Chemical structures in pyrodextrin determined by nuclear magnetic resonance spectroscopy

• Glycosidic linkages in a pyrodextrin were identified by NMR spectroscopy.
• α-(1,6), β-(1,6), α-(1,2), and β-(1,2) linkages were identified.
• 1,6-Anhydro-β-d-glucopyranosyl units were observed at the potential reducing end.
• Transglycosidation and depolymerization occurred during dextrinization.
• Structure of resulting pyrodextrin was highly branched.

Glycosidic linkages in a pyrodextrin were identified by NMR spectroscopy for the first time. Pyrodextrin was prepared by slurrying waxy maize starch at pH 3, filtering and drying at 40 °C to 10–15% moisture content, then heating at 170 °C for 4 h. 1H and 13C NMR resonances of the pyrodextrin were assigned with the assistance of 2D techniques including COSY, TOCSY, HSQC, and HMBC, all measured on a 500 MHz instrument. During dextrinization, native waxy maize starch was hydrolyzed and extensively branched with new glycosidic linkages. The resulting pyrodextrin became 100% soluble in water and produced lower viscosity solutions at 30% solids. There were only 1.2% reducing ends (α-form) detected in the pyrodextrin, but 1,6-anhydro-β-d-glucopyranosyl units accounted for 5.2% of repeating units and they were thought to be at the potential reducing end. New glycosyl linkages including α-1,6, β-1,6, α-1,2, and β-1,2 were identified. The total non-α-1,4 linkages in the pyrodextrin were about 17.8% compared to 5.8% in a maltodextrin prepared by α-amylase digestion. Transglycosidation and depolymerization occurred during dextrinization, and the resulting pyrodextrin was highly branched.