J Sci Food Agric 1998, 77, 387È392 The Effect of Green Ham pH and NaCl Concentration on Cathepsin Activities and the Sensory Characteristics of Dry-cured Hams Jacint Arnau,* Luis Guerrero and Carmen Sa rraga Institut de Recerca i Tecnologia Agroalimentàries (IRTA), Centre de Tecnologia de la Carn, Granja Camps i Armet, 17121-Monells, Girona, Spain (Received 17 January 1997 ; revised version received 17 July 1997 ; accepted 20 November 1997) Abstract : There is a tendency to reduce the amount of NaCl in the manufacturing process of Spanish dry-cured ham. NaCl, pH and temperature determine the stability of this product. This study was concerned with the evaluation of green ham pH and sodium chloride concentration on cathepsin activities, physico-chemical parameters and sensory characteristics of dry-cured hams. Two di†erent amounts of salt (55 and 80 g kg~1) and two di†erent pH levels (pH at 24 h post mortem \5É8 ; pH at 24 h post mortem [6É2) were used. Physicochemical composition, cathepsin activity and a number of sensory parameters were evaluated. Hams with high pH displayed lower cathepsin activity, NPN, saltiness and hardness whereas the levels of brightness, crumbliness, pastiness and adhesivity were found to be higher than in normal hams. A high level of salt produced greater cathepsin B and B ] L activity and lower pastiness and adhesivity than the samples with a low NaCl level. ( 1998 SCI. J Sci Food Agric 77, 387È392 (1998) Key words : pH ; salt ; cathepsins ; sensory properties ; dry-cured ham into dry cured ham should be pH \ 6É2. A high pH 24 24 also favours the formation of phosphate crystals (Arnau et al 1993) which can lower the level of consumer acceptance. Recent studies have shown an incidence of green hams with pH [ 6É2 from 5É4 to 12É5% in Spain 24 (Guerrero et al 1991 ; Garrido et al 1994). This kind of meat has less appropriate sensory and technological characteristics for the production of dry-cured ham than normal meat (Poma 1991). Texture is one of the sensory factors determining food acceptability. The soft and pasty texture sometimes found in dry-cured hams makes slicing more difficult and produces a mouthcoating sensation which could a†ect consumer acceptability (Arnau 1991). Parolari et al (1988) reported that softness is favoured by both high levels of intramuscular fat and low salt to moisture ratios, in particular when the cold-resting periods are short. The texture parameter is also a†ected by the temperature of the process and, of course, the characteristics of the meat itself (Parolari et al 1994 ; Gou et al 1995 ; Virgili et al 1995 ; Guerrero et al 1996 ; Arnau et al 1997a). INTRODUCTION The industrial processes used in the manufacture of drycured hams are based on traditional methods which rely mainly on the addition of NaCl and the dehydration process. At present, there is a general tendency to reduce the sodium content in foods. However, NaCl reduction in dry-cured ham can a†ect its stability and its typical sensory characteristics (Parolari et al 1988 ; Arnau 1991). pH is a fundamental parameter in the evaluation of meat quality and, together with water activity and temperature, it is one of the main factors determining the microbiological stability of the ham (Leistner 1985). Newton and Gill (1981) reported that meat with a high pH is prone to deterioration because of the low level of glucose and intermediate glycolitic compounds present in it. According to Poma (1980), the maximum value for pH at 24 h (pH ) post mortem for meat transformation 24 * To whom correspondence should be addressed. Contract/grant sponsor : INIA. Contract/grant number : Sc93-126. 387 ( 1998 SCI. J Sci Food Agric 0022È5142/98/$17.50. Printed in Great Britain J Arnau, L Guerrero, C Sa rraga 388 Previous studies on the role of muscle proteinases in cured ham have suggested that cathepsins are one of the factors responsible for proteolysis during ageing, since their activity is maintained throughout the process (Gil et al 1991 ; Parren8 o et al 1994) whereas calpain activity is not detected after the post-salting stage (Sarraga et al 1993). Parolari et al (1994) suggested the use of raw hams with a low level of cathepsin B activity in order to improve the texture and the quality of the product. The aim of this paper is to study the e†ect of green ham pH and sodium chloride concentration on cathepsin (EC numbers : BÈ18.104.22.168 ; LÈ22.214.171.124 ; DÈ 126.96.36.199) activities and the texture characteristics of Spanish dry-cured hams aged for 6 months. MATERIAL AND METHODS Raw material Gilt carcasses from a commercial slaughterhouse were selected according to pH and conductivity. pH was measured at 45 min (pH ) and 24 h post mortem (pH ) 45 24 with a combined electrode (Ingold 406, Ingold, Urdorf, Switzerland) attached to a portable pH-meter (Crison 507, Crison Instruments SA, Barcelona, Spain). Electrical conductivity was measured with a quality-meter (Tecpro) at 24 h post mortem (Swatland 1980). Both pH and conductivity were measured in the Semimembranosus muscle. Hams weighing between 9 and 10 kg with pH [ 6É0 and conductivity \6 lS were 45 selected. At 24 h post mortem the hams were divided into two groups according to their pH levels : pH [ 24 6É2 (HpH) and pH \ 5É8 (LpH). 24 Processing and sampling The hams were Ðrst treated with 0É8 g of KNO kg~1 3 and randomly assigned to two di†erent salting procedures : 6 hams were salted with 80 g of sodium chloride kg~1 of ham (batch 1) and 6 hams with 55 g kg~1 of ham (batch 2) in each group of selected pH. After salt absorption they were hung for 35 days at 4¡C and 80È90% RH. During the ageing process the hams were stored at 12È16¡C for 4 months and then at 24¡C (65È 85% RH) for 1 month. All the tests were carried out at the end of the process on the Biceps femoris muscle. A 100 g sample from each ham, sliced perpendicular to the femur from the middle of the Biceps femoris muscle, was used for chemical analysis. Physicochemical analysis Weight loss was determined at the end of the process with reference to the initial weight. The following analyses were carried out on each sample : ground meat pH, moisture as weight loss at 103 ^ 2¡C (Presidencia del Gobierno 1979), total protein (N ] 6É25) (Kjeldahl method) (Presidencia del Gobierno 1979), NaCl by the Charpentier-Volhard method (ISO 1970), phosphate determination (Presidencia del Gobierno 1979), tyrosine (Tyr) (Pearson 1968) and non-protein nitrogen (NPN) (Keresse 1984). Extraction of lysosomal enzymes Lysosomal enzymes were extracted according to the method of Etherington et al (1990) in which a portion of ground muscle was homogenised in four parts (w/v) of ice-cold 50 mM sodium acetate bu†er, pH 5É0, containing 1 mM EDTA and 0É2% Triton ] 100. The extract was stirred for 1 h at 4¡C and then centrifuged (10 000 ] g). The supernate was Ðltered to remove the debris and used as the source of cathepsins. Protein concentration of the enzyme extracts was determined by the method of Lowry et al (1951) using bovine serum albumin as standard. Assay of enzyme activities Cystein proteinases B and L were determined Ñuorimetrically using the method of Etherington and Wardale (1982). Cathepsin B and L were assayed with the common substrate N-CBZ-L-phenylalanyl-L-arginine 7-amido-4-methylcoumarin (Z-Phe-Arg-NHMec) (Bachem). Cathepsin B was measured with N-CBZ-Larginyl-L-arginine 7-amido-4-methylcoumarin (Z-ArgArg-NHMec) (Bachem). One unit of activity was deÐned as the amount of enzyme hydrolysing 1 nmol of substrate min~1 at 37¡C. Cathepsin D was assayed against denatured bovine haemoglobin (Sigma) (Etherington 1972) and the TCAsoluble peptides were measured by the method of Lowry et al (1951) using L-tyrosine as standard. One unit of activity was deÐned as the amount of enzyme releasing 1 lg of tyrosine min~1 at 45¡C. SpeciÐc activities were given in enzyme units mg~1 of extracted protein. Sensory analysis Sensory evaluation was carried out by a panel of eight trained panelists on 2-mm thick slices from the Biceps femoris muscles. A six-session randomised completeblock design was applied (Steel and Torrie 1980). Each ham was evaluated by the eight panelists in the same session and the panel average was recorded. To assess the hams, the order of presentation and the Ðrst-order carry-over e†ects were balanced (MacFie et al 1989). Sensory descriptors were selected from a descriptive proÐle generated by open discussion between the members of the panel and technicians working in the dry-cured ham industry. Brightness, hardness, crumbliness, pastiness, adhesivity and saltiness were evaluated pH and NaCl concentration in dry-cured hams 389 on a non-structured 10 cm length scale with anchor points 1 cm from each end, similar to that proposed by Stone et al (1974), where 0 means absence and 10 means great intensity. A number of dry-cured hams showing di†erent intensities were used to deÐne the scale for the descriptors. The assessors were selected and trained following ASTM standards (ASTM 1981). This panel has 7 years experience in texture proÐle, Ñavour proÐle and the descriptive analysis of a wide range of foods. Statistical analysis The data were analysed using the ANOVA procedure from SAS (SAS 1987). The model included pH, added NaCl and their interaction as Ðxed e†ects. The t-test was used for comparison of means. RESULTS AND DISCUSSION Table 1 shows the means and standard errors of the physico-chemical parameters and cathepsin activities of hams with di†erent pH levels and amounts of NaCl, as well as the signiÐcance of the pH ] NaCl interaction. The number of phosphate crystals on the surface was greater in the hams with high pH. However, the phosphate amount expressed as P O was lower in the 2 5 Biceps femoris of HpH hams due to greater phosphate migration to the surface of the ham (Arnau et al 1993). The P O concentration was not signiÐcantly a†ected 2 5 by the amount of salt ; though the tendency observed agrees with the results of Arnau et al (1997a). Even though the HpH hams had a higher surface rugosity which facilitates dehydration, they registered a higher moisture content than the LpH hams in the Biceps femoris muscle (P \ 0É05). This could be due to the increase of water-holding capacity with pH. Moisture in batch 1 was lower than in batch 2, possibly due to the higher osmotic dehydration produced by NaCl. Cathepsins are lysosomal proteolytic enzymes that show optimal pH between 4É0 and 5É5 (for reviews see : Goll et al 1983 ; Zeece and Katoh 1989 ; Ouali 1990 ; Roncales et al 1995) ; and this could be the reason for the higher activity rate found in the samples of Biceps femoris muscle from the LpH hams. The higher content of NPN and Tyr observed in the LpH hams (Table 1) suggested that the better cleavage of the myoÐbrilar structure produced by cathepsins in low meat pH conditions facilitates the action of other enzymes able to produce small peptides and amino acids. The hams in batch 1 showed an important increase in cystein proteinase activities when compared to the hams in batch 2. These results would conÐrm the idea of the stabilising e†ect that the salt has on these enzymatic activities (Toldrà and Etherington 1988). In the LpH hams the pH ] NaCl interaction displayed a greater NaCl e†ect on enzyme activity than in HpH hams (Table 2). NaCl concentration did not a†ect cathepsin D activity at the end of the process. NaCl facilitates changes in the myoÐbrilar structure, due to the increase of osmotic pressure, which favours the accessibility of myoÐbrilar proteins by proteinases. However, in in vitro studies, NaCl was found to inhibit protease activities (Sarraga et al 1989 ; Rico et al 1990). This could explain TABLE 1 Physico-chemical composition and enzymatic cathepsin activities of Biceps femoris musclesa pH 24 High L ow High level (80b) L ow level (55b) Mean SE Mean SE Mean SE Mean SE 6É58a 632a 258 79É9 5É099b 5É88b 33É3b 0É03 5É9 4É2 4É8 0É117 0É25 0É3 6É08b 613b 266 85É6 5É456a 7É16a 36É1a 0É03 5É3 2É2 5É1 0É093 0É36 0É8 6É34 613b 260 96É1a 5É196 6É45 35É1 0É07 5É3 3É3 2É2 0É131 0É38 0É9 6É32 633a 264 69É4b 5É359 6É59 34É4 0É09 6É2 3É7 3É6 0É099 0É35 0É6 NS NS NS NS NS NS NS Cathepsin activitiesd D 0É198b B 2É9b B]L 6É8b 0É012 1É13 1É91 0É282a 11a 22a 0É029 3É12 6É84 0É226 12É4a 25É5a 0É018 2É8 6É12 0É254 1É5b 3É3b 0É031 0É87 1É07 NS ** * pH Moistureb N ] 6É25b NaClb P O b 2 5 Tyrosinec NPNc a b c d pH ] NaCl Added NaCl Means within pH or added NaCl with di†erent following letters are signiÐcantly di†erent (P \ 0É05). 24 Results are given as g kg~1 of ham. Results as mg g~1 of N ] 6É25. Activities are given as units per mg of extracted protein. J Arnau, L Guerrero, C Sa rraga 390 TABLE 2 Values of the parameters showing signiÐcant interactionsa HpH NaCl low level Cathepsin Bb Cathepsins B ] Lb Brightness Pastiness L pH NaCl high level NaCl low level Mean SE Mean SE Mean SE 0É5b 1É8b 5É2a 3É3a 0É53 1É24 0É3 0É4 5É4a 11É7a 3É1b 1É6b 1É76 2É08 0É8 0É4 2É5b 4É7b 2É0 0É6 1É59 1É59 0É5 0É2 NaCl high level Mean 19É4a 39É3a 1É3 0É2 SE 3É39 9É18 0É2 0É1 a Means within HpH or LpH data with di†erent following letters are signiÐcantly di†erent (P \ 0É05). b Cathepsin activities are given as units per mg of extracted protein. the lack of signiÐcant di†erences found in NPN and Tyr between the batches manufactured with di†erent amounts of salt. According to Parren8 o et al (1994) and Sarraga et al (1993) cathepsins were more active during the initial period of the manufacturing process. Cathepsin B is the most stable of the enzymes studied (Parren8 o et al 1994) and cathepsin D activity decreased more quickly, registering from 10 to 20% of its initial activity at the end of the process (Sarraga et al 1993). According to our results, NaCl concentration and pH a†ected cathepsin B and B ] L activity to a greater extent than cathepsin D activity at the end of the process. The degree of proteolysis has been related to pastiness (Arnau 1991 ; Careri et al 1993) and brightness (Guerrero et al 1996). However, in this study the HpH hams registered more brightness, crumbliness, pastiness, adhesivity and less hardness than the LpH hams (Table 3) in spite of having a lower NPN content. These attributes could be explained by the higher level of moisture of Biceps femoris muscles in HpH (Table 1) and the higher degree of extractibility (O†er and Trinick 1983 ; Knight and Parson 1988) and functionality (higher water-holding capacity, solubility, viscosity, . . .) of meat proteins at high pH (Klement et al 1973, 1974 ; Shen 1981 ; Hamm 1986). The pH ] NaCl interaction (Table 2) showed that NaCl produced a more important decrease in brightness and pastiness at HpH than at LpH. The di†erences found in pastiness and adhesivity between batches 1 and 2 could be caused by the lower degree of functionality of meat proteins at high NaCl concentrations (Hamm 1986) since the di†erences found in the proteolysis estimated as NPN are not signiÐcant (Table 1). It is worth mentioning that the data were determined at the end of the process and the study of the proteolysis only at this point of the process was not enough to fully explain the sensory characteristics studied. LpH hams possessed the necessary characteristics for the product to be commercialised, whereas HpH hams needed a longer drying period in order to decrease their high moisture content (Table 1) and increase the hardness of the product. The surface of the HpH hams was rougher (more rugose) than LpH hams because the lean tissue is more easily deformed (Guerrero et al unpublished results) and the phosphate crystals on the surface formed a drying rim which made uniform retraction more difficult (Arnau et al 1997b). A similar phenomenon can be observed in Spanish non-acid dry sausages. TABLE 3 pH and NaCl added e†ects on sensory characteristics of BF musclea pH 24 High Brightness Hardness Crumbliness Pastiness Adhesivity Saltiness pH ] NaCl Added NaCl L ow High level (80b) L ow level (55b) Mean SE Mean SE Mean SE Mean SE 4É12a 2É52b 4É84a 2É47a 4É36a 4É32b 0É50 0É27 0É21 0É36 0É47 0É31 1É63b 4É79a 3É03b 0É38b 1É17b 5É34a 0É28 0É22 0É32 0É12 0É19 0É25 2É54 3É78 4É31 0É90b 2É17b 5É64a 0É47 0É41 0É31 0É30 0É49 0É15 3É22 3É53 3É56 1É96a 3É36a 4É02b 0É61 0É43 0É42 0É45 0É63 0É26 a Means within pH or added NaCl with di†erent following letters are signiÐcantly di†erent (P \ 0É05). 24 b g kg~1 of ham. * NS NS * NS NS pH and NaCl concentration in dry-cured hams The saltiness level was obviously higher in the high salt level batch than in the low salt level batch. The more intense salty taste in the LpH hams could be produced by the slightly higher NaCl concentration, the pH itself (Migaud and Frentz 1978), the higher concentration of products derived from proteolysis (Careri et al 1993) and the lower Na migration to the outer layer of the ham as Na HPO than that found in the HpH 2 4 hams. However, the higher water-holding capacity of the HpH hams could lead to a higher amount of water in certain parts of the ham which, in turn, could facilitate dissolution of the salt coming from the dryer outer parts following the natural tendency to equilibrate the NaCl/water ratio (Arnau et al 1995). A similar phenomenon was found by Stiebing and Rodel (1990) when they studied the inÑuence of the pH on the drying pattern in dry sausage. This migration is a†ected mainly by the drying dynamics and could increase the total amount of salt and the saltiness in the more humid zones. 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