V.A. Kovalenok, N.D. Lukin, V.G. Karpov
All-Russian Research Institute of Starch Products – the branch of the V.M. Gorbatov Federal Science Center of Food Systems of the RAS, ul. Nekrasova, 11, pos. Kraskovo, Moskovskaya obl., 140051, Russian Federation
Abstract. The duration of formation of starch xerogel structure is determined by cooling dynamics of starch gel and its moisture loss after extrusion. This is a very important factor influencing the making of technological charts for the extrusion products manufacture. We studied the cooling process and moisture loss by extrudates in the All-Russian Research Institute of Starch Products on the extrudate samples of corn starch, corn, and wheat groats, produced both at an industrial unit and a laboratory extruder. Values of thermophysical characteristics (heat conductivity, thermal capacity, and thermal diffusivity) of capillary and porous colloid bodies complexly depend on their structure and on the power transmission mechanism. To study these processes the formerly developed method was used allowing to characterize the convection process of extrudate heat exchange with a surrounding medium and to define their thermophysical characteristics on the basis of experimental data for the extrudate cooling process. Cooling process of extrudates at free convection can be divided into two stages. The first one is the unregulated stage which is characterized by the short duration of this period – no more than 10 sec. At the same time the internal energy accumulated by the processed mass in the course of extrusion processing is spent for the instantaneous self-evaporation of moisture from extrudates (from 25 to 50% of initial quantity), defining the nature of formation of a macrocellular structure of extrudates at the exit of starch gels from extruder matrix holes. The majority of an internal energy of the extruded mass is spent for this process. During the second, long-time cooling stage the final formation of the xerogel structure is going. The long-term storage of these extrudates in standard conditions is not recommended as it leads to worsening of their functional characteristics due to a moisture sorption from a surrounding medium.
Keywords: extrusion processing; starch products; technological mode; physical and chemical properties; heat-mass exchange; thermophysical characteristics; mathematical model; cooling of extrudates.
Author Details: V.A. Kovalenok, D. Sc. (Tech.), leading research fellow; N.D. Lukin, D. Sc. (Tech.), director (e-mail: Этот адрес электронной почты защищён от спам-ботов. У вас должен быть включен JavaScript для просмотра.); V.G. Karpov, D. Sc. (Tech.), leading research fellow.
For citation: Kovalenok V.A., Lukin N.D., Karpov V.G. Change of Temperature and Weight Fraction of Moisture in Extrudates of Starch and Starch-Containing Raw Materials // Dostizheniya nauki i tekhniki APK. 2017. Vol. 31. No. 11. Pp. 94-96 (in Russ.).