Characterisation of the substituent distribution in hydroxypropylated potato amylopectin starch

The distribution of substituents in hydroxypropylated potato amylopectin st arch (amylose deficient) modified in a slurry of granular starch (HPPAPg) o r in a polymer 'solution' of dissolved starch (HPPAPs), was investigated. T he molar substitution (MS) was determined by three different methods: proto n nuclear magnetic resonance (H-1 NMR) spectroscopy, gas-liquid chromatogra phy (GLC) with mass spectrometry, and a colourimetric method. The MS values obtained by H-1 NMR spectroscopy were higher than those obtained by GLC-ma ss spectrometry analysis and colourimetry. The relative ratio of 2-, 3-, an d B-substitution, as well as un-, mono-, and disubstitution in the anhydrog lucose unit (AGU) were determined by GLC-mass spectrometry analysis. Result s obtained showed no significant difference in molar distribution of hydrox ypropyl groups in the AGU between the two derivatives. For analysis of the distribution pattern along the polymer chain, the starch derivatives were h ydrolysed by enzymes with different selectivities. Debranching of the polym ers indicated that more substituents were located in close vicinity to bran ching points in HPPAPg than in HPPAPs. Simultaneous alpha-amylase and amylo glucosidase hydrolysis of HPPAPg liberated more unsubstituted glucose units than the hydrolysis of HPPAPs, indicating a more heterogeneous distributio n of substituents in HPPAPg. (C) 2000 Elsevier Science Ltd. All rights rese rved.