Structural characterisation of the olive pomace pectic polysaccharide arabinan side chains

Area of Science:

• Food Science
• Carbohydrate Chemistry
• Biochemistry

Background:

• Olive pomace is a rich source of polysaccharides.
• Arabinans are complex carbohydrates with potential applications.
• Understanding the structure of olive pomace arabinan is crucial for its utilization.

Purpose of the Study:

• To isolate and characterize an arabinan from olive pomace.
• To determine the linkage composition and molecular weight of the arabinan.
• To propose a tentative structure for the olive pomace arabinan.

Main Methods:

• Isolation of arabinan from alcohol-insoluble residue (AIR) of olive pomace using acid treatment and ethanol precipitation.
• Separation from pectic polysaccharides via anion-exchange chromatography.
• Molecular weight estimation using size-exclusion chromatography.
• Structural elucidation through methylation analysis and 1D/2D NMR spectroscopy (13C, 1H).

Main Results:

• An arabinan composed of 97% arabinose and 3% hexuronic acid was isolated.
• The arabinan has a molecular weight of 8.4 kDa.
• Methylation analysis revealed a linkage composition of (1-->5)-Araf, T-Araf, (1-->3,5)-Araf, and (1-->3)-Araf in a 5:4:3:1 ratio.
• NMR spectroscopy confirmed the linkage composition and alpha anomeric configuration, with some terminal beta-arabinofuranosyl residues.
• 2D NMR indicated that terminal beta-arabinofuranosyl residues were linked to (1-->5)-Araf residues within the (1-->5)-Araf backbone, with branched residues adjacent to linear ones.

Conclusions:

• A detailed structural characterization of an olive pomace arabinan was achieved.
• The proposed structure provides a basis for understanding its properties and potential applications.
• This research contributes to the knowledge of plant-derived polysaccharides and their structural diversity.