V.K. Jindal

Monitoring milling quality of rice by image analysis

Rough rice is milled to produce polished edible grain by first subjecting to dehusking or removal of hulls and then to the removal of brownish outer bran layer known as whitening. The control of whiteness (degree of milling) and percentage of broken kernels in milled rice is required to minimize the economic loss to the millers. Digital image analysis was used to determine the head rice yield (HRY), representing the proportion by weight of milled kernels with three quarters or more of their original length, and the whiteness of milled rice. Ten varieties of Thai rice were subjected to varying degrees of milling by adjusting the test duration from 0.5 to 2.5 min. Three-dimensional features (namely, length, perimeter and projected area) were extracted from the images of individual kernels in a milled sample and used to compute a characteristic dimension ratio (CDR) defined as the ratio of the sum of a particular dimensional feature of all head rice kernels to that of all kernels comprising head and broken rice in the sample. HRY and CDR were found to be related by power functions based on the above-mentioned dimensional features, with R 2 more than 0.99 in all cases. The CDR based on the projected area of kernels in their natural rest position provided the best estimate of the HRY with the lowest root mean square error of 1.1% among all dimensional features studied. In case of the whiteness of milled samples, the values provided by a commercial whiteness meter and the mean of gray level distribution determined by image analysis correlated with an R 2 value of 0.99. The results of this study showed that two-dimensional imaging of milled rice kernels could be used for making quantitative assessment of HRY and degree of milling for on-line monitoring and better control of the rice milling operation.

Comparison of Rice Flour Pasting Properties using Brabender Viscoamylograph and Rapid Visco Analyser for Evaluating Cooked Rice Texture

Pasting properties of ten Thai rice varieties, with amylose contents in the range of 16 to 33% and stored at 10, 30 and 40 °C for six months were compared using the Brabender Viscoamylograph (VAG) and the Rapid Visco Analyser (RVA) for evaluating the texture of cooked rice. Linear correlations between pasting temperature and viscosity parameters based on RVA showed a different pattern than those based on VAG with high negative correlation coefficients between the peak and breakdown viscosities. Both RVA and VAG indicated peak viscosity to be positively correlated with breakdown viscosity, and negatively with the setback viscosity. Setback and consistency viscosities correlated with each other in both instruments but indicating a negative correlation with breakdown viscosity in VAG only. Pasting temperature determined by VAG and RVA did not show good correlations for rice sample stored at different temperatures neither for individual nor for combined data. Only peak, breakdown and setback viscosities showed significant correlations in the overall data (r > 0.496). The VAG measurements performed better than the RVA in the development of predictive models for evaluating the hardness and adhesiveness of cooked rice based on instrumental texture profile analysis. The springiness and cohesiveness of cooked rice could not be estimated from the pasting properties of rice flour determined by both VAG and RVA. Results showed that both VAG and RVA could be used for evaluating the texture of cooked rice despite the differences in the measurements of the pasting properties of milled rice flours.

DRYING OF SOY PULP (OKARA) IN A BED OF INERT PARTICLES

ABSTRACT Drying of okara, an insoluble pulp residue waste byproduct of tofu production, was investigated in a continuously moving bed of inert particles subjected to vortex-like motion. The experimental variables in their respective ranges included the mass of Teflon pellets used as inert particles (0.4–1.2 kg), feed rate (0.5–1.4 kg/h), inlet air temperature (100–145°C) and airflow rate (195–271 m3/h). The dryer showed good performance in general and produced dry okara with moisture content ranging from 5 to 33% wb depending upon the operating conditions. The product recovery ranged from 80 to 90% on dry basis in most experiments. The specific water evaporation rate in okara drying increased with increasing of the feed rate and mass of Teflon pellets. However, the specific heat consumption decreased with an increase in the okara feed rate. Results showed that specific heat consumption for okara drying in a bed of inert particles was about 3 to 4 times higher in comparison with that of free water.

Artificial neural networks: a new tool for prediction of pressure drop of non-Newtonian fluid foods through tubes

Pressure gradients and the corresponding mass flow rates of five different non-Newtonian fluid foods: 1% solutions of sodium alginate and CMC, 1.5% CMC solution, two different tomato ketchups, oyster sauce, in four different diameter stainless steel tubes ranging from 7.51 to 16.34 mm i.d. were recorded using a continuous recording type tube flow viscometer capable of operating in both transient and continuous flow modes. The fluids were pseudoplastic in nature and followed the power law model. The flow was confined to the laminar flow regime and appreciable slippage occurred in all cases. Commercially available artificial neural networks based on back-propagation and generalized regression algorithm were applied to predict the pressure gradients in tube flow providing mass flow rate, consistency coefficients and flow behavior indices obtained from a low shear rate rotational viscometer, mass density and tube diameters as inputs. The net predicted values closely followed the experimental ones with an average absolute error below 5.44%.

Sorption Isotherms and Moisture Diffusivity in Fried Cassava-Shrimp Chips

Abstract Equilibrium moisture sorption isotherms of fried cassava-shrimp chips were investigated by measuring water activity at 20, 30, and 40°C for modeling transient diffusion of moisture. The sorption isotherms followed a type III shape in water activity range of 0.1–0.9 showing negligible influence of temperature, and were best represented by the GAB, Henderson, and modified Henderson equations. Effective moisture diffusivity of chips based on analytical solution of Ficks law ranged from 0.8 × 10−11 to 2.1 × 10−10 m2/s during exposure to fixed relative humidity (50, 70, and 90%) and temperature (20, 30, and 40°C) environments. An Arrhenius type relationship adequately described the dependence of effective moisture diffusivity both on temperature and relative humidity, and led to good agreement between experimental and estimated transient moisture sorption data.

EQUILIBRIUM MOISTURE CONTENT ISOTHERMS OF MUNGBEAN

ABSTRACT The moisture isotherms of mungbean were determined at temperatures of 35, 45 and 55°C using isopiestic method. The effect of initial moisture content of mungbean on equilibrium moisture content was also studied. Five different models namely, Henderson equation, Chung and Pfost equation, Halsey equation, Sehgal equation and G.A.B. equation were used to represent the experimental data. The Sehgal equation, which provided best fit for the experimental data, was subsequently used for calculating the latent heat of moisture vaporization from mungbean based on the Othmers equation.

Fluid flow characterization with tube viscometer data

Pressure gradients and the corresponding mass flow rates of five different non-Newtonian fluid foods: 1% solutions of sodium alginate and CMC, 1.5% CMC solution, two different tomato ketchups, oyster sauce, in four different diameter stainless steel tubes ranging from 7.51 to 16.34 mm i.d. were recorded using a tube viscometer capable of operating in both transient and continuous flow modes. The flow was confined to the laminar flow regime and appreciable slippage occurred in all cases. Power law parameters for the tube flow obtained from the plots of wall shear stress versus apparent wall shear rate are presented for various time-independent fluids in different diameter tubes in original and slip-corrected forms. Such experimental data should prove useful in developing an understanding of flow characterization of non-Newtonian fluids.

DRAG COEFFICIENTS OF AGRICULTURAL GRAINS IN VERTICAL PNEUMATIC CONVEYING

A study was made of drag coefficients in vertical pneumatic conveying of agricultural grains. From experiments conducted on rough rice and milled rice, it was found that the values of drag coefficient computed using the basic relationship for slip velocity of a single particle in an air stream were closely related to the solid flow rate per unit cross–sectional area of the conveying pipe and solid–to–air ratio. Generalized equations were developed for estimation of drag coefficient in terms of particle equivalent diameter, solid flow rate per unit cross–sectional area of pipe, and solid–to–air ratio. The equations were also verified for another agricultural grain, namely corn. The closeness between experimental and predicted values validated the equations for general use for grain particles ranging in size approximately from 3– to 7–mm mean diameter.

Relationship between sensory textural attributes and near infrared spectra of cooked rice

Fourteen varieties of Thai indica rice, cooked with five water-to-rice ratios ranging from 1.3 to 2.5 on a weight basis, were characterised by sensory and instrumental texture profile analysis. The potential of near infrared (NIR) reflectance spectroscopy was investigated as an alternative tool for evaluating eating quality attributes of cooked rice by developing predictive models for sensory hardness, stickiness and glossiness. Partial least squares regression models were developed which predicted sensory hardness and stickiness slightly better than the glossiness with r2v values ranging from 0.88 to 0.91 and standard errors of prediction (SEP) lower than 0.4 unit score on nine-point sensory intensity scales. Results indicated that NIR spectroscopy-based models could be used for estimating the sensory hardness, stickiness and glossiness scores of cooked rice with higher accuracy (lower SEP) compared to the instrumental texture profile analysis based-models.

SOLID VELOCITY ESTIMATION IN VERTICAL PNEUMATIC CONVEYING OF AGRICULTURAL GRAINS

An indirect method has been developed to estimate solid velocity in the vertical pneumatic conveying of agricultural grains. Experiments on vertical pneumatic conveying of rough rice, milled rice, and soybean indicated that solid velocity is a function of air velocity, solid flow rate, solid–to–air ratio, and grain equivalent diameter. An empirical equation has been developed to predict dispersed solids density, i.e. concentration of solids in pneumatic conveying. Knowing the solid flow rate and dispersed solids density, solid velocity was calculated. The method used for determining the solid velocity was validated based on the hypothesis that the average solid velocity is equal to zero when the limiting value of the air velocity is equal to the terminal velocity of the grains. The applicability of the developed relationships for estimating the solid velocity was verified for other agricultural grains like corn and mungbean.