This article introduces main factors that effects the color change of fresh meat, and main methods in meat processing to keep fresh meat in it’s original color, including meat storage and packaging methods
The color of the meat is generally red in different shades, which mainly depends on the pigment substance in the muscle-myoglobin and the pigment substance in the residual blood-hemoglobin. If bleeding is sufficient, myoglobin accounts for 80% to 90% of the pigment in the meat. The color of meat is determined by the content and changes of myoglobin (Mb) and hemoglobin (Hb) in the meat. Myoglobin is the meat’s own pigment protein, which determines the inherent color of the meat; hemoglobin exists in the blood It is greatly affected by the pre-mortem state and post-mortem bloodletting, which has an impact on the color of the meat.
The color of the meat also depends on the degree of pigment protein and oxygen binding and the degree of iron oxidation when the meat is stored in air. When the state of iron is not changed and it is still divalent iron, its color changes depending on the presence of oxygen. When reduced myoglobin and oxygen combine to form oxygenated myoglobin, the meat is bright red. When the meat is stored for a long time, myoglobin and oxygen undergo a strong oxidation to generate oxidized myoglobin, the divalent iron becomes trivalent, and the meat is brown.
However, the degree of permeation of oxygen in the air to the surface of the meat is shallow, only about 2 cm below the surface of the meat. Therefore, oxidized myoglobin is not produced in the deep part of the large meat, and the center of the cut surface of the meat is still bright red. The rate of oxidative discoloration of meat is affected by oxygen content, humidity, temperature, air flow rate, etc. The lower the temperature and the greater the humidity, the longer the bright red color remains. According to the test, burdock carcass can be placed under 7 ℃, which can promote the formation of bright red under good management.
At the same temperature, the air flows quickly, which promotes the drying of the meat surface and accelerates the oxidative browning of the meat.
Factors affecting fresh meat color
1) partial pressure of oxygen
When fresh meat is placed in the air, the surface myoglobin combines with oxygen to produce oxygenated myoglobin, and the meat appears bright red. This process is completed within 30 minutes. Over time, oxygenated myoglobin is oxidized to methemoglobin, and the oxidation speed is fastest when the oxygen partial pressure is between 666.7 and 933.3 Pa. The level of partial oxygen pressure determines whether myoglobin forms oxygenated myoglobin or methemoglobin. The formation of oxygenated myoglobin requires sufficient oxygen. Generally, the higher the oxygen partial pressure, the more favorable it is for formation. Oxidation to methemoglobin requires only a small amount of oxygen. The lower the oxygen partial pressure, the more favorable it is for the formation of methemoglobin, and an increase in the partial oxygen pressure inhibits its formation.
Animal muscle pH was 7.2 to 7.4 before slaughter. After slaughter, lactic acid accumulated in the muscle due to glycolysis, and the pH decreased. After the animals are slaughtered, the speed and extent of the decline in muscle pH have an impact on meat color, water retention, protein solubility and bacterial reproduction speed. Generally, the average pH drops, the final pH is about 5.6, and the color of the meat is normal. Meat with higher final pH is dark, such as DFD meat, black cut beef, and so on. Too fast a drop in pH can also cause protein denaturation, muscle dehydration, and PSE meat.
The reproduction of microorganisms accelerates the change of flesh color, especially the formation of methemoglobin. This is because the microorganisms consume the oxygen on the surface of the meat, which reduces the local oxygen partial pressure on the surface of the meat, which is conducive to the formation of ferritin. The presence of bacteria doubles the rate of discoloration of the meat, and the increase in temperature is more conducive to this change, because the reproduction rate of bacteria accelerates with increasing temperature. When the bacteria multiply to a certain degree (≥10’cfu / g), a large number of bacteria consume all the oxygen on the surface of the meat, making the surface of the meat an anoxic layer, so that the myofiin is reduced again. Instead, the contaminated meat surface had very little methemoglobin.
High ambient temperature, on the one hand, promotes the growth and reproduction of bacteria, thereby accelerating the formation of methemoglobin; on the other hand, high temperature accelerates the process of myoglobin oxidation reaction. Temperature has a positive correlation with the formation of methemoglobin, that is, with flesh color. It is determined that within a range of 3 to 30 ° C, the rate of oxidation of oxygenated myoglobin to methemoglobin increases 5 times for every 10 ° C increase, that is, Q10 is 5. In addition, temperature directly affects the activity of enzymes in the muscle and also has an important effect on flesh color.
High humidity in the environment can form a water vapor layer on the surface of meat, which affects the diffusion of oxygen and slows the oxidation of myoglobin. Low humidity and fast air flow speed up the formation of methemoglobin and accelerate the browning of the flesh.
6) other factors
In addition to the above five factors, light, freezing, salting, etc. will also affect the color of the meat. Light irradiation will increase the temperature of the meat surface, thereby promoting the formation of methemoglobin and darkening the color of the meat. Quick-frozen meat is lighter in color, because the ice crystals formed are small and the light transmittance is low, so it appears pale. Slow freezing looks crimson. Salt promotes the oxidation of flesh pigments and is not conducive to the maintenance of flesh color.
How to keep natural color of fresh meat in meat processing
In meat processing industry, by reducing the storage temperature, the change in fresh meat color can be delayed. In addition, you can also maintain the fresh meat color by vacuum packaging, modified atmosphere packaging, and adding antioxidants.
1) Vacuum packaging
In addition to freezing and refrigerating, vacuum packaging is currently the most commonly used measure for meat preservation. Vacuum packaging on the one hand can reduce bacterial reproduction and prolong the shelf life of fresh; on the other hand, it limits or reduces the formation of methemoglobin, keeping the meat’s myoglobin in a reduced state, showing a purple-red color, which can look like Fresh meat forms oxygenated myoglobin on the surface, which is bright red.
When choosing meat vacuum packing machines, meat processors always need to consider machine quality and output capacity. Shandong Kangbeite Food Packaging Machinery Co., Ltd. supplies top quality meat packaging machines with various output capacity, which fit wide range of production scale. You can choose double chamber vacuum packing machines for smaller business, or thermoforming packaging machines for massive production requirement.
2) Modified atmosphere packaging
Modified atmosphere packaging is to regulate the gas composition in the packaging bag or trays to inhibit the growth of aerobic microorganisms, thereby extending the storage time of meat. Modified atmosphere packaging also controls the oxygenation and oxidation of myoglobin, thereby regulating the color of meat. Without oxygen, the muscle myoglobin exists in a reduced state, showing a purple (red) color. Low oxygen (1%) is conducive to the formation of brown ferritin, while high oxygen is conducive to bright red oxygenated myoglobin. Protein formation. The gas composition of modified atmosphere packaging is various. The most commonly used are pure CO 2, CO 2 and O 2, and CO 2 and N 2 gas combination methods. When the CO2 reaches 25%, it can inhibit the growth of most bacteria, and the effect is best at 40% ~ 60%, but pure CO 2 packaging is not good for meat color, so most modified atmosphere packaging uses mixed gas, and CO2 Inhibits bacteria and maintains fresh meat color with O2.
(1) Vitamin E. Vitamin E is an antioxidant. Tests show that adding vitamin E to feed can effectively extend the retention time of meat color. This is mainly because vitamin E can reduce the oxidation rate of oxygenated myoglobin and promote the transfer of ferritin to oxygen. Myoglobin transformation.
(2) Vitamin C. It not only has anti-oxidation, but also has bacteriostatic effect, and can prolong the color retention period. Vitamin C injections have the same effect before animal slaughter.