Extraction and characterization of rubberwood starch for accurate structural and physicochemical properties analysis

Rubberwood has high starch content and is susceptible to fungal and microbial attack. The modification of starch can prevent it from becoming a nutrient source of microorganisms and realize the purpose of anti-mildew and anti-corrosion of rubber wood. Understanding the structure and physicochemical properties of rubberwood starch aids to explore suitable methods for starch modification. This study investigates the distribution of starch in rubberwood and explores the feasibility of extracting starch by three different methods (water extraction, sodium metabisulfite extraction and ethanol extraction). The results showed that the distribution of rubberwood starch was consistent with the typical distribution of wood starch, mainly distributed in thin-walled cells. Three extraction methods proved the feasibility of extracting starch from rubberwood thin-walled cells. The microstructure, physical and chemical properties and structure of rubberwood starch were investigated by means of scanning electron microscope, X-ray diffraction, polarizing light microscope and nuclear magnetic resonance analysis. The results showed that compared with the internal starch of rubberwood, the shape of the starches extracted by the three methods did not change significantly, and they were all spherical and elliptical, with stable A-type crystal structure and obvious Malta cross diffraction pattern. However, it is worth noting that sodium metabisulfite and ethanol will increase the swelling power of rubberwood starch, which provides new insights into other uses of rubberwood starch. This work not only enriched our understanding of the characteristics of rubberwood starch, but also laid a theoretical basis and practical guidance for the development of efficient mildew prevention technology of rubberwood products. •The rubberwood starch is mainly distributed in thin-walled cells.•The rubberwood starch is A-type with a distinct Maltese cross.•The starch has microporous and channels, which facilitate chemical reactions.•The low amylose content will affect starch’s stability during physical modification.