Effect of Surfactant Structure on the Pasting Properties of Wheat Flour and Starch Suspensions

Abstract

Cereal Chem. 82(1):44-52Systematic studies were performed on the effect of the surfactant alkyl chain length (10-16 carbon atoms) and the head group charge/structure (anionic, cationic, nonionic) on the pasting properties of wheat flour and starch aqueous suspensions by means of a Rapid Visco Analyser (RVA). An excellent agreement was observed between the effect of surfactants on the onset temperature of the pasting process (PT) and the time to reach peak viscosity (t peak ) of wheat flour and wheat starch suspensions. Moreover, a correlation was found between the effect of different surfactants on these two parameters. With the exception of the cationic surfactants (alkyl trimethyl ammonium bromides), the effect of surfactants (alkyl sulfates, maltosides, monoglycerides, and sucrose esters) was found to be strongly dependent on the surfactant chain length. Shorter chain surfactants (C10-C12) induced an earlier pasting, while longer chain surfactants (C14-C16) had the opposite effect. The effect of surfactants on PT and t peak of flour suspensions was enlarged when the surfactant concentration was increased from ≈1% to 15% (w/w) on a dry starch basis.When heated above a characteristic temperature in an excess of water, native starch granules undergo gelatinization. This process, which can be regarded as the disruption of the molecular order within the granule (loss of granule birefringence and crystallinity), results in the swelling of the starch granules and the leaching of the linear fraction of the starch polysaccharides (amylose). In concentrated aqueous suspensions of native starch, temperatureinduced swelling and amylose leaching lead to the formation of viscous pastes. These pastes are usually regarded as composite materials built up from a continuous polysaccharide phase with swollen starch granules as fillers. A sharp increase of the suspension viscosity, which is usually of a few orders of magnitude, takes place at the so-called pasting temperature (PT) and characterizes the onset of the pasting process.Surfactants (amphiphilic surface active molecules) are well known for their ability to affect different aspects of the starch gelatinization process and to ultimately modify the properties of starch-based products. In practice, surfactants are usually added to starch suspensions to modify their pasting properties as well as the viscosity and viscoelastic behavior of the resulting pastes and gels.The presence of native amphiphilic molecules as polar lipids (lysophosphatidyl choline, digalactosyl diglycerides, and free fatty acids) has been suggested to be associated with the higher pasting temperatures of wheat starches of high lipid contents (Eliasson et al 1981). It has also been related to the restricted amylose leaching of wheat and other cereal starches in comparison to other nonlipidcontaining starches (Doublier 1987). On the other hand, numerous studies have shown that the effect of added surfactants on the PT of starch suspensions can be diverse. In this sense, early studies by Osman and Dix (1960...

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