P.K. Chattopadhyay

Rheological properties of rice dough for making rice bread

The rheological properties of two varieties of rice with Hydroxy propyl methyl cellulose (HPMC) added as gluten substitute were studied using a farinograph and a rheometer and compared with wheat dough to find its suitability for making rice bread. The water absorption and dough development time data were obtained from the farinogram. The tests conducted in the rheometer were oscillation measurements (frequency sweep from 0.1 to 20 Hz at 1% strain), shear measurement (shearing from 0.1 to 5 s−1) and creep tests with an instant loading of 50 Pa for 60 S. Baking tests were conducted with all the dough samples and the loaf volume and moisture loss of bread were measured. The farinogram showed that rice flour supplemented with HPMC reached a consistency of 500 BU at a later time than that of standard wheat dough. The rheological measurements from the oscillation tests and creep tests showed that the rice dough with 1.5% and 3.0% HPMC had similar rheological properties to that of wheat flour dough and was suitable for making rice bread. The long grain rice sample produced a rice bread with better crumb texture.

Optimisation of osmotic preconcentration and fluidised bed drying to produce dehydrated quick-cooking potato cubes

Abstract Osmotic preconcentration followed by fluidised bed drying of potato pieces to produce dehydrated quick-cooking potato was studied. Process parameters of both operations were optimised using response surface methodology. Since solid gain affects taste of the product, the process was optimised for maximum water loss and minimum solid gain. A solution of 50% sugar and 10% salt at 47°C for 4 h was found to be optimum for osmotic preconcentration of potato cubes. Moisture content was reduced from 84% to 60% moisture content (w.b.). Minimisation of final moisture content and bulk density with acceptable colour was the basis for optimising the fluidised bed drying conditions. Drying at 140°C for 10 min at 5.3 m/s followed by thin layer air drying at 50–60°C and 0.75 m/s for about 7 h was found to be optimal. Time to rehydrate/cook the processed-potato was only half that for fresh-potato. Organoleptic overall acceptability of the cooked processed-potato was almost same as that of cooked fresh-potato.

Thermal conductivity and diffusivity of rice bran

A transient heat flow method for the simultaneous determination of thermal conductivity and diffusivity of rice bran is described. Experiments were performed to study the effects of moisture content, temperature and bulk density of rice bran on these properties. It was observed that the thermal conductivity and diffusivity of rice bran increased from 0·086 W/m°C and 9·34 × 10−8m2/s respectively to 0·158W/m°C and 12·1 × 10−8m2/s when the moisture content, temperature and bulk density of bran increased from 7% (w.b.), 42°C and 410kg/m3 to 15% (w.b.), 68°C and 490 kg/m3, respectively.

Moisture diffusion modelling of drying in parboiled paddy components. Part I: starchy endosperm

Abstract A non-dimensionalised isothermal liquid diffusion drying model in prolate spheroid geometry using prolate spheroidal co-ordinate system was developed, and applied to drying of parboiled polished rice. Using appropriate hydrothermal treatment the parboiled polished rice was prepared, and its drying characteristics were determined using fluidised bed drying at air temperatures varying from 50 to 100 ∘ C. A mathematical model simulating the drying was solved using the finite difference methodology. The liquid diffusion coefficients of starchy endosperm of parboiled polished rice while drying with various air temperatures were determined by minimising the sum of squared differences between experimentally observed and model predicted characteristics. The developed models showed good agreement with the experimentally observed data. Temperature dependence of liquid diffusion coefficients was expressed by an Arrhenius type of equation, which had a high correlation coefficient: D vs =1.079706×10 −7 exp (−2036.252438/T a ) [ r =0.9887]

COMBINATION SOAKING PROCEDURE FOR ROUGH RICE PARBOILING

Soaking of rough rice is the most time-consuming operation in the parboiling process. A combination soaking procedure for parboiling of rough rice was developed based on the gelatinization temperature of rice starch to achieve rapid completion of soaking. The objectives of this study were to determine the gelatinization temperature of rice starch, the soaking characteristics of the rough rice, and prescribe the operating parameters of the combination soaking procedure. Medium-grain rough rice (‘Pankaj’) was selected, and its starch gelatinization temperature was determined as 72°C using alkali degradation and hot stage microscopy methods. Soaking characteristics of rough rice were studied at 60°C, 70°C, and 80°C. Below the gelatinization temperature, soaking proceeded in the normal way; however, above the gelatinization temperature, excessive water absorption, husk splitting, actual cooking of rice kernels, and loss of quality due to soak water contamination were observed. The combination soaking procedure, involving 80°C water as the first stage until an intermediate moisture content of 35.0% d.b. (approx. 45 min) followed by 70°C as the second stage up to the saturation moisture content of 42.7% d.b. (approx. 3 h 15 min), resulted in a 67% time reduction when compared with single-stage soaking at 70°C. Rice from the combination procedure resembled that obtained from 70°C single-stage soaking in all respects. In milling analysis, after parboiling the rough rice from both soaking methods, the polished rice did not show any difference in terms of head rice yield, broken grains produced, and cracked grains produced.

Moisture diffusion modelling of drying in parboiled paddy components. Part II: Bran and Husk

Abstract Multi-component prolate spheroid geometry was used in developing a non-dimensional isothermal liquid diffusion drying model for studying the moisture movement in the composite solids using a prolate spheroidal co-ordinate system. The developed models were solved using a finite difference method and were applied to simulate the drying process of multi-component parboiled brown rice and parboiled paddy. The observed drying characteristics of the input materials prepared by suitable hydrothermal treatment were obtained using a fluidised bed dryer at drying air temperatures ranging from 50 ∘ C to 100 ∘ C. In the multi-component parboiled brown rice drying model, the diffusion coefficients of bran were determined from the diffusion coefficients of the starchy endosperm, and for the parboiled paddy model the diffusion coefficients of husk were determined from the values of starchy endosperm and bran successively. By minimising the sum of squared differences (SSD) between experimentally observed and model predicted characteristics the liquid diffusion coefficients of bran and husk were determined at the various air temperatures studied. The developed models showed good agreement with the observed drying characteristics of the input materials. The temperature dependence of the diffusion coefficients of the parboiled paddy components was expressed by Arrhenius type of equations Bran : D vb =3.985948×10 −6 exp (−4096.003100/T a ), ( r =0.9923), Husk : D vh =1.655885×10 −5 exp (−4230.121506/T a ), ( r =0.9859). The diffusion coefficients of the parboiled paddy components were comparable to the recent findings on raw paddy and the differences encountered may be attributed to the properties of the component material.

Mathematical prediction of moisture profile in layers of grain during pre-conditioning

Abstract Wheat grain soaking characteristics were modelled based on Ficks law of diffusion assuming the grain was a composite sphere having a starchy endospermic core and an outer concentric shell of bran. The governing equation in spherical co-ordinate was solved using a finite difference method. From soaking data collected for pearled wheat (starch) and whole wheat (starch and bran), liquid diffusion coefficients of starch and bran are evaluated as 1.91533 × 10−10 and 1.78339 × 10−10 m2/s, respectively at an ambient temperature of 30 °C, by minimising the sum of squared deviation between the observed and predicted soaking results. The developed models for soaking of pearled and whole wheat were capable of predicting the moisture profile as well as the individual component moisture content with time and were found to be in good agreement with experimental data.

Surface area of general ellipsoid shaped food materials by simplified regression equation method

Abstract Surface area of food materials resembling geometrical general ellipsoids can be evaluated theoretically using numerical techniques. The existing general ellipsoid surface area numerical model of triangular elements that was used to develop the ready reckoner table of surface area, was employed to develop individual linear regression equations for different thickness/length curves and an overall equation to cover the entire range of general ellipsoidal objects. As the thickness/length curves exhibited a linear nature, simple linear regression was carried out and the fitted individual equation produced very high correlation coefficients that were significant at the 99% level. Statistical analysis revealed that the null hypothesis on intercepts and slopes of the individual equations were rejected, showing the existence of a definite intercept and slope on every fitted thickness/length. The obtained smaller values of the confidence intervals at the 99% level of significance depicted the accuracy of the developed regression constants. Of the developed regression constants, the intercepts followed a clear linear trend whereas for the slopes a second-order polynomial was fitted, and from the obtained combined regression constants the overall regression equation was developed. In the error analysis, based on the absolute average error, the performance of the individual equations was better than the overall equation. The error produced by the developed equations reduced when the thickness/length and width/length increased. For a practical range of ellipsoidal objects having a thickness/length range greater than 0.1, the absolute average error produced would be less than 0.8652% for the individual equation and less than 1.7264% for the overall equation. The following overall equation with only five regression constants would be useful in finding the surface area and could completely replace the model and the ready reckoner table: A s =π −1.02274828×10 −2 L 2 +4.92988817×10 −2 LW+3.43560219×10 −1 LT−5.29422959×10 −2 WT+2.35999474×10 −1 WT 2 /L (R=0.999575).

On the development of a ready reckoner table for evaluating surface area of general ellipsoids based on numerical techniques

Surface areas of food materials resembling general ellipsoids can be obtained from the principal dimensions by numerical techniques. Nodes were identified on the surface along the principal planes in the developed model for generating a series of flat triangular element grids and their assembly gave the surface area of the ellipsoidal material. The model was validated against simpler geometries, such as sphere, prolate spheroids and oblate spheroids, and was found to be accurate. With the combination of non-dimensional input in the model and scaling factor a two-dimensional ready reckoner table of reduced surface areas was developed, which covered the entire range of sizes and shapes of general ellipsoid. The method of obtaining the intermediate values in the table by univariate and bivariate linear interpolation was also outlined and the interpolation error was in the range of 0.0-0.57%. The nomogram representation of the table can be utilised for rough estimates. The actual surface area of the object is obtained from the reduced surface area by multiplying it by the scaling factor.