A new method for the quantification of polysaccharide structural domain: Rapid quantification of type II arabinogalactan based on Yariv reagent.

Type II arabinogalactans (AG-II) are biologically significant plant polysaccharides that exist both in free form and as side chains covalently bound within complex polysaccharides. However, the specific quantification of these bioactive AG-II domains in complex matrices remains a critical analytical challenge. Although the β-glucosyl Yariv reagent is a classic chemical reagent used in plant biology for the qualitative identification of arabinogalactan proteins (AGPs), its quantitative potential has been constrained by the lack of standardized protocols. Here, we established a spectrophotometric method based on the Yariv reagent for AG-II quantification. The method demonstrated high sensitivity and reproducibility, achieving a limit of detection (LOD) of 0.25 μg/mL, a limit of quantification (LOQ) of 0.75 μg/mL, and a recovery of 101.95%, indicating excellent applicability. To address the response discrepancy between the generic standard and the specific AG-II analyte, we implemented a "dual-standard strategy" and determined a conversion factor (1.188), successfully establishing a quantitative link between the accessible standard and the target AG-II polysaccharides. The method was applied to analyze Lycium barbarum samples from various origins, successfully revealing significant variations in the content of AG-II across different geographical regions, providing a novel technical pathway for the precise quantification of AG-II.