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

The 2S and 12S proteins of rapeseed were isolated and subsequently hydrolyz ed by pepsin or a combination of pepsin plus trypsin. The resulting hydroly sates had a 15% degree of hydrolysis and were purified by gel filtration ch romatography in order to obtain homogeneous peptide fractions. Three major fractions, having an average peptide chain length of 7.5-71 amino acids, we re recovered. Purified peptide fractions were acylated with butyric anhydri de and sulfamidated with p-toluenesulfonyl chloride. The degree of modifica tion was always higher than 90%. Emulsifying and foaming properties of nati ve and chemically modified peptides were studied and compared to those of s odium dodecyl sulfate (SDS) as standard. A peptide fraction from the 15% hy drolysis of the 12S protein exhibited the best foaming properties. After su lfamidation, this peptide fraction showed a foam formation similar to that of SDS. Whereas the attachment of toluene groups generally improved the sur face properties, the incorporation of an aliphatic chain of four atoms of c arbon 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 emulsio n.