Adsorption of Methyl Orange on Starches

Abstract

Adsorption characteristics of methyl orange were investigated on kudzu, sweet potato, corn, rice, wheat, potato and snake gourd starches. No adsorption of methyl orange, an anionic dye, was observed on potato starch and snake gourd starch because of the presence of phosphate esters. Adsorption isotherms were found to fit both the Langmuir equation and Freundlich equation in a11 others. The degree of adsorption by kudzu, sweet potato, corn and wheat starches was related to the number of hydroxyl groups. We suggested methyl orange was confined to a monolayer on surface hydroxyl groups of the starches. sorbed on starch was calculated from decrease in absorbance of the supernatant. Specific surface areaSpecific surface area of starch was measured by the method described previously . Water and nitrogen surface areas of starch were calculated from the moisture sorption isotherm at 20°C and the nitrogen adsorption isotherm at liquid nitrogen temperature, respectively. INTRODUCTIONSTARCH can adsorb dyes, and adsorption capacity depends on the species of starch (Fujii et al., 1986). Adsorption of dye on starch is important in staining colors on bean-jam cake and starch confectioneries. The extent of adsorption of anionic dyes on starches was related to the ratio of amylopectin to amylose (Zografi and Mattocks, 1963;Carroll and Cheung, 1962). Schoch and Maywald (1956) showed potato starch did not adsorb anionic dyes because of the presence of phosphate esters. Vickerstaff (1954) proposed adsorption of dye occurred at the hydroxyl groups of starch.Estimation of starch content in kudzu starch products by a methyl orange adsorption method was reported by Boki et al. (1989). Amount of methyl orange adsorbed on sweet potato starch was greater than that on kudzu starch. The purpose of our study was to elucidate factors responsible for the difference in amount of methyl orange adsorbed on kudzu starch and sweet potato starch. Adsorption characteristics of methyl orange on corn, wheat, potato and snake gourd starches were also studied on the basis of specific surface area, neutral hydrophilic sites, pore volume, pore size distribution, phosphate content and amylose content.

Suitability of Starch Granule Porosity for Biosynthesis and Amylolysis Susceptibility

“…the fraction of the granule accessible to a given molecule, has been determined by physical adsorption of gas or by determination of mercury porosity [6]. These techniques for determining porosity in the dry state can easily be applied to solids.…”

Adsorption of Cationic Methylene Blue and Anionic Methyl Orange by Crude Drug Starches

“…The saturated amounts of ferric chloride adsorbed by 4 kinds of starches were not correlated to particle size. 6) There was no correlation between amounts of MO adsorbed by 7 kinds of starches and their specific surface area, 4) which were measured using the nitrogen adsorption method. It is suggested that the amounts adsorbed are not dominated by the surface area of the crude drug starch.…”

“…4) In this study, the factors responsible for the difference in amounts of cationic methylene blue (MB) and anionic methyl orange (MO) adsorbed were discussed, and a crude drug starch superior in the capacity to adsorb both cationic and anionic dyes was identified.…”

“…Both the Langmuir and Freundlich equations were applicable to the isotherm of anionic dye. 4) However, the adaptability of an adsorption equation has been evaluated based on a partial or uniform weighting of the amount adsorbed and residual concentration. 4 6) In the present study, a statistical analysis on the isotherm was performed using Akaike s information criterion (AIC) value 7) to solve this problem.…”

“…4) The adsorption properties of crude drug starches were investigated in an attempt to make profitable the use of starch from the extracted residues.…”