Food Emulsifiers and Stabilizers - Food Shelf Life Stability: Chemical, Biochemical, and Microbiological Changes - page 241

TABLE 7.12
Changes in Surface Hydrophobicity due to
Thermal Denaturation a

Hydrophobicity b

Temperature

(°C) Ov c 7S c κ -C c BLG c BSA c

20 10 260 430 2700 3200

50 10 260 480 2700 3100

60 10 270 600 2600 3000

70 15 400 750 2400 2500

80 1950 500 1050 1500 2000

a 0 to 2 wt% protein solutions in 0.1 M phosphate buffer (pH 7.4)
heated at a rate of 1°C min -1 from 20 to 80°C; and then immediately
cooled to 20°C after reaching the given temperature (data from
Kato, A., Osako, Y., Matsudomi, N., and Kobayashi, K., Agric. Biol.
Chem., 47, 33, 1983).
b Determined by fluorescent probe method using cis -parinaric acid.
c Abbreviations: Ov = ovalbumin; 7S = 7S soy globulin;

κ -C = κ -

casein; BSA = bovine serum albumin; BLG = β -lactoglobulin.

TABLE 7.13
Consequences of Alterations of Net Charge in the Chemical
Modification of Proteins, on the Surface Activity of the Protein

A. Isoelectric point changes.

B. Changes in protein associations, e.g., hydrophobic, electrostatic.

C. Randomness in protein structure due to electrostatic repulsion.

D. Stabilization against heat-induced denaturation (?).

E. Enhanced surface hydrophobicity or hydrophilicity.

F. Increased amphiphilic behavior of proteins, i.e., more surface-active (detergent-like).

affect the flexibility of the protein and as a result to change its hydrophobicity (BSA,
lysozyme, ovalbumin, -casein, and BLG); 172 and (3) thermal denaturation, which

affects the protein folding and protein association ability and alters the hydropho-
bicity of the protein ( Table 7.12 ).
Among the intrinsic modification it is worth noting that some chemical deriva-
tizations serve as a way of enhancing many of the functional surface characteristics
of the protein ( Table 7.13 ).
Some of the most common chemical modifications 7,173,174 are listed in Table 7.14
and a good example of the effect of the activity of BSA is shown in Table 7.15 . Of
all the chemical processes, acylation of lysine residues has been studied by many
investigators. The effect of both of these procedures is to increase the solubility of
proteins, thereby improving their functional properties in general, and their emulsi-
fying and foaming properties in particular ( Figure 7.9 ).

κ