Proteinaceous surfactants

Subsequent experimental work in this laboratory was aimed at the systematic development of an efficient method for isolating the proteinaceous surfactants, which help stabilize natural microbubbles, from both commercial agarose powder and from forest soil samples collected locally. Successful isolation of this glycopeptide fraction was eventually achieved (ref. 322), and the results obtained from an extended program of chemical analysis, to further characterize and compare chemically these proteinaceous surfactants from both natural substances, are described below. 

The isolated proteinaceous surfactants, obtained from commercial agarose powder and forest soil extract, were found to have extremely similar total amino acid compositions. Table 4.2 summarizes the amino acid values obtained from four determinations for each of the two surfactant preparations it can be seen that the rather unusual amino acid ratios obtained (among 17 different amino acids) for the two separate cases closely resemble one another. Specifically, in both of these cases the relative amounts of the different amino acids identified (excluding tryptophan which is completely destroyed during acid hydrolysis) were as follows glycine serine > aspartic acid (and/or aspara-... 

The striking similarity between the proteinaceous surfactants obtained from agarose powder and forest soil extract was further demonstrated by sodium dodecyl sulfate/polyacrylamide-... 

J.S. D Arrigo, Aromatic proteinaceous surfactants stabilize long-lived gas microbubbles from natural sources, J. Chem. Phys. 75 (1981)962-968. 

Proteinaceous Surfactants Prepared by Covalent Attachment of L-Leucine / -Alkyl Esters to Food Proteins by Modification with Papain... 

This enzymatic process may be applied to modifying protein functionality as well. Provided that a hydrophilic protein (substrate) and a highly hydrophobic or lipophilic amino acid ester (nucleophile) are used, it would be possible to obtain a product (P3 in Figure 1) with a structure such that hydrophilic and lipophilic regions in the molecule are localized from each other. It is expected, as a consequence, that a proteinaceous surfactant with an adequately amphiphilic function would be produced. 

The function of a surfactant depends on its hydrophilicity-lipo-philicity balance (HLB). Efficient emulsification of oil generally requires a low HLB, while the whipping characteristic arises at a larger HLB. This chapter is an attempt to prepare proteinaceous surfactants with different HLBs by the enzymatic attachment of amino acid esters with different lipophilicity. For this purpose L-leucine n-alkyl esters (Leu-OQ), the alkyl chain length, i, varying from 2 to 12, were used. As... 

Figure 4. Proposed amphiphilic structure for a proteinaceous surfactant...

Figure 6. Schematics of proteinaceous surfactant molecules arranged at an air-water interface (A) and at an oil-water interface (B) B, bound...

With a series of applications to well-known food products, we tested the suitability of the proteinaceous surfactants prepared from gelatin by the papain-catalyzed attachment of L-leucine n-alkyl esters. Using each of these surfactants we tried to prepare snow jelly, ice cream, mayonnaiselike food, and bread. 

This reaction, when applied to a mixture of a hydrophilic protein (substrate) and a lipophilic L-leucine n-alkyl ester (nucleophile), can produce a proteinaceous surfactant with proper amphiphilic functions (see Figure 4). 

Several of the proteinaceous surfactants prepared in the present work can be used in food applications. In particular, gelatin-Leu-OC6 and gelatin-Leu-OCi2 were useful as ingredients for selected food items the former for snow jelly (see Table VIII) and the latter for ice cream (see Table IX), mayonnaise (see Table X), and bread (see Table XI). 

Arai et al. [141] described a particular enzymatic reaction for producing a surface-active protein. A highly hydrophobic amino acid was covalently bound to a hydrophilic protein in an enzyme-catalyzed process for this purpose. The covalent attachment of L-Leu n-alkyl ester to gelatin in the presence of papain as catalyst resulted in a proteinaceous surfactant [141,142] with very good emulsifying properties. 

Watanabe M, Toyokawa H, Shimada A, Aral S. Proteinaceous surfactants produced from gelatin by enzymatic modification evaluation of their functionality. J Food Sci 1981 46 1467-1469. 

Shimada A, Yazawa E, Arai S. Preparation of proteinaceous surfactants by enzymatic modification and evaluation of their functional properties in a concentrated emulsion system. Agric Biol Chem 1982 46 173-182. 

Watanabe et al. [35] tried to use a more hydrophilic and commercially available protein, gelatin, as a substrate instead of asi-casein. The lypophiles used in this case were luecine n-alkyl esters with alkyl carbon numbers ranging from 2 to 12 in order to produce proteinaceous surfactants with a different hydrophilicity-lipophilicity balance. All of the enzymatically modified gelatin... 

The covalent attachment of fatty acids to protein molecules is a more direct method for producing amphoteric proteins than other physicochemical and enzymatic modifications. The attached fatty acyl chains fortify the amphiphilic structure, thereby leading to the formation of a polymerlike surfactant. Such proteinaceous surfactants are efficiently adsorbed at the interfaces, because the hydrophobic moiety rapidly penetrates into the hydrophobic layer and anchors the hydrophilic protein portions. Despite the importance of the covalent attachment of hydrophobic groups, enzymatic modifications are extremely more limited than chemical modifications. 

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