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Title: DETERMINATION OF THE BRANCHING RATIO IN STARCH USING 1H HR MAS NMR SPECTROSCOPY

Author
item Himmelsbach, David
item Meadows, Frederick

Submitted to: United States Japan Joint Protein Research Panels
Publication Type: Proceedings
Publication Acceptance Date: 3/20/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary: Proton high-resolution magic-angle spinning Nuclear Magnetic Resonance spectroscopy has been used to determine the branching ratio for two types of starch in rice. Both isolated starches and starches in rice flour were investigated in a gelatinized state. The branching ratio can be used as a quality parameter itself or it can provide an accurate alternative to the determination of apparent amylose. This method avoids errors of the apparent amylose method that is subject to interference from long linear chains in amylopectin and requires correction for the presence of residual lipids. The method has the potential of becoming the primary method for calibration of other measurement systems, such as near-infrared or Raman spectroscopy, for this quality parameter.

Technical Abstract: Proton high-resolution magic-angle spinning (1H HR MAS) NMR spectroscopy was used to determine the alpha-(1->4)/alpha-(1->6) branching ratio in rice starch. Both isolated starches and starches in rice flour were investigated. The branching ratio was determined by division of the sum of the integrals branched and non-reducing terminal H-1 anomeric protons of the linear alpha-(1->4) glycosidic linkage by the integral of the H-1 anomeric proton of alpha-(1->6) branch. The 1H HR MAS experiments were conducted using both a wide bore 300 MHz NMR system with a modified CP/MAS probe and a narrow bore 500 MHz NMR system using a 1H/13C gradient HR MAS probe. Both MAS systems provided increased signal/noise over the comparable solution NMR method, but with reduced resolution. It is shown that a 300 MHz NMR spectrometer system provides sufficient signal/noise to make accurate determinations of the branching ratio in the case of in situ starches. It also avoids the loss of signal to sidebands that are generate at higher field strengths. Two-dimensional correlation spectroscopy (COSY) and heteronuclear single quantum coherence (HSQC) experiments conducted at 500 MHz were used to confirm assignments and are being used to investigate further interactions between proteins and lipids with starch in rice flour. The method provides an accurate alternative to the determination of apparent amylose by the iodide complex method that is subject to interference by long linear chains in amylopectin and requires correction for the presence of residual lipids. The 1H HR MAS NMR method has the potential of becoming the primary method for calibration of other measurement systems for this quality parameter.