MODELLING THE PROCESS OF SQUEEZING THERMALLY PROCESSED LUPINE SEEDS

Dariusz Andrejko, Zbigniew Oszczak, Beata Ślaska-Grzywna
Department of Food Engineering and Machinery, Agricultural University of Lublin, Poland

ABSTRACT

The paper presents a method of choosing the function of nonlinear approximation and squeezing forces in relation to two independent variables of temperature and time of heating for the process of squeezing the thermally processed hot lupine seeds meant for grinding or slicing. The method was based on the mathematic modelling of unit functions of squeeze and unit energy depending on the temperature in the drying chamber and the time of heating the raw material. The method was illustrated by an example of preparing and testing the lupine seeds samples subjected to the process of heating in a universal drying device SUP-4 and squeezing hot seeds on a machine for resistance tests Instron 4320. The studies found out a statistically significant decrease of the values of energy and the force of squeezing the seeds earlier subjected to thermal treatment.

Key words: squeezing process, thermal treatment, mathematic projection.

Denotations:
a – seed thickness (the smallest dimension), mm,
b – seed width (the biggest dimension), mm,
t_p – temperature in the drying chamber, °C,
τ – time, min,
m – seed mass, g,
F – pressing power, kN,
E – energy, J,
w – initial moisture of seeds, %.

Lower indexes: 0 – concerns parameters of the environment,
t – concerns parameters after heating the seeds,
z – concerns the seeds,
z2 – concerns the squeeze of the seeds with a permanent value of 2 mm,
3 – concerns the squeeze or energy for the translocation of the measuring head by 3.0 mm,
g – concerns unit values (divided by the seed mass),
Obl – concerns computational values,
pom – concerns measurement values,
œr – concerns mean values.

INTRODUCTION

An increasing demand for ready-made food, produced by means of industrial methods cause greater requirements concerning technological treatments bringing about improved sensory and functional traits without losing any precious nutritive elements [7]. Thermal treatments conducted in proper conditions guarantee, for example:

• inactivation of anti-nutritious factors,

• increasing digestibility,

• positive changes in the content of aminoacids,

• destruction of microorganisms,

• improved taste.

Thermal treatment in food processing should take place in the conditions of increased or lowered temperature, increased or lowered humidity, with the minimum time of heating the product, especially concerning storing it at the temperature exceeding 100°C [6]. Keeping those conditions limits the decomposition of vitamins and proteins. During the thermal treatment the heat is transferred from the heated factor (hot air, water, oil, heating plate, etc.) to the surface of the material. Treatment of this kind triggers off a number of changes in the nutritious, physical properties as well as the chemical composition of the raw materials [4]. They are dependent on the one hand on the natural properties of the raw materials and, on the other, on the way and conditions of the thermal treatment [3].

One of the technological processes that a raw material is subjected to immediately after the thermal treatment, often being its integral part, is slicing. It gives a product ready for consumption in the form of easily assimilable slices. The material subjected to slicing must be characterized by lowered resistance to squeezing. Hence, the purpose of the studies was to find a method of selecting the parameters of thermal treatment (temperature in the drying chamber and the times of heating) for the squeezing process of hot lupine seeds meant for slicing. This method was based on mathematic projection of the function of unit forces of squeeze (F_z2g; F_3g) and the unit energy of squeeze (E_3g) depending on the times of heating (τ) and the temperature in the drying room (t_p). Minimization of unit values of squeezing forces (F_z2g; F_3g) and the unit energy of squeezing (E_3g) were the criterion for the quality evaluation of the process.

MATERIAL AND METHODS

The studies used yellow lupine seeds Piast cv. from the harvest in 2005. The moisture of the seeds was 11.8±0.2%. The measurements of moisture were conducted by a drier method according to the norm PN-91/A-74010. Before the tests the seeds were sorted out. A representative fraction, which was left on the sieves with round openings with the diameter of ø5 mm (which constituted about 80% of the population mass), was used for the tests. The measured and calculated mean values of the mass, thickness, width and standard deviations for the examined seeds were the following:

• m = 0.148 g; standard deviation 0.021 g; median 0.145 g,

• a = 5.019 61 mm; standard deviation 0.375 mm; median 5 mm;

• b = 5.877 mm; standard deviation 0.414 mm; median 5.9 mm;

• mass of 1000 seeds was 148.18 g.

The tests were conducted using:

• a resistance device INSTRON 4302 Series IX,

• a specially designed countershaft to decrease the drop of temperature of seeds during the measurements (an application for patent reservation was put),

• a universal drier SUP-4 with the power of 1200 W with a convector force of the air movement,

• scales WPS 210C with the measurement precision ±0.001 g.

With the aim of decreasing the effect of outside conditions on the changes of the temperature of hot seeds during the squeezing tests the seeds were placed in a special countershaft. After placing the sample (8 seeds) in the countershaft the seeds were heated in an oven and, after taking out, installed on Instron and subjected to squeezing tests. The total times needed for a test of one sample was about 10 minutes, i.e. the time needed to take the sample out of the oven and place it on Instron was about 3 minutes and the time of the squeezing test of the seeds was about 7 minutes (fig. 1).

Fig. 1. Changes of the value of temperature of hot lupine seeds placed in a thermally isolated (tzl) and non-isolated (tz) countershaft, depending on the time (t) of staying in the temperature of the environment

Because of small changes of the temperature of hot seeds and considerable simplification of the tests, further squeezing tests of the samples were conducted in a thermally non-isolated countershaft.

The measurements of parameters F_3g, F_z2g, E_3g (fig. 3) were performed for 8 repetitions for the following values of accommodation variables:

• temperature of the drying chamber (t_p); 50, 80, 110°C,

• times of heating (τ_p): 1, 2, 3, 5, 10 and 15 min.

The above values of the heating times (τ_p) and the temperatures in the drying room t_p were selected on the basis of the tests (fig. 2 and equation 1) in such a way that the final temperature of the grain did not exceed 80°C and the ranges of the accommodation parameters could fill in the areas of tests well.

Fig. 2. Effect of temperature (tp) in the chamber of the oven and the heating time (τp) on the values of temperature (tz) of lupine seeds

t_z = 22.8411 + 0.4665 · τ + 0.534 · t_p – 0.0944 · τ² + 0.031 · τ · t_p + 0.0003 · t_p²       (1)

The error of the calculations of seed temperature (t_z) with equation (1) did not exceed the value ±1.5°C.

The seeds placed in the seats of the countershaft were heated in the drier SUP-4. After taking out from the drier, the hot seeds were squeezed in a resistance machine Instron 4203. In order to estimate the quality of the process of squeezing, such choice of temperatures and heating times of seeds was adopted that minimum values could be achieved for the unit energies of squeezing (E_3g) and unit squeezing forces (F_3g, F_z2g) (fig. 3).

Fig. 3. Parameters of the estimation of the squeezing process F3, Fz2, E3

RESULTS

It follows from the data presented in figures 4, 5, 6 and 7 that thermal treatment of yellow lupine seeds cv. Piast was the cause of the changes of the values of energy and squeezing force. Within the range of temperature (t_p) from 50 to 110°C and the heating time (τ) from 6 to 10 minutes, a drop of the values of energy and the force squeezing individual lupine seeds was observed. The smallest values of energy and squeezing force were noted for t_p = 110°C and τ = 10 min. Longer heating of the seeds caused an increase of the measured values. That was caused by intensive drying of the surface layers of the seeds, and consequently by strengthened resistance of seed covers [3]. The obtained relationships are characteristic only of one material, which were the seeds of yellow lupine Piast cv. It was found out on the basis of the results of earlier studies [1, 2, 3] that the values of the squeezing force causing destruction of the seeds of white lupine Wat cv., caryopses of rye Warko cv. and soybean seeds Poland cv. got smaller after thermal treatment. The values of those forces were dependent on time and heating temperature. Lengthening the heating time and an increase of the value of the temperature caused a drop of the values of the measured forces. During the tests of squeezing individual seeds of soybean, lupine and rye caryopses considerable differences in the values of the squeezing forces were observed. The highest values of those forces were necessary to destroy the seeds of white lupine [1], while the lowest were found out in the squeezing tests of individual rye caryopses [2].

Similar conclusions were reached by Fasina et al. [5]. After thermal treatment of bean, pea and lentil the studies observed a drop of the forces destroying the seeds structure, and those values differed for particular materials although processed in the same conditions. Generally, it should be stated that the range of changes in seed resistance to squeezing caused by thermal treatment is dependent not only on time and temperature, which are outside factors, but also on inside ones (species of the studied material).

Fig. 4. Unit energy (E3g) of squeezing hot lupine seeds depending on temperature (tp) and heating time (τ)

Fig. 5. Unit energy (E3g) of squeezing hot lupine seeds depending on temperature (tp) and heating time (τ)

Fig. 6. Unit pressing power (F3g) of squeezing hot lupine seeds depending on temperature (tp) and heating time (τ)

Fig. 7. Unit pressing power (Fz2g) of squeezing hot lupine seeds depending on temperature (tp) and heating time (τ)

On the basis of the obtained results the following equations were obtained for E_3g, F_3g and F_z2g depending on the temperature in the drying room (t_p) and heating time (τ):

E_3q = 2.0005 + 0.0294 · t_p – 0.1214 · τ – 0.0002 · t_p² – 0.0024 · t_p · τ + 0.0124 · τ²       (2)

F_3q = 2.658 + 0.0208 · t_p – 0.1184 · τ – 0.0002 · t_p² – 0.0014 · t_p · τ + 0.012 · τ²           (3)

F_z2q = 3.753 + 0.0208 · t_p – 0.0579 · τ – 0.0002 · t_p² – 0.0004 · t_p · τ + 0.0031 · τ²        (4)

Equations (2, 3, 4) make it possible, within the range of the studies, to mark the range of parameters t_p and τ in order to obtained the minimum values E_3g, F_3g and F_z2g. To mark the relationships (2, 3, 4) the procedures of linearized nonlinear regression and nonlinear estimation of Statistica 5 were used.

CONCLUSIONS

The following conclusions were made on the basis of the obtained results of studies and observations:

• thermal treatment of yellow lupine seeds cv. Piast is the cause of changes in the values of energy and squeezing force,

• the obtained equations (2, 3, 4) constitute a projection of the mathematic process of squeezing thermally treated hot lupine seeds meant for grinding and slicing,

• on the basis of equations (2, 3, 4) and figures (4, 5, 6, 7) the following relationships were determines in for the assurance of decreased values E_3g, F_3g and F_z2g:

6 min ≤ τ ≥ 10 min
50°C ≤ t_p ≥ 110°C

• The lowest values of energy and squeezing force were noted for t_p = 110°C and τ = 10 min.

• The designed countershaft considerably decreases the drop of seed temperature and shortens the time of the measurement of resistance properties of the seeds,

• The use of a thermal screen allows for maintaining the temperature of the seeds placed in the countershaft higher by about 10°C,

• The obtained relationships are applied only for the studies described in the present paper.

REFERENCES

1. Andrejko D., Rydzak L., 2000. Wpływ procesu mikronizacji na własciwosci fizyczne nasion roslin straczkowych [Effect of micronization process on physical properties of pod plants seeds]. Inż. Roln. 5(16), 9-14 [in Polish].

2. Andrejko D., Grochowicz J., 2001. Zmiany wytrzymałosci ziaren żyta spowodowane oddziaływaniem promieniowania podczerwonego [Changes of resistance of rye seeds caused by the effect of infrared radiation]. Probl. Inż. Roln. 2(32), 37-44 [in Polish].

3. Andrejko D., 2005. Zmiany własciwosci fizycznych nasion soi pod wpływem promieniowania podczerwonego [Changes of physical properties of soybean under the effect of infrared radiation]. Rozpr. Nauk. 288, AR Lublin [in Polish].

4. Boldaji F., Goeger M.P., Nakaue H.S., Savage T.F., Arscott G.H., 1986. Effect of autoclaving and cooking on true metabolizable energy (TME) and N-corrected TMEn content of white lupin, yellow peas, and faba beans. Nutr. Rep. Int. Oregon State Univ. 34(2), 159-164.

5. Fasina O., Tyler B., Pickard M., Zheng G. H., Wang N., 2001. Effect of infrared heating on the properties of legume seeds. Int. J. Food Sci. Technol. 36(1), 79-87.

6. Pajak J.J., Kowalczyk J., Żebrowska T., Kowalik B., Długołęcka Z, 2001. Effect of extrusion-cooking temperature on the nutritive value of lupine seeds in fattening lambs. J. Anim. Feed Sci. 10, Suppl. 2, 357-362.

7. Pastuszewska B., Ochtabińska A., Lechowski R., 2001. Response of animals to dietary gramine. II. Effects of feeding high-gramine yellow lupin seeds on reproductive performance of rats and on selected hematological and biochemical parameters in offspring. Arch. Anim. Nutr. 55, 17-24.

 

Accepted for print: 16.01.2007

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Dariusz Andrejko
Department of Food Engineering and Machinery,
Agricultural University of Lublin, Poland
44 Doswiadczalna Street, 20-236 Lublin, Poland
phone: (+ 48 81) 461-00-61 ext.135
email: dariusz.andrejko@ar.lublin.pl

Zbigniew Oszczak
Department of Food Engineering and Machinery,
Agricultural University of Lublin, Poland
44 Doswiadczalna Street, 20-236 Lublin, Poland
phone: (+ 48 81) 461-00-61 ext.135

Beata Ślaska-Grzywna
Department of Food Engineering and Machinery,
Agricultural University of Lublin, Poland
44 Doswiadczalna Street, 20-236 Lublin, Poland
phone: (+ 48 81) 461-00-61 ext.135
email: beata.grzywna@ar.lublin.pl

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Responses to this article, comments are invited and should be submitted within three months of the publication of the article. If accepted for publication, they will be published in the chapter headed 'Discussions' and hyperlinked to the article.

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