J. Anim. Sci. 2003. 81:2219-2229
© 2003 American Society of Animal Science
Effect of conjugated linoleic acid on meat quality, lipid metabolism, and sensory characteristics of dry-cured hams from heavy pigs1
C. Corino*,2,
S. Magni*,
G. Pastorelli*,
R. Rossi* and
J. Mourot
* Department of Veterinary Sciences and Technologies for Food Safety, University of Milan, 20133 Milan, Italy and
and
I.N.R.A., Unité Mixte de Recherches sur le Veau et le Porc, 35590 Saint-Gilles, France
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Abstract
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We investigated conjugated linoleic acid (CLA) supplementation administered to heavy pigs, assessing carcass characteristics, meat quality, and sensory characteristics of dry-cured (Parma) ham. Thirty-six pigs, averaging 97 kg BW, were assigned randomly to three feeding groups in which diets were supplemented with either 0, 0.25, or 0.5% (as-fed basis) of a CLA preparation containing 65% CLA isomers. All pigs were slaughtered at 172 kg BW. No (P > 0.05) differences were observed in dressing percentage, loin and ham weight, or pH and color of longissimus and semimembranosus muscle. Tenth-rib backfat thickness tended to be lower (P < 0.10) in carcasses from CLA-fed pigs. The oxidative stability of longissimus muscle was greater (P < 0.05) in pigs fed CLA than control, but only at the longer (300 min) oxidation time. Acetyl-CoA carboxylase activity in adipose tissue of CLA-fed pigs was less (P < 0.05) than that of pigs fed diets devoid of supplemental CLA. Composition of ham fat was markedly affected (P < 0.01) by dietary CLA, with higher saturated fatty acids, lower monounsaturated fatty acids, and higher CLA in the fat of CLA-fed pigs regardless of supplementation level. Although melting quality was improved (P < 0.05), most sensory characteristics and the chemical composition of dry-cured hams were not (P > 0.05) affected by incorporation of CLA. Results indicated that dietary CLA alters lipid metabolism, producing lower concentrations of monounsaturated fatty acids and increased concentrations of CLA isomers in the fat of heavy pigs. Moreover, supplementing diets with CLA produced only minimal improvements in Parma ham sensory traits and had no appreciable effects on fresh pork quality.
Key Words: Cured Meat • Dienoic Fatty Acids • Ham • Meat Quality • Nutrition • Pigs
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Introduction
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Conjugated linoleic acids (CLA) are geometric and positional isomers of linoleic acid. Conjugated linoleic acid isomers, differing in the positions and configuration of the double-bond pairs, have been identified in milk fat (Pariza et al., 2001
). Conjugated linoleic acids are of interest for several biological effects, including antioxidant and antiobesity activity (Lin et al., 1995), as well as anticarcinogenic activity demonstrated in a wide range of animal models (Banni and Martin, 1998; Belury 1995; Ip et al., 1994). In other studies, CLA has been shown to protect against atherosclerosis in rabbits (Lee et al., 1994) and to exert a hypocholesterolemic effect in the same species (Corino et al., 2002b) and has modulated the immune system in several experimental models (Hwang, 2000; Bassaganya-Riera et al., 2001; Corino et al., 2002a;). Dietary CLA supplementation has been shown to increase feed efficiency in swine (Eggert et al., 1999; Thiel-Cooper et al., 2001; Wiegand et al., 2002) and may reduce body fat content in mice (West et al., 1998), swine (Cook et al., 1998; Thiel-Cooper et al., 2001; Wiegand et al., 2002), and rabbits (Corino et al., 2002b). This partitioning effect may be related to reduced skeletal muscle catabolism induced by immune stimulation (Cook et al., 1993). In addition, investigations of the metabolic effects of CLA in intact animals and adipocyte cultures suggest that CLA directly affects key enzymes and processes involved in lipid mobilization and storage (Park et al., 1997).
The sensitivity of Parma ham quality to fat composition and the consistent finding of positive effects of CLA on the technological characteristics of pig adipose tissue induced us to carry out the present study on the effects of CLA in heavy pigs destined for Parma ham production. Thus, the aim of the present study was to examine the effects of dietary supplementation of CLA in heavy pigs on carcass characteristics, meat quality, lipid metabolism, and dry-cured ham quality.
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Materials and Methods
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Animals and Diets
Thirty-six Large White pigs (18 barrows and 18 gilts) were assigned to one of the three dietary treatments according to balanced block design (two pens/treatment, six pigs/pen). The treatment began at 97 kg BW and continued to 172 kg BW. The diets, formulated to be isoenergetic (Table 1), differed in terms of added levels of CLA: 0, 0.25, or 0.5% (as-fed basis) of a CLA preparation containing 65% of CLA isomers (half cis-9,trans-11 and half trans-10,cis-12) in free fatty acid form (Conlinco, Inc., Detroit Lakes, Minnesota 56502 USA). The animals used in this experiment were cared for in accordance with European Union guidelines (No. 86/609/EEC) and approved by the Italian Ministry of Health (L.116/92).
Carcass Measurement and Tissue Sampling
The animals were slaughtered at 172.0 ± 14.81 kg live weight. Pigs were electrically stunned; following exsanguination, the carcasses were scalded, dehaired, and eviscerated. Samples of ham adipose tissue and a section of semimembranosus (SM) were taken from each carcass during slaughter, frozen in liquid N2, and stored at -80°C pending determination of lipogenic enzyme activity. Dressing percentage was calculated, and midline backfat depth opposite the first rib, last rib, and last lumbar vertebrae, as well as loin weight, were recorded.
Meat quality was assessed by pH (HI 9023 microcomputer, Hanna Instruments, Vila do Conde, Portugal) and color measurements at 45 min and 24 h postmortem on longissimus muscle (LM) at the last lumbar vertebra and in the caudal portion of SM. Tristimulus color coordinates (L*, a*, b*) were recorded using a Chroma meter (CR-300; Minolta Cameras, Osaka, Japan). The instrument was calibrated using the white calibration plate (Calibration Plate CR-A43, Minolta Cameras) at the beginning of each session. The colorimeter had an 8-mm measuring area and was illuminated with a pulsed Xenon arc lamp (illuminat C) at 0° viewing angle. Reflectance measurements were obtained at a viewing angle of 0° and the spectral component was included.
At 24 h postmortem, cold loin weight was recorded, and samples of LM at the last lumbar vertebra, as well as both layers of subcutaneous fat of the ham, were collected, frozen, and stored at -20°C pending analyses of oxidative stability and fatty acid composition respectively. Moreover, 36 green hams were weighted after cold-trimming and subjected to the aging process as specified by the regulation stated for Parma Ham Consortium (Gazzetta Ufficiale della Repubblica Italiana, 20/02/90). The production process of Parma ham is presented in Table 2 (Russo and Nanni Costa, 1995).
Hams, ripened for 12 mo, were sectioned perpendicular to the bone at the knee level and samples, containing essentially three muscles (semimembranosus, biceps femoris, and semitendinosus), were vacuum-packaged and stored at 4°C. Ham slices of equal thickness (0.5 mm) were used for sensory analyses and the remaining portion was used for chemical analyses.
Chemical Analysis of Parma Ham
Moisture, protein, fat, sodium chloride, and proteolysis indices were determined on seasoned ham samples according to the methods of Baldini et al. (1992). Moisture content was determined as loss on weighing following freeze-drying of 50 g for 48 h. Crude protein was determined by the Kjeldahl method, and total fat was extracted by Soxhlet extraction, using diethyl ether. Sodium chloride content was determined by Mohr titration and proteolysis index, percent ratio between nitrogen soluble in 5% trichloroacetic acid, determined by the Kjeldahl method after protein precipitation with trichloroacetic acid, and total nitrogen.
Fatty Acid Analysis
Lipids were extracted from subcutaneous tissue by chloroform/methanol (2:1) according to Folch et al. (1957). Fatty acid methyl esters were prepared with 20% boron trifluoride/methanol solution according to Morrison and Smith (1964). The methyl esters were separated on a gas chromatograph equipped with a fused-silica capillary column (25 m x 0.25 mm internal diameter) with BDS (base-deactivated silica) stationary phase (a 0.25-µm film thickness). Furnace temperature was 180°C, and injector and detector temperatures were 240°C. Iodine value was calculated from the fatty acid composition according to the AOAC equation (1995): Iodine value = (% hexadecenoic acid x 0.950) + (% octadecenoic acid x 0.860) + (% octadecadienoic acid x 1.732) + (% octadecatrienoic acid x 2.616) + (% eicosenoic acid x 0.785) + (% docosenoic x 0.723). The 
9 desaturase index was calculated as the ratio of monounsaturated fatty acids to the sum of saturated and monounsaturated fatty acids. This index has been proposed as an estimator of stearoyl CoA desaturase activity in dairy cows by Corl et al. (2001).
Measurement of Oxidative Stability
The oxidative stability of samples of LM was determined using a modification of the method described by Monahan et al. (1992), itself a combination of the Kornbrust and Mavis (1980) method for the induction of lipid peroxidation, and the Beuge and Aust (1978) method of determining the extent of lipid peroxidation by assaying 2-thiobarbituric acid-reactive substances (TBARS) as reported by Oriani et al. (2001). Briefly, 1 g of tissue was homogenized with 9 mL of 1.15% KCl. From the solution, 100 µL of homogenate was taken and incubated at 37°C in 80 mM Tris maleate buffer (pH 7.4) with 5 mM FeSO4 (to catalyse lipid peroxidation) in a total volume of 1 mL. At fixed time (60, 120, 200, and 300 min), aliquots were removed for measurements of TBARS, adding 2 mL of stock TCA-TBA-HCl reagent and mixing thoroughly. The solution was heated for 15 min in boiling water; after cooling, the precipitate was removed by centrifugation at 715 x g for 15 min. The absorbance of the sample is determined at 535 nm against a blank that contained all the reagents minus the homogenate. The TBARS values are expressed as nanomoles of malondialdehyde per gram of muscle tissue.
Enzyme Assays
To determine lipogenic enzyme activities in SM and adipose tissue, weighed quantities of tissue (approximately 1.5 g of SM; 0.7 g of adipose tissue) were homogenized in 0.25 M sucrose buffer and centrifuged at 30,000 x g for 40 min. Supernatant was analyzed for malic enzyme (ME, EC 1.1.1.40) and glucose 6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49) using a modification (Gandemer et al., 1983) of the methods of Hsu and Lardy (1969) and Fitch et al. (1959). Malic enzyme and glucose 6-phosphate dehydrogenase were assayed by measurement of NADPH formation at 37°C by absorbance at 340 nm. Acetyl-CoA carboxylase (CBX, EC 6.4.1.2) was assayed by the H14CO3-fixation method (Chang et al., 1967; Chakrabarty and Leiville, 1968; 1969). The activities of G6PDH and ME were expressed as micromoles of NADPH produced per gram of tissue, whereas CBX activity was expressed as nanomoles of bicarbonate incorporated per gram of tissue.
Sensory Analysis
Thirty-six hams were evaluated using conventional profiling (QDA) analyses (Stone et al., 1974). The panel of six male and six female assessors was trained in the first of two sessions to acquire a descriptive lexicon for ham, and, in the remaining sessions, panelist performance was monitored. Through guided discussion, redundant terms were eliminated from the lexicon, and the terms muscle color, fat color, presence of intramuscular fat (marbling), rancid flavor, seasoned flavor, saltiness, and mouth consistency (tenderness, brittleness, melting quality) were selected as the descriptors for use during sensory evaluation.
The sensory analysis took place in 12 sessions; in each session, three samples (one from each dietary treatment) were evaluated by all panelists. Each sample was presented as 0.5-mm thick slices on plastic dishes covered with aluminum foil. Within each session, the design was balanced for order and carryover effects (Macfie et al., 1989). Panelists were instructed to remove the aluminum cover and taste the samples. Then each panelist rated the descriptors on an anchored intensity line scale ranging from 0 (minimum intensity) to 10 (maximum intensity). Water and unsalted crackers were provided to cleanse the palate between samples. The evaluations were carried out in a certified sensory laboratory (UNI-ISO 8589, 1989).
Statistical Analyses
Statistical analysis of the data was performed with the general linear model (GLM) procedure of SPSS (SPSS/PC+ Statistics 11.0. SPSS Inc., Chicago, IL), and the residual error was used to test the main effect of dietary treatment. Meat quality, chemical composition of ham, fatty acid composition, enzyme activity, and TBARS data were analyzed as a one-way ANOVA in a completely randomized design structure with treatment serving as the fixed effect and time when appropriate (TBARS). Individual carcass was the experimental unit parameter. Data from the descriptive-attribute sensory panel were analyzed as a one-way ANOVA in a completely randomized design structure with treatment as a fixed effect and panelist as random effects. Ham was the experimental unit for sensory panel evaluation. Differences with probability levels of P < 0.05 were considered significant. Differences among means were determined using a Student-Newman-Keuls t-test.
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Results and Discussion
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Dietary CLA supplementation did not (P > 0.05) affect carcass weight, dressing percentage or backfat thickness (Table 3); however, fat depth tended to be lower (P = 0.10) in CLA-fed pigs. With the exception of a trend for 10th-rib fat depth to be reduced in carcasses from CLA-fed pigs, inclusion of 0.25 or 0.5% CLA in the diet of heavy pigs had no (P > 0.10) appreciable effects on carcass fatness or muscling. Results of the present study are consistent with those of Eggert et al. (2001) and Thiel-Cooper et al. (2001), who reported that 10th-rib fat depth was less in carcasses from CLA-fed pigs than controls. Moreover, Dugan et al. (1997) demonstrated that including 2% CLA in swine diet reduced subcutaneous fat by 6.8% and increased carcass lean content by 2.3%, compared to untreated controls.
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Table 3. Weights and carcass traits of pigs fed diets containing 0, 0.25, and 0.5% conjugated linoleic acid (CLA)a
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As noted by Eggert et al. (2001), results on the effects of dietary CLA supplementation on pork carcass composition are contradictory. This may be due to differences in pig genetics, levels of CLA supplementation, lengths of CLA supplementation, or the exact isomeric composition of the CLA preparations used in the various trials (Pariza et al., 2000; Mersmann, 2002).
Results of the SM quality evaluation are shown in Table 4. In the SM muscle, pH at 45 min was higher (P < 0.05) in the group fed 0.5% CLA than in the group fed 0.25% CLA, but there was no (P > 0.05) difference at 24 h. Dietary CLA supplementation did not (P > 0.05) affect loin weight or pH measured at 45 min or 24 h in the LM (Table 5). We are unable to explain this unexpected high pH in SM muscle. Dugan et al. (1999) found that feeding 2% CLA from 61.5 to 106 kg BW did not affect postmortem longissimus thoracis lactate accumulation or pH decline. No effect (P > 0.05) of dietary CLA was observed on color indices in either muscle. With regard to meat quality, previous studies (Dugan et al., 1999; Eggert et al., 2001; Joo et al., 2002) have found that color indices were unaffected by dietary CLA. By contrast, Wiegand et al. (2002) observed that chops from CLA-fed pigs had higher b* values, corresponding to a more yellow product.
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Table 4. Meat quality of semimembranosus muscle of pigs fed diets containing 0, 0.25, and 0.5% conjugated linoleic acid (CLA)a
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Table 5. Meat quality of longissimus muscle of pigs fed diets containing 0, 0.25, and 0.5% conjugated linoleic acid (CLA)a
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The TBARS values for the LM are presented in Figure 1. After 300 min of forced oxidation, the concentration of malondialdehyde was lower (P < 0.005) in LM from pigs fed 0.5% CLA than in the LM from controls. Results of our forced-oxidation studies (TBARS) indicate a positive effect of CLA supplementation on the oxidative stability of heavy pig muscle. However, greater stability was only evident in LM from pigs fed 0.5% CLA, and only after 300 min of forced oxidation. Joo et al. (2002) and Wiegand et al. (2002) also reported lower TBARS values in loin samples from pigs fed higher levels of CLA. Improved oxidative stability could be due to higher saturated fatty acid (SFA) and lower non-CLA unsaturated fatty acids in the CLA-fed pigs, as also observed in chicken meat patties (Du et al., 2000), as well as to greater oxidative stability of CLA compared to other PUFA (Shantha et al., 1995; Joo et al., 2002).
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Figure 1. Effect of dietary CLA supplementation on thiobarbituric acid-reactive substances (TBARS), measured as nmol of malondialdehyde (MDA)/g, of longissimus muscle of heavy pigs fed diets containing 0%, 0.25% and 0.5% CLA. Data points that do not have a common letter differ (P < 0.05).
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The activities of acetyl-CoA carboxylase, malic enzyme, and glucose 6-phosphate dehydrogenase in SM muscle and adipose tissue are shown in Table 6. No differences (P > 0.05) were found in enzyme activities in SM. Kouba and Mourot (1999) reported, in pigs, a positive correlation between the malic enzyme activity and the intramuscular fat content, with the correlation coefficient varying between 0.6 and 0.8 in relation to muscle localization. The present result corresponds with lipid content of Parma ham (Table 7) and with the observation of Bee (2001) that CLA supplementation did not affect intramuscular fat content in pigs.
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Table 6. Activity of acetyl CoA carboxylase, malic enzyme, and glucose 6-phosphate dehydrogenase in semimembranosus (SM) muscle and adipose tissue of heavy pigs fed diets containing 0, 0.25, and 0.5% conjugated linoleic acid (CLA)a
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Table 7. Fatty acid composition of adipose tissue of hams from pigs fed diets containing 0, 0.25, and 0.5% conjugated linoleic acid (CLA)a
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In adipose tissue, no differences (P > 0.05) were found in glucose 6-phosphate dehydrogenase and malic enzyme activities (P > 0.05); however, CLA supplementation reduced (P < 0.05) acetyl-CoA carboxylase activity. When compared to the controls, acetyl-CoA carboxylase activity tended to be lower (P = 0.06) in the tissue of pigs fed 0.25% CLA and was lower (P = 0.02) in adipose tissue of pigs fed 0.5% CLA. These results are in accord with our observations of significant reductions of acetyl-CoA carboxylase activity in perirenal fat of rabbits fed CLA (Corino et al., 2002b).
Neither dry matter, lipid, nor protein content of Parma hams was affected (P > 0.05) by dietary CLA supplementation (Table 8). Moreover, dietary CLA failed (P > 0.05) to influence the proteolytic index or salt content of dry-cured hams. No previous study reported the effects of CLA on chemical composition of dry-cured ham, but the values observed in the present study are in accord with standard values of Parma ham chemical composition reported by Russo and Nanni Costa (1995).
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Table 8. Chemical composition of Parma ham from pigs fed diets containing 0, 0.25, and 0.5% conjugated linoleic acid (CLA)a
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Fatty acid composition of adipose tissue is presented in Table 7
. Dietary CLA increased (P < 0.001) the SFA content and decreased (P < 0.002) the monounsaturated fatty acid (MUFA) content in pork adipose tissue. Polyunsaturated fatty acid concentrations were similar in all three groups. The CLA content in adipose tissue of pigs fed 0.25 and 0.5% CLA diets was similar, and higher (P < 0.001) than the CLA content in adipose tissue of control pigs (Table 7). The iodine value of adipose tissue was lower (P < 0.01) in CLA-fed pigs than the control group, with no difference (P > 0.05) between the two levels of CLA incorporation (Figure 2). Moreover the 9 desaturase index (ratio of MUFA to the sum of SFA and MUFA) was lower (P < 0.01) in CLA-fed pigs than controls (Figure 3).
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Figure 2. Effect of dietary CLA supplementation on iodine values of ham adipose tissue of heavy pigs fed diets containing 0%, 0.25% and 0.5% CLA. Bars that do not have a common letter differ (P < 0.01).
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Figure 3. Effect of dietary CLA supplementation on desaturase index of ham adipose tissue of heavy pigs fed diets containing 0%, 0.25% and 0.5% CLA. Bars that do not have a common letter differ (P < 0.01).
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In the present study, the fatty acid profile of ham fat was conspicuously modified by dietary CLA with increased SFA and total CLA isomers and decreased MUFA, which is consistent with other studies in pigs (O’Quinn et al., 2000; Bee, 2001; Eggert et al., 2001). Direct substitution of dietary fat into adipose, and modulation of stearoyl-CoA desaturase activity, by CLA are two likely reasons for the modified fatty acid profile of adipose tissues. The reduction in MUFA content is a reflection of decreased oleic acid (C18:1) content in adipose tissue from CLA-fed pigs, which, in turn, is likely a direct result of depressed stearoyl-CoA desaturase activity. Several studies have shown that dietary CLA inhibits the expression (Lee et al., 1998) and activity (Bretillon et al., 1999; Choi et al., 2000) of hepatic stearoyl-CoA desaturase. Moreover, Smith et al. (2002) reported a lower 9 desaturase index in CLA-fed pigs than pigs.
In contrast to previous studies (O’Quinn et al., 2000; Eggert et al., 2001; Thiel-Cooper et al., 2001), linoleic acid (C18:2) content in the adipose tissue of pigs in the present study was unchanged by dietary CLA supplementation. The relative effect of CLA on C18:2 levels is largely dependent on the C18:2 content of the base diet. Bee (2001) reported that in adipose tissue of finishing pigs there were no differences in C18:2 content between pigs fed diets containing CLA or lard (low C18:2 content); however, CLA supplementation caused a noticeable reduction in adipose tissue C18:2 compared to diet formulated with linoleic acid-enriched oil. Another mechanism by which the fatty acid profile of the diet can affect the overall fatty acid composition of adipose tissue is via activation of peroxisome proliferator-activated receptor-
(PPAR-) to induce peroxisomal ß-oxidation. Conjugated linoleic acid is a very high-affinity ligand and activator of PPAR- (Moya-Camarena et al., 1999), and increased lipid oxidation could contribute to the altered fatty acid composition of adipose tissue (Eggert et al., 2001). The changes in fatty acid composition associated with dietary CLA also resulted in the improvement of the technological quality of fat. This was evident by the lower iodine values in fat from CLA-supplemented pigs. To avoid fat quality problems, the Parma Ham Production Consortium recommends that the iodine value of Parma ham fat should not exceed 70 (Wood, 1984; Mourot et al., 1991). Girard et al. (1988) emphasized that achieving a stearic acid content in pork fat in excess of 12% would ensure good fat stability. In the present study, the stearic acid content was greater than 13% in all groups, whereas the stearic acid content of adipose tissue from pigs fed 0.25% CLA was higher than that from the other two groups.
Lipid oxidation volatiles produced during ham maturation are the major contributors to the characteristic flavor and aroma of Parma ham (Toldrà et al., 1997). These substances are derived from free fatty acids which, in turn, arise from the intense lipase-mediated hydrolysis of muscle and adipose tissue lipids that occurs during the earlier processing phase (Berdagué et al., 1993; Buscailhon et al., 1994). Because of their susceptibility to oxidation, high levels of PUFA can have detrimental effects on the sensorial quality, technological quality, and acceptability of pork products (Houben and Krol, 1980; Warnants et al., 1998). Lipid oxidation is one of the main mechanisms of quality deterioration during meat storage (Monahan et al., 1990), and it is desirable to inhibit the formation of volatile secondary oxidation products (similar to those that contribute to the delicate flavor of Parma ham) in order to enhance shelf life. The susceptibility of muscle lipids to oxidation is reduced by the presence of vitamin E, which improves the quality (color, drip loss and lipid oxidation) of raw pork from heavy pigs (Corino et al., 1999), as well as processed pork products (Dirinck et al., 1996; Chizzolini et al., 1999).
The effects of CLA supplementation on the fatty acid profile of adipose tissue and intramuscular fat raise the question of a possible influence on the sensory characteristics of Parma ham. Results of the sensory panel evaluation of Parma hams are presented in Table 9. Although panelists scored dry-cured hams from CLA-fed pigs higher (P < 0.05) for melting quality, sensory panel evaluated color, aroma, taste, and mouth and tactile consistencies of Parma hams were not (P > 0.05) affected by inclusion of CLA in the swine diet. In agreement with results from the present study, Larsen et al. (1998) failed to note an effect of dietary CLA supplementation on ham yields, sensory characteristics, or Warner-Bratzler shear values. Moreover, Dugan et al. (1999) and Wiegand et al. (2002) demonstrated that incorporating CLA in the finishing diets of swine had no appreciable effects on tenderness, juiciness, or flavor intensity of cooked pork.
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Table 9. Sensory characteristics of Parma hams from pigs fed diets containing 0, 0.25, and 0.5% conjugated linoleic acid (CLA)a
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Implications
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Conjugated linoleic acid has been shown to induce positive properties in animal nutrition and health. The inclusion of these fatty acids in the diet of heavy pigs, primarily destined for production of salami and dry-cured (Parma) ham, positively affected technological and nutritional quality of adipose tissue. These positive effects were obtained in combination with an improvement in melting quality in the mouth with no other effects on the sensory qualities of the Parma ham. However, additional studies are required to confirm the potential benefit of conjugated linoleic acid and to determine the most appropriate dose and length of supplementation in heavy pigs.
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Footnotes
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1 This study was supported by a grant from the Italian Ministry for Universities and Scientific and Technological Research (Cofin. 2000, Prof. Corino). The authors wish to thank Conlinco, Inc., of Detroit Lakes, MN, for kindly providing the conjugated linoleic acid supplement used in this project. 
2 Correspondence— phone: +39 02 50317900; fax: +39 02 50317898; E-mail: carlo.corino{at}unimi.it.
Received for publication November 13, 2002.
Accepted for publication May 26, 2003.
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Abstract
Introduction
