Publication no. C-1999-0804-04R |  VIEW ARTICLE

Extrusion Chemistry of Wheat Flour Proteins: I. Free Radical Formation.

K. M. Schaich (1,2) and C. A. Rebello (1,3). (1) Department of Food Science, Rutgers University, 65 Dudley Rd., New Brunswick, NJ 08901-8520. (2) Corresponding author. Phone: 732/932-9611, ext. 233; Fax: 609/497-9313; E-mail: <schaich@aesop.rutgers.edu> (3) Current address: Campbell Soup Company, Campbell Place, Camden, NJ 08103. Cereal Chem. 76(5):748-755. Accepted May 26, 1999. Copyright 1999 American Association of Cereal Chemists, Inc.

Electron paramagnetic resonance (EPR) spectroscopy was used to study free radical production in hard red wheat flours extruded according to a two-level fractional factorial experimental design (11 and 14% protein content, 160 and 185°C, 16 and 20% moisture, 300 and 500 rpm screw speed, and mass flow rate of 225 and 400 g/min). All spectra showed dominant broad singlets (g = 2.0053-2.0059) from nitrogen-centered radicals originating from heat-induced peptide scission and reactions of lipid radicals with side-chain amino groups. At 77 K, sulfur-oxyl or peroxyl radicals (g = 2.008-2.018), thiyl radicals (g = 2.025), and disulfide radical species (g = 2.032-2.035 and 2.05-2.06), resulting from intra- and intermolecular electron migration and shear-induced scission of disulfides, sometimes were present. The strongest EPR signals occurred under conditions of maximum free radical production and minimum opportunity for radical recombination: high protein flour (14%), high die temperature (180°C), and low moisture (16%). EPR signals correlated with sulfhydryl and disulfide (SH-SS) levels and physical properties of extrudates, indicating that free radicals are integrally involved in molecular changes that occur during extrusion.