Effect of High-Temperature Short-Time Treatment of Wheat Flour on Gluten Vitality and Structure

Cereal Chem. 73(3):375-378 The effect of high-temperature short-time (HTST) applications on changes in the extrinsic fluorescence (8-aniline-l-naphthalene sulfonate gluten in its natural flour environment was investigated. Changes occur[ANS] binding) revealed enhanced surface hydrophobicity, which howring in HTST-treated samples during storage and in samples subjected to ever, regressed on storage. Consistent with these observations was the severe thermal denaturation were studied. Sodium dodecyl sulfate polyamount of the associated water. It appears that it is the gluten surface acrylamide gel electrophoresis (SDS-PAGE) profiles of the gluten that is mainly affected by HTST treatment, and this could represent a polypeptides, and the intrinsic fluorescence, were modified only in the very early stage of heat damage of gluten. heat-denatured preparation. On the other hand, after HTST treatment High-temperature short-time (HTST) treatments are a recent development in food technology. Material in finely particulate form is conveyed through a rotating heated cylinder by a turbulent stream of hot air. During the run, the particles undergo repeated rapid contact with the hot surface. Time of passage and temperature of the contact surface and conveying air are controlled. Due to the small size of flour particles, HTST treatments provide uniform thermal input. Heat transfer is minimized and water evaporation is facilitated. HTST techniques applied to flour provide a useful model of heat transfer to gluten in conditions as close as possible to that of gluten's natural kernel surrounding. The effect of heat treatment on isolated gluten has been reported in the literature (Booth et al 1980, Weegels et al 1994b, Schofield et al 1983) and is currently under study in our laboratory (Cerletti et al 1994, Guerrieri et al 1996). In this article, we examine the behavior of gluten heated within flour, under conditions that are similar to those of the actual flour processing conditions. To remain as close as possible to the industrial situation, we preferred to apply the HTST treatment using industrial equipment under highly controlled conditions. The most widespread test for vitality is to measure the change in loaf volume that results after the addition of gluten to flour, followed by baking. This is a cumbersome procedure for routine industrial use, and the gluten in the flour itself could possibly interfere. Other assays for vitality are water absorption by gluten and extensibility of the hydrated gluten, but neither of these methods has proven totally reliable (Wadhanwan and Bushuk 1989a). Wadhanwan and Bushuk (1989a) studied gluten devitalization on 27 samples of commercial gluten and gluten isolated by hand washing in the laboratory. Dough development, dough stability, oc-amylase activity, and other chemical parameters were studied, but no definite correlation was found between these results and loaf volume, except for sodium content, which could be affected by the industrial preparation of gluten. lDipartimento di Scienze Molecolari Agroalimentari, Universita' degli Studi di Milano, via Celoria 2, 20133 Milano, Italy. Corresponding author: Fax: 39-2-70633062. Publication no. C-1996-0411-06R. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. American Association of Cereal Chemists, Inc., 1996. Positive correlations have been found between gluten vitality, gluten solubility in 0.05N acetic acid, and electrophoresis and fluorescence results (Wadhanwan and Bushuk 1989b). The turbidity of acid solutions of gluten has definitely been related to the thermal damage of gluten (Hay and Every 1990). Czuchajowska and Pomeranz (1991) evaluated commercial vital gluten by near-infrared reflectance (NIR) spectroscopy and developed calibration equations to predict gluten functionality. Good correlation was found between NIR wavelengths and solubility in 3M urea and protein content, but further results are required to correlate composition and vitality. In this study, properties related to vitality and protein structure were studied in gluten isolated from HTST-treated flours and, for reference purposes, in native or fully denatured gluten obtained from untreated flour. A comparison of the results can be used to assess whether the presence of starch and other flour components during HTST treatment influences the heat effects on gluten. MATERIALS AND METHODS