66 Handbook of Food Science and Technology 3
minerals and vitamins. However, their lipid and
water contents are quite
different.
The distribution of fat varies significantly in fish and meat. Lipids in oily
fish are primarily located in the muscle tissue, whereas they are mostly
contained in the liver of white fish. Lipids in meat can be intramuscular
(marbled), but are mainly extramuscular: this
includes subcutaneous or
external fat and visceral or internal fat. The overall biochemical
composition, in particular the lipid content of the muscle, refers here to the
composition of the skeletal muscle. Only intramuscular fat will be taken into
account, as subcutaneous (often removed during slaughter) and visceral fat
are generally not consumed.
2.1.1.
The structure and composition of meat and fish muscle
2.1.1.1.
Tissue structure
Meat
Meat and meat products vary significantly.
This is demonstrated by the
fact that there are almost 900 terms to define these products. Even if meat
were restricted to only muscle, there would still be a wide diversity; more
than 100 muscles with different structures and compositions are found on a
carcass and each muscle is itself heterogeneous.
The carcass of terrestrial animals consists of several types of tissue:
muscle, connective tissue, fat, blood, nerves and bones. Each contributes to
the sensory quality of the meat: muscle and connective tissue to tenderness,
blood
tissue to color, fatty tissue to flavor and so forth. Bone tissue is
generally not consumed, except in minced meat where a small proportion of
bone is permitted by law.
Animals have two main types of muscles: striated and smooth muscle.
They differ not only in their fibrous or non-fibrous appearance, clearly
visible under an optical microscope, but also in their color: smooth muscle is
white whereas striated muscle tends to be red. However,
white striated
muscle exists such as the pectoral muscle of chickens for example. Smooth
muscle is mainly found in the organs (stomach, intestines, etc.) and is
generally not consumed as meat. As a result,
we will focus mainly on
striated muscle.
From Muscle to Meat and Meat Products 67
Muscle tissue
Muscle tissue is highly differentiated and specialized to perform different
tasks. It is composed of fibers with metabolic or contractile properties, which
are held together by connective tissue. The main chemical component of
connective tissue is collagen. The typical characteristics of fibers are based
on the relative proportion of the constituent elements:
myoglobin, inter-
fibrous lipids, enzymes and so on. Thus, the chemical composition of a
muscle depends on the relative proportion of each type of constituent fiber,
but also the relative structure of the connective tissue (endomysium,
perimysium, epimysium and tendon; Figure 2.1).
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