledge, there has not yet been a systematic attempt to test both eating and technological quality (including composition factors) on the loin and ham respectively. France is actually increasing parameters being measured on the loin. Breed improvement in terms of meat quality could benefit from the advent of new technologies which are rapid, accurate and non destructive for the evaluation of pork quality. It has been estimated that fabricating cooked cured ham product from low quality meat could only cover the cost of the raw ham, but not the processing cost (I.T.P., 1996).

This paper reviewed the important technological quality parameters in ham processing that could be influenced by genetic factors. However, along with genetics, preslaughter handlings have long been identified as the most important factors on pork quality (Sellier and Monin, 1994). Therefore, it should be remembered that successful improvement program can still be negated by inappropriate preslaughter handling of hogs.

REFERENCES

Alviset, G., Brand, J. and Vidal, E. 1995. Influence du pH ultime et de trois types génétiques sur la qualité du tranchage des jambons label rouge commercialisés en libre service. Bull. Liaison CTSCCV, 5: 10.

Anonyme. 1995. Techni-Porc, 18.4.95 : 15-31.

Barton-Gade, P.A. 1985. Developments in the pre-slaughter treatment of slaughter animals. Proc. 31st Europ. Meet. Meat Res. Workers, Albena, p. 1.

Barton-Gade, P.A. 1988. The effect of breed on meat quality characteristics in pigs. Proc. 34th Int. Congress Meat Sci. Technol. Brisbane, p. 568.

DMV International. 1995. Cooked ham throughout the world. Food Tech. Europe, 12(1): 100.

Fernandez, X. and Monin, G. 1994. A major gene affecting pork quality: the RN gene. Meat Focus International, August: 332.

Gueblez, R., Le Maitre, C., Jacquet, B. and Zert, P. 1990a. Nouvelles équations de prédiction du rendement technologique de la fabrication du jambon de Paris. Journées rech. porcine en France, 22: 89.

Gueblez, R., Le Maitre, C. and Vaudelet, J.C. 1990b. La qualité de la viande mesurée B l'abattoir : Effet du sexe et relation avec la capacité de rétention d'eau du jambon et de la longe. Journées rech. porcine en France, 22: 83.

Harbitz, I., Chowdary, B., Thomsen, P.D., Davies, W., Kaufmann, U., Kran, S., Gustansson, S., Christensen, K. and Hange, J.G. 1993. Assignment of the porcine calcium release channel gene, a candidate for the malignant hyperthermia locus, to the 6 p. 11- q. 21 segment of the chromosome 6. Genomics, 6: 243.

Houde, A. and Pommier, S.A. 1993. Use of PCR technology to detect a mutation associated with malignant hyperthermia in different pig tissues. Meat Sci., 33: 349.

Hovenier, R., Kavis, E., van Asseldonk, Th. and Westerink, N.G. 1993. Breeding for pig meat quality in halothane negative population - a review. Pig News and Information, 14: 17N.

I.T.P. 1996. L'influence de la qualité de la matiPre premiPre sur les rendements et pertes au tranchage des jambons cuits supérieurs sans gras de couverture commercialisés au libre-service. V.P.C., 17: 95.

Jacquet, B., Sellier, P., Prunavot, J., Brault, D., Houix, Y., Perrochean, C., Gagné, J. and Boulard, J. 1984. Prédiction du rendement technologique de la fabrication du *jambon de Paris+ B l'aide de mesures prises B l'abattoir. Journées rech. porcine en France, 16: 49.

Marinova, P., Lefaucheur, L., Fernandez, X. and Monin, G. 1992. Relationship between metabolism and glycogen content in skeletal muscle fibres of Large White and Hampshire crossbred pigs. Journal of Muscle Foods, 3: 91.

Monin, G. 1988. Ivolution post-mortem du tissu musculaire et conséquences sur les qualités de la viande de porc. V.P.C., 9: 302.

Monin, G., Gurand, J., Laborde, D. and Sellier, P. 1984. L'effet Hampshire sur les qualités technologiques de la viande de porc. Journées rech. porcine en France, 16: 59.

Monin, G. and Ouali, A. 1991. Muscle differentiation and meat quality. In Developments in Meat Science, vol. 5, R.A. Lawrie, Ed., Elsevier Applied Science, London, 253 pp.

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Murray, A.C. 1995. The evaluation of muscle quality. In Quality and grading of carcasses of meat animals. S.D. Morgan Jones, Ed., CRC Press, New York, 234 pp.

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Table 1. Effect of muscle composition and ultimate pHu on technological yield(1)
Landrace
Large White
Duroc
Hampshire
pHu BF 5.53 bc 5.51 ab 5.56 c 5.47 a
pHu SM 5.60 c 5.56 b 5.54 b 5.47 a
pHu LD 5.48 a 5.49 a 5.57 b 5.51 a
% Prot. SM 21.77 a 21.62 a 21.24 b 20.76 c
% Water SM 75.54 b 75.85 a 74.49 c 75.61 ab
% Fat SM 2.05 ab 1.90 a 3.50 c 2.24 b
% 
Technological yield (USA Ham)
--- 0.6 2.2 4.0
(1) Barton-Gade P.A. (1988), Proc. 34th ICOMST, Brisbane, p. 568.

Table 2. Average values of heritability of some meat quality criteria(1)
Average h2(2)
No. of estimates
Range of estimates
pH1(3)
0.18
11
0.11 - 0.41
pHu
0.22
23
0.07 - 0.34
Reflectance
0.28
25
0.15 - 0.57
Water holding capacity
0.12
12
0.01 - 0.43
Subjective quality score
0.22
5
0.10 - 0.37
Intramuscular fat content
0.48
14
0.26 - 0.86
(1) Sellier, P. and Monin, G. 1994. Journal of Muscle Foods, 5: 187.
(2) Weighted mean of the h2 estimates.
(3) pH1: pH at 45-60 min postmortem; pHu: ultimate pH (24 h postmortem).

Figure 1. Effect of time postmortem on pH for several meat quality types.

Murray, A.C. 1995. The evaluation of muscle quality. In Quality and grading of carcasses of meat animals. S.D. Morgan Jones, Ed., CRC Press, New York, 234 pp.