Pentozanların Kimyasal Bileşimleri ve Yapıları

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.

Anahtar Kelimeler:

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

Chemical Composition and Structure of Pentosans (Turkish with English 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. ,

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