Molecular size and aggregation behavior of Erwinia gum in aqueous solution

Abstract

Erwinia (E) gum, a stabilizer and thickening agent of food, is composed of glucose, fucose, galactose, and glucuronic acid (1 : 0.1 : 0.05 : 0.3 by molar ratio). The apparent weight-average molecular weight M w and intrinsic viscosity [] in 0.2 M NaCl aqueous solution were measured to be 7.83 ϫ 10 5 and 268 mL g Ϫ1 , respectively, by light scattering and viscometry. The aggregation behavior of E gum in aqueous solution was investigated by gel permeation chromatography (GPC) and dynamic light scattering. The results showed that 7.5% E gum exists as an aggregate, whose diameter is 12 times greater than single-stranded chain, in aqueous solution at 25°C, and the aggregates' content decreased with increasing temperature or decreasing polymer concentration. The aggregates at higher temperature were more readily broken than in exceeding dilute solution. GPC analysis proved that a significant shoulder, corresponding to a fraction of higher molecular weight due to chain aggregation, appeared in the chromatogram of E gum in 0.05 M KH 2 PO 4 /5.7 ϫ 10 Ϫ3 M NaOH aqueous solution (pH 6.0) at 35°C, and decreased with increasing temperature, finally disappeared at 90°C. The disaggregation process of E gum in aqueous solution can be described as follows: with increasing temperature, large aggregates first were changed into the middle, then disrupted step by step into single-stranded chains.

Effects of the thermal history and concentration on the aggregation of Erwinia gum in an aqueous solution

“…This indicates that the E gum formed aggregates in the aqueous solution and that the aggregates were decomposed gradually with increasing temperature, similar to the results of dynamic light scattering. 21 Figures 8 and 9 show that w ag and M w , respectively, of the aggregates of E-3 in a 0.2 M NaCl aqueous solution decreased with an increase in temperature. Obviously, the decrease of w ag and M w of the aggregates resulted in the decrease of the apparent M w of the E gum in the 0.2 M aque- whereas the decrease of M w means a decrease in N ap .…”

“…E gum is composed of glucose, fucose, galactose, and glucuronic acid (in a 1/0.1/0.05/0.3 molar ratio). 21,23 The E-gum aqueous solution (0.4 wt %) was centrifuged at 7000 rpm for 12 h to remove the waterinsoluble gum, was then concentrated by rotary evaporation at reduced pressure and room temperature, and was finally precipitated by acetone. The E-gum precipitate was washed eight times with acetone and then vacuum-dried for 7 days to obtain a white powder.…”

“…E gum has been proven to be an ideal thickening agent because of the formation of aggregates in aqueous solutions; these aggregates have been studied by dynamic light scattering, gel permeation chromatography (GPC), membrane osmometry, and viscometry in our laboratory. [21][22][23] However, the effects of temperature, heating time, and polymer concentration on the molecular weight, N ap , and the disaggregation of this natural polysaccharide have not yet been clarified. We investigated the aggregation behavior, those factors affecting the aggregation and disaggregation process for E gum in an aqueous solution, by multiangle laser light scattering (MALLS) and GPC combined with static light scattering (GPC-LS).…”

Aggregation and disaggregation of Aeromonas gum in an aqueous solution under different conditions

“…The heating could break the aggregates into single chains. 24,27,31 This phenomenon indicated that once the aggregates of A gum decomposed at relatively higher temperatures, they hardly reaggregated at 25°C, suggesting that the aggregation was thermally irreversible. Therefore, the A-gum solution that was heated to 90°C into disaggregates could keep the disaggregation state at room temperature.…”

“…25 E gum, an heteropolysaccharide acid produced by Erwinia mituyensis 5796, 26 is aggregated in a 0.2 M NaCl aqueous solution at low temperatures and is broken up at high temperatures. 24,27 Moreover, E gum in water exhibits an exceedingly high viscosity similar to that of xanthan, a viscosity-enhancing agent. 28 Therefore, clarifying the mechanism of aggregation and disaggregation and the affecting factors is essential for successful applications in food, oil drilling, pharmaceuticals, environment protection, and so on.…”