Characterisation of the most odour-active compounds of bone tainted dry-cured Iberian ham

Meat Science 85 (2010) 54–58

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Characterisation of the most odour-active compounds of bone tainted dry-cured Iberian ham Ana I. Carrapiso a,*, Lourdes Martín a, Ángela Jurado b, Carmen García b a b

Tecnología de Alimentos, Escuela de Ingenierías Agrarias, Universidad de Extremadura, Ctra. de Cáceres s/n, 06071 Badajoz, Spain Tecnología de Alimentos, Facultad de Veterinaria, Universidad de Extremadura, Avda. de la Universidad s/n, 10071 Cáceres, Spain

a r t i c l e

i n f o

Article history: Received 10 September 2009 Received in revised form 30 November 2009 Accepted 5 December 2009

Keywords: Bone taint spoilage Gas chromatography–olfactometry Spoiled dry-cured meat Odourants

a b s t r a c t The most odour-active compounds of different bone tainted dry-cured Iberian hams were researched using the detection frequency method. Most of the odourants identified were found in all the Iberian hams (spoiled and unspoiled). Some compounds (ethyl butanoate, dimethyl disulfide, phenylacetaldehyde, acetic, propanoic, butanoic, 3-methylbutanoic and pentanoic acids) were identified in the spoiled hams as Iberian ham odourants for the first time. The detection frequency (DF) values for the spoiled and the unspoiled hams were markedly different. The main differences were found for 2-methylpropanal, ethyl-2-methylpropanoate, ethyl-2-methylbutanoate, phenylacetaldehyde and methional (the lowest DF values were found in the unspoiled ham) and hexanal (the largest DF value was found in the unspoiled ham). Spoiled hams with a different global odour had different DF values. Ó 2009 Elsevier Ltd. All rights reserved.

1. Introduction Bone taint or deep spoilage is one of the worst problems to deal with during the production of Iberian ham, an expensive dry-cured product from South-Western Europe. The occurrence of bone taint spoilage in dry-cured hams has decreased in the last decades with the widespread use of chilling during the initial stages of manufacture, but the problem is still the cause of important losses (Blanco et al., 1997). Starter cultures are not used during the production of Iberian and other Spanish dry-cured hams (Arnau, Serra, Comaposada, Gou, & Garriga, 2007; Sánchez-Molinero & Arnau, 2008) and microbial counts have to be kept low by chilling until stabilisation is reached by the decrease of water activity throughout the ripening process (by salt addition and dehydration). Large microbial populations during the first stages of production is generally accepted to determine spoilage (Arnau, Guerrero, Gou, & Monfort, 2001; García, Marti´n, Timo´n, & Co´rdoba, 2000). Bone tainted hams develop a strong and unpleasant odour (with a rotten note, and sometimes also with flowery, strawberry-like, or yeast-like notes) and sometimes a defective texture, leading to the rejection of the whole piece as soon as the spoilage is detected. When the extent of the spoilage is large, detection is easy even without slicing or cutting. However, sometimes the spoilage remains hidden in the deepest areas of the product (near the bones) and it is only detected when these areas are cut or sliced, which

* Corresponding author. Tel.: +34 924286200; fax: +34 924286201. E-mail address: [email protected] (A.I. Carrapiso). 0309-1740/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.meatsci.2009.12.003

causes not only the rejection of the fully ripened ham but also distrust about the quality of the products. Several studies have focused on the bone taint problem, most of them on characterising the microbial population and the chemical and physical–chemical changes (Giolitti, 1971; Losantos, Sanabria, Cornejo, & Carrascosa, 2000; Marin, Delarosa, Carrascosa, & Cornejo, 1992; Martín et al., 2008; Paarup, Nieto, Pelaez, & Reguera, 1999). Despite the unpleasant odour and flavour being the main cause of rejection, little research has been conducted on this topic. Traditionally ham spoilage has been detected in a non-destructive way by smelling a previously pricked area in the most troubling sections of the ham (Ventanas & Carrapiso, 2001). Compounds involved in the spoiled odour could therefore be checked to detect spoilage, for example by using a non-destructive extraction procedure (Ruiz, Ventanas, & Cava, 2001), but up to now the volatile compounds of bone tainted hams have been little researched. García et al. (2000) showed that spoiled hams possessed larger amounts of ketones, alcohols and esters than unspoiled hams. However, a large number of the compounds investigated in that study have high detection thresholds, and have not been reported as contributors to the odour of meat products. Therefore, it is unknown which compounds could be involved in the spoiled odour. Iberian and other dry-cured hams have a large number of volatile compounds (Berdagué, Denoyer, LeQueré, & Semon, 1991; Carrapiso, Jurado, & García, 2003; Flores, Grimm, Toldrá, & Spanier, 1997), but only a few of them are clearly involved in odour (Blank et al., 2001; Carrapiso, Jurado, Timón, & García, 2002; Carrapiso, Ventanas, & García, 2002; Flores et al., 1997). To know which

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volatile compounds take part in bone tainted ham odour it is necessary to characterise the odour-active compounds using GC–O (gas chromatography–olfactometry) (Grosch, 1993). The aim of this study was to characterise the most odour-active compounds of markedly bone tainted Iberian hams, and to compare them with those of unspoiled hams. This information is of great interest in understanding the bone tainted odour, and would be valuable for future studies on the volatile compounds of bone tainted ham.

2. Materials and methods 2.1. Samples Three markedly bone tainted dry-cured Iberian hams processed following the traditional method (Carrapiso & García, 2008) were collected from two local factories. The lean of all of them had a strong putrid odour, two of them having also a strawberry-like note (SPS1, SPS2), and the other ham (from a different factory) having a bread, yeast-like note (SPY) according to experts (two people experienced in the sensory analysis of Iberian ham). An unspoiled dry-cured Iberian ham (UNS) from the first factory was also analysed to compare the odourant profiles. Samples of the lean were taken from the core of each ham (from the closest areas to the cox femoral joint) for the chromatographic analyses because lean is the most valuable part of the ham and also the part most affected by bone taint. They were vacuum-packaged, frozen and kept at 80 °C. 2.2. Isolation of volatile compounds The visible fat of each frozen sample was removed because fat content influences odourant release (Carrapiso, 2007) and because there are differences between the odourants of the lean and the fat of Iberian ham (Carrapiso & García, 2004). About 0.5 cm of the surface layer was also removed. Then, a piece of the sample was minced and blended and 6 g were placed into a 30 mL (actual volume) glass flask for the extraction of volatile compounds. The isolation was carried out using an HP G1900A purge and trap concentrator (Hewlett–Packard). The headspace of the sample was swept onto a Tenax/silica gel/charcoal trap (Tekmar) using a helium stream at 40 mL/min. Conditions for the extraction were as follows: trap temperature during purge, 20 °C; sample temperature, 35 °C; preheat time, 1 min; purge time, 30 min. The volatile compounds were desorbed by heating the trap at 220 °C, and were immediately injected into the gas chromatograph (GC). The transfer line to the GC was held at 210 °C, and the trap heating was kept at 220 °C for 2 min. 2.3. Gas chromatography–olfactometry (GC–O) 2.3.1. GC–O conditions GC–O was performed using an HP 5890 series II chromatograph (Hewlett–Packard) equipped with a flame ionisation detector (FID) and a sniffing port ODO-1 (SGE, Ringwood, Australia). The effluent from the capillary column was split 1:1 between the FID and the sniffing port using two deactivated uncoated fused silica capillaries (50 cm  0.32 mm). An HP-FFAP (30 m  0.32 mm i.d., film thickness = 0.25 lm, Hewlett–Packard) and an HP-5 (50 m  0.32 mm i.d., film thickness = 1.05 lm, Hewlett–Packard) fused capillary columns were used. The injector and detector were maintained at 230 and 250 °C, respectively. After injection, oven conditions were as follows: 35 °C for 5 min, 10 °C/min to 150 °C, 20 °C/min to 250 °C, 250 °C for 10 min. Humidified air was added at the sniffing port at a flow of 500 mL/min.

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2.3.2. Odour detection frequency (DF) The detection frequency method (Pollien et al., 1997) was applied to identify and rank the odourants according to their odour potencies. A panel of 10 assessors experienced in sensory analysis and trained in GC–O (using reference solutions and the volatile compounds isolated by purge and trap from Iberian ham samples) was used. During GC–O, assessors were asked to give a description of each perceived odour. They were also asked about its length and intensity to aid odourant identification. The assessor order was randomised, and samples were randomly smelled. Ten replicates (one per assessor) of each ham were performed on the polar column (HP-FFAP) to calculate the detection frequencies: data were analysed, and for each ham the DF values of odours having the same linear retention index (LRI) and a similar description were calculated as the number of times they were smelt. Odours with a DF value smaller than 3 in all the hams were considered to be noise (Serot, Prost, Visan, & Burcea, 2001). DF values were considered to be significantly different when they differed at least in three units (Le Guen, Prost, & Demaimay, 2001; Pollien et al., 1997). Five replicates were used to aid the confirmation of odourant identities using the nonpolar column (HP-5). 2.4. Identification 2.4.1. LRI and odour description The identification of volatile compounds was performed by matching odour descriptions and LRI on the two capillary columns with those of reference compounds analysed under the same conditions or with odour descriptions and LRI data previously reported (Kerscher & Grosch, 1997; Rychlik, Schieberle, & Grosch, 1998). The reference compounds (indicated in Table 1) were obtained from Sigma and Aldrich (Steinheim, Germany), and the reference solutions were prepared at a concentration of 5 lL/mL of the reference compound in hexane or dichloromethane (HPLC grade). Solutions of hydrocarbons (C5–C25 for the HP-FFAP and C5–C18 for the HP5) were analysed under the same conditions to calculate LRI values. 2.4.2. Gas chromatography–mass spectrometry (GC–MS) GC–MS analysis was performed on an HP 5890 series II chromatograph (Hewlett–Packard) coupled to an HP 5971A mass spectrometer (Hewlett–Packard) and equipped with the two capillary columns described above (one column at a time). Chromatographic conditions were similar to those applied for GC–O. Mass spectra were generated by electronic impact at 70 eV, with a multiplier voltage of 1675 V. Data were collected at a rate of 1 scan/s over the m/z range 30–300. The transfer line to the mass spectrometer was held at 280 °C. Compounds were identified by comparison of mass spectra and LRI with those of reference compounds, or with mass spectra comprised in the Wiley and the NIST/EPA/NIH mass spectral libraries and LRI previously reported (Kerscher & Grosch, 1997; Rychlik et al., 1998). 3. Results and discussion Unspoiled samples (UNS) and samples from markedly bone tainted hams with a putrid, strawberry-like odour (SPS1 and SPS2) and a putrid, yeast-like odour (SPY) were analysed to know which compounds were the most involved in the global spoiled odour of each particular bone tainted ham. The extraction was performed under a milder temperature than those of previous studies on Iberian ham odourants to minimise artefact formation and compound generation. In fact, the compounds isolated from the unspoiled ham yielded detection frequency (DF) values for the odourants (Table 1) different from those previously reported for this product (Carrapiso, Jurado,

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Table 1 Most odour-active compounds of the headspace of spoiled (SPS1, SPS2, SPY) and unspoiled (UNS) Iberian hams. No.a

LRIb HP-FFAP

HP-5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

<800 828 909 922 970 1026 1054 1063 1080 1095 1169 1281 1309 1346 1388 1445 1456 1473 1489 1520 1591 1621 1638 1735

<500 556 665 653 759 – 747 854 802 – – 1020 992 920 956 – – 911 – 782 1052 837 874

Odourant

Odour descriptionc

Methanethiolf 2-Methylpropanale 2-Methylbutanale 3-Methylbutanale Ethyl-2-methylpropanoatee Ethyl butanoatef Dimethyl disulfidef Ethyl-2-methylbutanoatee Hexanale Unknown Unknown Octanale 1-Octen-3-onee 2-Acetyl-1-pyrrolineg Dimethyl trisulfidef Acetic acide Unknown Methionale Unknown Propanoic acidf Butanoic acide Phenylacetaldehydef 3-Methylbutanoic acide Pentanoic acide

Toasted, sewage-like Toasted, alcoholic Toasted, fruity Nutty, pungent Fruity, strawberry-like Fruity Rotten, spoiled ham, burnt Fruity, strawberry-like Cut-grass, fruity Fruity, apple-like Burnt, meaty Grass, fruity Mushroom-like, dirty Nutty, toasted, popcorn Rotten egg, sewage-like Sweaty, acid Toasted, burnt Potato-like, stew-like Toasted, stew-like Sweaty, acid, foot-like Sweaty, cheesy, spoiled ham Flowery, solvent-like, fruity Foot-like, acid, spoiled ham Meaty, toasted, spoiled ham

DFd SPS1

SPS2

SPY

UNS

1 4 4 10 6 2 1 9 4 1 1 2 5 1 6 1 2 5 1 3 2 2 3 3

3 2 3 7 8 3 0 7 4 0 0 1 4 1 5 3 2 6 3 1 1 3 1 2

1 8 2 5 3 1 3 1 2 3 1 1 3 2 2 1 3 3 0 1 3 5 0 0

2 1 4 5 0 1 1 1 7 0 3 3 3 3 4 0 0 2 0 0 0 0 0 0

a

Odours are presented in order of elution on the HP-FFAP column. LRI values: linear retention indices (LRI) are given on two different polarity capillary columns, when applicable. Odour quality perceived at the sniffing port using an HP-FFAP column. d Detection frequency (DF) determined using an HP-FFAP column. Differences of at least three in the DF value were considered significant. e The compound was identified by comparing it with the reference compounds on the basis of the following criteria: MS spectra, linear retention index (LRI) on two stationary phases, and odour quality as well as odour intensity perceived at the sniffing port. f The compound was tentatively identified by comparing it with literature data on the basis of the following criteria: MS spectra, LRI on two stationary phases, and odour quality as well as odour intensity perceived at the sniffing port. g The MS signals were too weak; the compound was tentatively identified by comparing it with literature data on the basis of the remaining criteria. b

c

et al., 2002; Carrapiso, Ventanas, et al., 2002). The most affected compounds were some sulfur-containing compounds: previous studies at higher temperatures than the current study reported that the DF values for hydrogen sulfide and methanethiol were among the largest ones, but as it is shown in Table 1 they were hardly smelt in this study, with DF values close to the noise level (DF < 3). Results agree with those of a study on the effect of temperature on Iberian ham odourants, which showed a marked effect of temperature on these compounds, whose DF values increase as temperature increases (Carrapiso & García, 2007). Previous studies also reported a significant effect of extraction temperature on the volatile compounds of Iberian ham (Ruiz, Cava, Ventanas, & Jensen, 1998) and other foodstuffs (Ahn, Jo, & Olson, 1999; Étievant, 1996). The odour-active chromatographic regions and the DF values obtained using the detection frequency method for spoiled (SPS1, SPS2, and SPY) and unspoiled (UNS) hams are shown in Table 1. Twenty-four odour-active chromatographic regions were found in the effluent of the capillary column, with a great variety of odours such as toasted, nutty, fruity, strawberry-like, mushroomlike, rotten egg-like, potato-like, and sweaty. The term spoiled ham was used only six times to describe the chromatographic peaks from the spoiled hams, but it was never applied to describe those from the unspoiled samples. As shown in Table 1, 18 compounds were identified as odourants with DF P 3 in the headspace of the bone tainted hams. One compound (ethyl butanoate) was identified for the first time in Iberian ham, but the rest of odourants were previously reported as constituents of Iberian ham, most being described as odourants (Carrapiso & García, 2004, 2007; Carrapiso, Jurado, et al., 2002; Carrapiso, Ventanas, et al., 2002) and others just as volatile compounds (García et al., 2000; Ruiz et al., 1998, 2001). Ethylbutanoate was found in the SPS hams. This compound has not been identified in unspoiled Iberian ham and it is not an odou-

rant of Parma (Blank et al., 2001) and American country (Song & Cadwallader, 2008) hams. However, it is an odourant of Serrano (Flores et al., 1997) and Jinhua (Song, Cadwallader, & Singh, 2008) hams. Other compounds were identified as Iberian ham odourants. All of them were previously reported in the list of volatile compounds (which includes compounds with and without odour) of Iberian ham. Probably spoilage causes an increase in their concentrations in the headspace so that they are large enough not only to allow identification using a MS detector but also to be smelt by panellists. These odourants were dimethyl disulfide, phenylacetaldehyde, and some acids (acetic acid, propanoic, butanoic, 3-methylbutanoic and pentanoic acids). Dimethyl disulfide was found as an odourant in the SPY ham samples. This compound was not identified as an odourant in previous studies on Iberian ham (Carrapiso, Jurado, et al., 2002; Carrapiso, Ventanas, et al., 2002), or in Parma (Blank et al., 2001), Jinhua (Song et al., 2008) and American country (Song & Cadwallader, 2008) hams. It is an odourant of Spanish Serrano ham (Flores et al., 1997), and is usually found among the volatile compounds of Iberian ham (Carrapiso et al., 2003; Jurado, García, Timón, & Carrapiso, 2007), and García et al. (2000) reported that this compound was much more abundant in spoiled than in unspoiled hams. Phenylacetaldehyde was smelt in all the spoiled hams but not in the unspoiled ham samples. Also, this flowery-smelling amino acid-derived compound has not been reported as odourant of Iberian ham (Carrapiso & García, 2007; Carrapiso, Jurado, et al., 2002; Carrapiso, Ventanas, et al., 2002), nor Serrano ham (Flores et al., 1997), although it was identified as a volatile compound in Iberian ham (Jurado et al., 2007; Timón, Ventanas, Carrapiso, Jurado, & García, 2001). It is an odourant of Parma ham (Blank et al., 2001), Jinhua ham (Song et al., 2008) and American country ham (Song

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& Cadwallader, 2008). Although phenylacetaldehyde and other flowery smelling compounds appear in dry-cured ham, it is known that overall odour of Spanish dry-cured hams becomes atypical when this note is evident (Arnau, 2000). Acetic acid and some short-chain fatty acids (propanoic, butanoic, 3-methylbutanoic and pentanoic acids) were found as Iberian ham odourants, and they were only in the spoiled samples. These acids have been reported as volatile compounds in the headspace of Iberian ham (Ruiz et al., 2001) and they are odourants of Parma (Blank et al., 2001), Jinhua (Song et al., 2008) and American country (Song & Cadwallader, 2008) hams. In Serrano ham, acetic acid has been identified as an odourant, but not the other short-chain fatty acids (Flores et al., 1997). In addition to the identification of compounds not previously reported as Iberian ham odourants, the spoilage caused other clear differences in the odour peak profile. In fact, the main differences were the changes in the DF values rather than the appearance of other compounds. The main differences between spoiled and unspoiled hams were found for 2-methylpropanal, ethyl-2-methylpropanoate, ethyl-2-methylbutanoate, phenylacetaldehyde and methional (the lowest DF values were found in the unspoiled ham) and hexanal (the largest DF value was found in the unspoiled ham). Differences in the DF values depended on the spoilage type: the DF values for the SPS1 and SPS2 (strawberry-putrid smelling) hams were similar, but they were markedly different from those of the SPY (yeast-putrid smelling) ham and also from those of the unspoiled ham. The most odour-active compounds of the SPS1 and SPS2 hams were 3-methylbutanal, ethyl-2-methylbutanoate and ethyl-2methylpropanoate. With regard to the differences in the DF values (differences were considered when the DF values differed by at least three units, i.e., when an odour was smelt by at least three or more panellists in the samples from one ham than in the samples from another ham), the only odourant that clearly reached a lower DF value in the SPS spoiled hams than in the unspoiled one was hexanal, a lipid oxidation, cut-grass smelling aldehyde commonly found in meat products. The effect of ham spoilage on hexanal agrees with results from García et al. (2000). Previous studies on dry-cured products also showed that microorganisms decrease hexanal content (Bruna et al., 2001; Stahnke, 1994). Differences between the unspoiled and the SPS1 and SPS2 hams were also found for ethyl-2-methylbutanoate and ethyl-2-methylpropanoate (which seem to cause the clear and strange strawberry note of the SPS spoiled hams), some Strecker aldehydes (2-methylpropanal, 3-methylbutanal, methional, phenylacetaldehyde) and some acids (acetic acid, propanoic acid, 3-methylbutanoic acid, pentanoic acid), all these compounds showing larger DF values in the spoiled hams than in the unspoiled one. These compounds originate from reactions involving amino acids, and in dry-cured products can be generated by microorganisms (Bruna et al., 2001; Montel, Reitz, Talon, Berdague, & Rousset-Akrim, 1996). García et al. (2000) also reported larger abundances in spoiled hams than in unspoiled ones for 2-methylbutanal, ethyl-2-methylbutanoate, acetic acid and some short-chain fatty acids, but not for 3-methylbutanal or methional. This could be due to a different type of spoilage. The spoiled yeast-smelling (SPY) samples had generally lower DF values for the odourants than the SPS ones, the largest being for 2-methylpropanal, 3-methylbutanal and phenylacetaldehyde. The rest of the compounds were perceived by less than 4 of the 10 panellists, and they were therefore close to the noise level (DF < 3). The DF values of the SPY samples were smaller than those of the unspoiled samples for hexanal. In the SPY samples (but not in the other samples) hexanal coeluted with an unknown compound, apparently absent in the other hams, which yielded a yeast-like note. Although the DF value for this coelution (DF = 2)

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was under the noise level (DF < 3), the contribution of the unknown compound could be relevant to the SPY spoiled odour because the DF values for the SPY ham were generally low. Otherwise, the DF values of the SPY samples were larger than those of the unspoiled samples for 2-methylpropanal, ethyl-2-methylpropanoate, two unknown compounds (nos. 10 and 17), butanoic acid and phenylacetaldehyde, which is in line with results for the SPS1 and SPS2 samples. Fruity, strawberry-like smelling esters were barely smelt, which would be related to the lack of a strawberry-like note in the odour of these samples. Bone tainted hams with odours different from those researched in this study probably have a different odourant profile and hams with a slightly perceptible bone tainted odour probably have different odourant profiles, but not as different from that of the unspoiled ham as those of the markedly bone tainted hams are. In conclusion, the most odour-active compounds of the bone tainted hams with a putrid, strawberry-like odour or a putrid, yeast-like odour are compounds usually found in the unspoiled product and in other dry-cured hams, most being odourants of Iberian ham. Changes in the relative contribution to odour of some compounds relate to the appearance of the spoiled odour.

Acknowledgments We thank the assessors for collaboration.

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