Sequential extraction of oligosaccharide and polysaccharides from defatted tiger nut (Cyperus esculentus) meal for its comprehensive utilization

While tiger nut (Cyperus esculentus L.) is regarded as a new oil resource, its tubers are also rich in polysaccharides and oligosaccharides. In this study, a sequential process was first developed to isolate various carbohydrate components from the tiger nut meal. Starch polysaccharide (SP) was the most extract (yield, 27.77%), with good gelatinization stability and digestion resistance. The second was oligosaccharide (OS, 15.28%), which contained 83.47% free sucrose. Four heteropolysaccharides (0.21-1.27%), namely water-soluble polysaccharide (WSP), alkali-soluble polysaccharides extracted by Na2CO3, 1 mol/L NaOH, and 4 mol/L NaOH (ASP-N, ASP-1, and ASP-4, respectively), from cell wall and composed mainly of alpha-d-Glcp, beta-d-Glcp, beta-d-Galp, alpha-d-Xylp, and alpha-l-Araf. Cellulose polysaccharide (CP) was the final product (5.47%). Their molecular weight distribution and thermal behavior were further characterized. The results demonstrate the usefulness of the sequential extraction process and provide the preliminary structure about tiger nut carbohydrates. This study contributes valuable information to promote the comprehensive utilization of tiger nuts.