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Oxidative stress associated with the imbalance between the production of reactive oxygen species and the antioxidant capacity. It is important to select and employ a stable and rapid method to assay antioxidant activity. The aim of this study was to accurately predict the antioxidant activity of S. sagittaria. L polysaccharide (Sap) by miniature fiber near-infrared (NIR) spectroscopy combined with chemometrics. The optimal extraction conditions of Sap through multi-mode divergent ultrasound assisted method were as follows: ultrasonic power 180 W, liquid-to-material ratio 40 mL/g, extraction time 16 min and extraction temperature 77 ℃, and the yield of Sap was 21.24%. The molecular weight of Sap was approximately 120.5 kDa, and its monosaccharide components predominantly consisted of Rha (15.7%), Ara (12.9%), Man (1.6%), Glc (36.4%), and Gal (33.4%). The application of NIR spectroscopy for determination of DPPH, ABTS and hydroxyl radical scavenging rate of Sap solution (0.125-1 mg/mL), and the coefficient of prediction (Rp) were 0.9568, 0.9667 and 0.9652, respectively. In developing model, five spectra preprocessing methods and three different linear regressions tools (i.e., partial least squares (PLS), interval Partial least Squares (iPLS), synergy interval partial least square (Si-PLS)) were optimized to improve the predictability and stability of the models. The overall results revealed the miniature fiber NIR spectroscopy with PLS and Si-PLS regression tools showed better predictive property, which has the potential to measure antioxidant activity in Sap.

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