Handbook of Food Science and Technology 3

2.1.3.
 Proteins 
There are three main types of proteins in the muscle: myofibrillar, 
sarcoplasmic and connective tissue protein. Table 2.5 shows the average 
protein composition of skeletal muscles.
 
Fish muscle 
Mammalian skeletal muscle 
Sarcoplasmic proteins 
(soluble fraction)
 
20–35 
30–35 
Myofibrillar proteins 
(poorly soluble fraction)
 
60–75 
50 
Stromal proteins 
(extracellular proteins)
 
3–10 
15–20 
Table 2.5.
Protein composition of meat and fish muscles
(in g per 100 g of total protein) (based on [LIN 94]) 
2.1.3.1.
 Muscle tissue proteins 
Soluble fraction: myoglobin 
Myoglobin is an essential element in the color of meat, which affects 
consumer purchasing decisions. Meat color is related to the quantity and 
quality (chemical state) of myoglobin. The fatness of the animal and the pH 
of the meat also play a role. The fish muscle most closely resembling meat in 
terms of myoglobin content is tuna. Similarly, the quality of bluefin tuna is 
also closely linked to the quality of its myoglobin. However, white muscle 
is more prevalent in other species of fish.
Myoglobin is a heteroprotein with a molecular weight of 18.7 kDa. It is 
very compact and belongs to the group of respiratory pigments. The 
molecule is composed of two parts: 
– a protein part (globin); 

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From Muscle to Meat and Meat Products 79 
– a non-protein part (heme), consisting of a tetrapyrrole (or porphyrin) 
ring that coordinates ferrous iron (Fe
2+
) in myogloblin or ferric iron (Fe
3+
) in 
metmyogloblin. The iron in the heme is coordinated to the four nitrogen 
atoms of the pyrrole rings and also to a nitrogen atom from a histidine 
residue. The sixth position (coordination site) for the iron is occupied by 
water in myoglobin and oxygen in oxymyoglobin.
Figure 2.7 shows the two primary myoglobin reactions affecting meat 
color.