Proteinaceous Surfactants Produced from Gelatin by Enzymatic Modification: Evaluation for Their Functionality

Proteinaceous surfactants were prepared by applying the “one-step process” which permitted covalent incorporation of amino acid esters directly into proteins during treatment with papain. Gelatin was used as a hydrophile and n-alkyl esters of L-leucine as lipophiles. Each of the hydrophile-lipophile mixtures was incubated with papain under the following conditions: medium, 1M carbonate (pH 9) or a 20:80 mixture of acetone-1M carbonate (pH 9) containing 2 mM 2-mercaptoethanol; concentration of gelatin in the medium, 33% (w/w); L-leucine ester vs gelatin ratio, 0.1 mole/100g; papain vs gelatin, 1% (w/w); incubation period, 15 min; and temperature, 37°C. The enzymatic reaction was stopped by adding 1N HCl and the product purified by dialysis followed by washing with hot acetone or dichloromethane to remove low-molecular species. Each product was found to be a mixture of peptides having a wide range of molecular weight, with an average at approximately 7,500 daltons. The amounts of the alkyl moieties covalently incorporated were in a range 1.1–1.2 moles per 7,500g of the products. Their surfactancy varied depending particularly on the carbon number of the alkyl moiety; the products resulting from the incorporation of C₄–C₆ alkyl esters of leucine showed greater whippability, whereas the incorporation of the C₁₀–C₁₂ alkyl esters gave products having a higher ability to stabilize an o/w type emulsions.