MODELLING of TEMPERATURE HISTORIES DURING VENTING of STILL RETORTS

Experimental tests were carried on a pilot retort to gather information on the temperature evolution inside batch retorts during the venting stage. to fit the coming-up curves the equation for the response of an over-damped second-order system to a step input was proposed. the parameters that characterize this equation were related to steam flow, initial temperature and retort load. Results allow the prediction of coming-up curves for different operating conditions.     

MODELING the POWER CONSUMPTION DURING SHEETING of DOUGHS FOR TRADITIONAL INDIAN FOODS

The model given by Levine has been extended to account for the effects of moisture, salt and fat through appropriate modifications based on theory and computational experience. Appropriate modifications to consistency index and flow behavior index as a function of moisture, salt and fat are given. the thickness of sheeted dough has been modeled as a function of gap, reduction ratio and the flow behavior index which constitutes an important contribution. the model so modified was fitted to experimental data on power consumption in sheeting dough prepared from two flour types, viz., whole wheat flour and resultant atta, respectively, at five combinations of gap and reduction ratios and three levels each of moisture, salt and fat (conforming to actual use ranges) using Nelder-Mead algorithm for nonlinear optimization. These models provided 12 constants for each flour type which gave fundamental information on the dough properties for each flour type. Three-dimensional graphics have been used to interpret the model. These models appear to be of much practical use.     

TIME-VARIABLE RETORT TEMPERATURE PROFILES FOR CYLINDRICAL CANS: BATCH PROCESS TIME,ENERGY CONSUMPTION,and QUALITY RETENTION MODEL1

The batch retort model developed uses a heat transfer equation for heat conduction in cylindrical cans, first order kinetics for microbial inactivation, first order kinetics for quality losses and a transient energy balance to estimate steam consumption. For a given retort, lethality process and quality retention, the transient energy balance equation in the model allowed the identification of feasible time-temperature profiles reducing energy consumption, total process time or both. In the examples analyzed and depending upon product specifications, time-variable retort temperatures reduced process time by 18–55 min. These examples suggested that a change from constant to time-variable retort temperatures could increase canning capacity by 20–50%.     

METHYL BROMIDE, TIME and TEMPERATURE of EXPOSURE ON APPLE QUALITY

ABSTRACT. The use of methyl bromide (MeBr) as a fumigant to control codling moth in 'Delicious'apples resulted in a loss of firmness, internal color and therefore a reduction in the amount of acceptable fruit. Time and temperature of MeBr exposure were directly related to firmness and internal color loss. As the exposure time was increased beyond 2 h and exposure temperature above 6°C firmness and internal color loss were accelerated. an 8-day ambient storage period exacerbated firmness and internal color loss as time and temperature of MeBr exposure were increased. A fumigation regime of 56 g MeBr/m³ at 6°C for 2 h resulted in acceptable fruit during a 60 day refrigerated storage period. Increased exposure times or temperatures beyond 56 g MeBr/m³ at 6°C for 2 h resulted in unacceptable firmness and internal color loss, coupled with a major loss in acceptable fruit.     

SCREW CONFIGURATION EFFECTS ON RESIDENCE TIME DISTRIBUTION AND MIXING IN TWIN-SCREW EXTRUDERS DURING EXTRUSION OF RICE FLOUR

Screw configuration effects on residence time distribution and mixing were investigated during twin-screw extrusion of rice flour. The type, length, and position of mixing elements, and spacing between two elements significantly affected residence time distribution and mixing. Mean residence time (t_mean) and extent of mixing were lower for screw profiles with KB than those with RSE. A systematic increase in t_mean was observed as the mixing elements were moved farther away from the die, with longer elements, and with increased spacing between two elements.     

RHEOLOGICAL MODELING of POTATO FLOUR DURING EXTRUSION COOKING

A generalized model for predicting the effects of shear rate, temperature, moisture content, time-temperature history and strain history on viscosity has been evaluated for extruded potato flour doughs. an Instron Capillary Rheometer and a 50 mm Baker Perkins co-rotating twin screw extruder were used to evaluate all effects incorporated in the model, except strain history. the power law model was used to describe shear rate effects in the range 10–10000 s^?1. the generalized model fit observed data for temperatures of 25–95°C and moisture contents ranging from 22 to 50%, wet basis. Since potato flour by its manufacturing process is pregelatinized, it was unnecessary to evaluate the effects of time-temperature history. Strain history was found to have an insignificant influence on the viscosity.     

EFFECT OF GERMINATION TIME,TEMPERATURE AND MOISTURE ON MALTING OF SORGHUM

The effect of germination conditions on sorghum malt quality and malting loss was studied by germinating sorghum for different periods of time up to 6 days over a range of temperatures (24 to approximately 36°C) and moisture conditions. The moisture conditions varied from that sufficient to maintain green malt weight to that where surface moisture remained on the malt throughout germination. Germination time, temperature, moisture and the three possible pairwise interactions all had a highly significant effect on malt diastatic power, free α-amino nitrogen and extract. Malting loss was highly significantly affected by germination time and moisture and their pair-wise interaction. However, over the range examined, germination temperature had no significant effect on malting loss. In general diastatic power, free α-amino nitrogen, extract, and malting loss all increased with germination time. Germination temperatures of 24° and 28°C were both equally good for the development of diastatic power, free α-amino nitrogen and extract but higher temperatures were progressively worse. Distatic power, free α-amino nitrogen, extract and malting loss were, in general, all increased by high moisture during germination. However, high moisture and a negative effect on diastatic power towards the end of the germination period.     

MATHEMATICAL MODELLING of MOISTURE, VOLUME and TEMPERATURE CHANGES DURING DRYING of PRETREATED APRICOTS

Simultaneous heat and mass transport in dehydration of apricots is presented. the moisture variation of apricots, pretreated with various combinations of sodium-meta-bisulphite and ethyl oleate solutions, was analyzed by Exponential and Page equations. Use of ethyl oleate in addition to sodium-meta—bisulphite as a pretreatment solution was observed to decrease drying times of apricots. the system of differential equations determining the unsteady-state temperature distribution was solved. Thermophysical properties were taken to be moisture dependent. the variation of volume upon drying (shrinkage) was introduced into the solution by taking space intervals to be variable in the apricot side while they were taken to be constants in the stone side. the dominant mass transfer mechanism was diffusion while diffusivity of water changed depending upon the pretreatment solution. Comparison between predicted and experimental data shows good agreement for both moisture and temperature variation of the apricots throughout the drying process.     

AMYLOLYSIS OF SORGHUM STARCH AS INFLUENCED BY CULTIVAR,GERMINATION TIME AND GELATINISATION TEMPERATURE

The susceptibility to amylolysis of starches derived from two improved Nigerian sorghum cultivars were evaluated at assay temperatures between 50°C and 75°C. Enhancement of gelatinisation rates at temperatures up to 65°C was not significant inspite of the apparent grain modification due to germination for four days. Greater starch gelatinisation rates (20–22%) were achieved in this study compared to previously reported values, suggesting possible roles for cultivar and malting methods. There was a statistical correlation between starch gelatinisation rates over the temperature range 65°C–75°C and the duration of grain germination (r=0.91 for KSV8 and r=0.5 for SK5912 starches). Gelatinisation rate and temperature were affected significantly by assay pH. The occurrence of two pH related maxima of starch gelatinisation for both cultivera at all temperatures examined indicates the possible presence of two sets of “binding forces” within the starch granules and features of starch retrogradation .     

RHEOLOGY OF RICE-FLOUR PASTES: EFFECT OF VARIETY, CONCENTRATION, AND TEMPERATURE AND TIME OF COOKING

Cooked pastes of rice flour showed time-dependent shear thinning (thixotropy). Yield stresses were observed at high concentrations and high pasting temperatures. The Herschel-Bulkley power law equation could be used with certain limitations to characterize the flow behaviour of the pastes. At low pasting temperatures (60°, 75°C), apparent viscosity increased with increasing concentration and time of cooking, and was higher for low-amylose than for high-amylose rice. But when cooked at 95°C, two distinct patterns were seen. At low concentrations, apparent viscosity again increased with increasing time of cooking and was higher for low-amylose than for high-amylose rice. But at concentrations above 7%, the pattern was totally reversed, viz., viscosity decreased with time of cooking and was higher for high-amylose rice.     

INFLUENCE of OIL TEMPERATURE ON CONVECTIVE HEAT TRANSFER DURING IMMERSION FRYING

The relationship between oil temperature, convective heat transfer coefficient, and heat flux during immersion frying was investigated. Potato cylinders were fried in 120, 150, and 180C oil and convective heat transfer coefficients and heat flux measurements were made. These measurements followed the expected trends predicted by fundamental heat transfer calculations. the maximum convective heat transfer coefficient and heat flux reached during frying increases as oil temperature increases. the process time to reach these maxima decreases as oil temperature increases. This research provides fundamental knowledge relevant to the effects of oil temperature on the coupled heat and mass transfer problem present during immersion frying. This knowledge will provide a first step towards better understanding the frying process, and eventual process optimization through manipulation of the time-temperature regime of the frying processes.