Optimization of Decolorization Process for Crude Polysaccharides from Vicia villosa Roth and Its Antioxidant and Growth-Promoting Activities

Vicia villosa Roth is an excellent green manure crop and offers promising applications in green agricultural production and bioactive substance exploitation. In this study, crude polysaccharides (VVP) were prepared from V. villosa using water extraction and alcohol precipitation. Single-factor experiments combined with Box–Behnken response surface methodology were employed to optimize the decolorization process of VVP with AB-8 macroporous resin. The optimal conditions were determined as follows: a resin-to-sample ratio of 1:140 (m/m), decolorization temperature of 78 °C, and a decolorization time of 300 min. Under these conditions, the decolorization rate reached 67.36% and the polysaccharide retention rate was 61.85%, with a relative error of only 2.1% between the model-predicted and experimental values. In vitro antioxidant assays showed that VVP possessed strong antioxidant activity. At a concentration of 2 mg/mL, the DPPH radical scavenging rate of VVP was 91.9%, and the ABTS+ radical scavenging rate reached 96% at 8 mg/mL. Moreover, VVP promoted crop growth and markedly alleviated the inhibition of salt stress on root development. To the best of our knowledge, this is the first report demonstrating that V. villosa crude polysaccharide extract simultaneously possesses strong antioxidant activity, salt-stress alleviation capacity, and plant growth-promoting effects, highlighting their potential as natural antioxidants and agricultural biostimulants.