SUMMARY AND CONCLUSIONS
The spouted bed is a modified version of fludised bed, where a cyclic movement of solids take place i.e., from the central spout to the periphery and back into the annulus. Coating is a special application of spouted bed in which a thin layer of liquid is deposited on the spouted solid particles in the bed and is dried by the action of hot air as the particles follow the cyclic motion in the bed. The advantage of this system is that a relatively uniform coating is obtained.
The present study was undertaken to find the effect of the processing parameters on the quality of the product. Tomato sauce was used to coat roasted gram in a laboratory scale spouted bed. Response surface method was used for designing the experimental combination as it has characteristics reduced number of experiments. The combination of experiments were based on the Central Composite Rotatable Design (CCRD) with 4 variables at 5 levels. The variables were inlet air temperature (60, 65, 70, 75 and 80�C), rate of addition of sauce (100, 125, 150, 175, 200 gm/h), sample size (650, 700, 750, 800, 850 gm) and air velocity (80, 90, 100, 110, 120 m/min). The effect of these parameters were seen on coating thickness, percentage gain in weight, final moisture content of the product, product output, attrition loss and the sensory qualities of the product. The results obtained are summarised below.
1. It was found that inlet air temperature, rate of addition of sauce, sample size and air velocity affected the coating thickness significantly (P<0.01). The coating thickness varied between 0.0899 mm to 0.2846 mm. To the data a second order model was fitted which had r2 value of 0.8947 and was acceptable at 1% level of significance. Optimization of process variables was done and it was found that the optimized values for inlet air temperature, sample size and air velocity lied far away from experimental range, thus, compromised optimumization was carried out. The compromised optimum conditions were obtained as 66.68�C for inlet air temperature, 158.15 gm/h for rate of addition of sauce, 688.05 gm for sample size and 86.17 m/min for air velocity. The maximum coating thickness which would be obtained under these conditions was found to be 0.320 mm.
2. Percentage weight gain varied between 2.01 to 4.68% and was affected by inlet air temperature, rate of addition of sauce and air velocity significantly (P<0.05). The second order model had r2 value of 0.94852 and was acceptable at 1% level of significance. The compromised optimum process conditions were 69.55�C temperature, 165.715 gm/h, sauce addition rate 746.619 gm sample size and 81.00 m/min air velocity. The maximum percentage gain in weight under these conditions were 4.39%.
3. The results show that final moisture content varied from 2.5776 to 5.9458. Rate of addition of sauce affected the final moisture content of the product while the other parameters did not affect significantly (P>0.1) . The r2 value for the model was 0.6979 and was significant at 5% level. The compromised optima was found to be 70.67�C temperature, 199.52 gm/h rate of addition of sauce, 741.5 gm sample size and 101.65 m/min air velocity. The final moisture content under these optimised conditions was 6.41%.
4. The final output obtained ranged from 558.82 to 671.51 gm and was found to be affected significantly (P<0.01) by the sample size. The model for output had r2 value of 0.8971 and was acceptable within 1% level of significance by F-test. The compromised optimum conditions were temperature 71.35�C, sauce addition rate 142.02 gm/h, sample size 842.7 gm and air velocity 105.85 m/min. to give an output of 691.35 gm.
5. It was found that sample size affected the attrition loss significantly (P<0.05). The linear form of temperature, air velocity did not affect the loss but their square terms affected significantly. The model had r2 of 0.757 and was acceptable within 5% level of significance. The compromised optima was found to be temperature 69.85�C, rate of addition of sauce 159.39 gm/h, sample size and 828.132 gm and air velocity 80.08 m/min. Under these conditions the maximum loss would be 78.63 gm.
6. Sensory evaluation of the product was done based on Hedonic rating and the ratings of overall acceptability of the product were analysed. It was found that the r2 value of the model was 0.7649 and was acceptable 5% level of significance. The square terms and the interaction terms were found to affect the ratings significantly (P<0.05). The optimised conditions were temperature 68.5�C, rate of addition of sauce 45.01 gm/h sample size 724.579, and air velocity 98.5 m/min. The ratings obtained at these conditions for taste, appearance, flavour hardness and overall acceptability lied in the range of ‘liked moderately’ to ‘liked very much’.
Based on the results the following conclusions were drawn :
1. Coating of tomato sauce on roasted gram can be achieved in spouted bed.
2. Lower temperature and air velocity resulted in greater coating thickness and percentage gain in weight. Loss due to attrition was greater at higher temperature and air velocity.
3. Temperature of 65�C, rate of addition of sauce of 160 gm/h, sample size of 750 gm and air velocity of 85 m/min would give better coating thickness, percentage gain in weight, lower loss due to attrition and would be accepted by the consumer.
Introduction Review material and methods results and discussion summary