Effect of pectin extraction method on properties of cellulose nanofibers isolated from sugar beet pulp

Mohammad L Hassan,Wafaa S Abou Elseoud,Enas A Hassan,Linn Berglund,Kristiina Oksman

doi:10.1007/s10570-021-04223-9

Abstract

In this study, the effect of pectin extraction method on the properties of cellulose nanofibers (CNFs) isolated from sugar beet pulp (SBP) was studied. Pectin was extracted by the industrially practiced method by sulfuric acid hydrolysis or by enzymatic hydrolysis using a cellulase/xylanase enzymes mixture. The CNFs were then isolated by high-pressure homogenization and investigated in terms of their chemical composition, crystallinity, size, degree of polymerization, and re-dispersion in water after freeze-drying. The mechanical properties and surface characteristics of CNF films were also studied. The results showed that fibrillation of the de-pectinated SBP was more efficient for the acid hydrolyzed SBP. CNFs from the acid-hydrolyzed SBP had a slightly wider diameter, higher crystallinity, viscosity, and α-cellulose content but a lower degree of polymerization than CNFs from the enzyme-hydrolyzed SBP. Owing to the presence of more residual hemicelluloses in the CNFs from the enzyme-hydrolyzed SBP, the CNFs had higher re-dispersion ability in water. CNF films from enzyme-hydrolyzed SBP displayed slightly better mechanical properties and higher water contact angle than acid-hydrolyzed CNF films.Graphic abstract

Highlights

Sugar beet pulp (SBP) is a common agricultural residue in different areas of the world as 20% of the world production of sugar comes from sugar beets (Stevanato et al 2019)
Pectin was extracted by sulfuric acid hydrolysis as it is practiced industrially or by enzymatic hydrolysis using a mixture of xylanase and cellulase enzymes; the conditions of pectin extraction by both methods were optimized in a previous publication to get highest pectin yield (Abou-Elseoud et al 2021); the pulp residues after pectin extraction were used to isolate cellulose nanofibers (CNFs)
This study has shown that the removal of pectin using sulfuric acid- or xylanase/cellulase enzymatic hydrolysis leads to a residue with a high cellulose content and to a suitable raw material for production of CNFs

Summary

Introduction

Sugar beet pulp (SBP) is a common agricultural residue in different areas of the world as 20% of the world production of sugar comes from sugar beets (Stevanato et al 2019). Sugar beets are cultivated in Europe, North and South America, Asia, and a few countries in Africa where temperate climates exist. The top producer is the Russian Federation, followed by France, the United States, Germany, and Turkey. In Africa, Egypt is the leading country in sugar beet cultivation and the 8th top producer in the world. SBP residue is rich in some carbohydrate polymers and other minor components. The chemical composition of SBP is approximately 21–30% pectin, 22–25% cellulose, 22–25% hemicelluloses, 5–10% protein, lignin \ 5%, phenolics \ 1%, and ash \ 1% (Fishman et al 2011; Li et al 2014)

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