The dry-cured ham industry is a traditional sector with an enormous economic importance in the Mediterranean area, particularly in Spain, where it is the pork product most preferred by consumers (Enge et al., 1998; ANICE, 2014). The intramuscular fat content (IMF) and fatty acid (FA) composition, especially the monounsaturated fatty acid (MUFA) content, influence the final quality of the dry-cured products, since they affect color, aspect and texture of ham slices, as well as the intensity and persistence of aroma (Ruiz-Carrascal et al., 2000; Gandemer, 2009; Lorido et al., 2015). Moreover, the consumption of dietary MUFA promotes healthy blood lipid profiles, mediates blood pressure, improves insulin sensitivity and regulates glucose levels (Gillingham et al., 2011).

MUFA represent the most abundant fatty acids in pork and oleic acid (C18:1n-9) is its major component, accounting for approximately 35-50% of total fatty acids (López-Bote, 1998; Wood et al., 2008; Tejerina et al., 2012). It has been shown that the oleic acid content is positively correlated with pork flavor, flavor liking and overall acceptability (Cameron et al., 2000; Tikk et al., 2007). A relevant part of the variation in MUFA and oleic acid has a genetic origin and thus can be attributed to differences between breeds (Wood et al., 2004; Reixach et al., 2008) and individuals within breed (Ros-Freixedes et al., 2012). A recent research of Estany et al. (2014) has shown that a haplotype in the promoter region of the stearoyl-CoA desaturase (SCD) gene, which enhances fat desaturation and, as a result, MUFA and oleic acid in muscle and subcutaneous fat, segregates in Duroc. This beneficial effect is maintained in purebred dry-cured Duroc hams (Henriquez-Rodriguez et al., 2015), despite the fatty acid compositional changes occurring through lipolysis and oxidation in the curing process (Narváez-Rivas et al., 2008; Gandemer, 2009).

The Iberian hams represent about 20% of total turnover of Spain´s dry-cured ham industry (Belmonte, 2006; Chamorro et al., 2008; Cruz, 2013). The Spanish Ministry of Agriculture guidelines (BOE, 2014) establishes two types of labelling for Iberian hams according to their genetic background: 100% Iberian (produced from purebred Iberian pigs) and Iberian (produced using Iberian crossbred pigs with a maximum 50% of Duroc). Nowadays, however, most of the Iberian marketed hams, around 94%, are based on crosses of Iberian sows with Duroc boars (Cruz, 2013). The objective of this study was to assess whether the haplotype segregating at the SCD gene in Duroc also affects the MUFA content of marketed Duroc × Iberian dry-cured hams.

For all the analyzed traits, the Monte Carlo SE was very small and the Geweke test did not detect lack of convergence.

Iberian hams, including Duroc × Iberian crossbreds, are characterized by a high level of fat infiltration, which is very appreciated by consumers and provides a high degree of marbling, a firm texture and an intense, delicate and very special flavor (Fernández et al., 2007). The official regulation concerning the required genetic types that can be used under the designation Iberian (BOE, 2014) are not always perfectly fulfilled by some producers and therefore it might be possible to find some Duroc × Iberian hams with a proportion of Duroc alleles greater than 50%. However, this is certainly not the case here because, as indicated above, all sampled packs were from pigs of identified origin. Moreover, the observed genotypic frequencies (0.58, for TT, and 0.42, for CT genotypes, with only 1 CC) is in line with the hypothesis that allele T is almost fixed in Iberian and segregating at an intermediate frequency in Duroc (Estany et al., 2014).

The IMF content has a positive influence on texture and appearance traits of hams, such as oiliness, brightness and juiciness (Ruiz-Carrascal et al., 2000). In this study the SCD genotype did not affect fat content, in agreement with what has been reported in Estany et al. (2014) for IMF in three distinct raw muscles. Similarly, the fat content was not affected by the gender, which is in accordance with what has been observed by some authors using Duroc × Iberian crossbred barrows and castrated and intact females (Serrano et al., 2008; Cordero et al., 2010), but not all. In particular, Muñoz et al. (2011) found that barrows had more IMF than intact females. However, these works were carried out with raw rather than dry-cured samples. Using samples of dry-cured Serrano hams, Soriano et al. (2005) did not find an effect of sex on IMF. However, because we analyzed entire slices, samples also included intermuscular fat and the untrimmed subcutaneous fat. Therefore, as determined, fat content here should be considered as total edible fat rather than IMF. Nevertheless, taking together, these results suggest that both the SCD polymorphism and the use of barrows instead of gilts do not exert a relevant influence on the edible fat content.

The main purpose of this study was to investigate the effect of the SCD polymorphism on the fatty acid profile of the edible fat in an entire slice. This approach was used for its simplicity but also because, from previous studies, we know that the correlation of fatty acid profile between fat tissues is relatively high (Ros-Freixedes et al., 2014) and the effect of the polymorphism is consistent across muscles and fat tissues (Estany et al., 2014). Fatty acid composition affects eating and meat quality traits of pork, particularly flavor, tenderness and juiciness (Antequera et al., 1992; Ruiz et al., 1999; Ruiz-Carrascal et al., 2000). In contrast to fat content, we found that both the SCD polymorphism and the gender influenced the fatty acid profile of fat. In line with previous results in purebred Duroc, either with raw meat (Estany et al., 2014) or with dry-cured hams (Henriquez-Rodriguez et al., 2015), the T allele increased MUFA (+0.95%). However, here, contrarily to these previous works, the increase in MUFA was at expense of PUFA (-0.59%), especially C18:2n-6 (-0.48%), rather than SFA (-0.35%). The side-effect of the marker on PUFA content is not obvious to explain, although it might be influenced by the sampling scheme used, which includes fat sources other than IMF, or by differing ripening conditions. It is known that the subcutaneous fat contains more PUFA than IMF (Ros-Freixedes & Estany, 2013) and that PUFA decrease across ripening due to oxidative reactions (Martín et al., 1999; Narváez-Rivas et al., 2008; Henriquez-Rodriguez et al., 2015). Therefore, changes in PUFA are expected to be more marked in samples from subcutaneous fat subjected to long dry-curing periods. The substitution of MUFA for PUFA is a side effect that indirectly may benefit the quality of the ham, since it is known that PUFA increase susceptibility to oxidative processes and off-flavors (Cava et al., 1999).

The substitution effect of the T allele for C18:1n-9 and MUFA (0.69% and 0.95%) was very close to the values obtained by Estany et al. (2014) for C18:1 (C18:1n-9+C18:1n-7, 0.70%) and MUFA (1.02%), thereby confirming that the favorable effect of the T allele on fat desaturation observed in purebred Duroc raw muscles is maintained in Duroc × Iberian dry-cured hams. The favorable effect of allele T on MUFA in Duroc × Iberian had already been reported in raw muscle (Estany et al., 2014). Although quality attributes of dry-cured ham are subjected to complex polygenic inheritance patterns (Pena et al., 2013), a number of associated genetic markers have been reported to use in pig breeding programs (Stalder et al., 2005; Renaville et al., 2010; Gou et al., 2012). However, only one of them, and likely as a result of a correlated change in overall fatness, affected the fatty acid composition of dry-cured hams (Reina et al., 2012). In practical terms, the results obtained indicate that the SCD polymorphism can be a good tool to discriminate among Duroc boars by their transmittance ability for increased MUFA content in ham. In fact, we have proved that its effects can even be detected in the total edible fat of dry-cured ham slices from commercial packs randomly sampled.

Barrows, as compared to gilts, increased SFA and decreased PUFA. It is a generalized result that castration decreases PUFA (Garitano et al., 2013; Henriquez-Rodriguez et al., 2015), but it is not clear whether this is mainly caused as a result of increased SFA, MUFA, or both. While in our experiment barrows had a greater proportion of SFA (but not MUFA) than gilts, in that of Garitano et al. (2013), based on Duroc × (Landrace × Large White) crossbreds, the barrows had more MUFA (but not SFA). On the other hand, although using raw muscle samples, Ramirez & Cava (2007) did not find differences for SFA, MUFA and PUFA between barrows and gilts in different crossbreds of Duroc × Iberian. However, interestingly, our findings proved that, in commercial Duroc × Iberian dry-cured hams, the investigated SCD polymorphism can have a greater impact on MUFA than using hams from barrows instead of gilts.