MATERIALS AND METHODS
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Preliminary experiments were conducted to explore the possibility of coating roasted gram with tomato sauce and identify the variables affecting the process. Based on the preliminary results the combination of final experiments were designed using Response Surface Methodology. A Central Composite Rotatable Design (CCRD) with 4 variables and 5 levels were used. The details of the materials, equipment, experimental design, and the procedures are reported below.
Roasted gram and tomato sauce were the main raw material. Roasted gram was processed from the main market, Rudrapur. Dehusked grains were separated from the lot. The moisture content of the lot was measured using standard method. The moisture content was found to be (8.34%). To have uniform initial moisture content of about 4%, the sample was then kept in oven at 60�C for about 4 hours.
The samples were then divided into 1 kg lot and sealed in polyethylene bags. Double polythene sealing was done to prevent moisture migration from the atmosphere. Standard brand tomato sauce produced by Kissan was procured from the local market, Pantnagar.
The items that were used in the study along with specifications are given below .
Table 3.1 : List of items and their specifications
| Equipment | Specification |
Make |
| Hot air oven | Temperature 40-150�C | |
| Triple beam balance | Least count 0.1 gm | Keroy |
| Electronic balance | Mass Capacity 100 gm | |
| (Meter AE 166) | Least count 0.0001 gm | AE 166 |
| Measuring cylinder | Capacity 1000 ml, 100 ml least count, 10 ml, 1 ml respectively | Borosil |
| Dessicator | Size 20 cm x 20 cm x 12 cm | |
| Thermometer | Least count, 1�C | |
| Anemometer | Max. 10,000 m, least count 1 m |
The experimental set-up consisted of a laboratory spouted bed which was designed and developed by Mukherjie and Tiwari (1981). It consisted of a drying/ coating chamber, air delivery system and air heating system.
The air delivery system consisted of a centrifugal air blower, driven by a 5 HP single phase electric motor. The diameter of the inlet pipe was 2 cm at the base of the drying chamber. A by-pass valve was provided to regulate the air flow of the blower.
The air heating system consisted of a single phase 4 KW heater (4 heaters of 1 KW each attached in series). This heater assembly was placed in the pipe connecting the blower and the inlet pipe. The heater was connected to a 220 V electric power supply through a dimmerstat. With the help of the dimmerstat, the input voltage for the heater was controlled to obtain the required temperature.
The drying coating system consisted of vertical glass cylinder of 15 cm diameter and was mounted on a conical base. The height of the chamber was 1.5 m. This height was sufficient to retain the particles in the chamber. The base of the conical portion consisted of an inlet port of 2 cm for air inlet. An outlet was provided near the base for with drawing the sample. The schematic layout of the spouted bed used in the experiment is shown in Fig. 3.1.
The preliminary experiments were conducted to identify the process valuables and their range to produce an acceptable product. The details of the preliminary trial and their results are summarised below.
3.4.1 Sample size
The sample size was decided based on the spouting behaviour of the grains at the maximum and minimum spouting air velocity of the equipment. It was found that the maximum air velocity for spouting that could be obtained on the set up was 130 m/min and the maximum spoutable sample size was 900 gm.
3.4.2 Sauce addition rate
It was found that product coating was possible between 100-225 gm/min rate of addition of sauce. Above this range agglomeration of the product took place and the coating processing became very irregular. Below this range the product was not satisfactory.
3.4.3 Drying temperature
The range was selected based on the capacity of the heater. It was found that the maximum temperature that could be attained was 90�C. The product was found to adhere to the wall surface for temperatures less than 60�C.
3.4.4 Drying time
Drying time of 30 min was sufficient to produce satisfactory product at the end of the process. Higher drying time resulted in loss of dry matter in the form of powder and also lowering of drying time resulted in sticky products.
Based on preliminary experiments temperature, air velocity, amount of sauce and sample size of roasted gram were selected as independent variables for coating in the spouted bed. The range of these variables was selected considering minimum and maximum values that were obtained during the preliminary experiments. Five levels of each variable were taken and are given in Table 3.2.
Response surface methodology was used to decide the combination and interactive effects of variables on the responses. The experimental combination is given in Table 3.3. The combinations consisted of 31 experiments with first 16 experiments as factorial point, next 8 as star points and remaining 7 at centre point.
Table 3.2 : Process variables and their levels
| Process variables | Code |
Coded levels |
||||
–2 |
–1 |
0 |
+1 |
+2 |
||
| Inlet air Temperature �C | X1 |
60 |
65 |
70 |
75 |
80 |
| Rate of addition of sauce gm/h | X2 |
100 |
125 |
150 |
175 |
200 |
| Sample size (gm) | X3 |
650 |
700 |
750 |
800 |
850 |
| Air velocity (m/min) | X4 |
80 |
90 |
100 |
110 |
120 |
To coat the gram with tomato sauce the following procedure was adopted. The spouted bed was run and the heater was turned on till the desired temperature and exit air velocity was obtained. The weighed sample, of gram, as per the experimental design, was then placed in the drying chamber. The tomato sauce and water in the ratio of 2:1 by volume was filled in the feeder and its outlet was so adjusted that the solution was fed at the desired rate. The experiment was allowed to run till the coating process was completed. The sample was then allowed to dry in the drying chamber for 30 min.
Samples were then withdrawn at the end of the experiments and kept in polyethylene bags and sealed. It was then used for quality sensory evaluation.
3.7.1 Moisture content
Moisture content of the samples drawn during the drying process was determined by the method suggested by Horwitz (1978).
Sample was first ground and spread in a flat bottom petridish having tight fitting cover and known weight. The sample was then placed in the oven maintained at 130�C and the cover was removed. The duration of drying was 90 min. After drying the cover was replaced and the samples were cooled in a desicator to room temperature. The sample with petridish was weighed immediately after cooling. Dish weight was substracted from the two weights (i.e., before and after placing the samples in the oven) and recorded as W1 and W2, respectively.
The moisture content, wet basis (w.b.) of the sample was calculated by using the equation.
% Moisture content, (w.b.) = {(W1 – W2)/W1 }/100
Where,
W1 = Weight of original sample, gm
W2 = Weight of sample after oven drying, gm.
3.7.2 Determination of coating thickness
Thickness of coating was determined by following the procedure developed by Jindal (1974). A known number of steel balls were taken and their diameter and weight measured. A thin uniform layer of varnish was applied over the balls. These balls were then put in a box containing sand. The box was thoroughly shaken so that a uniform layer of sand particles get adhered to the surface of the balls. The balls were then taken out from the box and weighed. From the above data, weight of sand that adhered to the surface of one steel ball, was computed. Then a known number of grains (coated and uncoated) particles were taken and the procedure was repeated for each case. The weight of sand that adhered over the surface of one grain particle was thus obtained. The surface area of one particle was then computed by the following equation.
S1 / W1 = S2 / W2
Where,
S1 = Surface area of one steel ball
S2 = Surface area of one grain particle.
W1 = Weight of sand adhered over steel ball.
W2 = Weight of sand adhered over a grain particle
Once the surface area of the grain particles were obtained the diameter of the grains were calculated. The coating thickness was the difference between the radius of the coated and uncoated grain particle.
3.7.3 Weight gain (%)
The standard methods to evaluate the change in weight of the coated and uncoated material could not be applied to the spouted bed, as there was considerable loss due to attrition of the particles. One hundred whole grains were selected from the coated and uncoated gram and the difference of weights of the two were taken. Five such replications were done and average of these were recorded. The percentage gain in weight was then computed.
3.7.4 Attrition loss
It was observed that there was sufficient loss of material in the form of powders due to attrition between the particles. Direct measurement of which was not possible as the powders escaping from the system could not be trapped. So, the loss due to attrition was calculated by the difference in the theoretical and experimental output of the product based on the dry matter content of the sauce and the roasted gram.
3.7.5 Dry matter content of product
The coated samples were drawn from the spouted bed at the end of the process and sealed in polythene bags. Their weights were recorded. The moisture content of the samples were measured. The dry matter content of the product was then calculated by the following formula.
dm = W (1– M/100)
Where,
dm = dry matter content of sample, gm
W = Weight of sample
M = Moisture content of material w.b.
Sensory quality is the combination of different senses of perception coming into play in choosing and eating a food. The sensory quality is important to both the consumer and the processor.
To test the organoleptic characteristics, sensory evaluation was carried out with the help of 10 member panel. The sensory evaluation was done on a 9 point hedonic scale. The sensory evaluation was done for liking on the basis of flavour, taste, appearance, hardness and overall acceptability of the product.
Sensory evaluation of sauces coated roasted gram
Hedonic Rating
| Liked extremely | 9 |
| Liked very much | 8 |
| Liked moderately | 7 |
| Liked slightly | 6 |
| Neither liked nor disliked | 5 |
| Disliked slightly | 4 |
| Disliked moderately | 3 |
| Disliked very much | 2 |
| Disliked extremely | 1 |
The data were analysed using MINITAB Statistical Package on a Hewlett Packard Computer. Second Order Quadratic equations were developed for the best estimate of parameters contour plotting and for optimisation. Analysis was done with the help of spread sheet Lotus 123, Harvard Graphics-3, Minitab, MR (Multiple Response Methodology) and surfer. The results of the data analysis are given in chapter 4 and discussed.
Response surface design of experiments (CCRD in 4 variable)
Expt. No. |
X1 |
X2 |
X3 |
X4 |
|
1 |
Factorial point | –1 |
–1 |
–1 |
–1 |
2 |
+1 |
–1 |
–1 |
–1 |
|
3 |
–1 |
+1 |
–1 |
–1 |
|
4 |
+1 |
+1 |
–1 |
–1 |
|
5 |
–1 |
–1 |
+1 |
–1 |
|
6 |
+1 |
–1 |
+1 |
–1 |
|
7 |
–1 |
+1 |
+1 |
–1 |
|
8 |
+1 |
+1 |
+1 |
–1 |
|
9 |
–1 |
–1 |
–1 |
+1 |
|
10 |
+1 |
–1 |
–1 |
+1 |
|
11 |
–1 |
+1 |
–1 |
+1 |
|
12 |
+1 |
+1 |
–1 |
+1 |
|
13 |
–1 |
–1 |
+1 |
+1 |
|
14 |
+1 |
–1 |
+1 |
+1 |
|
15 |
–1 |
+1 |
+1 |
+1 |
|
16 |
+1 |
+1 |
+1 |
+1 |
|
17 |
Star point | –2 |
0 |
0 |
0 |
18 |
+2 |
0 |
0 |
0 |
|
19 |
0 |
–2 |
0 |
0 |
|
20 |
0 |
+2 |
0 |
0 |
|
21 |
0 |
0 |
–2 |
0 |
|
22 |
0 |
0 |
+2 |
0 |
|
23 |
0 |
0 |
0 |
–2 |
|
24 |
0 |
0 |
0 |
+2 |
|
25 |
Centre point | 0 |
0 |
0 |
0 |
26 |
0 |
0 |
0 |
0 |
|
27 |
0 |
0 |
0 |
0 |
|
28 |
0 |
0 |
0 |
0 |
|
29 |
0 |
0 |
0 |
0 |
|
30 |
0 |
0 |
0 |
0 |
|
31 |
0 |
0 |
0 |
0 |
Introduction Review material and methods results and discussion summary literature cited
