How can a boneless, dry-cured, whole ham be preserved?

Dry-cured ham is a meat-based product made from salted leg of pork left to age over time to gain aroma and flavour. At the end of the aging process (more than 12 months), dry-cured ham is stable because it has an average humidity percentage of 61% (minimum 57%, maximum 63%), an average ratio between the percentage of sodium chloride and the humidity of 8.9% (minimum 7.8%, maximum 11.2%). Finally, it has an Aw value (Water Activity: water used by spoilage bacteria to grow) markedly lower than 0.90.

The dry-cured ham is sold whole with bone, whole boneless, in vacuum packed slices or sliced and packaged in an oxygen-free Controlled Atmosphere. The packaging prevents the product acquiring humidity from the environment, oxidising quickly on contact with oxygen or being contaminated with pathogenic micro-organisms of human or environmental origin, even though these are not able to grow on the ham.

The consumer, after buying ham in slices or whole boneless or receiving it as a gift, faces the problem of how to preserve it after opening the packaging. Indeed, often while being kept in the fridge, the unpackaged product decays, loses its “freshness” and the “initial aromatic quality” because it goes rancid, darkens or absorbs the odours in the fridge. The choice of preservation technique is problematic since there is no golden rule.  Various methods exist that are widely used by families; techniques sometimes recommended by experts in food production.  The best system is to repackage the product under vacuum every time part is sliced off. This method, however, is almost impossible to achieve in the home unless the family owns a packaging machine. Some experts recommend wrapping the product in a slightly damp cloth and placing it in the fridge. Others and, in my opinion, they are absolutely right, recommend wrapping the part of the muscle that has been sliced with foil or, even better, plastic film.  In this way, excessive surface humidity that could produce a high degree of “blooming” or the appearance of salts and amino acids (tyrosine etc.) is avoided. Furthermore, this simple method prevents the ham’s surface darkening and becoming impregnated with odours from the fridge itself. Finally, the sliced ham can also be kept in the fridge without any packaging. If, however, consumption takes place too slowly, a greasy film may be seen due to a mixture of water, salt and fat. This film must be removed with the first slice and then the rest will be edible and acceptable. It’s then best to place it in a pantry at room temperature (maximum 18°C) in a dry environment. The ham will remain stable: at most, a slight superficial dehydration will be noted; this dehydration will not influence the quality of the product. A dry environment and a maximum temperature of 18 °C will prevent the formation of greasy films connected to the fat and the humidity condensing on the product.

 

Prof. Giuseppe Comi

 

Pregnancy and toxoplasmosis. Why eating dry cured ham appear to be safe.

During pregnancy future mums need to follow a suitable diet. This simply means a varied diet including: milk and dairy products, meat, fish, eggs, pulses, cereals and cereal products, fruit and vegetables, and olive oil. A number of precautions have to be taken, such as avoiding the consumption of raw or undercooked meat or fish, as well as salamis, to prevent the risk of acquiring dangerous intestinal infections or toxoplasmosis, an infection which can cause serious harm to the unborn child if acquired by women who are not immune during the early stages of pregnancy.

Toxoplasma gondii is a protozoan which generally lives in the intestines of cats, which become infected by consuming small rodents.

Cats provide a breeding ground for this microorganism, since cats’ intestines are the perfect environment for the sexual reproduction cycle of toxoplasma. The oocysts are expelled in the cat’s faeces and may be ingested by other animals or humans, which act as its intermediate hosts. Toxoplasmosis is a typical syndrome affecting pets.

In man, toxoplasmosis manifests itself in a number of different ways, such as asymptomatic infections and encephalitis. It can produce serious complications in pregnant women, including miscarriage, premature labour and neonatal mortality. Congenital toxoplasmosis (transmitted via the placenta) derives from an acute primary infection of the mother during pregnancy or just before (infection at least six months before becoming pregnant makes it unlikely that the unborn child will be infected). The severity and incidence depend on the trimester of pregnancy.

Toxoplasmosis is one of the commonest infections in the world: it is more common in warm temperate zones at low altitude and less common in cold climates and mountainous regions.

The disease can be acquired in different ways: through the accidental ingestion of oocysts expelled by cats and matured in the external environment (when handling earth and cat litter, contact with anything that has been in contact with cat faeces); eating poorly washed raw vegetables; eating raw or undercooked meats (especially pork, lamb and game), fresh sausages or insufficiently aged salamis and unpasteurised dairy products contaminated by oocysts; accidental ingestion of cysts through contact between the mouth and hands which have handled raw meats. Prolonged refrigeration and freezing, as well as heat (60°C for 20 minutes or 70°C for 10 minutes) remove oocysts from foods. Meat-based products aged for more than 2 months appear to be safe. Dry cured hams, such as Prosciutto di San Daniele, Prosciutto di Parma, Prosciutto di Veneto Berico Euganeo and others should be considered safe since they are salted and matured for over 13 months. Salt, dehydrations (Aw < 0.92) and aging over a long period (more than 13 months) seem to deactivate any oocysts present in the muscles, as demonstrated by numerous international articles.

 

Bibliography:

www.dpd.cdc.gov; www.cdc.gov

Bayarri S, Gracia MJ, Pérez-Arquillué C, Lázaro R, Herrera A. (2012) Toxoplasma gondii in commercially available pork meat and cured ham: a contribution to risk assessment for consumers. J. Food Protect. 5(3):597-600.Bayarri S, Gracia MJ, Lázaro R, Pe Rez-Arquillué C, Barberán M, Herrera A. (2010) Determination of the viability of Toxoplasma gondii in cured ham using bioassay: influence of technological processing and food safety implications. J. Food Protect. 73(12):2239-43.

 

Prof. Giuseppe Comi

Traditional smoking and preservation of meat

Smoking is a chemical and physical process used in the preparation of various preserved foods, such as meat, fish, sausages and cheese. This food preservation method has been used since prehistoric times and makes it possible to preserve the treated pay for homework products because the smoke prevents microbial growth and delays fat oxidation.

The smoking process can be performed hot or cold. During cold smoking, the food is exposed to temperatures of between 20°C and 45°C. The smoke penetrates the food slowly. This technique is primarily used for fish, such as salmon, and some smoked meats (speck). During hot smoking, the temperature ranges from 50°C to 90°C. In this case the treatment period is reduced to just a few hours. It is used for some fish and salted meats. The molecules released by the combustion of plant material not only have antiseptic and antioxidant properties, but also create a specific aroma. In fact, the smoke produces aromas that also have antimicrobial properties. Furthermore, added nitrites and nitrates create an oxygen-deprived environment, encouraging the formation of HNO2 (nitrous acid), which prevents the germination of Clostridium botulinum spores. The preservative effect derives from the surface dehydration of the product and from the presence of aliphatic and aromatic (phenols) compounds, acetic and propionic acids, and formaldehyde. These compounds constitute the gaseous phase of the smoke, which also contains solid and liquid components with sizes varying between 50 and 800 microns. The unwanted substances, such as PAHs (benzopyrenes, and other polycyclic aromatic hydrocarbons), which are believed to be carcinogenic, are contained in the solid phase known as particulate. Consequently, electrostatic filters which retain the particulate are used to purify the smoke of all harmful and carcinogenic components. Today, precisely in order to remove the particulate from the smoke, the pyrolysis chambers, which contain the smoke generators, must be separated from the smoking chambers. In this way, the smoke is passed through electrostatic filters or water before it reaches the smoking chamber and comes into contact with the product.

In traditional smoking, the smoke is produced by the pyrolysis of beech wood (Italian Ministerial Decree 31/03/1965) in the pyrolysis or combustion chamber, which is separated from the smoking chamber. As a result of this separation, the smoke is channelled through filters, where it is sprayed with water, which retains the solid components, thereby preventing the risk of carcinogenic molecules (PAHs) being present in the finished product. Smoked products are therefore as healthy as non-smoked products, if not better. In fact, smoked foods have a higher nutritional value than other foods, because the dehydration leads to a concentration of nutrients. Furthermore, they have more flavour and contain less salt. In fact, as a result of its antimicrobial properties, smoking means that less salt is needed to preserve the foods.

Nitrous acid: an acid that derives from the added nitrite – it acts as an oxidant in acidic environments, and as a reductant in alkaline environments.

Clostridium botulinum: spore-forming bacterium that causes severe poisoning.

Pyrolysis: combustion of wood in the absence of oxygen.
PAHs: polycyclic aromatic hydrocarbons, e.g. benzopyrene: carcinogenic and mutagenic substances.

 

Can coeliacs eat dry-cured ham?

Gluten intolerance seems to be becoming increasingly widespread, therefore raising questions amongst those who are diagnosed with this intolerance as to whether dry-cured ham is one of the products to be avoided.

We asked the Associazione Italiana Celiachia (AIC – Italian Coeliac Association – http://www.celiachia.it) to give their opinion, an organisation which represents the over 120,000 people diagnosed with coeliac disease in Italy to date (data from the latest Parliamentary Report on coeliac disease). With around 65,000 members, it has been working for over thirty years to promote care for coeliacs, organising important initiatives designed to encourage gluten-free dietary compliance (Food Handbook, Eating Out, dietary education in schools), providing doctors with information about diagnostic and therapeutic possibilities, encouraging scientific research, and raising awareness in political, administrative and healthcare environments. It operates across Italy, through its 20 Regional Associations.

Associazione Italiana Celiachia

Associazione Italiana Celiachia

Over the years, the AIC has achieved a number of important objectives, including the free distribution of gluten-free nutritional/therapeutic products to all those diagnosed with coeliac disease by the Italian National Health Service and the publication of a specific framework law on coeliac disease designed to protect the rights of coeliacs and encourage their normal inclusion in daily life (Italian Law 123/2005).

The Associazione Italiana Celiachia includes dry-cured ham amongst the allowed food types, which can therefore be freely consumed by coeliacs.

In fact, the introduction to the AIC Food Handbook states: “dry-cured ham, from which the sugna (pork fat), i.e. the whitish yellow layer not covered by the rind, must be carefully removed, is the only risk-free cold cut.

In fact the sugna normally consists of fat, salt and flour (rice flour in 75% of cases). It is removed completely before slicing the product and, moreover, even if the flour used happened to be wheat flour, there is no possibility of gluten penetrating or migrating into the edible part of the dry-cured ham.”

Ham quality: the Tyrosine’s role.

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The quality of dry-cured ham is achieved by controlling chemical parameters, such as the salt (NaCl) concentration, humidity and the cialis super active proteolysis index. Proteolysis has an effect on the digestibility, the texture, the colour and the frequently observed white surface sheen of the dry-cured ham, as well as the precipitation of tyrosine crystals*.

In fact, it is often the case that when a well-aged, dry-cured ham is cut, whitish, chalky-looking formations can be observed, consisting of amino acids deriving from the proteolysis caused by meat proteases*. More specifically, they consist of tyrosine and, to a lesser extent, phenylalanine* and other amino acids. The origin of these formations is still controversial and various different theories are still being explored. Table 1 shows the most important and most reliable of these. Proteolysis by tissue enzymes seems to be the most reliable.

In fact, meat enzymes, also known as cathepsins, act on the denatured muscle proteins resulting in the release of peptides* and amino acids, including tyrosine and phenylalanine.

Due to the low water solubility , the pH (degree of acidity) and the aw* (water activity) of dry-cured ham, these then precipitate and crystallise to produce the well-known “tyrosine crystals”. The theory regarding the production of tyrosine due to bacterial activity (proteolysis or synthesis), despite being supported by the available evidence, is not very reliable. In fact, bacterial activity in dry-cured ham is only superficial as few bacteria are present in the muscle and their metabolism is limited by the salt. In other words, the concentration of tyrosine in the granules cannot be justified by bacterial activity alone.

Therefore, tyrosine production primarily derives from the activity of cathepsins*. From the very start of the aging process, they break down the proteins and begin by releasing peptides (chains of amino acids). Later on, the peptides are broken down into amino acids which, depending on their degree of solubility, precipitate to form granules. The same white surface sheen, which is sometimes found on the cut surface of dry-cured ham, is not formed by salt but by amino acids.

Cutting dry-cured ham

Cutting dry-cured ham

The presence of granules is often considered to be a defect. The texture of the resulting dry-cured ham is not as good as that of a dry-cured ham without the granules: it seems softer. Moreover, the quantity of free nitrogenous fragments (amino acids) may give the dry-cured ham a bitter and metallic taste, compromising its organoleptic properties. However, in my opinion, if we ignore the sensation of chewing “chalk”, the product has a high proteolysis index and is therefore more digestible, because it contains many free amino acids which are easily digested by the body.
Table 1: Theories regarding the formation of tyrosine crystals

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a)     proteolysis by tissue enzymes

b)    proteolysis by microbial enzymes

c)     microbial amino acid synthesis

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aw: Water activity: free water, used by bacteria or enzymes in order to carry out their functions. The lower it is (due to added salt or molecules that bind water), the less active the enzymes and bacteria.

Proteolysis index: soluble nitrogen/total nitrogen ratio (e.g. soluble nitrogen – amino acids / total nitrogen – proteins + amino acids).

Precipitation of tyrosine crystals: tyrosine amino acid is not very soluble in water, meaning that it accumulates and forms crystals or granules. For example, if we added sand to a glass of water it would not dissolve, but instead would precipitate to the bottom, and the same thing would happen if we added tyrosine to water.

Meat proteases (cathepsins): these enzymes break down proteins (chains of amino acids) resulting in the release of individual amino acids or peptides (small chains of amino acids).

Phenylalanine: an amino acid found in proteins.

Peptides: chains of amino acids (from 2 to 12 and more amino acids).

Cathepsins: meat proteases that break down proteins and turn them into peptides and individual amino acids. They break apart proteins (chains of amino acids) resulting in the release of peptides and individual amino acids.

Fats inside dry cured ham

Dry cured ham is the leading product in the Italian charcuterie industry, both with respect to tradition and organoleptic properties. As a meat-based product, it is made up of 2 components: the lean part consisting of the thigh muscles, and the fatty part, consisting of the adipose fat (covering the meat and under the rind), and the muscular fat (intramuscular, marbling and intermuscular).

The percentage of fat varies according to the breed, the genetics and the diet of the pig, accounting for between 11 and 18 per cent of the edible part of the ham.

Fat has a high nutritional value, because it is made up of saturated fatty acids*1, monounsaturated fatty acids*2 and polyunsaturated fatty acids*2.

The latter are fundamental to human health and are similar to those contained in vegetable oils (olive and seed oils) and in fish (omega-3 and omega-6). A 50 g portion of Prosciutto di San Daniele can contain as much alpha-linolenic acid (omega-3) as 100 g of salmon.  Moreover, the fat in ham contains essential fatty acids such as linoleic acid*3 (omega-6), arachidonic acid*4 (omega-6), and alpha-linolenic acid*5 (omega-3). From these acids, humans are able to synthesise all other polyunsaturated fatty acids, essential precursors in biological membranes,  the development of the nervous system, growth, immune defence, fighting cancer and regulating blood cholesterol levels. Consequently, these fatty acids help to prevent hardening of the arteries (arteriosclerosis). Contradictory to what was believed previously, dry cured ham contains a low percentage of cholesterol (max. 33 mg/100 g of the edible part). This percentage is lower than that found in some fish (sea bass) and shellfish. Furthermore, on the basis of these considerations (low cholesterol concentration, higher percentage of unsaturated fatty acids than saturated fatty acids, presence of omega-3 and omega-6 fatty acids), nutritionists and health experts have, just recently, extensively re-evaluated the consumption of pork, and dry cured ham in particular.  They finally realised (it was about time) that dry cured ham is a food suitable for everyone, and that its lean/fatty component is fundamental to physical and mental wellbeing in children, adolescents, adults and the elderly.

Table. Percentage of fatty acids in the fat of dry cured ham

Table. Percentage of fatty acids in the fat of dry cured ham

Notes

1. Saturated fatty acids consist of a saturated carbon chain comprised solely of single C-C bonds. Saturated fatty acids, along with monounsaturated or polyunsaturated omega-6 fatty acids reduce LDL cholesterol (“bad cholesterol”).

2. Unsaturated fatty acids are characterised by one or more double bonds in the carbon chain. They are usually found in liquid form, and are contained in olive oil (rich in monounsaturated fatty acids, that is with just one double bond) and seed oil (rich in mono and polyunsaturated fatty acids, with two or more double bonds). Like linoleic acid and monounsaturated fatty acids, unsaturated fatty acids actually increase HDL cholesterol (“good cholesterol”) levels, which in turn increases the removal of triglycerides from the bloodstream. Of all the polyunsaturated fatty acids, a particularly important role is played by the long-chain omega-3 fatty acids, which are primarily found in fish oils. Consumption of a balanced ratio of omega-3/omega-6 is very beneficial to humans. In fact there is evidence, albeit inconclusive, to support the theory that these fatty acids protect against fatal heart disease.

3. Linoleic acid is one of the essential fatty acids and belongs to the omega-6 group. Linoleic acid is found in all vegetable oils and is abundant in many of them, particularly safflower oil and sunflower oil, but also, to a lesser extent, in corn oil, soya bean oil, green coffee and others. It is also found in some animal fats.

4. The arachidonic acid found in the human body is introduced through the diet or derives from linoleic acid (essential fatty acid).

5. Alpha-linolenic acid (omega-3) is one of two essential fatty acids that humans and other animals need to consume in their diet in order to maintain a good state of health. This is because the body requires this fatty acid for various biological processes, and also because it cannot be synthesised endogenously, but needs to be absorbed through the diet.