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Green hams electrical impedance spectroscopy (EIS) measures and pastiness prediction of dry cured hams
Meat Science 66 (2004) 289–294 www.elsevier.com/locate/meatsci
Green hams electrical impedance spectroscopy (EIS) measures and pastiness prediction of dry cured hams Luis Guerreroa,*, Idoia Gobantesa, Ma A`ngels Olivera, Jacint Arnaua, M. Dolors Gua`rdiaa, Jordi Elvirab, Pere Riuc, Narcı´s Gre`bold, Josep Ma Monforta a
IRTA-CTC. Institut de Recerca i Tecnologia Agroalimenta`ries. Centre de Tecnologia de la Carn. Granja Camps i Armet. 17121 Monells, Girona, Spain b NTE, S.A., Can Male´, s/n, 08186 Barcelona, Spain c Department of Electronic Engineering, Telecommunication Engineering School, UPC, Gran Capita`, s/n. Modul C4, 08034 Barcelona, Spain d Esteban Espun˜a, S.A., Mestre Turina 39-41, 17800 Olot, Girona, Spain Received 22 November 2002; received in revised form 24 April 2003; accepted 24 April 2003
Abstract The objective of this study was to assess the value of electrical impedance spectroscopy (EIS) as a predictor of certain dry-cured ham sensory properties in green hams of different technological meat qualities and processed commercially. Measurements of technological meat quality (weight, ham conformation, subcutaneous fat thickness, pH45 and pHu) and some sensory properties (adhesiveness, hardness, crumbliness, pastiness, fibrousness and saltiness) were carried out on the Biceps femoris (BF) and Semimembranosus (SM) muscles. The electrical parameters, Ro, Rinf, ratio (Rinf/Ro), Fc and , were obtained with EIS equipment applied to two different regions of the ham at 36 h post mortem (BF and SM). Principal component (PC) analysis was used to describe the relationship between sensory properties and electrical parameters. For BF muscle there were no clear relationships between the electrical parameters and the sensory properties. However, for SM muscle, pastiness was correlated positively with the ratio and Fc obtained by EIS. None of the electrical parameters obtained by EIS were able to differentiate between groups of hams classified according to their level of pastiness in the BF muscle. However, in the SM muscle, the origin of the pastiness was related to the use of PSE meat and was predicted by the electrical impedance measurements. The EIS prototype correctly detected 69.2 and 56.0% (for SM and BF muscles, respectively) of the problem hams in terms of pastiness. These results could be of use in the selection of the raw material to reduce the incidence of dry-cured hams with defective texture. # 2003 Elsevier Ltd. All rights reserved. Keywords: Dry-cured ham; Meat quality; Electrical impedance spectroscopy (EIS); Sensory properties
1. Introduction Sensory quality of dry-cured ham is strongly affected by raw material characteristics and technological processes. The influence of breed (Guerrero, Gou, Alonso, & Arnau, 1996), fatness (Santoro, 1984) and sex (Gou, Guerrero, & Arnau, 1995) on green ham properties has been studied showing the importance of these properties in the final eating characteristics. Dry-cured ham characteristics are also affected by green meat technological quality: PSE affects salt uptake (Arnau, Guerrero, Casademont, & Gou, 1995), saltiness and texture (Ordon˜ez, 2001) and * Corresponding author. Tel.: +34-972-63-00-52; fax: +34-972-6303-73. E-mail address: [email protected] (L. Guerrero). 0309-1740/03/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0309-1740(03)00101-3
DFD hams, among others, increase the risk of spoilage (Guerrero, Arnau, & Garriga, 1991), undesirable pastiness and adhesiveness (Guerrero, Gou, & Arnau, 1999) and the incidence of phosphate crystals (Arnau, Guerrero, & Gou, 1998) decreasing consumer acceptability. During processing the different steps can be modified according to the raw material to reduce the incidence of flavour and texture defects in the final product (Arnau, 1998, 2000). In this way, the classification of the green hams in different quality groups would be advisable to optimise processing. Different instruments have been developed for the prediction of PSE or meat with low water holding capacity (WHC) such as FOP (fibre optic probe) and QM (quality meter) that measure PSE status by internal light scattering and electrical conductivity (EC), respec-
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tively. The pH at 45 min post-mortem (pH45) is considered the best predictor of WHC (Oliver, Gispert, Tibau, & Diestre, 1991; Warris, Brown, Lopez-Bote, Bevis, & Adams, 1989), but it is difficult to measure on the slaughter-line due to the speed of the line and the low temperatures in the refrigeration tunnel where carcasses are stored after evisceration. Since the 1980s different instruments have been developed for electrical conductivity measurements, in meat, Schmitten, Schepers, and Festerling (1987) used the Konduktometer LF DIGI 550 and the new model LF191 operating at a frequency of 4 and 1 KHz, respectively. Forrest et al. (2000) used the purdue tetrapolar probe (PTP) for impedance measurements. Two instruments to measure EC of the muscle were used by Lee et al. (2000): the NWK LT K21 and a probe type device, the WO 99/ 01754. In general EC is not related to drip losses caused by PSE meat (Byrne, Troy, & Buckley, 1997). Regarding DFD meat, in some industries an ultimate pH (pHu), defined as the pH at 24 h post-mortem, higher than 6.0 in the Semimembranosus muscle (SM), is used to eliminate this type of meat. However, pH measurement needs frequent calibration and presents problems when used under industrial conditions due to the fragility of the electrodes. Another important parameter in the final sensory properties of dry-cured ham is the percentage of intramuscular fat (IMF) (Guerrero et al., 1996). Madsen, Borgaard, Rasmussen, and Christensen (1999) developed an on-line instrument based on electrical impedance to predict the IMF percentage in beef. They found that a percentage of IMF at 1/2 lumbar could be predicted with a correlation coefficient of 0.83 and a standard error of prediction (SEP) of 1.4% when measuring 185 carcasses at the end of the slaughter line. Oliver et al. (2001), evaluated a new prototype based on electrical impedance spectroscopy (EIS) to select green hams on the basis of pH45, final pH and fatness. The results of this study showed that electrical parameters obtained in the SM at 36 h post-mortem may classify 88.46% of the green hams with pH45 > 6.10 and 92.31% with pHu < 5.95. Despite the relatively high classification accuracy of this new prototype there is no information about the relationship between all these electrical parameters and the final sensory properties of the dry-cured ham. The aim of this study was to assess the EIS prototype as predictor of saltiness and texture of dry-cured hams obtained from green hams with different technological meat qualities.
2. Materials and methods This study was carried out on 86 PSE (pH45 < 5.85) and normal hams (pH45 > 5.85 and pHu< 6.0) selected
from commercial carcasses. The carcasses were weighed (kg) and classified in a slaughterhouse with the Fat-oMeter (SFK, Technology A/S, Herlev, Denmark). In order to obtain a sample that included the full range of technological meat quality, 14 additional hams with a pH24 higher than 6.0 (DFD hams) in the Semimembranosus muscle were selected in a dry-cured processing factory at 24 h post-mortem. 2.1. Measurements of meat quality Raw meat quality was recorded at 45 min post-mortem in the slaughterhouse using a portable pH meter (Crison 507, Crison Instruments S.A., Barcelona, Spain) equipped with a combined glass electrode (Ingold 406, Ingold, Urdorf, Switzerland) (pH45) in the Semimembranosus muscle (SM). The following measurements were made at 24 h post-mortem: weight of each ham (kg); the ham conformation (H), that was defined as the maximum height (cm) from the rind to the higher point of the Semimembranosus muscle, was measured with a calliper; subcutaneous fat thickness in the rump (FTR) was measured with a ruler (cm); and muscle pH (pHu) in the SM was measured with a portable pH meter (Crison). At 36 h post-mortem the electrical parameters were obtained with the EIS equipment in the BF and SM muscles (Biceps femoris and Semimembranosus regions, respectively). The system was controlled by software that allowed electrical impedance scanning from 8 kHz to 1MHz (Oliver et al., 2001). The device was able to measure four parameters: Ro is the electrical impedance modulus at lower frequencies and it is expressed in ohms ( ), Rinf is the electrical impedance modulus at high frequencies and is expressed in ohms ( ), is a shape adjustment parameter, and Fc is the characteristic frequency of the region under measurement that corresponds to the frequency at which the imaginary part of the electrical impedance is the largest in absolute value and is expressed in KHz. A fifth parameter is introduced: the ratio between Rinf and Ro. This parameter is proportional to the ratio of extracellular water to total water in the meat (Lozano, Rosell, & Palla`s-Areny, 1995). 2.2. Manufacturing process and sampling All the green hams were salted at 36 hours postmortem with a mixture of NaCl, KNO3 and NaNO2 (99, 0.5 and 0.5%, respectively). After 6 days of resting fully covered with this mixture at 0–4 C and relative humidity (RH) higher than 85%, they were covered
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with another mixture of NaCl, dextrose and sodium ascorbate (95, 3 and 1%, respectively) until a total salting time of 1.3 days per kg of green ham weight was reached. Afterwards they were washed in cold water and hung at 2–6 C and RH of 70–90% for 35 days. The ageing process consisted of three different steps: 10–14 C and RH of 60–80% for 70 days; 18– 22 C and RH of 60–75% for 70 days; 26–30 C and RH of 60–70% for 21 days. At the end of the drying period the hams were individually weighed, deboned and sliced. The chemical and sensory analyses were performed on slices perpendicular to the centre of the femur. 2.3. Chemical and sensory analysis Moisture as weight loss at 103 2 C (Presidencia del Gobierno, 1979) and sodium chloride by the Charpentier–Volhard method (ISO, 1970) were determined for the SM and BF muscles in each dry-cured ham. The sensory analysis was carried out separately for SM and BF muscles using an expert panel of six members. In each session each assessor evaluated the same four hams randomly selected, blocking the order of presentation and the first-order carry-over effects (Macfie, Bratchell, Greenhoff, & Vallis, 1989). The descriptors (hardness, pastiness, crumbliness, adhesiveness, fibrousness and saltiness) were quantified using a nonstructured scale ranging from 0 (absence) to 10 (intense). The definition of each texture attribute, as well as the references used to illustrate the maximum intensity of each of them, was as described by Guerrero et al. (1999). Chemical and sensory analyses were carried out in 74 hams: 14 DFD, 50 Normal and 10 PSE. 2.4. Statistical analysis Data were analysed using the MEANS, GLM, PRINCOMP and DISCRIM procedures from the SAS statistical package (SAS, 1987). In order to analyse the effect of the different variables on the pastiness, all the hams were classified in three groups according to their sensory score for this descriptor and for each muscle: (H) High pastiness group (mean pastiness over the six assessors greater than 2); (M) Medium pastiness group (mean pastiness between 1 and 2) and (L) Low pastiness group (mean pastiness score lower than 1). For the principal component analysis, and in order to group the different hams, and locate then in the biplot, they were classified in three groups according to their pH45 and pHu. Hams having pH45 lower than 5.85 were classified as PSE, hams with pHu higher than 6.0 as DFD and the rest as normal hams (Oliver et al., 2001).
3. Results and discussion The mean carcass weight and fat thickness measured with the Fat-o-Meter for the 86 animals selected at the slaughterhouse was 78.90 5.44 kg and 14.47 2.88 mm, respectively. These values are typical for pig carcasses in Spain, demonstrating a wide range of fat thicknesses (Gispert & Diestre, 2000). Table 1 shows the main traits of the different hams used for this study and Table 2 the mean values for the different hams classified according to their level of pastiness. The ham weight and its conformation may have an effect on the texture of the final product since as ham conformation increases, salt diffusion to the inner muscles (e.g. BF) is slowed down and increases such textural defects as pastiness (Guerrero et al., 1996). In the present study, ham conformation did not differ between different levels of pastiness either in SM or BF muscles. Ham weight was significantly higher in the H group only for the BF muscle. This suggests that others factors such as proteolytic potential (Parolari, Virgili, & Chivazappa, 1994; Parren˜o, Cusso´, Gil, & Sa´rraga, 1994; Sa´rraga, Gil, & Garcı´a-Regueiro, 1993) ham fatness (Gou et al., 1995) or pH and NaCl content (Arnau, Guerrero, & Sa´rraga, 1998) should also be taken into account to explain these results. Despite adjusting the salting time for each ham according to their weight, Table 1 Descriptive statistics of meat quality characteristics and sensory properties (mean values over assessors) Characteristics
Mean
S.D.
Max.
Min.
Nb
Ham weight (kg) Conformation (cm) Fat thickness rump (cm) pHa45 pHu Ham weight loss (%) BF muscle Adhesiveness Hardness Crumbliness Pastiness Fibrousness Saltiness NaCl (%) (dry matter) Humidity (%) SM muscle Adhesiveness Hardness Crumbliness Pastiness Fibrouness Saltiness NaCl (%) (dry matter) Humidity (%)
11.10 14.96 1.20 6.09 5.75 30.08
0.81 1.00 0.64 0.32 0.37 3.32
13.51 17.10 5.30 6.90 6.84 40.91
8.93 12.10 0.20 5.45 5.38 22.95
100 100 100 86 100 100
3.6 3.8 4.3 1.7 1.8 3.1 9.49 70.22
1.48 0.69 0.84 1.53 0.57 0.57 1.66 1.44
8.0 5.3 6.5 8.1 3.5 4.4 14.38 73.12
1.0 2.3 2.9 0.3 0.5 1.5 5.32 63.52
74 74 74 74 74 74 74 74
2.5 3.7 5.3 1.9 2.0 2.6 13.21 62.81
1.49 0.73 0.75 1.65 0.88 0.48 1.56 1.18
7.6 5.9 7.5 8.5 4.9 3.6 16.71 65.47
0.55 2.33 3.88 0.25 0.60 1.25 9.02 60.45
74 74 74 74 74 74 74 74
a
Data not available for DFD hams (selected at 24 h post-mortem). Sensory analysis was only carried out on 74 hams (10 PSE, 50 Normal and 14 DFD). b
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Table 2 Mean of ANOVA results for the three groups of pastiness: H ( >2), M (1–2) and L (<1) Variable
Ham weight (kg) H (cm)c FTR (cm)d pH45a pHu Ro BF Rinf BF Ratio BF Fc BF Alfa BF Ro SM Rinf SM Ratio SM Fc SM Alfa SM Adhesiveness Hardness Crumbliness Pastiness Fibrouness Saltiness Humidity (%) NaCl (%) (dry matter) Weight losses (%) % of the DFD hams % of the Normal hams % of the PSE hams
Muscle BF
Muscle SM
H (n=25)
M (n=21)
L (n=28)
RMSEb
H (n=26)
M (n=28)
L (n=20)
RMSEb
11.45a 15.05 1.45 6.07 5.96a 134.53 53.50 0.46 54.44 0.32 103.44 39.07 0.44 53.12 0.30 5.2a 3.4c 4.7a 3.7a 1.3c 2.8b 70.03 9.11 28.97 79 24 20
10.96b 15.00 1.10 6.09 5.62b 114.49 53.71 0.50 59.88 0.32 99.68 41.63 0.48 49.52 0.30 3.3b 3.7b 4.3ab 1.3b 1.7b 3.2a 70.10 9.67 29.45 7 34 30
10.90b 14.87 1.09 6.04 5.65b 123.24 54.78 0.48 56.70 0.32 97.65 39.85 0.46 50.42 0.32 2.7c 4.3a 4.0b 0.6c 2.1a 3.2a 70.27 9.46 30.71 14 42 50
0.723 1.015 0.631 0.319 0.342 47.057 5.494 0.139 29.010 0.024 42.524 5.255 0.194 32.702 0.043 1.057 0.583 0.788 0.768 0.474 0.548 1.509 1.637 3.243
11.17 14.63 1.28 5.97b 5.62b 96.65b 53.60 0.58a 73.62a 0.32ab 76.41b 39.94 0.56a 67.68a 0.30 3.9a 3.2c 5.6a 3.9a 1.2c 2.4b 62.82 13.40 29.77 21 34 60
11.05 15.15 1.30 6.06ab 5.86a 144.38a 54.26 0.42b 49.47b 0.31b 122.07a 41.15 0.40b 42.75b 0.30 2.1b 3.7b 5.4ab 1.4b 1.9b 2.6b 62.37 12.96 29.36 64 36 10
11.05 15.15 0.98 6.16a 5.75ab 134.62a 54.36 0.43b 44.82b 0.33a 101.57a 38.78 0.41b 40.81b 0.32 1.6b 4.2a 5.1b 0.6c 2.8a 2.8a 62.83 13.67 30.59 14 30 30
0.749 0.987 0.636 0.312 0.359 42.542 5.515 0.118 26.067 0.023 37.675 5.268 0.179 30.208 0.043 1.115 0.625 0.727 0.903 0.642 0.443 1.145 1.567 3.282
Means with different letters within a muscle differ significantly (P <0.05). a Data not available for DFD hams (selected at 24 hours post-mortem). b Residual Standard Deviation (RMSE). c H is the ham conformation measured by a calliper. d FTR is the fat thickness rump is the fat measured with a ruler in the rump region.
pastiness may have been affected because the same resting period and maturing time was used for all hams. A high value of intermuscular, intramuscular or subcutaneous fat could make NaCl and water diffusion more difficult and consequently increase pastiness and/ or adhesiveness (Gou et al., 1995). In this study there was a tendency for the pastiness to increase as the fat thickness in the rump increased. The pH values show the expected wide range, including both PSE and DFD hams. In general the variation in all the parameters measured was enough to determine a correlation between these variables and the electrical data recorded. H group showed significant (P < 0.05) lower pH45 than the L group in SM muscle. pHu was significantly lower in SM muscle in H group than in M group and higher in BF muscle. NaCl content (dry matter basis) did not differ among different levels of pastiness. However, the group with the highest pastiness had the lowest saltiness in both muscles. Thus, different causes could account for the observed differences in pastiness between the two muscles. For the BF muscle pastiness and adhesiveness seems to be related to a higher pHu (Guerrero et al., 1999) and for SM muscle the origin of pastiness seems
to be different and related to a lower pH that makes cathepsins more active (Virgili & Chivazappa, 2002) and facilitates their release from lysosomes (O’Halloran, Troy, Buckley, & Reville, 1997). A total of 56.8% of the hams (42 out of 74) changed class from one muscle to another. With DFD hams all the hams that changed class (9 out of 14) moved from the High (H) pastiness group in BF muscle to the Medium (M) or Low (L) group in SM muscle. According to this, it seems that pastiness due to the use of DFD hams affects BF muscle, in agreement with Guerrero et al. (1999). In normal hams 54% of them changed class (27 out of 50) in both directions, i.e. 59% of the cases increasing in pastiness from BF to SM and 41% of the cases vice versa. Finally, in PSE hams all the changes in classification (6 out of 10) mean an increase in pastiness from BF to SM. This last result tends to indicate that pastiness in PSE hams is mainly located in the SM muscle. According to this, and regarding the distribution of the hams in the different groups, 79% of the DFD hams were classified in the High pastiness group for BF muscle, and for PSE hams 60% of them had a high pastiness score in the SM muscle.
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Table 3 Classification error for each pastiness group (H, M and L) obtained through discriminant analysis in each muscle, BF and SM, using the electrical variables obtained with the EIS prototype applied at 36 h post-mortem
Muscle BF H M L Total Percent
H
M
L
Total
14 56.00 3 14.29 5 17.86 22 29.73
4 16.00 10 47.62 5 17.86 19 25.68
7 28.00 8 38.10 18 64.29 33 44.59
25 100.00 21 100.00 28 100.00 74 100.00
Error count estimates for Pastiness Rate 0.4400 0.5238 0.3333 0.3333 Muscle SM H 18 3 69.23 11.54 M 4 18 14.29 64.29 L 5 2 25.00 10.00 Total 27 23 Percent 36.49 31.08 Error count estimates for Pastiness Rate 0.3077 0.3571 0.3333 0.3333
0.3571 0.3333 5 19.23 6 21.43 13 65.00 24 32.43
0.3500 0.3333
0.4403
26 100.00 28 100.00 20 100.00 74 100.00
0.3383
For the electrical parameters there were no significant differences (P > 0.05) among groups for pastiness for BF muscle. However, for SM muscle three of the electrical variables (R0, ratio and Fc) measured in the BF and SM showed significantly different mean values for H group. Using discriminant analysis (Table 3), the electrical measurements obtained were able to classify 69.2% of the hams correctly with high pastiness values in the SM muscle compared with the 56.0% for the BF muscle. The ability of electrical parameters to predict pastiness could be related to the capacity to predict PSE hams. This result tends to indicate that PSE hams had a higher incidence of pastiness in SM muscles in agreement with Ordon˜ez (2001). Fig. 1 shows the relationship between the different parameters for each muscle obtained through principal component analysis. It is important to note the differences found between the two muscles. For the BF muscle the second dimension shows that pastiness was correlated with the fat thickness in the rump (FTR) and closer to DFD hams. Arnau et al. (1998) and Guerrero et al. (1999) also observed that the use of DFD meat was not advisable for dry-cured ham because important defects in texture were found. In the positive direction
Fig. 1. Principal component analysis for Biceps femoris (a) and Semimembranosus (b) muscles.
of the second dimension, PSE hams tend to have higher weight losses, hardness and saltiness. For BF muscle the relationship between electrical and sensory parameters was less clear than for SM muscle. In both muscles, BF and SM, hardness was negatively correlated with pastiness and adhesiveness and positively with salty taste, fibrousness and weight losses. In conclusion, the results of the present study suggest that the electrical parameters evaluated in green hams by the EIS prototype could be useful for predicting pastiness in dry-cured ham.
Acknowledgements This study has been supported by the European Union under project IN207191 (Multi-frequency impedance measurements technology for meat quality control). We thank INIA (Instituto Nacional de Investigacio´n y Tecnologı´a Agraria y Alimentaria) for a postdoctoral grant to research student Idoia Gobantes. The authors wish to acknowledge J. Arbone´s, A. Quintana and B. Guerra for their technical assistance.
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Green hams electrical impedance spectroscopy (EIS) measures and pastiness prediction of dry cured hams Luis Guerreroa,*, Idoia Gobantesa, Ma A`ngels Olivera, Jacint Arnaua, M. Dolors Gua`rdiaa, Jordi Elvirab, Pere Riuc, Narcı´s Gre`bold, Josep Ma Monforta a
IRTA-CTC. Institut de Recerca i Tecnologia Agroalimenta`ries. Centre de Tecnologia de la Carn. Granja Camps i Armet. 17121 Monells, Girona, Spain b NTE, S.A., Can Male´, s/n, 08186 Barcelona, Spain c Department of Electronic Engineering, Telecommunication Engineering School, UPC, Gran Capita`, s/n. Modul C4, 08034 Barcelona, Spain d Esteban Espun˜a, S.A., Mestre Turina 39-41, 17800 Olot, Girona, Spain Received 22 November 2002; received in revised form 24 April 2003; accepted 24 April 2003
Abstract The objective of this study was to assess the value of electrical impedance spectroscopy (EIS) as a predictor of certain dry-cured ham sensory properties in green hams of different technological meat qualities and processed commercially. Measurements of technological meat quality (weight, ham conformation, subcutaneous fat thickness, pH45 and pHu) and some sensory properties (adhesiveness, hardness, crumbliness, pastiness, fibrousness and saltiness) were carried out on the Biceps femoris (BF) and Semimembranosus (SM) muscles. The electrical parameters, Ro, Rinf, ratio (Rinf/Ro), Fc and , were obtained with EIS equipment applied to two different regions of the ham at 36 h post mortem (BF and SM). Principal component (PC) analysis was used to describe the relationship between sensory properties and electrical parameters. For BF muscle there were no clear relationships between the electrical parameters and the sensory properties. However, for SM muscle, pastiness was correlated positively with the ratio and Fc obtained by EIS. None of the electrical parameters obtained by EIS were able to differentiate between groups of hams classified according to their level of pastiness in the BF muscle. However, in the SM muscle, the origin of the pastiness was related to the use of PSE meat and was predicted by the electrical impedance measurements. The EIS prototype correctly detected 69.2 and 56.0% (for SM and BF muscles, respectively) of the problem hams in terms of pastiness. These results could be of use in the selection of the raw material to reduce the incidence of dry-cured hams with defective texture. # 2003 Elsevier Ltd. All rights reserved. Keywords: Dry-cured ham; Meat quality; Electrical impedance spectroscopy (EIS); Sensory properties
1. Introduction Sensory quality of dry-cured ham is strongly affected by raw material characteristics and technological processes. The influence of breed (Guerrero, Gou, Alonso, & Arnau, 1996), fatness (Santoro, 1984) and sex (Gou, Guerrero, & Arnau, 1995) on green ham properties has been studied showing the importance of these properties in the final eating characteristics. Dry-cured ham characteristics are also affected by green meat technological quality: PSE affects salt uptake (Arnau, Guerrero, Casademont, & Gou, 1995), saltiness and texture (Ordon˜ez, 2001) and * Corresponding author. Tel.: +34-972-63-00-52; fax: +34-972-6303-73. E-mail address: [email protected] (L. Guerrero). 0309-1740/03/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0309-1740(03)00101-3
DFD hams, among others, increase the risk of spoilage (Guerrero, Arnau, & Garriga, 1991), undesirable pastiness and adhesiveness (Guerrero, Gou, & Arnau, 1999) and the incidence of phosphate crystals (Arnau, Guerrero, & Gou, 1998) decreasing consumer acceptability. During processing the different steps can be modified according to the raw material to reduce the incidence of flavour and texture defects in the final product (Arnau, 1998, 2000). In this way, the classification of the green hams in different quality groups would be advisable to optimise processing. Different instruments have been developed for the prediction of PSE or meat with low water holding capacity (WHC) such as FOP (fibre optic probe) and QM (quality meter) that measure PSE status by internal light scattering and electrical conductivity (EC), respec-
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tively. The pH at 45 min post-mortem (pH45) is considered the best predictor of WHC (Oliver, Gispert, Tibau, & Diestre, 1991; Warris, Brown, Lopez-Bote, Bevis, & Adams, 1989), but it is difficult to measure on the slaughter-line due to the speed of the line and the low temperatures in the refrigeration tunnel where carcasses are stored after evisceration. Since the 1980s different instruments have been developed for electrical conductivity measurements, in meat, Schmitten, Schepers, and Festerling (1987) used the Konduktometer LF DIGI 550 and the new model LF191 operating at a frequency of 4 and 1 KHz, respectively. Forrest et al. (2000) used the purdue tetrapolar probe (PTP) for impedance measurements. Two instruments to measure EC of the muscle were used by Lee et al. (2000): the NWK LT K21 and a probe type device, the WO 99/ 01754. In general EC is not related to drip losses caused by PSE meat (Byrne, Troy, & Buckley, 1997). Regarding DFD meat, in some industries an ultimate pH (pHu), defined as the pH at 24 h post-mortem, higher than 6.0 in the Semimembranosus muscle (SM), is used to eliminate this type of meat. However, pH measurement needs frequent calibration and presents problems when used under industrial conditions due to the fragility of the electrodes. Another important parameter in the final sensory properties of dry-cured ham is the percentage of intramuscular fat (IMF) (Guerrero et al., 1996). Madsen, Borgaard, Rasmussen, and Christensen (1999) developed an on-line instrument based on electrical impedance to predict the IMF percentage in beef. They found that a percentage of IMF at 1/2 lumbar could be predicted with a correlation coefficient of 0.83 and a standard error of prediction (SEP) of 1.4% when measuring 185 carcasses at the end of the slaughter line. Oliver et al. (2001), evaluated a new prototype based on electrical impedance spectroscopy (EIS) to select green hams on the basis of pH45, final pH and fatness. The results of this study showed that electrical parameters obtained in the SM at 36 h post-mortem may classify 88.46% of the green hams with pH45 > 6.10 and 92.31% with pHu < 5.95. Despite the relatively high classification accuracy of this new prototype there is no information about the relationship between all these electrical parameters and the final sensory properties of the dry-cured ham. The aim of this study was to assess the EIS prototype as predictor of saltiness and texture of dry-cured hams obtained from green hams with different technological meat qualities.
2. Materials and methods This study was carried out on 86 PSE (pH45 < 5.85) and normal hams (pH45 > 5.85 and pHu< 6.0) selected
from commercial carcasses. The carcasses were weighed (kg) and classified in a slaughterhouse with the Fat-oMeter (SFK, Technology A/S, Herlev, Denmark). In order to obtain a sample that included the full range of technological meat quality, 14 additional hams with a pH24 higher than 6.0 (DFD hams) in the Semimembranosus muscle were selected in a dry-cured processing factory at 24 h post-mortem. 2.1. Measurements of meat quality Raw meat quality was recorded at 45 min post-mortem in the slaughterhouse using a portable pH meter (Crison 507, Crison Instruments S.A., Barcelona, Spain) equipped with a combined glass electrode (Ingold 406, Ingold, Urdorf, Switzerland) (pH45) in the Semimembranosus muscle (SM). The following measurements were made at 24 h post-mortem: weight of each ham (kg); the ham conformation (H), that was defined as the maximum height (cm) from the rind to the higher point of the Semimembranosus muscle, was measured with a calliper; subcutaneous fat thickness in the rump (FTR) was measured with a ruler (cm); and muscle pH (pHu) in the SM was measured with a portable pH meter (Crison). At 36 h post-mortem the electrical parameters were obtained with the EIS equipment in the BF and SM muscles (Biceps femoris and Semimembranosus regions, respectively). The system was controlled by software that allowed electrical impedance scanning from 8 kHz to 1MHz (Oliver et al., 2001). The device was able to measure four parameters: Ro is the electrical impedance modulus at lower frequencies and it is expressed in ohms ( ), Rinf is the electrical impedance modulus at high frequencies and is expressed in ohms ( ), is a shape adjustment parameter, and Fc is the characteristic frequency of the region under measurement that corresponds to the frequency at which the imaginary part of the electrical impedance is the largest in absolute value and is expressed in KHz. A fifth parameter is introduced: the ratio between Rinf and Ro. This parameter is proportional to the ratio of extracellular water to total water in the meat (Lozano, Rosell, & Palla`s-Areny, 1995). 2.2. Manufacturing process and sampling All the green hams were salted at 36 hours postmortem with a mixture of NaCl, KNO3 and NaNO2 (99, 0.5 and 0.5%, respectively). After 6 days of resting fully covered with this mixture at 0–4 C and relative humidity (RH) higher than 85%, they were covered
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with another mixture of NaCl, dextrose and sodium ascorbate (95, 3 and 1%, respectively) until a total salting time of 1.3 days per kg of green ham weight was reached. Afterwards they were washed in cold water and hung at 2–6 C and RH of 70–90% for 35 days. The ageing process consisted of three different steps: 10–14 C and RH of 60–80% for 70 days; 18– 22 C and RH of 60–75% for 70 days; 26–30 C and RH of 60–70% for 21 days. At the end of the drying period the hams were individually weighed, deboned and sliced. The chemical and sensory analyses were performed on slices perpendicular to the centre of the femur. 2.3. Chemical and sensory analysis Moisture as weight loss at 103 2 C (Presidencia del Gobierno, 1979) and sodium chloride by the Charpentier–Volhard method (ISO, 1970) were determined for the SM and BF muscles in each dry-cured ham. The sensory analysis was carried out separately for SM and BF muscles using an expert panel of six members. In each session each assessor evaluated the same four hams randomly selected, blocking the order of presentation and the first-order carry-over effects (Macfie, Bratchell, Greenhoff, & Vallis, 1989). The descriptors (hardness, pastiness, crumbliness, adhesiveness, fibrousness and saltiness) were quantified using a nonstructured scale ranging from 0 (absence) to 10 (intense). The definition of each texture attribute, as well as the references used to illustrate the maximum intensity of each of them, was as described by Guerrero et al. (1999). Chemical and sensory analyses were carried out in 74 hams: 14 DFD, 50 Normal and 10 PSE. 2.4. Statistical analysis Data were analysed using the MEANS, GLM, PRINCOMP and DISCRIM procedures from the SAS statistical package (SAS, 1987). In order to analyse the effect of the different variables on the pastiness, all the hams were classified in three groups according to their sensory score for this descriptor and for each muscle: (H) High pastiness group (mean pastiness over the six assessors greater than 2); (M) Medium pastiness group (mean pastiness between 1 and 2) and (L) Low pastiness group (mean pastiness score lower than 1). For the principal component analysis, and in order to group the different hams, and locate then in the biplot, they were classified in three groups according to their pH45 and pHu. Hams having pH45 lower than 5.85 were classified as PSE, hams with pHu higher than 6.0 as DFD and the rest as normal hams (Oliver et al., 2001).
3. Results and discussion The mean carcass weight and fat thickness measured with the Fat-o-Meter for the 86 animals selected at the slaughterhouse was 78.90 5.44 kg and 14.47 2.88 mm, respectively. These values are typical for pig carcasses in Spain, demonstrating a wide range of fat thicknesses (Gispert & Diestre, 2000). Table 1 shows the main traits of the different hams used for this study and Table 2 the mean values for the different hams classified according to their level of pastiness. The ham weight and its conformation may have an effect on the texture of the final product since as ham conformation increases, salt diffusion to the inner muscles (e.g. BF) is slowed down and increases such textural defects as pastiness (Guerrero et al., 1996). In the present study, ham conformation did not differ between different levels of pastiness either in SM or BF muscles. Ham weight was significantly higher in the H group only for the BF muscle. This suggests that others factors such as proteolytic potential (Parolari, Virgili, & Chivazappa, 1994; Parren˜o, Cusso´, Gil, & Sa´rraga, 1994; Sa´rraga, Gil, & Garcı´a-Regueiro, 1993) ham fatness (Gou et al., 1995) or pH and NaCl content (Arnau, Guerrero, & Sa´rraga, 1998) should also be taken into account to explain these results. Despite adjusting the salting time for each ham according to their weight, Table 1 Descriptive statistics of meat quality characteristics and sensory properties (mean values over assessors) Characteristics
Mean
S.D.
Max.
Min.
Nb
Ham weight (kg) Conformation (cm) Fat thickness rump (cm) pHa45 pHu Ham weight loss (%) BF muscle Adhesiveness Hardness Crumbliness Pastiness Fibrousness Saltiness NaCl (%) (dry matter) Humidity (%) SM muscle Adhesiveness Hardness Crumbliness Pastiness Fibrouness Saltiness NaCl (%) (dry matter) Humidity (%)
11.10 14.96 1.20 6.09 5.75 30.08
0.81 1.00 0.64 0.32 0.37 3.32
13.51 17.10 5.30 6.90 6.84 40.91
8.93 12.10 0.20 5.45 5.38 22.95
100 100 100 86 100 100
3.6 3.8 4.3 1.7 1.8 3.1 9.49 70.22
1.48 0.69 0.84 1.53 0.57 0.57 1.66 1.44
8.0 5.3 6.5 8.1 3.5 4.4 14.38 73.12
1.0 2.3 2.9 0.3 0.5 1.5 5.32 63.52
74 74 74 74 74 74 74 74
2.5 3.7 5.3 1.9 2.0 2.6 13.21 62.81
1.49 0.73 0.75 1.65 0.88 0.48 1.56 1.18
7.6 5.9 7.5 8.5 4.9 3.6 16.71 65.47
0.55 2.33 3.88 0.25 0.60 1.25 9.02 60.45
74 74 74 74 74 74 74 74
a
Data not available for DFD hams (selected at 24 h post-mortem). Sensory analysis was only carried out on 74 hams (10 PSE, 50 Normal and 14 DFD). b
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Table 2 Mean of ANOVA results for the three groups of pastiness: H ( >2), M (1–2) and L (<1) Variable
Ham weight (kg) H (cm)c FTR (cm)d pH45a pHu Ro BF Rinf BF Ratio BF Fc BF Alfa BF Ro SM Rinf SM Ratio SM Fc SM Alfa SM Adhesiveness Hardness Crumbliness Pastiness Fibrouness Saltiness Humidity (%) NaCl (%) (dry matter) Weight losses (%) % of the DFD hams % of the Normal hams % of the PSE hams
Muscle BF
Muscle SM
H (n=25)
M (n=21)
L (n=28)
RMSEb
H (n=26)
M (n=28)
L (n=20)
RMSEb
11.45a 15.05 1.45 6.07 5.96a 134.53 53.50 0.46 54.44 0.32 103.44 39.07 0.44 53.12 0.30 5.2a 3.4c 4.7a 3.7a 1.3c 2.8b 70.03 9.11 28.97 79 24 20
10.96b 15.00 1.10 6.09 5.62b 114.49 53.71 0.50 59.88 0.32 99.68 41.63 0.48 49.52 0.30 3.3b 3.7b 4.3ab 1.3b 1.7b 3.2a 70.10 9.67 29.45 7 34 30
10.90b 14.87 1.09 6.04 5.65b 123.24 54.78 0.48 56.70 0.32 97.65 39.85 0.46 50.42 0.32 2.7c 4.3a 4.0b 0.6c 2.1a 3.2a 70.27 9.46 30.71 14 42 50
0.723 1.015 0.631 0.319 0.342 47.057 5.494 0.139 29.010 0.024 42.524 5.255 0.194 32.702 0.043 1.057 0.583 0.788 0.768 0.474 0.548 1.509 1.637 3.243
11.17 14.63 1.28 5.97b 5.62b 96.65b 53.60 0.58a 73.62a 0.32ab 76.41b 39.94 0.56a 67.68a 0.30 3.9a 3.2c 5.6a 3.9a 1.2c 2.4b 62.82 13.40 29.77 21 34 60
11.05 15.15 1.30 6.06ab 5.86a 144.38a 54.26 0.42b 49.47b 0.31b 122.07a 41.15 0.40b 42.75b 0.30 2.1b 3.7b 5.4ab 1.4b 1.9b 2.6b 62.37 12.96 29.36 64 36 10
11.05 15.15 0.98 6.16a 5.75ab 134.62a 54.36 0.43b 44.82b 0.33a 101.57a 38.78 0.41b 40.81b 0.32 1.6b 4.2a 5.1b 0.6c 2.8a 2.8a 62.83 13.67 30.59 14 30 30
0.749 0.987 0.636 0.312 0.359 42.542 5.515 0.118 26.067 0.023 37.675 5.268 0.179 30.208 0.043 1.115 0.625 0.727 0.903 0.642 0.443 1.145 1.567 3.282
Means with different letters within a muscle differ significantly (P <0.05). a Data not available for DFD hams (selected at 24 hours post-mortem). b Residual Standard Deviation (RMSE). c H is the ham conformation measured by a calliper. d FTR is the fat thickness rump is the fat measured with a ruler in the rump region.
pastiness may have been affected because the same resting period and maturing time was used for all hams. A high value of intermuscular, intramuscular or subcutaneous fat could make NaCl and water diffusion more difficult and consequently increase pastiness and/ or adhesiveness (Gou et al., 1995). In this study there was a tendency for the pastiness to increase as the fat thickness in the rump increased. The pH values show the expected wide range, including both PSE and DFD hams. In general the variation in all the parameters measured was enough to determine a correlation between these variables and the electrical data recorded. H group showed significant (P < 0.05) lower pH45 than the L group in SM muscle. pHu was significantly lower in SM muscle in H group than in M group and higher in BF muscle. NaCl content (dry matter basis) did not differ among different levels of pastiness. However, the group with the highest pastiness had the lowest saltiness in both muscles. Thus, different causes could account for the observed differences in pastiness between the two muscles. For the BF muscle pastiness and adhesiveness seems to be related to a higher pHu (Guerrero et al., 1999) and for SM muscle the origin of pastiness seems
to be different and related to a lower pH that makes cathepsins more active (Virgili & Chivazappa, 2002) and facilitates their release from lysosomes (O’Halloran, Troy, Buckley, & Reville, 1997). A total of 56.8% of the hams (42 out of 74) changed class from one muscle to another. With DFD hams all the hams that changed class (9 out of 14) moved from the High (H) pastiness group in BF muscle to the Medium (M) or Low (L) group in SM muscle. According to this, it seems that pastiness due to the use of DFD hams affects BF muscle, in agreement with Guerrero et al. (1999). In normal hams 54% of them changed class (27 out of 50) in both directions, i.e. 59% of the cases increasing in pastiness from BF to SM and 41% of the cases vice versa. Finally, in PSE hams all the changes in classification (6 out of 10) mean an increase in pastiness from BF to SM. This last result tends to indicate that pastiness in PSE hams is mainly located in the SM muscle. According to this, and regarding the distribution of the hams in the different groups, 79% of the DFD hams were classified in the High pastiness group for BF muscle, and for PSE hams 60% of them had a high pastiness score in the SM muscle.
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Table 3 Classification error for each pastiness group (H, M and L) obtained through discriminant analysis in each muscle, BF and SM, using the electrical variables obtained with the EIS prototype applied at 36 h post-mortem
Muscle BF H M L Total Percent
H
M
L
Total
14 56.00 3 14.29 5 17.86 22 29.73
4 16.00 10 47.62 5 17.86 19 25.68
7 28.00 8 38.10 18 64.29 33 44.59
25 100.00 21 100.00 28 100.00 74 100.00
Error count estimates for Pastiness Rate 0.4400 0.5238 0.3333 0.3333 Muscle SM H 18 3 69.23 11.54 M 4 18 14.29 64.29 L 5 2 25.00 10.00 Total 27 23 Percent 36.49 31.08 Error count estimates for Pastiness Rate 0.3077 0.3571 0.3333 0.3333
0.3571 0.3333 5 19.23 6 21.43 13 65.00 24 32.43
0.3500 0.3333
0.4403
26 100.00 28 100.00 20 100.00 74 100.00
0.3383
For the electrical parameters there were no significant differences (P > 0.05) among groups for pastiness for BF muscle. However, for SM muscle three of the electrical variables (R0, ratio and Fc) measured in the BF and SM showed significantly different mean values for H group. Using discriminant analysis (Table 3), the electrical measurements obtained were able to classify 69.2% of the hams correctly with high pastiness values in the SM muscle compared with the 56.0% for the BF muscle. The ability of electrical parameters to predict pastiness could be related to the capacity to predict PSE hams. This result tends to indicate that PSE hams had a higher incidence of pastiness in SM muscles in agreement with Ordon˜ez (2001). Fig. 1 shows the relationship between the different parameters for each muscle obtained through principal component analysis. It is important to note the differences found between the two muscles. For the BF muscle the second dimension shows that pastiness was correlated with the fat thickness in the rump (FTR) and closer to DFD hams. Arnau et al. (1998) and Guerrero et al. (1999) also observed that the use of DFD meat was not advisable for dry-cured ham because important defects in texture were found. In the positive direction
Fig. 1. Principal component analysis for Biceps femoris (a) and Semimembranosus (b) muscles.
of the second dimension, PSE hams tend to have higher weight losses, hardness and saltiness. For BF muscle the relationship between electrical and sensory parameters was less clear than for SM muscle. In both muscles, BF and SM, hardness was negatively correlated with pastiness and adhesiveness and positively with salty taste, fibrousness and weight losses. In conclusion, the results of the present study suggest that the electrical parameters evaluated in green hams by the EIS prototype could be useful for predicting pastiness in dry-cured ham.
Acknowledgements This study has been supported by the European Union under project IN207191 (Multi-frequency impedance measurements technology for meat quality control). We thank INIA (Instituto Nacional de Investigacio´n y Tecnologı´a Agraria y Alimentaria) for a postdoctoral grant to research student Idoia Gobantes. The authors wish to acknowledge J. Arbone´s, A. Quintana and B. Guerra for their technical assistance.
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