Prosciutto di Parma - The King of Hams

Introduction

Dry-cured ham is a traditional food product which is well known all over the world. Do you know that prosciutto is a type of dry-cured ham? Prosciutto can taste sweet or spicy by adding different kinds of seasoning powders such as red chillies and black pepper. However, different countries and areas have their own styles. The most famous prosciutto is known as Parma Ham from Parma, Italy. Parma is a city in the northern Italian region of Emilia-Romagna and the word 'prosciutto' is the Italian word for ham. Since 1970, the designation of origin has been legally protected and no other air-dried ham may use the name of ‘Prosciutto di Parma’.

Source, structure and composition of Prosciutto

Fresh hind legs of pigs are the raw material in producing prosciutto. There are few main muscular areas in the ham as shown in Figure 1. A different muscular area has a different rate of biochemical changes. Biceps femoris is an internal muscle located under a thick layer of subcutaneous fat. This slows down salt uptake and contributes to the higher rate of proteolysis in this muscle. Semimembranosus muscle is located close to the surface without fat covering. This lean meat muscle absorbs salt faster during the salting stage. Proteolysis index for semimembranosus muscle (18 %) is lower than biceps femoris (25 %) after curing.

Figure 1: Main muscular area in ham

Adapted from: Petrova et. al (2015) Manufacture of dry‑cured ham: a review. Part 1. Biochemical changes during the technological process. Springer-Verlag Berlin Heidelberg.

The main components of muscle meat are water, proteins, lipids, minerals, and trace quantities of carbohydrates. The composition of macronutrient in prosciutto is shown in Table 1. 

Table 1: Macronutrient composition expressed in grams and energy value on 100g of Parma ham

Composition	Content (100 g of Parma ham)
Water	50.3 g
Protein	25.9 g
Lipid	18.3 g
Carbohydrate	0.3 g
Energy value	269 kcal / 1127 kJ

Adapted from: The Parma Ham Consortium (2012). Parma Ham Well-being and diet Nutritional values. Consorzio del Prosciutto di Parma.

Physiological and Biochemical changes during Prosciutto production

       A traditional and authentic prosciutto must be produced naturally without additives such as nitrates according to ancient tradition. The processing stages of prosciutto production are illustrated in the flowchart as shown in Figure 2.

Figure 2: Processing stages of prosciutto production

The main stages of traditional production of prosciutto consist of salting, resting, and drying–ripening. During salting as shown in Figure 3, the hams are massaged with coarse salt and an osmotic dehydration process takes place. Absorption of salt increases solute concentration in meat muscles. Water is then forced to diffuse out due to the high solute concentration in meat muscle. However, the time of salt diffusion depends on the size of the ham, but generally it is between 14 and 21 days.  After salting, the hams are chilled at low temperature for at least 3 months. This allows uniform distribution of salt in the meat muscle. At the end of the salting period, hams weigh about 3.5 - 4 % less.

Figure 3: Salting of prosciutto

Hams are then washed to eliminate excess salt and moved to a drying chamber with convective air-drying at a low velocity rate (0.1– 0.5 ms⁻¹) for another 3 months. High air velocities can cause the surface layer of ham dries out and deteriorate the quality of prosciutto. During drying stage, water evaporates from meat surface and water diffuses out from the inner meat tissues towards the surface simultaneously due to vapour pressure gradient. As a result,  a lower moisture content leads to a higher salt concentration in meat muscle tissues. This affects the rate of the enzymatic reactions influencing the final organoleptic characteristics of prosciutto. In the seventh month, the cut surfaces are covered with softened lard to control the rate of drying.

Figure 4: Aging of hams after applying softened lard

The hams are then aged for a minimum 12 months and each ham will loss 30 % of its original weight and hence concentration the flavour of prosciutto at the end of ripening process. Ripening process involves proteolysis and lipolysis in meat muscles. Enzymatic degradation of muscle proteins and lipids is essential for the development of texture and flavour during prosciutto production. During proteolysis, proteases break down muscle proteins to large peptides while peptidases hydrolyze large peptides to smaller peptides and to free amino acids. Protein inhibitors such as cystatins can control protein degradation and protect meat cells from unwanted proteolysis. Besides, proteolysis index is the highest when the meat muscles are ripened at optimum temperature of 30 °C. Lowering the temperature may lower the degree of proteolysis. The rate of protein degradation decreases with time of ripening due to denaturation of enzyme and the decreasing water activity.

During lipolysis, lipases degrade triacylglycerols, monoacylglycerols and lipoproteins while phospholipases hydrolyze phospholipids to release free fatty acids. Phospholipids are considered as the most important fractions for the flavor formation in prosciutto because most of the free amino acids originating from phospholipids. Lipid oxidation is promoted by light, elevated temperature and the presence of salt. This means that lipolytic enzymes are active and stable during salting and drying-ripening processes. During lipid oxidation, hydroperoxides are formed first as primary oxidation products which can be degraded to secondary oxidation products such as aldehydes, ketones, hydrocarbons, esters, alcohols, and lactones. Secondary products of oxidation contribute to the specific taste and flavour of prosciutto.

Free amino and fatty acids are further degraded to form volatile compounds through enzymatic and chemical reactions. Lysine, alanine, and glutamic acid are the most abundant free amino acids that correspond to the taste of prosciutto while methanethiol, 2-methylpropanal, 3-methylbutanal, hexanal, 2-heptanone, and 1-octen-3-ol are the most readily identified odorants that contribute to a wide variety of odor qualities such as fruity, cheesy, mushroom-like, nutty or cured ham-like. Each room of curing prosciutto at different stages has a very different smell. Prosciutto smells like meat and salt at the beginning of ripening process. As the prosciutto is getting ripened, it would exactly smell like strawberry. Some prosciutto may smell spicy when different kind of spices are added to it.

Authenticity of prosciutto

Once prosciutto is ready for the official stamp of certification, the pork leg is fire branded with a five point ‘ducal crown’ as shown as figure below. This identification mark signifies the authenticity of Prosciutto after passing through several verification and regulations. 

Figure 5: A five point ‘ducal crown’

Quality of prosciutto

To determine a good quality of prosciutto, qualitative parameters such as salt content, moisture content and soluble nitrogen content are evaluated. For a high-quality Parma Ham weighing between 7 to 9 kg must contain a limited quantity of sodium chloride (4.5 - 6.9 %) and moisture (59 - 64 %), while soluble nitrogen content as proteolysis index must be controlled between 24 to 31 % as the proteolysis index has been found to adversely affect the consistency of the lean meat. Parma ham is controlled to have water activity about 0.94 and pH about 5.7.

Serve it right

Figure 6: Slices of prosciutto

The cured prosciutto is usually thinly sliced and pieces too small to slice can be diced as a great topping for pizza. Parma ham has a uniformly pink or red colour, marbled with white fat when sliced. Besides, Parma ham has a mild and delicate flavour, slightly salty with a fragrant and distinctive aroma. Prosciutto can be served uncooked as  'prosciutto crudo' and the style is different from the cooked ham called as 'prosciutto cotto'. The raw prosciutto is ready to eat due to the long curing process.

Last but not least

It is important to identify the structure of meat muscle as different muscular area has a different rate of biochemical changes. Enzymatic degradation of muscle proteins and lipids in meat muscles are the main processes to produce a good quality of prosciutto with desirable texture and flavour. Proteolysis and lipolysis lead to production of free amino acids and fatty acids which contribute to the flavour and odour quality during ripening of hams. The rates and the extent of ripening are determined by the water activity and the temperature. Therefore, the duration of ripening, initial salt content and drying rate must be controlled to produce good quality of prosciutto.

Watch the video below to get a better picture in making of prosciutto!

Parma Ham Consortium - "Aria di Parma"

from https://www.youtube.com/watch?v=okgg4cQoxGA&t=11s

References

1. Petrova et. al (2015) Manufacture of dry‑cured ham: a review. Part 1. Biochemical changes during the technological process. Springer-Verlag Berlin Heidelberg.
2. The Parma Ham Consortium (2012). Parma Ham Well-being and diet Nutritional values. Consorzio del Prosciutto di Parma.