Comparative study of green peas using with blanching & without blanching techniques

Available at www.sciencedirect.com INFORMATION PROCESSING IN AGRICULTURE 6 (2019) 285–296 journal homepage: www.elsevier.com/locate/inpa

Comparative study of green peas using with blanching & without blanching techniques Om Prakash Pandey a,*, Bimal Kumar Mishra b, Ashok Misra a a b

Department of Mechanical Engineering, Birla Institute of Technology, Mesra, Ranchi, India Department of Mathematics, Birla Institute of Technology, Mesra, Ranchi, India

A R T I C L E I N F O

A B S T R A C T

Article history:

This paper attempts to analyze the kinetics involved in the drying of green peas in ‘with

Received 20 June 2018

blanching’ and ‘without blanching’ techniques. Blanching by hot water mixed with a solu-

Received in revised form

tion of citric acid (0.1–0.2 mg/ml) at 70 °C–100 °C is the treatment provided to the samples of

1 October 2018

green peas. Experimental analysis shows that the moisture content in green peas of three

Accepted 8 October 2018

different sizes is reduced at different temperatures and demonstrates the effect of the rate

Available online 12 December 2018

of drying of the moisture content. Under different diameters and temperatures, the parameters are analyzed using ‘with blanching’ and ‘without blanching’ techniques. It is observed

Keywords:

that ‘with blanching’ process plays a significant role in the reduction of moisture content

Hot air drying

under different temperatures and diameters in a lesser time as compared to ‘without

Green peas

blanching’. The operative activation energy and moisture diffusivity are described by using

Drying kinetics

Fick’s law of diffusion. The calculation of effective moisture diffusivity can be done via the

Blanching

utilization of slope. The drying data is subjected to two models of mathematical nature:

Fluidized bed dryer

Simple Exponential model, and Page model. The performance of these models is examined by means of comparing the coefficient of determination (R2), chi-square (v2 ) and root mean square error (RMSE) between the experimental and forecasted value of moisture ratio obtained ‘with blanching’ and ‘without blanching’. The experimental data was seen to be in accordance with the Page model. The comparisons of energy consumption, energy efficiency and also the cost of the drying processes for ‘with blanching’ and ‘without blanching’ have been accomplished to optimize and reduce process condition and the cost of the process, respectively. Ó 2018 China Agricultural University. Production and hosting by Elsevier B.V. on behalf of KeAi. This is an open access article under the CC BY-NC-ND license (http://creativecommons. org/licenses/by-nc-nd/4.0/).

1.

Introduction

These days dried food products with high nutritional value are in demand. The primary goal in the process of drying products is to reduce the moisture content to a particular

level so that the spoilage due to microbes and worsening chemical reactions are minimized [1]. Green peas production in 2014 was nearly 11.3 million tons worldwide because it is not only an excellent source of vitamins, proteins, minerals and other nutrients but also high in fiber, low in fat and have no cholesterol [2]. Green peas contain high initial moisture content (approx. 70–75%), so dehydration becomes necessary operation prior to storage. Many physical, chemical and nutritional changes occur in foods product during

* Corresponding author. E-mail address: [email protected] (O. Prakash Pandey). Peer review under responsibility of China Agricultural University. https://doi.org/10.1016/j.inpa.2018.10.002 2214-3173 Ó 2018 China Agricultural University. Production and hosting by Elsevier B.V. on behalf of KeAi. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

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the drying process are a function of shrinkage, moisture content, temperature and time; the value of changes depends upon the chosen process of drying [3]. Preserving of green peas can be best done via drying. Drying of green peas is desirable due to extended shelf life, lower cost and ease of transportation because of lightweight and condensed volume of final products [4]. Change in color of green peas during the drying process has been observed, which is not desirable, hence their pre-treatment like blanching becomes necessary [5]. The blanching of green peas was carried out with hot water for one minute at temperature 75 °C
95 °C, the time and the temperature range depends on the kind of vegetables [6]. Blanching of vegetables and fruits either by heated water or steam is most common pre-treatment process which involves heat treatment for a short period of time [7]. The process of blanching happens to be an indispensable method before the processing of vegetables and fruits is carried out, because of its several advantages. One major effect of blanching is to inactivate enzymes [8]. Fluidized bed dryer is one of the most reliable and effective equipment for drying of the majority of agro products [9]. Fluidized bed dryer is utilized to evaluate the drying of green peas under atmospheric freeze-drying conditions and has shown that it allows gathering samples which possess higher levels of rehydration ability, green color and floatability [10]. One of the primary reasons for using a fluidized bed dryer is that the rate of drying can be greatly influenced by agitation of the product being dried. The agitation of the product during the fluidized bed drying is one of the advantages of this method with respect to the conventional drying methods (hot-air and vacuum drying). The rising air current contributes to this mixing which gives rise to the high values of mass and energy transfer coefficients [11]. A great solid mixing, a high rate of heat transfer, easy transport of material inside the dryer, low maintenance cost & ease of control are the main gains of the fluidized bed dryer [12]. Drying is governed by factors such as the nature of the product, types of dryer, drying kinetics parameters such as moisture content, air velocity, drying rate, and temperature. The moisture removal during the period is majorly diffusion controlled. Thus it becomes imperative to study the effect of shape and temperature on drying kinetics [13]. Operative moisture diffusivity, the activation energy of agro products are an important parameter for optimum design and dryer application [14]. It is the most important challenge for the drying industry to perform energy analysis to achieve optimum process conditions and reduction of energy utilization because drying process utilizes high energy due to the high latent heat of water evaporation and relatively low energy efficiency of dryers [15]. The main objective of this research is drying the green peas via two different processes i.e. ‘with blanching’ and ‘without blanching’ in a fluidized bed dryer to investigate the effect of air temperature and the particle size on drying kinetics using two different models and effective moisture diffusivity of the samples. It also aims to analyze the total energy consumption, energy efficiency and cost of the drying process to optimize process condition and reduce the cost of process.

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2.

Materials and methods

2.1.

Fluidized bed dryer

Fluidized bed dryers are the most efficient equipment [9] compared with conventional drying systems i.e. tray or cabinet dryer, for food processing because it has shorter drying time due to the high thermal efficiency of the equipment and having higher drying capacity. Fig. 1 depicts the schematic diagram of a fluidized bed dryer (FBD). Fluidized bed dryer basically consists of a centrifugal blower, an electrical heating unit, an air plenum chamber, a dryer chamber and an electronic proportional controller. The air temperature was controlled by means of a proportional controller. The air-flow rate was regulated by a blower. The air passed from the heating unit and heated to the desired temperature and channeled to the drying chamber. The temperature of the hot inlet air and exit air were monitored throughout the experiment using a digital temperature sensor.

2.2.

Experimental procedure

The fresh green peas (Pisum sativum) pods were procured from the local market. Dented, undeveloped and dry pods were manually removed after visual examination. For sake of simplicity, roughly spherical peas were selected for the experiment. Experiments were conducted using on green peas of different spherical diameters (7.64 mm, 9.13 mm, and 9.94 mm) ± 5% tolerance measured by means of the Digital Vernier Calipers. The drying process was studied with blanching and without blanching technique. The green peas were fed to the dryer directly without any intervention of boiled water in case of ‘without blanching’. In case of blanching, pretreatment of green peas with a solution of citric acid (0.1– 0.2 mg/ml) in hot water at a temperature of 70 °C–100 °C was performed for 1 min. The flowchart shown in Fig. 2 elaborates the experimental procedure. The drying process was done at three dissimilar sample sizes of diameters 7.64 mm, 9.13 mm, and 9.94 mm at three different temperatures 60 °C, 70 °C and 80 °C and a constant air velocity of 1.5 m/s. The velocity of air passing through the system was measured using digital anemometer GM816 whose velocity range is 0–30 m/s. Data were recorded at an interval of 10 min in both the cases. Weight loss of samples was recorded by using a digital balance (Mettler-Toledo, model PL835S) with a capacity of 81 g and an accuracy of 0.01 g. The moisture content of the green peas during the drying process was determined by the difference in weight resulting from the weighing sample. Drying was carried out until the final moisture content reached to a level less than 4% (w.b).

2.3.

Mathematical analysis

2.3.1.

Moisture content

Moisture content investigation is a critical component of the agro product quality and a function of quality control of the food. Moisture content determination is important for food analysis due to different reasons such as microbial stability,

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Fig. 1 – Schematic diagram of fluidized bed dryer.

Fig. 2 – Flow chart showing the experimental procedure. food quality, food processing operation, etc. The moisture content of the agro product is determined by the following Equation [16].
 Wt
Wd ; ð1Þ MC ¼ Wt where Wt and Wd are mass of green peas at any time ‘t’ and mass of green peas dry matter respectively.

2.3.2.

Moisture ratio

The moisture content remains the same for all samples because of the natural and inherent variances in the initial

moisture content of the samples [17]. It is calculated using the Eq. (2) [18].
 Mt
Me ; ð2Þ MR ¼ M0
Me where Mt, Me, and M0 are the moisture content at any random time, equilibrium moisture content, and initial moisture content respectively. In this model values of equilibrium moisture content (Me) are comparatively small to Mt and M0, hence the error involved in the explanation by assuming that Me is approximately equal to zero and this can be neglected.

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2.3.3.

Effective moisture diffusivity

The mechanism of diffusion has been accepted as the main mechanism involved in the transport of moisture to the surface which then gets evaporated during the drying process. Upon solving Fick’s equation, with the assumptions of negligible shrinkage, moisture relocation by diffusion, temperature, and constant diffusion coefficients, for a sphere, we obtain Eq. (3). MR ¼

    1 2 M
Me 6 X 1 2 p Deff t exp
n ¼ 2 p n¼1 n2 r2 M
M0

ð3Þ

where M, Mo, and Me are the local, initial, and equilibrium moisture content (gm/gm wb) respectively. r, t, and Deff are the radius (m), time (min) and the effective diffusivity (m2/s) respectively. For extensive drying periods, the Eq. (3) can be further modified to consist only of the first term in the expanded series. In such cases, the moisture ratio is denoted by Eq. (4). MR ¼

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2.3.5.

Mathematical model

Many drying models for agro products have been reported in the literature [12,17]. A pair of moisture ratio models was utilized in the fitting of the drying curves. These models are extensively used in most food and biological materials [20]; namely Page and exponential models. Simplification of the general series solution of Fick’s second law results in the derivation of these models. This model was utilized in predicting the drying characteristics of green peas. The exponential model, involving Eq. (10) happens to be a simple lumped model which is often used to explain the process of mass transfer in drying [21]. Because of its uncomplicatedness and high correlation to most of the drying data this model was mostly used. MR ¼ expð
ktÞ


2  p Deff t 6 exp p2 r2

ð4Þ

The logarithmic form of Eq. (4) is: ln ðMRÞ ¼ ln

ln k and 1/ðT þ 273:15Þ plots were used to ascertain the k0 and Ea parameters.



2  p Deff t 6
p2 r2

ð5Þ

From Eq. (5), a plot of ln(MR) versus time is obtained which is a straight line is having a slope as expressed in Eq. (6) as:
2  p Deff ð6Þ Slope ¼ 2 r

ð10Þ

The shortcomings of the Lewis model were overcome in another empirical model called the Page model which has been effectively describing the drying characteristics of certain agricultural products [22,23]. MR ¼ expð
ktn Þ

2.3.6.

ð11Þ

Statistical analysis

To evaluate the goodness of fit for various models, statistical test such as R2, reduced chi-square (v2 ) and root mean square error (RMSE) are used. Lower v2 and RMSE values whereas

The Arrhenius relationship has been used to account for the effect of temperature on effective diffusivity in order to gain the better agreement of the predicted curve with the experimental data. The effect of temperature is demonstrated using the eminent relationship as mentioned in Eq. (7):  
Ea ð7Þ Deff ¼ D0 exp RðT þ 273:15Þ

higher R2 values were selected as the criterion measuring the goodness of fit. These parameters are given by the Eqs. (12), (13) & (14) reported by [24,25,26]:

where Do is the pre-exponential factor (m2/s). Ea, T, and R are the activation energy for moisture diffusion (kJ/mol), temperature (K), and gas constant (8.314 J/mol K) respectively.

n  2 1 X MRpre;i
MRexp;i RMSE ¼ N i¼1

2.3.4.

Activation energy

For obtaining Ea , Eq. (7) can be written in logarithmic form as follows [19]: 

Ea 1 ð8Þ ln ðDeff Þ ¼ ln ðD0 Þ
ðT þ 273:15Þ R The slope of the straight line obtained by the Arrhenius equation provides the value for activation energy (Ea), and the intercept gives the value of pre-exponential factor Do for ‘with blanching’ and ‘without blanching’ technique. The dependency of the two drying constants ks and kp of the two models was evaluated using an Arrhenius type equation, which is shown below in Eq. (9):  
Ea ð9Þ k ¼ k0 exp RðT þ 273:15Þ
1

where, k and k0 are the drying constant (h ), and the reference value of drying constant (h
1) respectively.

Pn  v ¼ 2

i¼1

MRexp;i
MRpre;i N
z

2

"

ð12Þ #1=2

 Pn  Pn  i¼1 MRi
MRpre;i : i¼1 ðMRi
MRexp;i R2 ¼ rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi hP  2 ihPn  2 i n i¼1 MRi
MRpre;i i¼1 MRi
MRexp;i

2.4.

ð13Þ

ð14Þ

Energy consumption

In a Fluidized bed dryer, energy consumption can be calculated using thermal energy (Eth) and mechanical energy (Emec). Thermal energy and mechanical energy consumed by blower were calculated using Eq. (15) [27] and Eq. (16) [28], respectively. Eth ¼ ðAvqa Ca DTÞt

ð15Þ

Emec ¼ DPvair At

ð16Þ

where A is the tray area (m2), v is the air flow rate (ms
1) and, DT is the temperature difference (approx. 3–5 K). Also, DP, Ca, and qa are pressure difference (mbar), specific heat capacity (kJ

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kg
1 K
1) and density (kg m
3) of inlet air, respectively, and are calculated using Eq. (17) and Eq. (18) [15], respectively: 101:325 ð17Þ qa ¼ 0:287Tabs 3:83719Tabs 9:45378Tabs 2 5:4903Tabs 3 þ
104 107 1010 4 7:92981Tabs þ 1014

Ca ¼ 1:04841


2.4.1.

ð18Þ

Energy efficiency

Energy efficiency of the dryer is obtained using the ratio of the energy used for evaporation of moisture from the sample to the total consumed energy. Energy efficiency was determined using Eq. (19) [28]: Qw ge ¼ Eth þ Emec

ð19Þ

Fig. 3a – Comparison of moisture content, ‘with blanching’ and ‘without blanching’ technique for diameter 7.64 mm at temperature 60 °C, 70 °C and 80 °C.

where Qw has consumed energy for the moisture evaporation (kJ) and was calculated using Eq. (20) [27]: Q w ¼ hfg  mw

ð20Þ

hfg and mw are the latent heat of vaporization and the mass of removed water (kg), and was calculated using Eqs. (21a) or (21b) [29] and Eq. (22): hfg ¼ 2:503  106
2:386  103 ðTabs
273:15Þ

273:16

 Tabs ðKÞ  338:72   0:5 hfg ¼ 7:33  1012
1:60  107 Tabs 2

ð21aÞ 338:72

 Tabs ðKÞ  533:16

ð21bÞ

W0 ðM0
Mf Þ 100
Mf

ð22Þ

mw ¼

Mf is the final moisture content of drying samples (g water/g wet matter) and Tabs is the absolute temperature of drying air.

2.4.2.

Fig. 3b – Comparison of moisture content, ‘with blanching’ and ‘without blanching’ technique for diameter 9.13 mm at temperature 60 °C, 70 °C and 80 °C.

Energy cost analysis

To present effective cost estimation for drying of green peas we have considered the energy utilized in drying. In blanching process, we have considered the cost for thermal energy (it consists of thermal energy for drying and energy used for boiling the water for blanching), the mechanical energy of the blower and chemical used for blanching. For ‘without blanching’ technique only thermal energy for drying and mechanical energy of the blower were considered. So we can calculate total cost using the Eq. (23): ð23Þ

3.

Results and discussion

The curve depicted the removal of moisture of three different dimensions with drying temperature at 60 °C, 70 °C and 80 °C using ‘with blanching’ and ‘without blanching’ techniques are given in Figs. 3(a), 3(b) and 3(c). The variation of moisture ratio of three different dimensions with drying temperature at 60 °C, 70 °C and 80 °C using ‘with blanching’ and ‘without blanching’ techniques have been shown in Figs. 4(a), 4(b) and 4(c).

Fig. 3c – Comparison of moisture content, ‘with blanching’ and ‘without blanching’ technique for diameter 9.94 mm at temperature 60 °C, 70 °C and 80 °C.

3.1. Comparison of moisture content for blanching & without blanching technique The initial moisture content of green peas was approximately 67–74% on the wet basis for with blanching and 72–77% on the

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gone ‘with blanching’ decreased more rapidly in comparison to ‘without blanching’ technique as shown in Figs. 3(a), 3(b) and 3(c). This was due to the fact that blanching of the green peas increased the rate of drying by aiding water loss from the internal regions of the product to its surface during the drying process. Drying time for moisture content of green peas ‘with blanching’ took lesser time in comparison to ‘without blanching’. It also shows that as drying temperature increases, the reduction in moisture also increases in both techniques. This result was similar and confirmed the observations on red pepper [30], Black carrot [31], and peach slices [32]. Drying time also increased with an increase in the diameter of green peas. The shape has no significant effect on the drying time.

Fig. 4a – Comparison of moisture ratio, ‘with blanching’ and ‘without blanching’ technique for diameter 7.64 mm at temperature 60 °C, 70 °C and 80 °C.

3.2. Comparison of moisture ratio for ‘with blanching’ & ‘without blanching’ technique Figs. 4(a), 4(b) and 4(c) shows that when ‘with blanching’ treatment of green peas was done; the moisture ratio reduces more rapidly in comparison to ‘without blanching’. It was also observed that as drying temperature increases, the reduction in moisture ratio also increases in both techniques. It also shows that the moisture ratio of green peas at 80 °C took lesser drying time in comparison to 60 °C and 70 °C.

3.3.

Fig. 4b – Comparison of moisture ratio, ‘with blanching’ and ‘without blanching’ technique for diameter 9.13 mm at temperature 60 °C, 70 °C and 80 °C.

Effective moisture diffusivity

The Eq. (7) was used to calculate the operative moisture diffusivity, using the slopes obtained from the linear regression of ln(MR) versus time using ‘with blanching’ and ‘without blanching’ technique as shown in Fig. 5. The coefficient of regressions of a linear relationship and moisture diffusivity evaluated at different temperature and diameter has been presented in Table 1(a) for ‘with blanching’ and Table 1(b) for ‘without blanching’. An increase in the drying temperature results in the increase in the effective moisture diffusivity values as clearly observed from Tables 1(a) and 1(b). This was attributed to the fact that moisture diffusion happens to be an internal process depending upon product temperature which increases with an increase in drying temperature. The effective moisture diffusivity of green peas, ‘with blanching’ technique was more as compared to ‘without blanching’ technique. Author [33] reported a similar trend, which says that the effective moisture diffusivity has a higher

Fig. 4c – Comparison of moisture ratio, ‘with blanching’ and ‘without blanching’ technique for diameter 9.94 mm at temperature 60 °C, 70 °C and 80 °C.

wet basis for without blanching, which reached a final level of less than 4% when drying of the sample at 60–80 °C. It was observed that moisture content of green peas when under-

Fig. 5 – Drying Curves of moisture ratio (MR) with drying time at different temperature.

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Table 1a – Effective diffusivity and regression coefficient values ‘with blanching’ technique. Diameter (mm)

Drying temperature (°C)

Drying time (min.)

Regression equation

Moisture diffusivity (m2/s)

R2

7.64

60 70 80 60 70 80 60 70 80

100 80 60 160 140 130 190 160 140

y =
0.055x + 0.53 y =
0.072x + 0.67 y =
0.088x + 0.79 y =
0.053x + 0.59 y =
0.068x + 0.61 y =
0.083x + 0.87 y =
0.047x + 0.68 y =
0.065x + 0.75 y =
0.077x + 0.91

5.43  10
9 7.10  10
9 8.68  10
9 7.468  10
9 9.58  10
9 11.69  10
9 7.85  10
9 10.86  10
9 12.86  10
9

0.99 0.99 0.98 0.98 0.99 0.98 0.99 0.99 0.99

9.13

9.94

Table 1b – Effective diffusivity and regression coefficient values ‘without blanching’ technique. Diameter (mm)

Drying temperature (°C)

Drying time (min.)

Regression equation

Moisture diffusivity (m2/s)

R2

7.64

60 70 80 60 70 80 60 70 80

130 110 100 190 170 130 260 240 200

y =
0.036x + 0.49 y =
0.052x + 0.53 y =
0.068x + 0.63 y =
0.029x + 0.61 y =
0.044x + 0.72 y =
0.059x + 0.85 y =
0.022x + 0.64 y =
0.035x + 0.76 y =
0.048x + 0.81

3.55  10
9 5.08  10
9 6.615  10
9 4.08  10
9 5.53  10
9 8.03  10
9 3.67  10
9 5.0  10
9 6.35  10
9

0.99 0.99 0.98 0.98 0.99 0.98 0.99 0.99 0.99

9.13

9.94

value for blanched pineapple in comparison with unblanched pineapple slices. As the diameter of green peas increases, an increase in the effective moisture diffusivity was observed. The determined value of the effective moisture diffusivity of green peas for diameter 7.64 mm, 9.13 mm and 9.94 mm (with blanching) was found to be in range between 5.43  10
9 m2/s to 8.68  10
9 m2/s, 7.468  10
9 m2/s to 11.69  10
9 m2/s and 7.85  10
9 m2/s to 12.86  10
9 m2/s respectively and for ‘without blanching’ it was found to be ranged between 3.55  10
9 m2/s to 6.615  10
9 m2/s, 4.08  10
9 m2/s to 8.03  10
9 m2/s and 3.67  10
9 m2/s to 6.35  10
9 m2/s. These values were within the normal range 10
09–10
10 m2/s for drying of food materials as reported by other authors [13,34].

3.4.

Activation energy

A plot of ln Deff versus 1/ (T + 273.15) for ‘with blanching’ and ‘without blanching’ technique is shown in Fig. 6 and both kinetic parameters (Ea and Do) of Eq. (8) can be estimated from the slope and intercept of the plot of ln(Deff) versus 1/(T + 273.15). The obtained parameters (Ea, Do, and Ko) of Eqs. (8) and (9) for different diameter of green peas are mentioned in Table 2 (a) for ‘with blanching’ and Table 2(b) for ‘without blanching’ for both, Simple and Page models. It was clearly observed that activation energy increases as the size of the green peas increases and it was also observed that for ‘with blanching’ technique require less activation energy in comparison to ‘without blanching’ technique as predicted in Tables 2(a) and 2(b). This was happened due to moisture travels faster in

Fig. 6 – Arrhenius type relationship between effective diffusivity and temperature.

blanched green peas. This is an indication that blanching as a pretreatment can be used to optimize the drying process of green peas in terms of energy utilization. The result showed a similar trend reported by other authors [30,35] who observed that less activation energy is required for ‘with blanching’ technique in comparison to ‘without blanching’ technique. The activation energy values were found to be 19.54 kJ/mol, 19.82 kJ/mol and 20.16 kJ/mol for green peas diameter 7.64 mm, 9.13 mm and 9.94 mm respectively using ‘with blanching’ technique (Table 2(a)) and 26.189 kJ/mol, 26.391 kJ/mol and 26.712 kJ/mol using ‘without blanching’ technique (Table 2(b)). This value was similar to those proposed by other authors [13,20] for green peas and other food products.

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Table 2a – Activation energy Ea for different diameter of green peas using experimental data and values obtained from models (with blanching). Diameter (mm)

Experimental value
6

7.64 9.13 9.94

Exponential model

Page’s model

D0  10

Ea (kJ/mol)

K0

Ea (kJ/mol)

K0

Ea (kJ/mol)

7.50 9.63 11.4

19.54 19.82 20.16

285.72 304.30 359.96

13.551 13.967 14.549

539.15 639.06 690.00

14.716 15.630 16.046

Table 2b – Activation energy Ea for different shapes of green peas using experimental data and values obtained from models (without blanching). Diameter (mm)

7.64 9.13 9.94

3.5.

Experimental value

Exponential model

Page’s model

D0  10
5

Ea (kJ/mol)

K0

Ea (kJ/mol)

K0

Ea (kJ/mol)

4.50 6.25 8.49

26.189 26.391 26.712

321.8 388.77 446.75

14.550 15.547 16.378

561.16 651.97 730.00

15.298 15.797 16.212

Statistical analysis

Two thin layer drying equation models were supplied with the drying data obtained and the statistical results attained from the nonlinear regression of the models was used for appraising goodness of fit (R2, v2, RMSE). The model having the highest R2 and lowest v2, as well as RMSE values, were selected to describe the drying characteristics of the green peas. It was observed that Page model and Simple exponential model gave R2 values greater than or equal to 0.98 and v2 as well as RMSE values were lower than 0.00009 as shown in Table 3(a) (with blanching) and Table 3(b) (without blanching). R2 > 0.95 and RMSE < 10% has been selected as the criterion for an acceptable fit to the model. Our result also agrees with [2,25,36]. It has been observed that temperature affects the drying constant in Page model (kp) and exponential model (ks). An increase in the temperature of drying results in an increase in the drying constant in exponential (ks) and Page model (kp) for ‘with blanching’ and ‘without blanching’. For diameter 7.64 mm, ks increased from 1.815 to 2.900 h
1 with an increase in air temperature from 60 °C to 80 °C for ‘with
1

blanching’ and 1.589 to 2.539 h for ‘without blanching’ as given in Tables 4(a) and 4(b) respectively. The kp increases 2.060 to 3.129 h
1 for ‘with blanching’ and from 1.758 to 2.510 h
1 for ‘without blanching’ as given in Tables 4(a) and 4(b) respectively for the same increase in temperature. A like

result was obtained for another diameter of green peas as well. The temperature had a more prominent effect upon the Page model. The value of ‘n’ has no significant bearing (p > 0.05) as far as the Page model was considered. Upon comparison amid the values of R2 , v2 and RMSE the Page model was found to be a better fit than simple (exponential) model. The energy activation values assessed from diffusivity data were found to be in close estimation to the energy activation values obtained from drying kinetics data. It was also observed that the experimental data is very close to the statistical model (Page model and simple exponential model) which gives a strong validation of our result as shown in Figs. 7(a) and 7(b).

3.6.

Total energy consumption and energy efficiency

The total energy consumed in drying green peas at different air temperatures is presented in Figs. 8(a) and 8(b). From this Figure, it can be seen that energy consumption of drying process decreases from 10.478 to 6.2866 kWh for ‘with blanching’ technique and from 13.621 to 10.478 kWh for ‘without blanching’ technique with increasing air temperature from 60 to 80 °C. Figs. 8(a) and 8(b) shows the values of energy efficiency for the green peas drying. Energy efficiency varies from 5.24 to 8.738 for ‘with blanching’ technique and from 4.033 to 5.243 for ‘without blanching’ technique. These values agree well with those reported in the literature. Moreover, the obtained results

Table 3a – Coefficients of R2 ; v2 and RMSE of the models using fluidized bed dryer for green peas (With blanching). Model

Page simple exponential

R2

v2

RMSE

60 °C

70 °C

80 °C

60 °C

70 °C

80 °C

60 °C

70 °C

80 °C

0.998 0.998

0.999 0.998

0.998 0.999

0.00008 0.00009

0.000078 0.000089

0.00008 0.00009

0.0074 0.0086

0.0071 0.0084

0.0074 0.0086

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Table 3b – Coefficients of R2 ; v2 and RMSE of the models using fluidized bed dryer for green peas (without blanching). R2

Model

Page simple exponential

v2

RMSE

60 °C

70 °C

80 °C

60 °C

70 °C

80 °C

60 °C

70 °C

80 °C

0.999 0.999

0.999 0.998

0.998 0.999

0.000081 0.000089

0.00008 0.00009

0.000079 0.00009

0.0074 0.0084

0.0074 0.0086

0.0073 0.0086

Table 4a – Regression analysis for drying models (with blanching). Diameter (mm)

7.64

9.13

9.94

Simple (exponential) model
1

Page model 2

T (°C)

ks (h )

R

60 70 80 60 70 80 60 70 80

1.815 2.323 2.900 1.613 2.133 2.709 1.425 1.925 2.690

0.99 0.99 0.99 0.99 0.98 0.99 0.99 0.98 0.99

kp (h
1)

N

R2

2.060 2.618 3.129 1.789 2.374 3.031 1.515 2.135 2.712

0.992 0.981 0.970 0.901 0.982 0.971 0.985 0.970 0.961

0.99 0.99 0.99 0.99 0.99 0.99 0.99 0.99 0.99

Table 4b – Regression analysis for drying models (without blanching). Diameter (mm)

7.64

9.13

9.94

Simple (exponential) model
1

Page model 2

T (°C)

ks (h )

R

60 70 80 60 70 80 60 70 80

1.589 2.012 2.539 1.323 1.616 2.129 1.105 1.576 2.109

0.99 0.98 0.99 0.99 0.99 0.99 0.98 0.99 0.99

Fig. 7a – Comparison of experimental and predicted moisture ratio of Green peas ‘with blanching, technique.

kp (h
1)

n

R2

1.758 2.141 2.510 1.447 2.002 2.450 1.235 1.658 2.150

0.965 0.949 0.938 0.972 0.955 0.947 0.981 0.969 0.958

0.99 0.99 0.989 0.99 0.99 0.98 0.98 0.99 0.99

Fig. 7b – Comparison of experimental and predicted moisture ratio of Green peas ‘without blanching’ technique.

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3.7.

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Cost analysis

From Table 5, it has been observed that the cost incurred for drying ‘with blanching’ technique was (43.43–26.24) and for ‘without blanching’ technique was (55.85–42.96). Hence, ‘with blanching technique’ is comparatively effective instead of ‘without blanching technique’ based on drying cost of green peas.

3.8.

Fig. 8a – Energy consumption (kWh) for drying of green peas at different air temperatures and 7.64 mm diameter.

indicate that increasing temperature increases the energy efficiency. Energy efficiency was calculated using Eq. (19), and the results are shown in Table 5. These observations were in good agreement with the results reported for thin layer drying of apple slices [15], Chamomile [27], and Russian olive [37].

Conclusion

In this research work, the drying of green peas has been studied under with blanching & without blanching techniques using Fluidized bed dryer at a temperature of 60 °C to 80 °C. The study investigates the effect of particle diameter and drying air temperature on drying kinetics and also investigates energy consumption, energy efficiency and the cost of drying processes. The results from the experiment indicate that as the diameter of green peas increases, the drying time to attain equilibrium moisture content also increases. The moisture content, as well as moisture ratio, reduces as drying time increases and finally, it retains less than 4% moisture

Fig. 8b – Energy efficiency (%) for drying of green peas at different air temperatures and 7.64 mm diameter.

Table 5 – Values of the energy efficiency and cost for drying green peas having diameter 7.64 mm. Air temp. (°C)

60 70 80

Air flow rate (m s
1)

1.5

Drying time (min)

Energy efficiency (%)

Cost ( )

With blanching

Without blanching

With blanching

Without blanching

With blanching

Without blanching

100 80 60

130 110 100

5.24 6.553 8.738

4.033 4.766 5.243

43.4272 34.8336 26.2425

55.8461 47.2525 42.9598

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content. The time taken with blanching was less compared to without blanching. The effective moisture diffusivity increased with increase in drying air temperature and also it increases with the diameter of green peas for both the techniques. Diffusivity is higher in case of with blanching technique as compared to without blanching technique. Further, drying data were fitted to ‘‘two thin layers drying models” in both techniques and goodness of fit has been determined using R2, v2 and RMSE. Page model was selected as the best model, on the basis of goodness of fit. Total energy consumption decreases with an increase in air temperature for with blanching and without blanching techniques. In case of without blanching technique, it consumed more energy as compared to with blanching technique. Energy efficiency varies from (4.0–8.7)% and increases with the drying air temperature. Hence, without blanching technique exhibited (22–40)% more expensive compared to the blanching technique. With blanching technique not only shows cost reduction of drying but also maintains the good quality of green peas.

Conflict of interest The authors declare that there is no conflicts of interest.

Acknowledgments The authors acknowledge special thanks to Mr. Ravi Kumar for helpful discussion.

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