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A study was conducted to investigate the behaviour of different moisture contents of Jatropha curcas L. seeds under compression loading. To obtain jatropha seeds of different moisture contents ranging from 1% (w.b.) to 37% (w.b.), the seeds were soaked in water and kept in a refrigerator at 5°C for different number of days. Compression devices, namely ZDM 50-2313/56/18, pressing vessel with diameter of 76 mm and a pressing plunger of 90 mm height, were used. The amount of seeds in the pressing vessel was measured as 40 mm with compression force of 98,100 N. The results from the experiment showed that increasing the moisture content of the jatropha seeds influenced the force-deformation characteristic curve, deformation energy, maximum deformation and energy per unit volume. While moisture contents 1% (w.b.) and 10% (w.b.) displayed normal force-deformation characteristic, moisture contents 32% (w.b.) and 37% (w.b.) showed wave-effect characteristic. The R² coefficient of determination value of 0.87 obtained from the effect of moisture content on deformation energy and unit volume energy shows that jatropha seeds of moisture content 16% (w.b.) would require minimum energy but high efficiency during compression.

Herák D., Kabutey A., Sedláček A., GŰrdil G., 2012. Mechanical behaviour of several layers of selected plant seeds under compression loading. Res. Agr. Eng., This article is focused on the determination of the mechanical behaviour of several layers of plant seeds namely; garden pea (Pisum sativum L.), common bean (Phaseolus vulgaris L.), common sunflower (Helianthus annuus L.) and jatropha (Jatropha curcas L.) seeds under compression loading. The results from the experiment showed that during compression plant seeds may change their mechanical behaviour that is deformation characteristic ceases to be a function of growing and beginning to resemble that of trigonometric functions and this behaviour is called the "wave effect". Also the strain value at which there is no further change of the mechanical behaviour is actually a local maximum of deformation characteristic and this is called the limit deformation. Exceeding this value can cause vibration of the presser including other negative factors which influences the process of pressing. The amounts of the limit deformation, strain energy and volume energy for jatropha, common bean, common sunflower and garden pea were determined in this experiment. From the calculated amounts of the volume energy, garden pea had the best resistance to change in the mechanical behaviour due to the fact that its change in the mechanical behaviour was not discovered. The other plant seeds; common beans, common sunflower and jatropha with respect to resistance to change in the mechanical behaviour followed in that order of magnitude.Keywords: jatropha; common bean; garden pea; common sunflower; pressing; wave effect In oil extrusion with usual extruders used in industrial practice, there is non-linear compression of pressed mixture incurred during the processing. This means that the compression is combination of translational movement moving and rotational movement. For better understanding of mechanical behaviour of plant seeds under compression loading, it is necessary first to understand mechanical behaviour of one free placed seed and one layer of seeds with limited deformation and also mechanical behaviour of more layers of the seeds. Earlier experiments conducted with plant seeds, namely jatropha, palm oil, sunflower and knotweed, showed that the specific strain energy required for deformation of one free placed seed was much greater than for pressing the same seeds layer (Fomin 1978; Blahovec, Řezníček 1980;Herák et al. 2007). There is a dynamic effect on plant tissue and thus higher cell damage (Addy et al. 1975), which is arising due to radial pressure during pressing, the gradual deformation of seeds, seeds of mutual friction and friction of the seed on the pressing vessel. There is also a required gradient of pressing pressure, and thus if the pressure gradient is inVol. 58, 2012, No. 1: 24-29 Res. Agr. Eng.

Herák D., Kabutey A., Sedláček A., Gűrdil G., 2011. Tangent curve utilization for description of mechanical behaviour of pressed mixture. Res. Agr. Eng., This article is focused on the utilization of tangent curve for description of mechanical behaviour of pressed mixture under compression loading. The aim of this experiment was to determine the general equation describing deformation characteristics of pressed mixtures under compression loading and to verify this equation. The experiment was carried out using mixture of seeds of common sunflower (Heliantus annuus L.), jatropha ( Jatropha curcas L.), garden pea (Pisum sativum L.), common bean (Phaseolus vulgaris L.), and also mixture of spruce wood chips and waste paper chips. The results from the experiment showed that mechanical behaviour of the pressed mixtures under compression loading can be described by tangent curve function. From the determined coefficients of determination R 2 it was clear that fitted tangent curve functions described the measured amounts exactly for all pressed mixtures. It can be therefore assumed that this tangent curve function is appropriate for use in pressing any pressed mixtures during linear compression.

The effect of heating and freezing pretreatments on rapeseed oil yield and the volume of oil energy under uniaxial compression loading was investigated. Four separate experiments were carried out to achieve the study objective. The first and second experiments were performed to determine the compression parameters (deformation, mass of oil, oil yield, oil expression efficiency, energy, volume of oil and volume of oil energy). The third and fourth experiments identified the optimal factors (heating temperatures: 40, 60 and 80 °C, freezing temperatures: −2, −22 and −36 °C, heating times: 15, 30 and 45 min and speeds: 5, 10 and 15 mm/min) using the Box–Behnken design via the response surface methodology where the oil yield and volume of oil energy were the main responses. The optimal operating factors for obtaining a volume of oil energy of 0.0443 kJ/mL were a heating temperature of 40 °C, heating time of 45 min and speed of 15 mm/min. The volume of oil energy of 0.169 kJ/mL was reached at the optimal conditions of a freezing temperature of −36 °C, freezing time of 37.5 min and speed of 15 mm/min. The regression model established was adequate for predicting the volume of oil energy only under heating conditions.