Foam stability, effect hydrolysis

The emulsifying activity of proteins [143] increased in the pH range of 2-9 [144] upon hydrolysis of soy proteins. Emulsifying capacity was also increased by hydrolysis of soy. Proteolysis of soy protein had no effect on foam stability [144,118], but hydrolysis of zein increased foam stability [145]. 

There have been a limited number of studies on the effects of enzymic modification of protein concentrates on functional properties other than solubility. Studies on functional properties, as modified by enzymic treatments, emphasize foam formation and emulsifying characteristics of the hydrolysates. Treatment of chicken egg albumen alters the functional properties of the egg proteins in terms of foam volume and stability and the behavior of the proteins in angel food cakes (25). Various proteolytic enzymes were used to degrade the egg albumen partially. However, proteolytic enzyme inhibitors indigenous to the egg proteins repressed hydrolysis of the egg proteins compared with casein. 

To preserve beer colloidal stability, brewers usually remove haze-active materials [34]. To get rid of haze-active proteins, precipitation with tannic acid, hydrolysis with papain and adsorption to bentonite [35] or silica gel [36, 37] are very effective, but unfortunately in some cases, such procedures also remove foam proteins. To remove haze-active polyphenols, the most usual way is adsorption to polyvinylpolypyrrolidone-PVPP. Because of the structural analogy between these compounds and proline [38], pyrrolidone rings bind polymerized flavanoids through hydrogen and ionic bonds. 

Their compatibility with other surfactants, electrolytes, and hard-water ions is excellent. Their stability to oxidizing agents, hydrolysis, acids, and alkalis is also remarkable. These surfactants are good emulsifiers and show optimal wetting and detergency under alkaline pH. They are good foamers at neutral and alkaline pH but lose their foaming properties under acidic conditions (i.e., behave essentially as cationics). They are substantive to surfaces and provide antistatic effects. They provide skin and eye irritancy reduction in combination with anionics. 

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