Effect of harvest time and drying on supersweet sweet corn seed quality

A supersweet sweet corn hybrid, Pacific H5, was grown under field conditions in South-East Queensland to study the effects of harvest time and drying conditions on seed quality. Cobs were harvested at different times to obtain seed with two moisture percentage ranges (20-30% and 40-50%) and dried to 12% moisture under different combinations of drying temperatures (30 degrees C, 40 degrees C and 50 degrees C) and air velocities (1.25 m/s, 2.75 m/s and 4.30 m/s). Dried seed was stored at 30 degrees C with bimonthly monitoring of seed quality for 12 months. For standard as well as cold test germinations, statistical analysis yielded significant main effects for temperature, air velocity and harvest moisture content and significant interactions for drying temperature by harvest moisture and drying temperature by air velocity. Germination at the beginning of storage was unaffected by drying temperatures up to 40 degrees C regardless of harvest moisture but was lower at 50 degrees C for higher moisture. However, germination at the end of the storage period of 12 months was greatest for seed harvested at higher moisture and dried at temperatures up to 40 degrees C. Germination was not affected by air velocity for drying temperatures up to 40 degrees C but at 50 degrees C it generally decreased with increase in air velocity. To slow down seed deterioration during storage, it is recommended that sweet corn seed should be harvested at a higher moisture range (40-50%) and dried at 40 degrees C and 4.30 m/s air velocity. The drying temperature can be raised to 50 degrees C for seed harvested at a low moisture range (20-30%) provided the air velocity is kept low (1.25 m/s).

An evaluation of selective Helicoverpa armigera control options in sweet corn

Helicoverpa armigera is a serious insect pest of sweet corn in Australia and is becoming increasingly difficult to manage with conventional chemical insecticides due to resistance problems. A number of alternative H. armigera control options were evaluated in sweet corn and compared with deltamethrin and no action (control). The alternative tactics evaluated were: heliothis nuclear polyhedrosis virus plus Trichogramma nr. brassicae releases; Bacillus thuringiensis; and Trichogramma alone. The H. tea nuclear polyhedrosis virus + Trichogramma plots had the lowest cob damage (6.0%), followed by the B. thuringiensis plots (12.0%), Trichogramma alone plots (20.2%), control plots (23.2%) and deltamethrin plots (53.5%). There was no evidence to suggest that the Trichogramma nr. brassicae releases had any impact on H. armigera egg mortality. However, there was a large natural population of Trichogramma pretiosum in all plots. The application of deltamethrin reduced the action of these wasps and predators, resulting in higher larval infestation and significantly more cob damage. The findings indicate that the pathogens heliothis nuclear polyhedrosis virus and B. thuringiensis can effectively control H. armigera when their action complements high natural levels of egg parasitism, and that they have potential for use in integrated pest management programs in sweet corn.

Physical properties and fluidization behaviour of fresh green bean particulates during fluidized bed drying

Changes in the physical properties (such as particle density, bulk density of the bed, shrinkage and bed porosity) of fresh green bean particulates were investigated during drying. Three length:diameter ratios (1:1, 2:1 and 3:1) were considered, using drying conditions of 50 +/- 2 degrees C and 13 +/- 2% relative humidity in a heat pump dehumidifier system. The fluidization behaviour was also evaluated at 10 levels of moisture content. The fluidization experiments demonstrated that the minimum fluidization velocity decreases as the drying proceeds due to the reduced moisture content and changes in the physical properties of the bean particulates. Empirical relationships of the following nature were developed for the change in shrinkage [VR = 1 - Be-kMR], particle density [rho(p) = A + BMR + C (exp)(-D MR)], bulk density [rho(b) = a(1) + b(1)MR + c(1)MR(2)] and bed porosity [epsilon = a(2) + b(2)MR + c(2)MR(2)] with the moisture content during fluidized bed drying.

Problems associated with spray drying of sugar-rich foods

Stickiness is a major reason that limits the spray drying of various sugar-rich food products. Higher hygroscopicity of amorphous powder, increase in solubility of sugars with temperature, and lower melting point and glass transition temperature, contribute to the stickiness problem. So far, the glass transition temperature has been widely accepted as a best indicator for stickiness. There are various manoeuvres that have been applied to spray dry such products. Some of them are the addition of drying aids, modification of drier design and use of mild drying temperature conditions. This review paper highlights the major research works that deal with the stickiness property of sugar-rich foods.

A semi-empirical approach to optimise the quantity of drying aids required to spray dry sugar-rich foods

A semi-empirical linear equation has been developed to optimise the amount of maltodextrin additive (DE 6) required to successfully spray dry a sugar-rich product on the basis of its composition. Based on spray drying experiments, drying index values for individual sugars (sucrose, glucose, frutose) and citric acid were determined, and us;ng these index values an equation for model mixtures of these components was established. This equation has been tested with two sugar-rich natural products, pineapple juice and honey. The relationship was found to be valid for these products.

Effects of process modification and heat pump drying on physical and sensory properties of Chinese style shredded beef

Chinese-style dried, shredded meat is traditionally prepared by sequential cooking, shredding, pre-drying, and final drying (roasting) of lean meat. In this study, shredded dried beef (a(w)<0.6) was prepared by omitting roasting but prolonging pre-drying. Sensory scores of the modified product were lower than those for the traditional product. When heat pump drying replaced traditional oven drying, drying time was shortened without significant difference in quality attributes. Desorption curves were established for shredded beef at several drying temperatures.

A dynamic model with on-line identification for rotary sugar drying processes

A dynamic modelling methodology, which combines on-line variable estimation and parameter identification with physical laws to form an adaptive model for rotary sugar drying processes, is developed in this paper. In contrast to the conventional rate-based models using empirical transfer coefficients, the heat and mass transfer rates are estimated by using on-line measurements in the new model. Furthermore, a set of improved sectional solid transport equations with localized parameters is developed in this work to reidentified on-line using measurement data, the model is able to closely track the dynamic behaviour of rotary drying processes within a broad range of operational conditions. This adaptive model is validated against experimental data obtained from a pilot-scale rotary sugar dryer. The proposed modelling methodology can be easily incorporated into nonlinear model based control schemes to form a unified modelling and control framework.place the global correlation for the computation of solid retention time. Since a number of key model variables and parameters are identified on-line using measurement data, the model is able to closely track the dynamic behaviour of rotary drying processes within a broad range of operational conditions. This adaptive model is validated against experimental data obtained from a pilot-scale rotary sugar dryer. The proposed modelling methodology can be easily incorporated into nonlinear model based control schemes to form a unified modelling and control framework.

Evaluation of various pre-treatments for the dehydration of banana and selection of suitable drying models

The thin-layer drying behaviour of bananas in a beat pump dehumidifier dryer was examined. Four pre-treatments (blanching, chilling, freezing and combined blanching and freezing) were applied to the bananas, which were dried at 50 degreesC with an air velocity of 3.1 m s(-1) and with the relative humidity of the inlet air of 10-35%. Three drying models, the simple model, the two-term exponential model and the Page model were examined. All models were evaluated using three statistical measures, correlation coefficient, root means square error, and mean absolute percent error. Moisture diffusivity was calculated based on the diffusion equation for an infinite cylindrical shape using the slope method. The rate of drying was higher for the pre-treatments involving freezing. The sample which was blanched only did not show any improvement in drying rate. In fact, a longer drying time resulted due to water absorption during blanching. There was no change in the rate for the chilled sample compared with the control. While all models closely fitted the drying data, the simple model showed greatest deviation from the experimental results. The two-term exponential model was found to be the best model for describing the drying curves of bananas because its parameters represent better the physical characteristics of the drying process. Moisture diffusivities of bananas were in the range 4.3-13.2 x 10(-10) m(2)s(-1). (C) 2002 Published by Elsevier Science Ltd.

Influence of planting date, method of handling and seed size on supersweet sweet corn seed quality

A supersweet sweet corn hybrid, Pacific H5, was planted at weekly intervals (P-1 to P-5) in spring in South-Eastern Queensland. All plantings were harvested at the same time resulting in immature seed for the last planting (P-5). The seed was handled by three methods: manual harvest and processing (M-1), manual harvest and mechanical processing (M-2) and mechanical harvest and processing (M-3), and later graded into three sizes (small, medium and large). After eight months storage at 12-14degreesC, seed was maintained at 30degreesC with bimonthly monitoring of germination for fourteen months and seed damage at the end of this period. Seed quality was greatest for M-1 and was reduced by mechanical processing but not by mechanical harvesting. Large and medium seed had higher germination due to greater storage reserves but also more seed damage during mechanical processing. Immature seed from premature harvest (P-5) had poor quality especially when processed mechanically and reinforced the need for harvested seed to be physiologically mature.

Characterization of the surface stickiness of fructose-maltodextrin solutions during drying

A probe tack test has been used for the in situ characterization of the surface stickiness of hemispherical drops with an initial radius of 3.5 mm while drying. Surface stickiness of drops of fructose and maltodextrin solutions dried at 63degreesC and 95degreesC was determined. The effect of addition of maltodextrin on fructose solution-was studied with fructose/maltodextrin solid mass ratios of 4: 1, 1: 1, and 1:4. Pure fructose solutions remained completely sticky and failed cohesively even when their moisture approached zero. Shortly after the start of drying, the surface of the maltodextrin drops formed a skin, which rapidly grew in thickness. Subsequently the drop surface became completely nonsticky probably due to transformation of outer layers into a glassy material. Addition of malto,dextrin significantly altered the surface stickiness of drops of fructose solutions, demonstrating its use as an effective drying aid.

Effect of lifter design on drying performance in rotary dryers

Lifter use in dryers improves mass transfer by increasing the amount of surface area available for transfer and also by increasing the velocity of gas over the particle surface. An even cross-sectional distribution of particles in a dryer improves the efficiency of operation by ensuring that evaporation from falling particles is taking place for the maximum fraction of the rotation period of the drier. Studies on lifter design to improve the cross-sectional particle distribution were performed on angled lifters. A single lifter was used and the mass-transfer rate examined as a function of angular lifter displacement. Analysis of the mass transfer characteristics of single lifters allowed performance comparisons and recommendations for lifter design.