Please use this identifier to cite or link to this item: https://hdl.handle.net/2440/106664
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Type: Journal article
Title: The effects of acid hydrolysis on protein biosurfactant molecular, interfacial, and foam properties: pH responsive protein hydrolysates
Author: Dimitrijev-Dwyer, M.
He, L.
James, M.
Nelson, A.
Wang, L.
Middelberg, A.
Citation: Soft Matter, 2012; 8(19):5131-5139
Publisher: Royal Society of Chemistry
Issue Date: 2012
ISSN: 1744-683X
1744-6848
Statement of
Responsibility: 
Mirjana Dimitrijev-Dwyer, Lizhong He, Michael James, Andrew Nelson, Liguang Wang and Anton P. J. Middelberg
Abstract: The success of hydrolysis in improving the functional foaming properties of surface-active proteins is usually attributed to three factors: decreased molecular size; increased hydrophobicity; and microchemical changes, specifically deamidation of glutamine and asparagine. Studying these individual factors is difficult using naturally-occurring proteins, as hydrolysate products are complex mixed systems, and the mechanisms of foam stabilization are likewise complex. To address this complexity we report studies of a recombinant protein (DAMP4) which comprises four peptide surfactant (DAMP1) molecules connected by acid-labile amino acid (Asp-Pro) linkers. Hydrolysis of DAMP4 under conditions of low pH and high temperature produced h-DAMP1, a mixture of deamidated variants of the chemically-synthesized DAMP1 peptide surfactant. By examining foaming performance of these molecules, we are able to isolate the effects of molecule size (DAMP1 vs. DAMP4) and deamidation (h-DAMP1 vs. DAMP1). Molecule size had little effect on foaming for the conditions studied. However, deamidation completely changed foaming behaviour, most likely due to alteration of interfacial charge structure (through deamidation of glutamine to glutamic acid) and consequent effects on thin-film stability. Good foaming was observed only at pH values away from the isoelectric points (pI) of the biomolecules where an electrostatic barrier to film rupture can occur. The addition of Zn²⁺ to DAMP4, h-DAMP1 and DAMP1 caused visible aggregation under all conditions, which assisted in stabilising foams only in situations where a net charge would be expected.
Rights: This journal is © The Royal Society of Chemistry 2012
DOI: 10.1039/c2sm25082a
Grant ID: http://purl.org/au-research/grants/arc/DP1093056
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Chemical Engineering publications

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