Analysis of Intermolecular Interaction among Pectin Molecules in Aqueous Sugar Solutions

Abstract

Although the viscosity of aqueous solution of high methoxyl pectin is known to increase drastically when sugars coexist, the detailed mechanism for the increase in viscosity was not fully understood. Therefore, the viscosity of citrus and apple pectin solutions with various sugars compositions was measured with temperature varying from 5 to 40℃ to analyze the intermolecular interactions among pectin molecules. For single-composition pectin solutions, the activation energy for viscosity, E a , increased from 17.5 to 31.9 kJ/mol with an increase in pectin concentration up to 2% for the case of citrus pectin, reflecting the increase in pectin-pectin interaction. For pectin solutions with coexisting sugars, E a increased more with increasing sugar concentration. When compared at the same water activity, the increase in E a is also dependent on the type of sugar. Sugars with stronger solvent-ordering activity produced greater increases in E a . These results suggest that sugars increase the pectin-pectin interaction both through their own hydration effect, which enhances the hydrogen bonding among pectin molecules, and through the solventordering effect to enhance the hydrophobic interaction.

Analysis of Apparent Viscosity of Aqueous Macromolecule Solutions Containing Sucrose

“…the same A w range, E a for the sucrose solution increased from 17.5 to 22.1 kJ/mol (Sato and Miyawaki, 2008). Table 2 summarizes the present results of the apparent viscosity measurement of the aqueous macromolecule solution containing sucrose.…”

“…E a is dependent on the concentration of the macromolecule. As for the citrus pectin solution, the E a measured was very close to that of pure water in a dilute solution and increased along with an increase in the pectin concentration (Sato et al, 2008), showing an increase in pectin-pectin interactions. Figure 4 shows the effect of the coexistence of sucrose on η a H of the macromolecule solutions at 25℃.…”

“…suggesting that the coexistence of sucrose causes an increase in the intermolecular interactions among macromolecules. As for pectin, inter-macromolecular interaction comprises hydrogen bonding and hydrophobic interaction (Oakenful and Scott, 1984), both of which have been reported to increase by the coexistence of sugars (Sato and Miyawaki, 2008). For xanthan, −d η a sp /d A w interestingly gave a negative value, suggesting that the coexistence of sucrose weaken the intermacromolecular interactions in this case.…”

“…1. Open cross symbols ( ) with a smooth solid line correspond to the sucrose solution (Sato et al, 2008). suggesting that the coexistence of sucrose causes an increase in the intermolecular interactions among macromolecules.…”

“…Viscosity measurement is a method used to analyze inter-macromolecular interactions in solutions. Moreover, inter-macromolecular interactions are affected by the coexistence of low-molecules, which also affects water activity (A w ) (Sato et al, 2004;Sato and Miyawaki, 2008).…”