Journal of Cereal Science 33 (2001) 331–340 doi:10.1006/jcrs.2001.0370, available online at http://www.idealibrary.com on Dielectric Relaxations of Frozen Wheat Doughs Containing Sucrose, NaCl, Ascorbic Acid and Their Mixtures T. J. Laaksonen∗ and Y. H. Roos† ∗ University of Helsinki, Department of Food Technology, P.O. Box 27 (Latokartanonkaari 7) FI-00014 Helsinki, Finland; † University College, Cork Department of Food Science and Technology, Cork, Ireland Received 15 September 2000 ABSTRACT The effects of sucrose, NaCl, and ascorbic acid on dielectric relaxations of frozen wheat doughs were investigated using dielectric analysis (DEA). All ingredients were dissolved in distilled water used to prepare wheat flour doughs to optimum consistency using a 10 g bowl Micro-Mixer. DEA meas- urements were made at a heating rate of 1 °C/min from −150 to 10 °C. Before the measurements, samples were equilibrated at −30 °C for 15 min to allow maximum ice formation, and then cooled at 1 °C/min to −150 °C. The frequencies used were 0·1, 0·5, 1, 5, 10, 20, 50, 100 and 1000 Hz. The dissipation factor (tan ) of DEA showed an -relaxation (glass transition), two low temperature relaxations ( and ) and ice dissolution. Added NaCl had a markedly depressed the glass transition temperature (T g ′) and onset of melting of ice temperature (T m ′), probably because of the higher conductivity of the frozen material, and the decreased transition temperatures of the unfrozen solute phase. At the higher frequencies, the -relaxation coincided with melting of ice, and all relaxation temperatures (, and ) increased with increasing frequencies. 2001 Academic Press Keywords: dielectric analysis, glass transition, relaxation, frozen wheat dough. in foods is that they sensitively indicate changes INTRODUCTION in dielectric properties that occur in amorphous Dielectric analysis (DEA) has been used widely to food materials in solid and liquid states 7 . Never- measure dielectric properties of food materials, theless, this technique has not been used ex- mainly using microwave frequencies 1–6 . Dielectric tensively in the determination of phase and state properties of food materials are related to physical transitions of frozen doughs. state and are significantly affected by phase trans- The dielectric behaviour of ice is well-established 8–12 . itions, such as melting of ice and the glass Ice has two main structures; hexagonal (tridymite-type) transition, which often govern the physical state and cubic (cristobalite-type) 13 , even though ice may exist of frozen foods. The importance of dielectric re- in nine other crystalline polymorphic structures 14 . Ac- laxations in relation to phase and state transitions cording to Gough and Davidson 15 no differences were found between the dielectric properties of hexagonal and cubic ice, which was probably due to a similarity of structure between them. The features of a dielectric : DEA=dielectric analysis; DMA= spectrum suggest that absorption of an electromagnetic dynamic-mechanical analysis. radiation in ice is mainly due to an orientation po- ∗ E-mail: tommi.laaksonen@helsinki.fi † E-mail: yrjo.roos@ucc.ie larisation of water molecules characterised by a sum of 0733–5210/01/030331+09 $35.00/0 2001 Academic Press