Author: Monica 

Enzymatic reaction in meat

During early postmodern, enzymatic reactions take place due to the hydrolysis of fatty acid. The absence of blood allows lactic acid to be accumulated into muscle and produce pH drop to 5.6 within a few hours. In addition, during the rigor mortis, the pH levels decline (Toldrá, 2009). The amount of water retained in the myofibril structure also decreased, lead to contraction and meat size reduction. The reduction of the space within the structure is due to pH6, the isoelectric point of proteins. The higher the intramuscular content is present in the meat, the longer the time required for efficient salt diffusion (at pH6) and appropriate moisture loss levels will take longer to attain (Toldrá, 2007).

Meat composition

Red meat has many fibres large amount of myoglobin, lipid and high oxidative enzymatic activity. The dipeptides in the muscles are the anti-oxidant which to act as the neurotransmitter and modulators of in the enzyme reaction. As mentioned earlier, the higher the intramuscular content is present in the meat, the longer the time required for salt diffusion and moisture loss.

Apart from the addition of salt in cured meat, migration of water from depth of meat to surface of the meat also decrease the water activity in the meat (Toldrá, 2009). There are two types of water migration. One is from depth to product and second is water evaporation in the surface. Together with process such as curing and smoking, the decrease in water activity in cured meat products meant less favourable conditions are created for the microorganisms to thrive, since microorganism thrives lesser in levels 0.80_aw.  Diffusion coefficient depends on the salt and water, which is irreversible correlated to the fat content (Toldrá, 2007).

Fats in the meat also affect the dehydration process (Doyle, 2007). Although intramuscular fat gives marbling which is the main factor affecting the juicing, it also controls the reaction of desiccation and the development of flavour. Lipoxygenase catalyze the incorporation of molecular oxygen in polyunsaturated fatty acids, to give a conjugated hydroperoxide as final products (Toldrá, 2007).

Process

When the beef is slaughtered, the beef is drained off. After the drain off, the cow’s hide is carefully cut off.  Care is also taken to prevent puncturing the intestine. This is to prevent microorganism from the hide and intestine from contaminating the meat. Water is then sprayed to wash off remaining blood and bone pieces. Then the cut meat is being rubbed with curing ingredients and is stored in the chiller at 0-4°C. It takes 12-15 hours to chill the meat to an internal temperature to 4°C (USDA, 2009). This is essential to prevent anaerobic bacteria at bone joints to cause bone souring spoilage before the salt penetrates the centre of the meat cut (Frederick K, 1981). Lower than 4 degree Celsius may slow down curing process or even halt it. This prevents the development of bacteria and may not be able to react with nitrites. Higher temperatures may increase the curing process but also encourage the growth of undesired micro-organisms.

Ordinary table salt (sodium chloride) is added because of its effect on flavor. Sugar is added to reduce the harshness of salt. Spices and other flavorings often are added to achieve a characteristic "brand" flavor. Nitrate is used as dry curing salt, having the mixture of nitrate, common salt and sucrose are rubbed into the meat. After which the cuts of meat are placed in the curing room.  Curing process has other purpose such as removing water, activating some chemical reactions to develop taste and flavor. The refrigerator temperature is used as for optimum reaction between meat and nitrites. Also on the other hand, the low temperature discourages most microorganism growth

It takes about 24 hours to smoke and cook hams. Smoking is usually accomplished in three stages. During curing process first phase, or drying stage, the smokehouse is heated to 51°C. All dampers are opened to allow all excess moisture to escape and there is no smoking during this 8-hour period (Otwell, 2006). During the next eight-hour stage, the dampers are partially closed and the temperature on the house increased to 57°C. Smoke is generated at this phase. The smoke is continued throughout the third stage with all dampers closed, and the temperature on the house raised to 82°C (Otwell, 2006).. The humidity is kept at above 80% to increase heat transfer. The wood used to generate the smoke should be logs from hardwood species. Unlike pine or any other resinous wood or sawdust, smoke from hardwood does not give sooty smoke. Cured meat products are smoked after the curing process to impart a smoked meat flavor. The temperature of the smokehouse will maintain at 82°c, until the temperature inside the product reaches 61°C. During curing, water comes out from the ham, and as mentioned earlier, the decrease in water activity lesser chance for a variety of microorganisms to thrive.

Smoke

Smoking is usually combined with meat drying in meat preservation in many countries. Both smoking and curing reduce water activity reduction. In addition, smoking has bacteriostatic effect on pH (Doyle, 2007). Both techniques have uses the effect of enzymes and heat to help increase protein and lipid changes in the previously salted material. This helps in increasing nutritional quality and also increases the shelf life and safety quality of the product. 

Smoke imparts flavor, color, and other sensory effects to foods. Smoking also creates a physical barrier for the meat. When the meat is being smoked, a layer of “skin” is being formed on the surface of the meat. Not only that, smoke also provides preservation to the food product. It functions as an antimicrobial and antifungal agent. In a study done by Wendorff (1981), the results of antibacterial and antifungal activities from a few smoke condensates show that the phenolic content of smoke contributes greatly to the antimicrobial and antifungal effects of smoke. But when it is faced with a few types of microorganisms, smoke is not an effective antimicrobial agent. Therefore, the usage of other hurdles such as salt or nitrates is used together with smoking.

In dry cured meat, the desired value of water value activity of 0.8, and moisture value of 24%. This is the value that can ensure good keeping shelf-quality. However, these moisture value and water activity are actually too dry for most preference. In order not to compromise the preservation quality while trying to retain enough moisture to suit most people’s taste, products which have undergone drying are accompanied with the use of smoking to increase the preservation of the product quality. In addition, drying and smoking are deployed with other technology in preservation, which are refrigeration, curing, salting, spicing, package and storage.

Packaging

Vacuum Packaging

Vacuum packaging is needed for the dry cured beef ham so as to prevent continued weight lost. Too much weight loss affects the sensory quality of the product. Vacuum packaging also prevents freezer burn by protecting the meat with vacuumed packed plastics. It also prevents unwanted colour change from freezer burn, thus preventing unsightly products (Stringer, 2000).

Vacuum packaging is widely used in the packaging industry. Before hermetic sealing, air is evacuated from a pack.  The removal of atmospheric air inhibits the growth of aerobic and anaerobic spoilage micro-organism and thus, reduces the rate of oxidative deterioration. Therefore it is capable of extending the shelf life of perishable foods. It is an established technique for packaging chilled foods like primal red meats, cured meats and cheese. The presence of anaerobic Clostridium botulisum in the affected food product suggests that carbon dioxide from the atmospheric air has entered into the product due to faults from the packaging, since there should be no air in vacuum packaging (Doyle, 2007). 

Refer to next post on the details of the packaging materials and the specific measurement regarding vacuum processing 

Material

Packing materials

Materials for vacuum products need to have high O₂ barrier and high levels of seal integrity. The plastic bags normally used for vacuum packing are made of multi-ply formulations based on polyolefin resins, with either polyvinylidene chloride or ethylvinyl alcohol as the gas barrier component (Sprenger, 2004). The oxygen permeability of packaging films is measured in terms of the amount of oxygen which passes through a square metre of film in 24hours at atmospheric pressure. This measurement is called the oxygen transmission rate (OTR) and has units of ml/m₂/24hr/atmosphere. O₂ transmission rates of less than 15cm³m-²day-1atm-1 are required for vacuum packaging. Any greater OTR leads to oxygen and accumulation of oxygen in the pack (Otwell, 2006). The diffusion of atmospheric air will spoil the vacuum condition and make microorganisms viable. The material, in addition, must consist of coextruded or laminated films. This highly ductile plastic barrier laminate which will be draped gently over the food product (Stringer, 2000), this prevents formation of ice-crystals from gathering on the product surface during freezing. During the manufacturing process, the top and bottom web films are sealed from the edge of pack to edge of product, pack integrity is maximized and juice exudation is limited.

Therefore from the above discussed properties of an ideal vacuum packing material, PVDC (poly vinylinden chloride) is chosen. In addition of the properties mentioned above, it also has barrier properties which prevent the transmission of water vapor or oxygen (Sprenger, 2004). Apart from preventing the ice crystal formation, this plastic material also helps in eliminating freezer burn and dehydration, which helps in the preservation of the product’s sensory qualities.

There are 2 methods in which the process is carried out, Grace System and chamber system. The Grace system is carried out by subjecting the bag interiors to a vacuum i.e., reduced pressure after which the bags are sealed by any suitable means such as by the application of clips round the bag neck or by heat sealing the openings of the bag. The chamber system is carried out in a sealed vacuum chamber which is capable of being subjected to reduced pressure; in the chamber the bags previously filled with the meat, are sealed, and then the chamber is returned to atmospheric pressure by the admission of air so that the material of the bag is drawn into contact with the meat (Spooncer, 2010).

The reason for using curing and vacuum packaging

Vacuum packaging is needed for the dry cured beef ham so as to prevent continued weight lost. During curing, water comes out from the ham. During curing, salt is rubbed over the surface of the ham and it is pressed. This pressing helps draw out the moisture. Moisture is drawn out from the ham by the sodium chloride which preserves it. The salt penetrates through the beef ham and draw out moisture from it. Vacuum packaging also prevents freezer burn by protecting the meat with vacuumed packed plastics. It also prevents unwanted colour change from freezer burn, thus preventing unsightly products.

Storage

The spores of the bacteria grow best in the presence of oxygen, a pH environment of 4.6 or higher, a low salt environment of 7% and below and a high moisture environment of 95%. The food product should also not be stored in the temperature of above 3^oC (Stringer, 2000).  As light accelerates oxidation, the manufacturer can store the vacuum meat product in chiller storage with dim light. However, the light must be bright enough for workers to realize any damage in the products such as holes and discolouration (Doyle, 2007).