Submitted to: American Association of Cereal Chemists Meetings
Publication Type: Abstract Only
Publication Acceptance Date: October 17, 2001
Publication Date: N/A
Technical Abstract: Proton high-resolution magic-angle spinning**1 H 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 calculated by division of the sum of the integrals of the linear alpha-(1--4), branched and non-reducing terminal proton signals by the integral of the signal due to the anomeric proton of the a-(1--6) branch alone. The 1 H 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 1-H/13-C gradient HR MAS probe. Both MAS systems provided increased signal/noise over the comparable solution NMR method, but with reduced resolution. It is shown from this work that a 300 MHZ NMR 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 generated at higher field strengths. Two-dimensional correlation spectroscopy (COSY) and heteronuclear single quantum coherence (HSQC) experiments were used to confirm spectral assignments. The method provides an accurate alternative to the determination of apparent amylose that is subject to interference by long linear chains in amylopectin and requires correction for the presence of lipids. It has the potential of becoming the primary method for calibration of other measurement systems for this quality parameter and of being used to investigate interactions between proteins and lipids with starch in rice flour.