Dietary fibre profiles of Turkish Tombul hazelnut (Corylus avellana L.) and hazelnut skin

Abstract

Dietary fibre (DF) profiles of natural hazelnut, roasted hazelnut and hazelnut skin were analyzed. Insoluble (IDF) and soluble (SDF) DFs were examined for monosaccharide and glycosyl-linkage compositions using gas chromatography-mass spectrometry (GC-MS). Total DF contents of natural hazelnut, roasted hazelnut, and hazelnut skin were 17.8, 15.4, and 69.8%, respectively; majority of which (> 96%) were water-insoluble. IDFs of natural and roasted hazelnuts were composed of cellulose (similar to 49%), pectic polysaccharides (similar to 30%), and xyloglucans (similar to 15%), whereas that of hazelnut skin made up lignin (similar to 55%) and fibre polysaccharides (cellulose, pectic polysaccharides, and xyloglucans, similar to 45%). Unlike the ones from other sources, pectic polysaccharides in IDFs had lower proportion of smooth region and higher proportion of hairy region that is heavily branched with arabinan and galactan side chains. Xyloglucans were also densely branched with monomeric and/or dimeric side chains. SDFs of the samples were composed of heavily branched heteromannans (similar to 60%), slightly branched pectic polysaccharides (similar to 25%), and xyloglucans possessing monomeric side chains (similar to 5%). These results suggest that hazelnut is rich in DFs that have potential to improve large bowel function and hazelnut skin, a byproduct of hazelnut roasting process, could be utilized for the production of functional carbohydrates having prebiotic capacities.