exposure to cold temperature could be counteracted by increasing the proportion of fatty
acyl chains having a higher degree of unsaturation and therefore a lower melting point.
Thus, the membrane will tend to remain fluid even at a lower temperature. An increase in
gel-phase lipid domains can result in the loss of compartmentalization. The differences in
the mobility properties of phospholipid acyl chains can cause packing imperfections at the
interface between gel and liquid crystalline phases, and these regions can become leaky to
calcium ions and protons that are highly compartmentalized. The membrane proteins are
also excluded from the gel phase into the liquid crystalline phase. Thus, during examinations
of membrane structure by freeze fracture electron microscopy, the gel-phase domains can
appear as regions devoid of proteins (Paliyath and Thompson, 1990).
3.2.3 Proteins
Fruits, in general, are not very rich sources of proteins. During the early growth phase of
fruits, the chloroplasts and mitochondria are the major organelles that contain structural proteins.
The structural proteins include the light-harvesting complexes in chloroplast or the respiratory
enzyme/protein complexes in mitochondria. Ribulose-bis-phosphate carboxylase/
oxygenase (Rubisco) is the most abundant enzyme in photosynthetic tissues. Fruits do not
store proteins as an energy source. The green fruits such as bell peppers and tomato have a
higher level of chloroplast proteins