Characterization of traditional Istrian dry-cured ham by means of physical and chemical analyses and volatile compounds
Introduction
Dry-cured hams are manufactured in many countries, but production is mainly located in the Mediterranean area (Álvarez de la Puente, 2003). There is a great variety of dry-cured hams in this area, some of the most important being Spanish Iberian and Serrano, Italian Parma and San Daniele, and French Bayonne hams. These varieties differ in the pig breed, type of feed, meat weight, type of cut and processing conditions (Martín-Bejarano, 2001, Ockerman et al., 2002, Toldrá, 1998, Ventanas et al., 2001). Istrian dry-cured ham is a high quality product as well as the dry-cured ham types mentioned above and their traditional method of production is unique, leading to particular properties which make them different from all other Mediterranean dry-cured ham types. Istrian dry-cured ham has protected designation of origin and geographical indication by the Official Gazette of the Republic Croatia (NN 78/99, 127/99, and 173/03).
The production process of Istrian dry-cured ham has four phases: salting, pressing, drying and ripening. At the beginning of the salting stage pepper, garlic and laurel are added. The whole production process is very long (12–18 months) (Comia, Orlic, Redzepović, Ursoa, & Iacumina 2004). Istrian dry-cured ham is produced without pig skin and is not smoked. The reason why it is produced without skin is only tradition, because of the high price of pig fat in the past. It should also be pointed out, that nitrite salts or other additives are not used for curing of Istrian dry-cured ham, and it is not subjected to smoke curing, which makes it an even more valuable food product.
The most important quality parameter of ham is aroma, and it is due to the presence of many volatile compounds, most of them produced by chemical and enzymatic mechanisms during the post-mortem process (Flores, Grimm, Toldra, & Spanier, 1997); the main biochemical reactions being lipolysis and proteolysis (Toldrá, 1998). Muscle proteins undergo an intense proteolysis resulting in a great number of small peptides and high amounts of free amino acids. The enzymes responsible of these changes are proteinases (cathepsins, calpains, peptidases and aminopeptidases). Muscle and adipose tissue lipids are subject to intense lipolysis generating free fatty acids by the action of lipases (lysosomal acid lipase, acid phospholipase and adipose tissue lipase) that are transformed to volatiles as a result of oxidation. (Toldrá, Flores and Sanz, 1997, Toldrá and Flores, 1998).
Muscle proteases and lipases are involved in important biochemical mechanisms taking place during the processing of dry-cured meat products which are directly related to the final quality. These enzymes are affected by the conditions typically found in the processing of dry-cured meat products, dehydration being one of the most important factors (Toldrá, 2006).
Except volatile compounds derived from lipolysis and proteolysis aroma can be formed from spices added in the production process like from garlic (Ansorena, Astiasarán, & Bello, 2000) or pepper (Sabio, Vidal-Aragon, Bernalte, & Gata, 1998).
Solid-phase microextraction (SPME) is a relatively new technique for the rapid, solventless extraction of volatile and semi-volatile organic compounds. It utilizes the partitioning of organic components between a bulk aqueous or vapour phase and the thin polymeric films coated onto fused silica fibres in the SPME apparatus (Harmon, 1997).
In addition, SPME allows using mild sampling conditions, such as an extraction temperature below 50 °C, avoiding artefacts formation during sample analysis (Nigel, Brunton, Cronin, & Monahan, 2000). In comparison to traditional techniques for analyzing volatile constituents of foodstuffs, SPME is inexpensive, solvent free, easy to handle, sensitive, and selective (Zhang & Pawliszyn, 1993). SPME has been used, among other applications, to describe the volatile flavour profile of foodstuffs (Díaz et al., 2009, Rega et al., 2009, Figoli et al., 2010, Culleré et al., 2010, Oliveira et al., 2010).
The aim of this study was to determine the characteristics (chemical composition and instrumental colour) of Istrian dry-cured ham and to identify, for the first time, the volatile flavour compounds by SPME.
Section snippets
Traditional production process
Istrian dry-cured hams were produced from pigs (Duroc breed) fed a concentrate diet to grow rapidly to a final body mass of 190–200 kg. Then, the hogs were slaughtered, cut up, cooled and the raw hams trimmed. Legs were trimmed in the traditional Istrian manner, medially and laterally without skin and the subcutaneous adipose tissue, with the aitch bones and without the foot. Dry salting of hams was conducted using a sea salt with an addition of the following ground black pepper, powdered garlic
Chemical composition, colour measurements and TBARs values
Results of physical and chemical analysis are shown in Table 1. Water content was in the range of 37.91 g–41.45 g/100 g. The results were in accordance with those reported by other authors (Karolyi, 2006, Krvavica et al., 2008) for Istrian dry-cured ham. Production without pig skin and adipose tissue enables deeper penetration of NaCl resulting in lower water content. Due to this, we obtained lower values for water content in comparison with Iberian (49.00 g/100 g) (Carrapiso & García, 2008),
Conclusion
Istrian dry-cured ham is a valuable food product thanks to excellent organoleptic properties—pleasant odour and taste and high protein content. About 50 volatile compounds were identified and quantified which belonged to several classes of chemicals: 5 alcohols, 8 aldehydes, 7 alkanes, 1 ketone, 2 esters, 9 monoterpenes and 15 sesquiterpenes. It is known that flavour formation in dry-cured hams is related to lipolysis–oxidation of fat and to proteolysis, amino acid degradation which is shown in
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