Biomedical Engineering Reference
FIGURE 7.9 Effect of pH on the emulsifying activity of various types of modified BSA.
Optical density at 550 nm is plotted against pH for diluted solution (pH 7.0, 0.1M NaCl) and
an oil phase volume fraction of 0.6. The urea-denatured sample was obtained by treating BSA
with urea for 6 h at 37°C. The reduced sample was obtained by treating BSA with 0.01 M
dithiothreitol for 4 h at 40°C. Acylation was accomplished with 10:1 ratio by weight of
anhydride to protein at pH 8 to 9 for 1 h at 25°C. (From Waniska, R. D., Shetty, J. K., and
Kinsella, J. E., J. Agric. Food Chem., 29, 826, 1981. With permission.)
proteins. Partial hydrolysis of these proteins under well-controlled conditions pro-
duce emulsifying and whipping agents for food processing, and many of these are
produced on an industrial scale. Some of the industrial produced protein hydrolysates
exhibit excellent emulsifying properties. 176 This is evaluated by gradually adding
soybean oil to an aqueous solution of protein hydrolysate under controlled conditions
until the resulting emulsion reverts from an oil-in-water to a water-in-oil system.
Other protein hydrolysates have functional properties such as whipping expansion
and foam stability. 177
More sophisticated processes include attachment of amino acid esters to improve
hydrophobicity. 178 An excellent example is the dramatic change in enzymatically mod-
ified gelatin (EMG). Such modified proteins (EMG-1 and EMG-6) were shown to
significantly improve the quality of food products such as mayonnaise, baked bread,
and ice cream by changing the emulsification capacity (efficiency) of the proteins.