Enzymatic and enzyme-physical modification of citrus fiber by xylanase and planetary ball milling treatment

Abstract

In this work, three methods were utilized to modify citrus fiber (CF), xylanase hydrolysis, combination of xylanase treatment and water media ball milling (WMBM) or dry micronization by ball mill (DMBM). The chemical composition results showed xylanase treatment could increase the content of soluble dietary fiber (SDF) from 10.31 to 19.12 g/100 g CF and decrease the cellulose content from 38.97 to 35.85 g/100 g as well as the hemicellulose content from 22.16 to 18.83 g/100 g. WMBM could further change the chemical components, while DMBM showed tiny effects. The physicochemical properties of all modified CF are higher than the raw material, especially the enzyme-WMBM treatment could significantly increase the water holding capacity (WHC) by 2.08-folds, the oil retention capacity (ORC) by 1.53-folds and the water swelling capacity (WSC) by 4.56-folds higher than the unmodified CF. Besides, the modifications improved the cholesterol adsorption capacity (CAC), the glucose adsorption (GAC) and total antioxidant capacity (TAC) of the CFs progressively. The FT-IR spectra showed no spectra transform but peak intensity changes in the three modified CFs, the crystalline decreased from 28.16% to 18.60% after xylanase treatment, while increased from 18.60% to 24.00% (19.05%) after WMBM (DMBM) treatment, the SEM results showed the structure of CFs became looser and more porous, the thermogravimetric analysis showed the thermal ability of CF was improved after the modifications. The modifications altered the distribution of monosaccharides of CF as well. Overall results suggest that the modifications could change the structure of CF, the xylanase and xylanase-WMBM treatment could effectively improve the hydration capacities of CF.