Emulsifying and foaming properties of native and chemically modified peptides from the 2S and 12S proteins of rapeseed (Brassica napus L.)

Abstract

The 2S and 12S proteins of rapeseed were isolated and subsequently hydrolyzed by pepsin or a combination of pepsin plus trypsin. The resulting hydrolysates had a 15% degree of hydrolysis and were purified by gel filtration chromatography in order to obtain homogeneous peptide fractions. Three major fractions, having an average peptide chain length of 7.5-11 amino acids, were recovered. Purified peptide fractions were acylated with butyric anhydride and sulfamidated with ptoluenesulfonyl chloride. The degree of modification was always higher than 90%. Emulsifying and foaming properties of native and chemically modified peptides were studied and compared to those of sodium dodecyl sulfate (SDS) as standard. A peptide fraction from the 15% hydrolysis of the 12S protein exhibited the best foaming properties. After sulfamidation, this peptide fraction showed a foam formation similar to that of SDS. Whereas the attachment of toluene groups generally improved the surface properties, the incorporation of an aliphatic chain of four atoms of carbon was detrimental in most of the cases. On the other hand, none of the native or hydrophobized peptide fractions was able to form a stable emulsion.Paper no. J9679 in JAOCS 78, 235-241 (March 2001). KEY WORDS:Chemical modification of peptides, cruciferin, enzymatic hydrolysis of proteins, foaming and emulsifying properties, napin.Proteins are recognized to be much more than a simple source of nutrients. Because of their amphiphilic nature, proteins are also involved in functional aspects of foods, such as the formation of emulsions and foams. Proteins can be adsorbed at oil-water and air-water interfaces, decreasing surface tension values, and, hence facilitating the formation of emulsions and foams. This adsorption is believed to occur in three distinct steps. First, protein molecules diffuse to the subsurface just below the interface; second, they are adsorbed; and finally, they unfold at the interface to adopt a thermodynamically optimized conformation. In addition, proteins form a continuous viscoelastic film around the oil droplets or air bubbles that stabilize emulsions and foams (1). Therefore, the formation of a stable foam or emulsion is a complex phenomenon that depends on the physicochemical characteristics of the protein, such as net charge, solubility, hydrophobicity, flexibility, etc.(2). Protein structure can be intentionally modified in order to improve these surface properties. Such protein modifications can be easily performed by enzymatic or chemical treatments. Enzymatic hydrolysis improves the solubility of proteins, even if the degree of hydrolysis is low. The increase of ionic groups after hydrolysis makes the peptides more soluble with respect to the original protein throughout the pH range (3,4), and consequently enhances the diffusion of the protein and facilitates the formation of emulsions (5). In addition, enzymatic hydrolysis can increase the surface hydrophobicity of peptides by exposing hydrophobic groups that are generally buried in the core of nat...

Foaming Properties of Acylated Rapeseed (Brassica napus L.) Hydrolysates

“…These values are closer to that of BSA (4.96 ml) than to that of SDS (6.48 ml) and equivalent to data obtained for other lipophilized peptides (11). In contrast, the drainage FIG.…”

“…Previous results obtained by our group show that hydrophobized peptides are very promising foaming agents with a behavior, in same cases, comparable to that of standard surfactants (11). Consequently, the aim of this work is to continue with the preparation and study of surface properties of new hydrophobized peptides generated from inexpensive raw materials that can make possible a large-scale application of the end product, for example, as a green surfactant.…”

Comparison of biological value and technological properties of oil seed proteins

“…The rape protein isolate had also highest foam and emulsifying capacities comparing with sunflower and soy protein isolates (Figure 4, b), though most rape protein isolates were reported to have poor foaming capacity [47,48]. At the same time foam of rape protein suspension was unstable.…”

Effect of pH and NaCl on the Emulsifying Properties of a Napin Protein Isolate

“…In contrast, Wu and Muir [5] reported napin to have lower EAI values, formed larger oil droplets and had lower stability than cruciferin, and was a major factor contributing to the inferior functionality of mixed canola protein isolates. And, Malabat, Nchez-Vioque, Rabiller & Guguen reported napin could only form an emulsion when chemically modified [22]. In the present study, the overall objective was to investigate the effect of pH and NaCl on the emulsifying properties of a napin protein isolate.…”