Modeling and Process Optimization of Parboiling of Paddy Rice
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Date
2018
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Addis Ababa University
Abstract
Now a day’s parboiled rice has become popular in the world. This paper concentrate on finding a
mathematical model that describes the parboiling processes and selection of process time and
temperature for adequate parboiling. For this purpose different mathematical models were
selected and fitted to the experimental moisture ratio of soaking and drying process. The best
mathematical models were selected based on maximum value of R2, and minimum value of
standard error and mean square deviation. For the soaking process four mathematical models
were fitted to the experimental moisture ratio obtained by soaking the paddy at the temperature
of 30, 40, 55 and 650C for 1, 2, 3 and four 4hr. After doing non linear regression with SPSS,
Henderson and Pabis model gave the best result (with R2=0.997, standard error = 6.36×10-3 and
mean square deviation =8.1×10-5). The coefficient of the Henderson and pabis model a and k
were determined in terms of soaking temperature. The drying process takes place in two stage
drying operation by fluidized bed and oven drying method respectively. The first stage drying
process carried out at a temperature of 40, 60, 80 and 1000C and relative humidity of 50, 35, 25
and 15% at constant air velocity of 2.7m/s to reduce the moisture content from 37.25% to 19%
wet basis. In the second stage of drying the moisture content were reduced from 19 to 11.32%
wet basis at 450C. To select the best mathematical models that describe the drying process non
linear regression were performed by SPSS on eight selected thin layer mathematical models. The
regression result showed the Two Term parameter model gave maximum R2 (0.994) ,
minimum standard error (0.02903038) and minimum mean square deviation (1.405×10-3) .The
degree of gelatinization (x) during the steaming process were calculated from the absorbance
value by using amylose iodine method . The absorbance values were measured after the paddy
steamed at 70, 80, 90 and1000C for 12, 13.5, 15 and 16.5 min. The regression analysis of
−��������(1 − ����) against time showed a linear relationship with R2 of 0.968. This indicate that the
gelatinization process follow a first order reaction. The rate constant of the gelatinization process
were calculated by using the degree of gelatinization. The activation energy of the gelatinization
process was 55.695KJ/mol. The selection of the parboiling process was carried out by the
minimum time require to soak, steam and the maximum value of head rice yield during the
drying process. Based on these criteria the time required to soak the paddy at 55°C was 5.13hr
and the time require to steam the rice to gelatinize the up to completion (99.99999999%) at
120°C was 62.2min. In the case of drying the optimum time and temperature were 40°Cand 20.989min in the fluidized bed drying and 45°C and 209.911min in the oven drying. The
advantage of parboiling over un parboiled rice were evaluated and it have better nutritional
value (calcium=365.54mg/kg, phosphorous=3594.75mg/kg, potassium=2503mg/kg and
carbohydrate=79.68%), high head rice yield (72.48%), minimum solid loss (0.41%) during
cooking, better sensory characteristics and good textural characteristics than un parboiled rice.
The parboiling process is feasible and has rate of return 27.37% and payback period of 2.35year.
Description
Keywords
Parboiling, modeling, optimization, soaking, drying, gelatinization, yield, paddy rice, moisture ratio