Macromolecular Dimensions and Mechanical Properties of Monolayer Films of Sonorean Mesquite Gum
✍ Scribed by Yolanda L. López-Franco; Miguel A. Valdez; Javier Hernández; Ana M. Calderón de la Barca; Marguerite Rinaudo; Francisco M. Goycoolea
- Publisher
- John Wiley and Sons
- Year
- 2004
- Tongue
- English
- Weight
- 227 KB
- Volume
- 4
- Category
- Article
- ISSN
- 1616-5187
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✦ Synopsis
Abstract
Summary: Mesquite gum sourced from Prosopis velutina trees and gum arabic (Acacia spp.) were characterized using light scattering and Langmuir isotherms. Both gum materials were fractionated by hydrophobic interaction chromatography, yielding four fractions for both gums: FI, FIIa, FIIb and FIII in mesquite gum and FI, FII, FIIIa and FIIIb in gum arabic. In mesquite gum, the obtained fractions had different protein content (7.18–38.60 wt.‐%) and macromolecular dimensions ($\overline M _{\rm w}$ ≈ 3.89 × 10^5^–8.06 × 10^5^ g · mol^−1^, R~G~ ≈ 48.83–71.11 nm, R~H~ ≈ 9.61–24.06 nm) and architecture given by the structure factor (R~G~/R~H~ ratio ≈2.96–5.27). The mechanical properties of Langmuir monolayers at the air‐water interface were very different on each gum and their fractions. For mesquite gum, the most active species at the interface were those comprised in Fractions IIa and IIb and III, while Fraction I the π/A isotherm lied below that of the whole gum. In gum arabic only Fraction III developed greater surface pressure at the same surface per milligram of material than whole gum. This is rationalized in terms of structural differences in both materials. Mesquite gum tertiary structure seems to fit best with an elongated polydisperse macrocoil in agreement with the “twisted hairy rope” proposal for arabinogalactan proteoglycans.
Compression isotherms of gum arabic and mesquite gum.
imageCompression isotherms of gum arabic and mesquite gum.