Molecular size and aggregation behavior of Erwinia gum in aqueous solution

✍ Scribed by Lina Zhang; Xiaojuan Xu; Mei Zhang; Jinghua Chen; Diya Meng; Liwei Ren; Hideki Iijima

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 145 KB
• Volume: 75
• Category: Article
• ISSN: 0021-8995
• DOI: 10.1002/(sici)1097-4628(20000222)75:8<1083::aid-app13>3.0.co;2-t

✦ Synopsis

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.