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* Stazione Sperimentale per l’Industria delle Conserve Alimentari, 43100 Parma, Italy;
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Istituto Sperimentale per la Zootecnia, 41100 Modena, Italy;
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Centro Ricerche Produzioni Animali (CRPA), 42100 Reggio Emilia, Italy; and
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Dipartimento di Morfofisiologia e Produzioni Animali Università di Bologna, 40100 Bologna, Italy
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Key Words: Age • Cured Meat • Enzymes • Hams • Pigs • Proteolysis
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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; Virgili et al., 1995). Oiliness, yellowness, and rancid flavor increased in ham containing high concentrations of PUFA in the external fat; in fact, established regulations for dry-cured Italian hams limit the linoleic acid percentage and iodine value of fresh ham to no more than 15% and 70, respectively (Consortium for Parma Ham, 1992). A high degree of proteolysis leads to increased muscle softness, formation of a white surface film, and a bitter taste (Guerrero et al., 1996; Virgili et al., 1998).
The postmortem activity of cathepsin B in pork has been shown to be related to proteolysis in Italian dry-cured hams (Schivazappa et al., 2002), whereas high residual cathepsin activities at the end of manufacturing have been associated with impaired texture in dry-cured ham (Garcia-Garrido et al., 2000). Among the proteolytic enzymes, alanyl aminopeptidase (or aminopeptidase puromycin-sensitive) and arginyl aminopeptidase (or aminopeptidase B) account for 83% and 11% of muscle aminopeptidase activity, respectively (Flores et al., 1997b). Toldrà et al. (1995) indicated that the aminopeptidases were responsible for the generation of free AA during processing. The activity of these proteolytic enzymes varies according to swine genetics (Armero et al., 1999; Russo et al., 2000), weight, age (Sarraga et al., 1993; Toldrà et al., 1996), and nutrition (Van den Hemel-Grooten et al., 1997). Therefore, the objective of this study was to determine whether the age at slaughter affects the quality of typical, Italian dry-cured hams.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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All pigs were fed a wet-meal (3:1 water:feed ratio) diet formulated to meet the dietary requirements of finishing swine (Table 1). At the beginning of the trial, feed intake was limited to 1.6 kg/d, and feed allocations were increased by 100 g/d up to the eighth week of the feeding period. Then, the amount of feed offered to pigs was increased by 70 g/d until a maximal ADFI of 2.96 kg/d was achieved at 16 wk of age. Daily feed intake was not altered thereafter, and the daily allotted feed was based on the amount consumed by the group showing the lowest feed intake in two daily 30-min meals. Pigs were individually weighed every 28 d to monitor growth rate (data not reported) and before slaughter to calculate ADG. Pigs were transported approximately 80 km and slaughtered after 139 d (8 mo of age) or 202 d (10 mo of age) on trial.
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). At the end of the trimming line, hams were weighed, and a five-member, trained panel of experts evaluated fresh hams for overall fatness and marbling on a five-point scale (0 = absence of fatness/marbling to 5 = abundant fatness/marbling). Average panel scores for each fresh ham were recorded, and hams were sorted into three categories based on fatness/marbling scores (0 to 2.5 = "low," 2.5 to 3.5 = "medium," 3.5 to 5.0 = "high"). Area of the longissimus muscle (LM) was measured on the cut surface at the 11th-/12th-rib interface, and the LM area:hot carcass weight ratio was calculated and reported as the muscularity index (Petersen et al., 1989).
Muscle Sampling.
A 50-g sample of semimembranosus was excised from hams 24 h postmortem and subsequently refrigerated at 0 to 2°C to determine the hydrolyzing activities of cathepsin B, cathepsin B+L, arginyl aminopeptidase, and alanyl aminopeptidase, as well as proximate composition (AOAC, 1990). Additionally, a boneless LM chop from the 12th- to 13th-rib region was trimmed free of subcutaneous fat and connective tissue for analysis of drip and cooking loss percentages.
Proteolytic Enzyme Assays.
Enzyme activities were assayed 36 to 48 h postmortem. Cathepsin B and B+L were determined using N-CBZ-Arg-Arg-AMC and N-CBZ-Phe-Arg-AMC (Sigma, Milan, Italy), respectively, as described by Barrett and Kirschke (1981). Muscle aminopeptidase activity was determined according to Toldrà et al. (1992b) with the substrates L-Ala-AMC and L-Arg-AMC (Sigma), and the measured activities were reported as alanyl aminopeptidase and arginyl aminopeptidase hydrolyzing activities, respectively. Activities were expressed as nmol of substrate hydrolyzed•min-1•g protein-1.
Meat Quality Measurements.
Semimembranosus pH was measured at 1 and 24 h postmortem with a Hamilton glass electrode probe attached to a portable pH meter (WTW pH330, Weilheim, Germany). Additionally, drip-loss was determined on the LM chop according to the procedure of Virgili et al. (1995). Briefly, a 3.0-cm-thick LM chop was weighed and placed in a polyethylene bag (15 x 30 cm), sealed, suspended, and stored at 2°C for 24 h. Afterwards, each core was removed from its bag, blotted with a paper towel, reweighed, and drip loss was expressed as a percentage of the original LM chop weight. On the third day after slaughter, a 1- x 1- x 2-cm sample of LM, free of all external fat and connective tissue, was weighed, placed in Pyrex sealed tubes, and heated in a water bath at 68°C for 1 h according to the procedure of Tornberg et al. (1992). Samples were then chilled at 2°C for 24 h, reweighed, and cooking loss percentage was calculated by dividing the difference between pre- and postcooked weights by the precooked weight. Instrumental color of the semimembranosus (SM) was measured 24 h postmortem with a CR-200 Chroma Meter (Minolta, Milan, Italy) with D65 illuminant. Lightness (L*), redness (a*), and yellowness (b*) of SM samples were the mean of three random readings, and the colorimetry information was used to calculate hue angle (tan-1 [b*/a*]), chroma ([a*2+b*2]1/2), and the a*:b* ratio.
Adipose Tissue Measurements.
At 24 h postmortem, approximately 100 g of ham subcutaneous fat (inner and outer layers) was collected beneath the biceps femoris, wrapped in aluminum foil, vacuum packaged, and frozen at -18°C for determination of moisture and fatty acid composition. Moisture content of fat was determined at 103°C. Fatty acid composition was determined according to the procedures of Della Casa et al. (1999), where 0.5 g of fat was dissolved in 10 mL pentane and transmethylated with 0.5 mL of 2N methanolic KOH. The organic phase was filtered through anhydrous sodium sulfate and injected into a Fisons HRGC-MEGA 2 (Milan, Italy) gas chromatograph equipped with a flame ionization detector and a 50-m silica column SP 2340 (Supelco-Sigma, Milan, Italy) with an internal diameter of 0.25 µm and a film thickness of 0.20 µm. Working conditions were as follows: hydrogen carrier gas, 79 kPa; split ratio, 70:1; injector temperature, 250°C; detector temperature, 250°C; and initial oven temperature, 150°C for 4 min increasing to 180°C at a rate of 1.5°C/min. The fatty acid methyl esters were identified by comparison with methyl ester standards, and results were expressed as percentages of total fatty acid methyl esters.
Statistical Analysis.
Data were analyzed as a randomized complete block design with the general linear models procedures of SAS (SAS Inst., Inc., Cary, NC). Pen was the experimental unit for the analysis of performance data, whereas pig was the experimental unit in the analysis of carcass data. Additionally, age at slaughter was the lone main effect included in the model, and the pooled error term was used to test the main effect. Least squares means were computed for the main effect, and the Bonferroni t-test was used to statistically separate least squares means when P < 0.05. Distributions of fresh hams according to fatness/marbling categories were analyzed using Pearson 
2 and Fisher’s exact test procedure of SAS.
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Results and Discussion |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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). Established regulations for dry-cured, typical Italian hams (Consortium for Parma Ham, 1992) stipulate that the slaughtering weight of heavy pigs aged at least 9 mo must be 160 kg ± 10%; therefore, DG must be approximately 750 g/d. The variability found for pig carcass weight (8% CV) is in agreement with recent studies carried out on Italian heavy pig populations by Lo Fiego et al. (2000) and Rossi et al. (2001), who reported 10.0% and 7.7%, respectively.
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; Whittemore 1994; Candek-Potokar et al., 1998). Previous research studies performed on heavy pigs (Bittante et al., 1990; Franci et al., 1994a) did not show consistent differences in growth rate between pigs slaughtered at different ages and weights, but the dietary regimens were not reported and the compared slaughtering weights were lower than in the present trial (110 to 145 and 131 to 159 kg, respectively, vs. 143 to 182).
Dressing percentage was higher (P < 0.01) for older and heavier pigs (Table 3), which is in agreement with Bittante et al. (1990) and Franci et al. (1994b). Age increase is characterized by the growth of lean, bone, and fat, with greater fat deposition being mostly responsible for the increase in dressing percentage detected in the older pigs. The increase (P < 0.01) in LM area with age (and weight) supports the previous finding of Candek-Potokar et al. (1998), who studied pigs in the 100- to 130-kg range and with about one month’s difference in slaughtering age. Muscularity index was lower (P < 0.01) in 10- vs. 8-mo-old pigs, which is in agreement with the greater backfat thickness and higher total fat found in older, heavier pigs (Bittante et al., 1990; Garcia-Macias et al., 1996; Candek-Potokar et al., 1998). The weight of the lean cuts increased (P < 0.01) with age, but lean cut yield decreased (P < 0.01) in carcasses from older pigs (P < 0.01). It is assumed that factors such as lower growth rate for primal cuts than for the rest of the body and a higher fat deposition in other areas of the carcass during the two additional months of feeding may contribute to the decrease in yield of lean cuts.
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). Even though a* (redness) values were not different (P > 0.05) between slaughter ages, the SM from pigs slaughtered at 8 mo of age was more (P < 0.01) yellow (higher b* value) than that from older (10-mo-old) pigs. Higher a* values were reported by Franci et al. (1994b) in older pigs. Moreover, Garcia-Macias et al. (1996) observed higher a* values for the SM of heavier pigs; however, carcass weights of their study were considerably lighter than carcasses of pigs in the present study. Fernández-López et al. (2000) stated that the a* values in pork depend on the concentration of myoglobin and not on its state (deoxygenated, oxygenated, or oxidized). Results presented in Table 4 demonstrate that, under the conditions of the reported trial, extending the slaughter age two additional months does not yield appreciable differences in redness of pork color.
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, a high a*:b* ratio is indicative of a high concentration of either myoglobin or oxymyoglobin on the surface of the meat, whereas a low a*:b* value is due to a high concentration of metmyoglobin. Because there was no (P > 0.05) difference in a* values between the older and the younger pigs (Table 4
), differences in a*:b* may be attributed to a lower amount of metmyoglobin in the SM from 10-mo-old pigs. In this respect, a delay of 2 mo in slaughtering may result in significant differences in color, attributable not to the amount of meat pigment but to its oxidative status.
Pigs slaughtered at 10 mo had lower (P < 0.01) L* and hue angle values, indicating a darker, truer red color than pigs slaughtered at 8 mo. When studying the relationship between fresh muscle and the corresponding dry-cured color, Chizzolini et al. (1996) reported that L* and hue angle had the highest correlation coefficients (negative association), with the "redness" score of corresponding dry-cured hams. On the basis of the present results, pigs slaughtered at 10 mo, when other dry-curing parameters with a potential effect on color (such as weight loss, salt and moisture content, and degree of proteolysis) can be kept constant, yielded redder dry-cured hams.
The pH values, measured at 1 and 24 h postmortem, were lower (P < 0.01) in the SM from pigs slaughtered at 10 than 8 mo of age. This is in accordance with the results obtained by Cisneros et al. (1996) for pigs slaughtered between 100 and 160 kg, and Beattie et al. (1999) for pigs slaughtered at lighter weights (70 to 100 kg). The SM is a white muscle susceptible to PSE and DFD conditions (Warner et al., 1993). The higher frequency of hams with 1-h pH values less than 6.0 was noted among pigs slaughtered at 10 mo compared to younger pigs (23 vs. 8%), whereas hams with ultimate (24-h) pH values in excess of 6.0 were 10 and 2% for pigs slaughtered at 8 and 10 mo, respectively. Various events might be considered to account for the differences reported in mean pH values and distribution between the two age groups of pigs. The higher pH values measured in hams of younger pigs might reflect higher glycogen consumption during the preslaughtering phases (Swatland 1994). Moreover, older pigs, characterized by producing heavier carcasses, were more muscular and fatter, which may depress heat transfer during chilling and result in more rapid postmortem metabolism and pH decline (Cisneros et al., 1996). Similar results were found in studies carried out on pork LM, where lower pH values were measured in muscles removed from carcasses of increasing weight and external fat thickness (Beattie et al., 1999).
Despite the higher pH value of younger pigs, the drip and cooking losses were higher (P < 0.01) for younger pigs (Table 4). The effect of age detected for drip and cooking loss may be related either to the replacement of water by lipid in older pigs (Beattie et al., 1999), even though no relationship was found between i.m. fat, drip and cooking loss, or to the lower moisture:protein ratio found in heavier carcasses (Garcia-Macias et al., 1996).
A difference of 2 mo in pig slaughtering age did not cause significant differences in moisture, protein, or i.m. fat of SM, whereas the moisture content was lower (P < 0.01) in the LM of older than younger pigs (Table 5). This inconsistency may be partly attributable to the sampling method, because only the surface (0.5 cm thickness) of the SM was removed to allow thighs to be processed, whereas a complete 4-cm-thick section of LM was taken (see Materials and Methods).
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) reported a lower i.m. fat content in the SM compared with other ham muscles (biceps femoris and semitendinosus). Nevertheless, subjective assessment of marbling score (Table 6) of trimmed hams where surface sections of SM, BF, and ST are visible, were not affected by age at slaughter, in agreement with analytical data of i.m. fat assayed in SM. These results are in accordance with Beattie et al. (1999), who found only a tendency for marbling to increase in carcasses of older and heavier pigs, and Mayoral et al. (1999), who reported slight changes for i.m. fat during the fattening of Iberian pigs reared outdoors. However, Candek-Potokar et al. (1998) found that i.m. fat increased as both age and weight of pigs fed ad libitum increased until slaughtering.
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) showed an effect for age (P < 0.01 for Pearson 2 and Fisher’s exact test), and was independent of the marbling score. If compared with the carcasses of the younger pigs, the older pigs were mostly rated as medium or high for "ham fatness" on the distribution of hams into fatness categories. The higher sensory fatness in older pigs is supported by the concomitant reduction in the percentage of lean cuts (Table 3).
Muscle Biochemistry
Proteolytic enzymes cause the formation of small peptides and free AA from proteins, which affect the flavor profile of aged products, such as dry-cured ham (Flores et al., 1997a, Virgili et al; 1999). Cathepsins and aminopeptidases, whose activities are kept at low-water activity values, are responsible for peptide and free AA generation throughout the entire manufacturing period of dry-cured ham (Toldrà et al., 1992a).
Slaughter age affected the activities of cathepsin B and B+L (Table 7). The older pigs had lower cathepsin B (P < 0.01) and B+L (P < 0.05) activities than the younger pigs, which is in agreement with reports of Sarraga et al. (1993), Rosell et al. (1998), and Armero at al. (1999). Fresh muscle activities of cathepsin B are closely associated with the final proteolysis of dry-cured hams (Virgili et al., 1998; Schivazappa et al., 2002). Both excessive final proteolysis and residual cathepsin activity are considered to be responsible for defects in the texture and taste of hams, such as softness, pastiness, and bitter taste (Virgili et al., 1995; Guerrero et al., 1996; Garcia-Garrido et al., 2000). Cathepsins, because they are involved in the first step of the proteolytic mechanism, are rate-limiting for the whole proteolytic process (Kirschke et al., 1995).
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), but this role has not yet been confirmed in the case of dry-cured ham. Alanyl aminopeptidase has a broad substrate specificity for aromatic, aliphatic and basic amino-acyl bonds, whereas arginyl aminopeptidase is a chloride-activated enzyme with a specificity for basic amino-acyl bonds (Flores et al., 1997b). The aminopeptidase hydrolyzing activities were higher (P < 0.01) in the SM from older than younger pigs, supporting the opposing trend between cathepsins and aminopeptidases reported by Toldrà et al. (1996). Thus, hams from younger pigs may be more susceptible to excessive proteolysis during the manufacturing period, possibly resulting in extreme softness and bitterness in dry-cured ham. The degree of proteolysis in ham may be influenced by several parameters, such as pH, ham weight, ham weight loss, salt diffusion, and water activity within the muscles of hams (O’Halloran et al., 1999; Schivazappa et al., 2002).
Fatty Acid Composition of Subcutaneous Fat
Age at slaughter yielded differences in the moisture content of fat (P < 0.01) and in monounsaturated fatty acid and PUFA composition (P < 0.01), with the exception of C16:1 (P < 0.05; Table 8). Ham subcutaneous fat from 10-mo-old pigs had greater percentages of palmitic (P < 0.05) and oleic (P < 0.01) acids and lower (P < 0.01) moisture and linoleic and linolenic acids than subcutaneous fat from 8-mo-old pigs.
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), energy intake, dietary fatty acid composition (Mordenti et al., 1994; Della Casa et al., 1999), carcass weight and composition (Cameron et al., 1990; Zappa and Pugliese, 1991; Piedrafita et al., 2001), and genetic background (Lo Fiego, 1988). Wood (1984) reported that, with an increase in the triglyceride content of fat tissue cells, the moisture content decreased. With increasing age and weight, the partition of ingested energy turns from muscular to adipose tissue growth, which increases the ratio between de novo synthesized fatty acids (mainly C18:1; Enser, 1991) and dietary fatty acids (C18:2 and C18:3). The higher sensory fatness score achieved by older pigs (Table 6) is supported the changes found in fatty acid composition. Zappa and Pugliese (1991) reported a positive correlation between monounsaturated fatty acid and backfat thickness, and a negative correlation between backfat thickness and both backfat moisture and PUFA.
No differences (P > 0.05) were detected for concentrations of stearic acid in ham subcutaneous fat between younger and older pigs. Cameron et al. (1990) and Piedrafita et al. (2001) reported positive correlations between saturated fatty acids and backfat thickness in the case of pigs fed an ad libitum dietary regimen, whereas pigs in the present study were limit-fed. Cameron et al. (1990) reported that the changes in fatty acid composition of the subcutaneous fat of heavier pigs were greater for ad libitum-fed pigs than for those with restricted access to feed. Nevertheless, ham subcutaneous fat from pigs slaughtered at 10 mo, characterized by lower percentages of PUFA, appears more suitable for dry-cured ham production, meeting the requirements of the tutelary consortia (Consortium for Parma Ham, 1992).
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Implications |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Footnotes |
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2 Correspondence: V.le F. Tanara 31/A (phone: 39-0521795237; fax: 39-0521771829; E-mail: r.virgili{at}rsadvnet.it).
Received for publication May 2, 2002. Accepted for publication June 3, 2003.
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Literature Cited |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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andek-Potokar, M., B. Zlender, L. Lefacheur, and M. Bonneau. 1998. Effects of age and/or weight at slaughter on Longissimus dorsi muscle: biochemical traits and sensory quality in pigs. Meat Sci. 48:287–300.
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