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48
Section 2. Food processing industry
https://doi.org/10.29013/AJT-19-9.10-8-13
Gafurov Karim Khakimovich, E-mail: kgafurov@yahoo.com Hikmatov Doniyor Nematovich,
Safarov Odil Fayzullaevich,
Bukhara Engineering-Technology Institute
INFLUENCE OF THE PULSED IR-RADIATION ON THERMO-PHYSICAL CHARACTERISTICS OF FRUITS
Abstract. The development of unconventional production methods for processing and drying fruits requires additional studies of characteristics that can have a big impact on the drying process and the properties of fruits. This article discusses the hygroscopic characteristics, moisture binding energy, and pore distribution for apricot drying.
Keywords: desorption; infra-red irradiation processing; moisture content; moisture bond.
The evaporation of the moisture from solids we field processing on changes to the cellular structure
call desorption. The character of the isotherms of sorption and desorption depends on the type of the moisture bond with the material. The moisture bond depends on the material structure and its characteristics. We report on the influence of electromagnetic
of apricot. In this study, desorption isotherms were investigated after IR-irradiation processing for apricots in syrup with sugar concentrations of50, 60 and 70% at various air temperatures (25-60 °C) and humidity between 10-70%.
a) b)
Figure 1. Desorption isotherms of apricot: a) immersed in sugar syrup: (1) at t=25 (2) at t = 60 °C;b) (1) at t =25 (2) at t = 25 ^ and IR-irradiation processing (3) at t = 60 °C, (4) at t = 60 °C and IR-irradiation processing
0 0.2 0,4 0.6 0,8 1 1.2
Relative air humidity, % (lg( 1 /1 -<p))AOr5
Figure 2. Rectilinear modification of the averaged apricot desorption isotherm before and after thermal processing at different temperatures: 1) at 25 °C; 2) after IR irradiation processing and immersing in 70% sugar syrup at 25 °C; 3) at 60 °C;
4) after IR irradiation processing and immersing in 70% sugar syrup at 60 °C
The analytical way to find the dependence of Experimental results of apricot desorption iso-
apricot equilibrium moisture content on relative air therms are shown on (Fig. 2) as a graphical depen-
humidity and temperature for different kinds of apri- dence W = f(lg(l/1-ty). As shown on the (Fig. 2 )
cot does not exist yet. Therefore formula for calculat- modified broken lines of the apricot desorption iso-
ing desorption isotherms was developed on the basis therms have characteristic points which divide them
of experimental data. on three zones (Table 1).
Table 1. - Rectilinear modification of the averaged apricot desorption isotherm before and after thermal processing at different temperatures
Apricot processing method at 25 °C at 60 °C
0.% W % 0.% W %
Without any processing 0-10 0-7.4 0-10 0-5.2
10-40 7.4-17. 8 10-40 5.2-9.3
40-90 17.8-52 40-90 9.3-34.8
After IR-irradiation processing 0-10 0-7.3 0-10 0-4.5
10-42 7.3-16.2 10-42 4. 5-8.0
42-90 16.2-48 42-90 8.0-31.5
After IR-irradiation processing and immersing in sugar syrup 0-10 0-8.5 0-10 0-8.2
10-52 8.5-22. 6 10-52 8.2-18.9
52-90 22.6-56.8 52-90 18.9-46.5
The aim of the dividing of the desorption isotherm to zones is to define the type of the moisture content in the apricot. According to classification of A. V. Lykov and Lengmure first zone is related to adsorption monomolecular lair with relative air humidity 0 < f <10% where equilibrium moisture content in apricot without processing is 0 < W < 7.4% and 0 < W < 8.5% in apricot after IR-irradiation processing and immersing in sugar syrup.
The middle zone is related to poly molecular adsorption where at 10 < f < 40% equilibrium moisture content in apricot without processing is 7.4 < We < 17.8%, at 10< f < 52% equilibrium moisture content in apricot after immersing in sugar syrup is 8.5 < W < 22.6%.
Third zone characterises the moisture content in micro capillaries. At relative air humidity 40 < f < 90% equilibrium moisture content in apricot after immersing in sugar syrup is 17.8 < We < 52%, at 52 < f < 90% it is 22.6 < W < 56.8%. After IR-irradiation and immersing apricot in 70% sugar syrup the volume of pores is increased and equilibrium moisture content is increased up to 1.15 times at 25 °C and moisture content 60-70%.
An empirical formula for calculating the equilibrium moisture content of apricots as a function of humidity and temperature was developed, based on the experimental data:
ww; = a+B(t)+C(t )(ig(i/i-p))1/2 (1)
where f - relative air humidity,% f = P/P; Wec - equilibrium moisture content in apricot during desorption,%; Pp - vapour partial pressure, kPa; Ps -saturated vapour partial pressure, kPa; A, B, C - coef-
Table 2. Calculations of the
ficients which have been defined for the each of characteristic zones.
So, the formula of equilibrium moisture content in the apricot after IR-irradiation and immersing in 70% sugar syrup at relative air humidity 10-70% and temperature 25-60 °C is next:
i
,0.5
W = 6.47 - 0.265t +18.170
For the third zone:
loq x
1 -p
(2)
W = 41.5 - 0.78 x t -15.54'
0.25
n 0.5
l°gX
1 -p
(3)
For the defining the effective pores diameter and apricot porosity authors used the method described by A. Ginzburg and E. Savina [3].
The specific surface of the distant film of water which forms in the beginning of the capillary condensation section is:
1 rUs / ,\
S = — f Ar x du (4)
G JUn
u
where G - a liquid surface tension, N/m; Us - moisture content in material, Mol/kg; Un - moisture content in the beginning of the capillary condensation section, Mol/kg; L- bond energy or differential work during product dehydration, kJ/moist kg
L = -RT lnp (5)
where R - universal gas constant, J/K Mol%.
So the effective diameter of pores is:
d = 4GVm / RTln(Pn / Pn) (6)
where G - surface tension of the apricot juice which depend on sugar content, mN/m; Vm - molar voluem of the water, m3/Mol and can be defined from next equation:
V = U • V (7)
m v '
Calculations of the effective diameter of pores are showed in (Table 2 and Table 3). effective diameter of pores
Air humidity in chamber Apricot desorption at temperature 25 0C without processing Apricot desorption at temperature 60 0C after IR-irradiation
W. kg/kg U,mol/kg LJ/mol D10-9 m wp kg/kg U, mol/kg L J/mol D10-9 m
1 2 3 4 5 6 7 8 9
90 0.52 28.9 260.1 20.5 0.348 19.33 290.7 17.85
1 2 3 4 5 6 7 8 9
80 0.43 23.8 552.0 9.66 0.225 12.5 617.4 8.4
65 0.30 16.7 1068 4.99 0.16 8.8 1193 4.35
54 0.248 13.6 1526 3.49 0.12 6.8 1705 3.04
35 0.155 8.61 2602 2.05 0.075 4.16 2907 1.78
25 0.125 6.94 3434 1.55 0.055 3.05 3837 1.35
10 0.074 4.11 5698 0.93 0.052 2.88 6368 0.815
Table 3. Calculations of the effective diameter of pores
Air humidity in chamber Apricot desorption after IR-irradiation Apricot desorption after IR-irradiation
and immersing in sugar syrup, 250C and immersing in sugar syrup, 60oC
é,% Wp kg/kg U, Mol/kg L J/Mol D10-9 m Wp kg/kg U, Mol/kg LJ/Mol D10-9 m
90 0.56 31.1 260.1 22.0 0.465 25.8 290.7 19.7
80 0.44 24.4 552.0 10.4 0.34 18.8 617.4 9.28
65 0.32 16.9 1068 5.36 0.245 13.6 1193 4.8
54 0.25 14.5 1526 3.75 0.18 10.0 1705 3.36
35 0.175 9.72 2602 2.2 0.14 7.77 2907 1.97
25 0.14 7.77 3434 1.67 0.12 6.66 3837 1.49
10 0.085 4.72 5698 1.01 0.082 4.55 6368 0.9
As we can see the moisture bond energy ofthe apricot has shown that it increases from 280 to 1200J/mol with moisture content reducing from 56% to 25%, and steps from 1200 up to 1700J/mol with moisture con-
07
0.6
s o.$
m ^
> 0.4
S 0,3
ft
w*
/
0.2
0.1
0
___
/
S 10 IS 20
Pones diamclcr. D-IO , m
a)
25
tent reducing from 25% to 18%. In this connection at calculation of the expense of heat on drying of an apricot with up to 25% moisture the specific heat of evaporation will be increased by 4.0%-5.0%.
0.9 0B 0.7
"3 0.6
' I .libel
Lbc2
0.5 OA 0.3 0.2 0.1 0
— Unci — i.int;
5 ID 15 20
I'ores diameter, D IO"*, m
26
b)
Figure 3. a) Dependence of the moisture volume on pores diameter; b) Curve of the pores volume distribution by effective diameters
The graphical dependence of the moisture vol- shown on the graph the maximum point is 6-10-11m. ume on pores diameter is shown on the Fig. 3. As it On desorption isotherm the beginning of the curve
bend correlate with value P n/Ph =0,05. It means that the most part of pores in apricot cells have a diameter, therefore they can be related to micro pores. It is the characteristics of the colloid capillary-porous matters. So, for the calculation of the apricot drying process we can use general kinetic methods for the drying of colloid capillary-porous matters.
Analysis of a desorption isotherm of an apricot after IR-irradiation processing shows that the moisture in poly molecular section decreases by 1.15 times, and after immersing in a sugar syrup and IR-irradiation processing increases by 1.4 times. So, during IR-irradiation influence on an apricot its cellular structure partially collapses,
and when immersed in a sugar syrup the moisture holding ability of cells due to penetration of the sugar increases.
The results of the study can be used to improve drying process efficiency through:
- defining conditions of storage and need to consider critical points of the apricot moisture content at various temperatures and relative humidity of air in calculations of drying process;
- correlating moisture bond energy with a product;
- defining thermodynamic parameters;
- by calculating porosity and the sizes of pores of the fruit.
References:
1. Patent of Republic of Uzbekistan No. IAP 03320-15.03.2007. "Method of fruit powder processing".
2. Patent of Republic of Uzbekistan No. IAP 03373-30.05.2007. "Fruit drying method".
3. Ginzburg A. S., Savina I. M., "Mass and moisture transfer characteristics of food products", - M.: Light and Food Industry, 1982. - 280 p.
