Cereal Chem 66:310-313   |  VIEW ARTICLE

An Assay of Molecular Mobility in Solid Corn Meal by Front-Face Fluorescence Anisotropy.

S. M. Gibson and G. Strauss. Copyright 1989 by the American Association of Cereal Chemists, Inc. 

A new technique based on front-face fluorescence anisotropy was developed to study molecular mobilities in solid corn meal samples before and after extrusion cooking. Anisotropy was determined by measuring the polarization of fluorescence of vitamin A, a natural constituent of corn meal, or that of an added probe, calcein. A conventional fluorescence spectrophotometer was modified by constructing a cuvette holder that allowed the cuvette, filled with a powdered sample, to be oriented at variable angles. Positive anisotropy errors due to polarized stray light were measured and allowed for. Negative errors due to depolarization at air-sample interfaces were eliminated by immersing the powdered samples in a liquid of matching refractive index. In uncooked corn meal the anisotropies were low, indicating high mobility of the fluorophore. In corn meal extrudates, the anisotropies increased with increasing extrusion temperature and decreasing moisture, showing loss of mobility. Anisotropy measurement is a simple and rapid method for relating structural changes at the molecular level with process conditions.