Effects of Citric Acid on the Viscoelasticity of Cornstarch Pastes
Effects of Citric Acid on the Viscoelasticity of Cornstarch Pastes
MADOKA HIRASHIMA, RHEO TAKAHASHI,
AND
KATSUYOSHI NISHINARI*
Department of Food and Human Health Sciences, Graduate School of Human Life Science, Osaka City University, Sumiyoshi, Osaka 558-8585, Japan
The effects of citric acid on the rheological properties of cornstarch pastes were studied by steady shear and dynamic oscillatory viscoelasticity, intrinsic viscosity measurements and microscopic observation. The pH of cornstarch dispersion was adjusted between 6.0 and 3.0. The viscosity of the pastes was increased by lowering the pH (between 5.5 and 3.6), while the viscosity of samples with pH below 3.5 decreased further than that of the control (pH ) 6.3). Citric acid promoted the collapse of starch granules; however, adding excessive citric acid led to the hydrolysis of glucose chains. No decrease in the viscoelasticity was observed for cornstarch pastes by adding acid at 25 °C after gelatinization.
KEYWORDS: Cornstarch; viscoelasticity; citric acid; pH
INTRODUCTION
Starch has been widely used as a thickener, stabilizer, or gelling ingredient in the food industry. The main constituents of starch are amylose and amylopectin, which consist of linked R-D-glucose residues that make large polysaccharide molecules. Starch is present in the form of granules, which are not soluble in water. When starch is heated in water, the starch granules swell and rupture. Amylose and amylopectin can be leached out from the granules, and the starch suspension becomes a viscous paste. This process is known as gelatinization. Starch has been added to many kinds of food using this property. To overcome the disadvantages of native starches such as its gummy or cohesive texture and the formation of rigid and opaque gels, many kinds of modified starches have been designed. Acid-hydrolyzed starch is one of them. Because starch is hydrolyzed by acid, aqueous hydrochloric acid is used to make acid-hydrolyzed
MADOKA HIRASHIMA, RHEO TAKAHASHI,
AND
KATSUYOSHI NISHINARI*
Department of Food and Human Health Sciences, Graduate School of Human Life Science, Osaka City University, Sumiyoshi, Osaka 558-8585, Japan
The effects of citric acid on the rheological properties of cornstarch pastes were studied by steady shear and dynamic oscillatory viscoelasticity, intrinsic viscosity measurements and microscopic observation. The pH of cornstarch dispersion was adjusted between 6.0 and 3.0. The viscosity of the pastes was increased by lowering the pH (between 5.5 and 3.6), while the viscosity of samples with pH below 3.5 decreased further than that of the control (pH ) 6.3). Citric acid promoted the collapse of starch granules; however, adding excessive citric acid led to the hydrolysis of glucose chains. No decrease in the viscoelasticity was observed for cornstarch pastes by adding acid at 25 °C after gelatinization.
KEYWORDS: Cornstarch; viscoelasticity; citric acid; pH
INTRODUCTION
Starch has been widely used as a thickener, stabilizer, or gelling ingredient in the food industry. The main constituents of starch are amylose and amylopectin, which consist of linked R-D-glucose residues that make large polysaccharide molecules. Starch is present in the form of granules, which are not soluble in water. When starch is heated in water, the starch granules swell and rupture. Amylose and amylopectin can be leached out from the granules, and the starch suspension becomes a viscous paste. This process is known as gelatinization. Starch has been added to many kinds of food using this property. To overcome the disadvantages of native starches such as its gummy or cohesive texture and the formation of rigid and opaque gels, many kinds of modified starches have been designed. Acid-hydrolyzed starch is one of them. Because starch is hydrolyzed by acid, aqueous hydrochloric acid is used to make acid-hydrolyzed
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