Sukumar Bandyopadhyay

Optimization of Extrusion Process Variables Using a Genetic Algorithm

Optimization of process variables during single screw extrusion cooking of a fish and rice flour blend was carried out using a genetic algorithm (GA). Second-degree regression equations were developed for the extrudate properties such as expansion ratio (ER), bulk density (BD), hardness (H) and water solubility index (WSI) in terms of the independent variables: barrel temperature (°C), screw speed (rpm), fish content (%) and feed moisture content (%). These equations were used as the objective function to find the optimum process conditions separately for each (individual) and commonly for all (common) extrudate properties. The regression equations of ER and WSI were maximized and BD and H were minimized for both types of optimum process conditions. A maximum population of 100, and 100 iterations, was sufficient for successful convergence. A high barrel temperature, of about 200°C, and screw speed of 110 rpm were identified as both individual and common optimum process conditions for all the extrudate properties except for WSI. Fish content and feed moisture content were identified as two interacting process variables. Under individual optimum process conditions, maximum ER and minimum hardness required a low fish content of 5% (w/w) and feed moisture contents of 60 and 40%, respectively, and minimum BD and maximum WSI required high fish content of 41–45% and medium moisture content of about 40%, respectively. However under common optimum process conditions all four extrudate properties were optimized at a high fish content of 41–45% and medium moisture content of 40%. The experimental extrudate properties matched the values predicted for ‘common optimum’ conditions more closely than those for individual optimum process conditions.

Specific heat and thermal conductivity of shrimp meat

Abstract Apparent specific heat and thermal conductivity of shrimp meat were measured in the temperature range of 30 °C to −30 °C using the differential scanning calorimetry (DSC) and probe methods, respectively. These properties of shrimp meat were also calculated and compared with the measured values to check the accuracy of some existing models and the model proposed in the present work. The modified Schwartzberg model gave comparatively better accuracy of prediction of apparent specific heat. A proposed model predicted thermal conductivity better than the existing ones.

Aquafeed Extrudate Flow Rate and Pellet Characteristics from Low-Cost Single-Screw Extruder

Abstract Extrudate flow rate and effects of extrusion variables on extrudate properties were studied in a laboratory (small-scale) singlescrew, cooking extruder by extruding a marine shrimp feed mix. Response surface design was followed to examine the effect of screw speed (20-140 rev/min), L/D ratio (8-16), barrel temperature (60-100°C) and moisture content of feed mix (20-60%). All the variables were highly significant having positive linear relationship (r2 = 0.99) with the experimental flow rate QExp. QTheo calculation from the simplified flow model, however, over-predicted QExp within 9 to 89%. Prediction improved with increased L/D ratio, screw speed, mosture content, and barrel temperature. The combined effects on water stability, expansion ratio and true density of extrudate showed that L/D 12-14 and moisture content 30-35% were optimum for the three properties, and 92-94 rev/min was the optimum speed for water stability and true density. Barrel temperature showed optimum values within 68-94°C. The most desirable values of the properties were 90.3% water stability, 0.99 expansion ratio, and 1347.9 kg/m3 true density.

A comparative study of shrimp feed pellets processed through cooking extruder and meat mincer

Performance of three types of shrimp feed pellets, processed through cooking extruder, meat mincer and pellet mill (commercial diet served as the control), was compared by studying the results on proximate composition, physical properties and growth of Penaeus monodon F. juveniles in aquariums. A single screw variable length cooking extruder, designed and fabricated at the Institute, was used to extrude the feed mix dough under optimal conditions of screw speed (92 rev min−1), L/D ratio (14), barrel temperature (94.4°C) and moisture content of feed mix (35.4%). No commercial binder was used in cooking extruder and meat mincer. The commercial diet was found to be most water stable among the three. There was significant difference between the water stability of extruder pellet and commercial diet only at 30 min of immersion period at P<0.05 and P<0.01 for remainder of the period up to 4 h. Whole wheat flour, used in the formulation might have contributed to water stability of extruder pellets. Compacted sinking type pellets with minimum expansion ratio and high density was achieved in the extruder run under the optimal processing conditions. Feed conversion ratio (FCR) was essentially the same for the commercial and extruder pellets.

Prediction of aeration performance of paddle wheel aerators

Abstract Aeration experiments were conducted in brick masonry rectangular tanks of dimensions 2.9×2.9×1.6 and 5.9×2.9×1.6 m to study the effect of geometric and dynamic variables on aeration process based on dimension analysis. Non-dimensional numbers relating to standard aeration efficiency (SAE), effective power (P) and theoretical power per unit volume (P/V) termed as SAE′, Ne and X, respectively, are proposed. An optimal geometric similarity of various linear dimensions was established. It has been established that neither the Reynolds criterion nor the Froude criterion is singularly valid to simulate either SAE′ or Ne, simultaneously for different sizes of aerators, even though they are geometrically similar. Occurrence of scale effects due to the Reynolds and the Froude laws of similitude on both SAE′ and Ne are also evaluated. Simulation equations uniquely correlating SAE′, Ne and X were developed which can predict the aeration performance of paddle wheel aerators having the optimised geometric dimensions as established.

Effect of extrusion cooking on anti-nutritional factor tannin in linseed (Linum usitatissimum) meal

Primary objective Various oilseeds and their by-products usually constitute a major source of dietary protein as aquafeeds for warmwater herbivorous/omnivorous fish species. The oilseed meals available in India are fairly rich in protein and most of them are traditionally used as valuable feed for farm animals. However, among the factors that limit incorporation of these ingredients in aquafeeds are amino-acid imbalance and presence of anti-nutritional factors. Enhancement of the nutritive value of these ingredients and reduction (or removal) of anti-nutritional factors can be attempted by processing so as to increase the bio-availability of these nutrients. It has been found that various anti-nutritional factors can be destroyed by the process of extrusion cooking. Extrusion is a process whereby raw feed material is exposed to controlled conditions of high temperature, pressure and moisture. In the present experiment, extrusion cooking is used to reduce the anti-nutritional factor tannin in linseed (Linum usitatissimum) meal. Research design A single-screw cooking extruder, designed and manufactured at the Indian Institute of Technology, Kharagpur, was used for the study. Experiments were carried out following a rotatable central composite design to determine the optimum values of the process variables for which maximum reduction of tannin (Y) occurs. The process variables selected for the study were: barrel temperature (X1) (60–100°C), extruder speed (X2) (60–100 rpm) and oilseed moisture content (X3) (30–50%). Following the design, a second-order response model was fitted. Main outcomes and results The optimized values of the process variables were found to be X1=82.5°C, X2=90 rpm and X3=41.22%, and the value of the predicted response (i.e. reduction of tannin Y) was found to be 61.25%.

Performance of packed column aerator at low hydraulic loading.

Abstract A laboratory-scale packed column aerator filled with ceramic Raschig rings was tested for its performance with hydraulic loadings in the range of 16–86·3 m 3 m −2 h −1 . Two columns of 0·19 m and 0·24 m inside diameter and packing sizes of 15, 25 and 36 mm were used. The system equation developed by previous workers for trickling filters in waste-water treatment was not generally applicable across the lower hydraulic loadings. The system coefficient incorporating the oxygen absorption coefficient (k L a) was found to vary within the range of hydraulic loadings studied. The oxygen transfer rate equation developed for surface and submerged aerators was used for estimating standard oxygen transfer efficiency of the packed column aerator, which, in this case, ranged from 6·2 to 22·6 kg O 2 kWh −1 .

Kinetics of Storage Losses & Sensory Characteristics for Coextrudates of Fish and Rice Flour

Extrusion cooking of fish and rice flour blends can produce products rich of amino acids, vitamins and minerals. In the present study storage and nutritional kinetics and sensory characteristics of fish and rice flour coextrudates were studied. The process variables used for the development of fish and rice flour coextrudates were barrel temperature (200° C), screw speed (109 rev/min) fish content of feed (44 %) and feed moisture content (39 %). Sorption isotherm drawn at 30° C indicated that the safe aw levels of the extrudates were 0.4-0.7. The GAB model has described the best the sorption isotherm process and has fitted the best with an r2 value of 0.99. Monolayer moisture content based on the GAB model was found to be 0.058 g/g (dry basis). Nutritional and storage characteristics indicated that during the first 15 days of storage a loss of 53.1 % and 50 % of vitamin-A (IU/g) and total tocopherols (%) was observed and whereas the peroxide and free fatty content increased from 46 to 109 mg/kg and 3.8 to 7.7 %. Non-linear model (This equation is not available in html. Please view the pdf version.) described the best the loss of vitamin-A, and tocopherols and gain in peroxide values and free fatty acid content. The loss of vitamin-A and total tocopherols almost followed the same trend during the complete storage period of 45 days whereas on the other hand the gain in peroxides was more prominent compared to free fatty acid content during the initial 15 days of storage. The ANOVA table indicated that the sensory attributes of the product fried for different times (15-120 sec) were significantly different and the scores of the sensory attributes of the product fried at 15 sec were most acceptable.

Preliminary study on dynamic characteristics of sewage-mixed water body for aquaculture

Abstract To investigate the dynamic characteristics of a ‘sewage-fed’ aquaculture system, a study was conducted in bench-scale culture tanks using water mixed with domestic sewage in different ratios under simulated solar radiation. Results showed that the dissolved oxygen concentration and pH of the system were affected considerably and the dynamics of their changes initially followed the pattern of impulse disturbance. The changes in dissolved oxygen concentration and pH depended on the quality of the sewage and the extent of dilution.