Chemical Composition and Structure of Pentosans (Turkish with English Abstract)

Abstract

Pentosans, which are the main non-starch polysaccharides of wheat kernel can be separated in to water-soluble and water-insoluble fractions. Arabinoxylans and arabinogalactans are the fundamental constituents of both. Arabinoxylans have a backbone of (1-4)-linked β-D-xylopyranosyl residues, which may be un-, mono-, or di-substituted with terminal α-L arabinofuranosyl residues. Arabinogalactans have a branch structure with β-D-galactopyranosyl residues linked through (1-3) and (1-6) glycosidic bonds and terminal α-L arabinofuranosyl residues. When compared with arabinoxylans, arabinogalactans have a higher ratio of galactose and lower ratio of xylose. Arabinose and xylose is the main constituent of water insoluble pentosans. Arabinoxylans form an average 60% of them. Arabinose to xylose ratio of water insoluble pentosans is higher than water soluble pentosans. Therefore they have higher branched structure, molecular weight and water binding capacity than water-extractable pentosans.

Keywords

• Non-Starch Polysaccharides, Water-Extractable Pentosans, Water-Unextractable Pentosans, Arabinoxylan, Arabinogalactan.  

Pentozanların Kimyasal Bileşimleri ve Yapıları

Abstract

Buğday tanesinde bulunan başlıca nişasta dışı polisakkaritlerden olan pentozanlar; suda çözünen ve suda çözünmeyen pentozanlar olmak üzere iki grup altında incelenirler. Her ikisinin de yapısında arabinoksilan ve arabinogalaktan fraksiyonları bulunur. Arabinoksilanın temel yapısını birbirlerine β (1-4) glikozidik bağları ile bağlanmış anhidro-D-ksilopiranozil birimleri ile yan zincirlere tekli veya ikili olarak bağlanmış tek birimlik α-L arabinofuranozlar oluşturur. Arabinogalaktan, birbirlerine β-(1-3) ve β-(1-6) glikozidik bağları ile bağlanmış galaktopiranozil ünitelerinden oluşmuş dallı bir yapıya sahiptir. Sadece tek birimlik arabinoz üniteleri esas galaktoz ünitesine β- glikozidik olarak bağlanmıştır. Arabinoksilan ile karşılaştırıldığı zaman, arabinogalaktanın, galaktoz oranı yüksek, ksiloz oranı düşüktür. Suda çözünmeyen pentozanların da başlıca bileşenleri arabinoz ve ksilozdur ve bu pentozanların yaklaşık %60’ını arabinoksilanlar oluşturur. Suda çözünen pentozanlara göre, arabinozun ksiloza oranı daha yüksektir. Bu nedenle dallanma dereceleri, molekül ağırlıkları ve su bağlama kapasiteleri suda çözünen pentozanlara göre daha fazladır.

Keywords

• Nişasta Dışı Polisakkaritler, Suda Çözünen Pentozanlar, Suda Çözünmeyen Pentozanlar, Arabinoksilan, Arabinogalaktan.Nişasta Dışı Polisakkaritler, Suda Çözünen Pentozanlar, Suda Çözünmeyen Pentozanlar, Arabinoksilan, Arabinogalaktan.

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