Structural Elucidation and Bioactivity Assessment of Lignin Mildly Extracted from Root and Tuber Crop Byproducts Using Γ-Valerolactone

In this research, the utilization value of lignin from six types of root and tuber crop byproducts using the solvent fractionation method with γ-valerolactone (GVL) was elucidated based on a comparative analysis with commercially alkali lignin in terms of structural composition and bioactivities. Fourier transform infrared spectroscopy and nuclear magnetic resonance results showed minimal structural degradation of GVL in extracting lignin. Specifically, the phenolic hydroxyl content of lignin from sweet potato vines was as high as 0.31 mmol/g. Bioactivity results showed the antioxidant activity of cassava stalk lignin reached 65 g Trolox equivalent per 100 g of dry weight, and the UVB blocking rate of potato residue lignin reached 86%. Lignin obtained from sweet potato byproducts completely inhibited the growth of Escherichia coli and Staphylococcus aureus at 6 mg/mL. This study suggested that lignin from these agricultural waste materials can be transformed into a sustainable, value-added product suitable for industrial applications.