Experimental Determination Of Soft Wheat Flour Thermal Parameters

Abstract

6Acta Technologica Agriculturae 1/2015 Monika BOŽIKOVÁ et al.Recent results of thermophysical research applied to biobased materials are very important because these materials go through the thermal manipulation during storage and processing to final products. Thermophysical parameters are significant characteristics that can be used for improving of technological processes. If we know the basic thermal parameters, we can determine optimal storage conditions. From changes of thermophysical parameter values during temperature stabilisation, we can predict structural changes of bio-based materials. These facts are very useful in agriculture and food industry for detection of materials quality. Characteristics of flourThe flour that is used in baking comes mainly from wheat, although it can be milled from corn, rice, nuts, legumes, and some fruits and vegetables. Different types of flour are suited to different items. In Slovakia, soft wheat flour, middle cut wheat flour, and whole wheat flour are mostly used. Our research was focused on measuring the selected soft wheat flour thermophysical parameters because this type of flour is usually used for baking. Fine texture is typical for soft wheat flour. One hundred grams of soft wheat flour contain 10.6 g of proteins, 74.1 g of saccharine and 1.3 g of fats. Energy content per 100 g is 1,474 kJ (Danster et al., 2008).The thermophysical parameters of the sample were measured by the thermal analyser Isomet. Measurement by the thermal analyser is based on two types of thermophysical methods -the hot wire method and plane source method. In this case, mainly the plane source method was used for measurements. The hot wire method was used for data reliability comparison. These methods are shortly described in the following text, and detailed description of methods can be found in literature (Božiková and Hlaváč, 2010; Božiková, 2008). The range of the plane and needle probe was chosen according to the thermophysical parameters that are known from literature. During the measurement, the probe is placed into the measured material. There should be very good contact between the measured sample and probe. The thickness of the measured material was 10 mm for the plane source method. The volume of the sample for the hot wire method was 300 ml, and the probe was placed in the centre of the sample with a cylindrical shape. Heat was generated by the probe, and there was analysed the temperature relation in time. The thermophysical parameters -thermal conductivity, thermal diffusivity and volume specific heat were calculated from the timetemperature relation.The hot wire method is a standard transient dynamic technique based on measuring the temperature rise in a defined distance from a linear heat source (hot wire) embedded in the test material. If the heat source is assumed to have a constant and uniform output along the length of test sample, thermal conductivity can be derived directly from the resulting change in temperature over a known time interval (Davis, 1984). Acta Technolog...

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