Cereal Chem. 73 (6):702-707 |
Quantitative Method for the Survey of Starch Phosphate Derivatives and Starch Phospholipids by (^31)P Nuclear Magnetic Resonance Spectroscopy (1).
Tunyawat Kasemsuwan (2) and Jay-Lin Jane (2,3). (1) Journal Paper J-16410 of the Iowa Agriculture and Home Economics Experiment Station, Ames. Project No. 3258. (2) Dept. Food Science and Human Nutrition, Iowa State University, Ames, IA 50011. (3) Corresponding author. Fax: 515/294-8181. Accepted July 12, 1996. Copyright 1996 by the American Association of Cereal Chemists, Inc.
Phosphorus of different chemical structures (e.g., phospholipids, starch phosphate monoester, and inorganic phosphate) are found in starch. In contrast to the colorimetric chemical method (Smith and Caruso 1964), which determines total phosphorus content in starch without differentiating phosphate monoester from phospholipids, (^31)P nuclear magnetic resonance (NMR) spectroscopy determines phosphorus chemical structures and their individual contents. The relaxation times (T(1)) of starch phosphate monoesters, phospholipids, inorganic phosphate, and phosphate derivatives in nicotinamide adenine dinucleotide (NAD) (internal reference standard) ranged from 1.0 to 2.1 sec. To ensure full relaxation between pulses for quantitative results, a relaxation delay of 11 sec was programmed between data acquisitions. Dimethyl sulfoxide solution (45%, v/v) (DMSO) was used to improve alpha-limited dextrin solubility. (^31)P NMR spectroscopy of this solution provided quantitative results. (^31)P NMR results showed that potato starch contained mainly phosphate monoester (0.086%), wheat starch contained mostly phospholipids (0.058%), mung bean starch contained mainly phosphate monoester (0.0083%) and phospholipids (0.0006%), tapioca starch contained mainly phosphate monoester (0.0065%), high-amylose (50% amylose) maize starch contained mainly phospholipids (0.015%) and phosphate monoester (0.0049%), and waxy maize starch contained only a trace of phosphate monoester. The total phosphorus contents in starches obtained by (^31)P NMR spectroscopy agreed with those obtained from the colorimetric chemical method. Acid hydrolysis of starch and high-temperature operation were attempted to improve the alpha-limited dextrin solubility, but the amylose-phospholipid complexes remained insoluble in the aqueous solution, and the structures of phosphate derivatives and phospholipids were altered.