Mobility Characterization of Waxy Corn Starch Using Wide-Line 1H Nuclear Magnetic Resonance

• Published in: Journal of agricultural and food chemistry 2000-11, Vol.48 (11), p.5489-5495
• Main Authors: Kou, Y, Dickinson, L. C, Chinachoti, P
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Food industries; Fundamental and applied biological sciences. Psychology; Starch and starchy product industries
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf000633x

The molecular mobility of waxy corn starch was studied by using wide-line 1H nuclear magnetic resonance (NMR) spectroscopy. A suite of NMR techniques was used to measure relaxation times (i.e., T 2*, T 2, and T 1) and to characterize water and solid (starch) mobility of waxy corn starch. It was observed that the spectrum of each sample includes a complex broad proton component upon which is superimposed a narrow proton component over water activity (a w) ranges from 0.33 to 0.97 (i.e., 10.−25.6% water content) at 25 °C. Line shape analysis and relaxation times of both broad and narrow components show that T 2* and T 2 values decrease (i.e., decreasing mobility) with increasing solid concentration and show a “break point” in a concentration range between 19.8 and 21.9% water content. The T 1 shows a “T 1 minimum” in the same concentration range. Starch samples change from the glassy to viscous rubbery state in this same concentration range. This demonstrates that wide-line 1H NMR relaxation times (i.e., T 2*, T 2, and T 1) may be useful as indicators of glass transition for starch samples in the solid state. The results demonstrate that wide-line 1H NMR spectroscopy is able to separate modes and quantitate the magnitude of molecular mobility in complex systems. Keywords: Waxy corn starch; NMR; nuclear magnetic resonance; relaxation times; mobility