Ralph P. Cavalieri

High-temperature-short-time thermal quarantine methods

Abstract In this paper, kinetic models are discussed with respect to their uses in describing the intrinsic thermal mortality of insect pests. A unique heating block system was used to obtain kinetic information for the thermal mortality of codling moth larvae. The kinetic data demonstrated the possibility to develop high-temperature-short-time thermal treatments to control codling moth and reduce thermal impact on product quality. Equations are presented to evaluate cumulative effects of any time–temperature history on the thermal mortality of target insect pests and on the quality of host materials. Computer simulation results demonstrated that the cumulative thermal effects on product quality during the heating period in conventional hot air or hot water treatments are much more important than the cooling period. Radio frequency (RF) heating or microwave heating is suggested as an alternative to reduce adverse thermal impact to treated commodities during the heating period. A case study is presented to demonstrate the effect of RF heating in a high-temperature-short-time thermal treatment to control codling moth larvae in in-shell walnuts.

Process protocols based on radio frequency energy to control field and storage pests in in-shell walnuts

A practical process protocol was developed to control insect pests in in-shell walnuts using a 27 MHz pilot scale radio frequency (RF) system. Fifth-instars, that had been determined to be the most heat resistant life stage for navel orangeworm (Amyelois transitella [Walker]) using a heating block system, were selected as the targeted insect in the protocol development. RF heating to 55 °C and holding in hot air for at least 5 min resulted in 100% mortality of the fifth-instar navel orangeworm. Rancidity, sensory qualities and shell characteristics were not affected by the treatments. The process slightly reduced the moisture content of the walnut kernels, which could prove an additional benefit by providing even nut moisture content and reducing the growth of microorganisms. If this method can be economically integrated into the handling process, it should have excellent potential as a disinfestation method for in-shell walnuts.

DIFFERENTIAL HEATING OF INSECTS IN DRIED NUTS AND FRUITS ASSOCIATED WITH RADIO FREQUENCY AND MICROWAVE TREATMENTS

This research was conducted to provide a theoretical basis and experimental evidence to support the hypothesis that insect larvae can be preferentially heated in dry nuts and fruits by radio frequency (RF) heating for pest control. We selected codling moth larvae as the target insect and in–shell walnuts as the host material for this study, and focused our attention on one RF frequency (27 MHz) and one microwave frequency (915 MHz). Dielectric properties measurements showed that the loss factor ratio between codling moth larvae and walnut kernels at 20.C was 397 at 27 MHz and 4 at 915 MHz. The theoretical prediction for a 3 min treatment at 0.27 kW/kg suggested 12.0.C preferential heating of insect larvae for the loss factor ratio of 397 (corresponding to 27 MHz) and 0.1.C for the ratio of 4 (corresponding to 915 MHz), when the heat transfer coefficient between insects and walnuts was set at 500 W/m2 .C. To prove differential heating predicted by the theoretical model, a gellan gel with dielectric properties similar to those of insects was used as a model insect. When walnut kernels were heated at 27 MHz from 20.C to 53.C, the model insects were differentially heated from 12.6.C to 21.2.C higher than the kernel temperature, depending on the power used and the treatment time. These values corresponded to a heating rate for the model insect of 1.4 to 1.7 times greater than that for walnut kernels. As predicted by the theoretical model, microwave heating at 915 MHz caused no differential heating of insects. Preferential heating of insects in dry nuts and fruits at radio frequencies can be used in developing thermal treatments to control insects without adversely affecting product quality.

Modeling fruit internal heating rates for hot air and hot water treatments

Hot air and hot water heating methods have been extensively studied as thermal treatments to control insect pests in fruits to replace chemical fumigation. An inherent difficulty in using these methods is that slow heating rates may result in long treatment times and possible damage to fruit quality. Many factors influence heating time. A systematic analysis of those influences is desirable to help in designing effective treatment protocols. A simulation model based on heat transfer theory was developed to study the effect of fruit thermal property, fruit size, heating medium and heating medium speed on heat transfer rates within spherical fruits. The simulation demonstrated that the small variation in thermal diffusivity among fruits had little effect on heating time. Fruit internal heat transfer rate was significantly influenced by fruit size and by heating medium. Water was a more efficient medium than air and increasing air speed increased heating rates. Water circulation speeds had little influence on heat transfer rate. The Biot number showed that internal energy transfer by conduction was a heating rate limiting factor. Combining low frequency electromagnetic energy with hot air or hot water eliminated conduction as a major rate-limiting factor because the energy was directly delivered to the fruit interior.

Combined microwave and spouted bed drying of diced apples: Effect of drying conditions on drying kinetics and product temperature

ABSTRACT The influence of microwave power (0 to 8.0 W/g, dry basis) and hot air temperature (25°C to 95 °C) on drying rate and product temperature of diced apples (from 31 % to 5% moisture content, dry basis) in a laboratory microwave and spouted-bed combined dryer was investigated. Product temperature initially increased sharply to a plateau about 12 to 15°C above the spouted bed air temperature at a microwave input power 6.4 W/g. This temperature remained almost constant thereafter. Uniform microwave heating was achieved as evidenced by uniform product color and product temperature. Drying rates increased with increasing spouted-bed air temperature or microwave power level, But higher microwave power caused more darkening of the product. Drying of the diced apples in the microwave and spouted bed drying system exhibited two falling rates periods. The influence of air temperature on effective moisture diffusivity followed an Arrhenius type equation. The activation energies were 23.7 kJ/mol and 26.7 kJ/mo...

Modeling Potato Tuber Mass with Tuber Dimensions

ABSTRACT THIRTEEN models for predicting potato tuber mass from tuber dimensions were identified and used to evaluate theoretical limits of performance for mechanical and electronic potato tuber sorting devices. The models were divided into three classes based on: (1) single and multiple variable regression of the tuber length, width and height, (2) approximation of tuber shape by an ellipsoid, and (3) approximation of tuber shape by summation of thin disks. Tuber silhouettes were recorded and analyzed using digital imaging equipment and techniques. Class 3 models were most accurate, followed by Class 2 and Class 1 models. Class 1 models were the most simple, Class 3 most complex. Class 3 models could predict tuber mass within 25 g only 70% of the time, Class 2 models, 90% of the time and Class 1 models over 99% of the time..

Enzyme-electropolymer-based amperometric biosensors : An innovative platform for time-temperature integrators

A novel exogenous time-temperature integrator (TTI) based on an amperometric glucose oxidase biosensor is presented. The TTI consists of the enzyme entrapped within an electrochemically generated poly(o-phenylenediamine) (PoPD) thin film deposited on the interior wall of a platinum (Pt) or a platinized stainless steel (Pt-SS) capsule. After thermal treatment, the TTI is mounted in a continuous flow system and connected to a potentiostat for amperometric detection of residual enzyme activity. A measurement is completed within 10 min. Isothermal treatments were carried out between 70 and 79.7 degrees C. Thermal inactivation of the immobilized enzyme followed apparent first-order kinetics with z values of 6.2 +/- 0.6 and 6.6 +/- 0.8 degrees C for Pt and Pt-SS capsules, respectively. These z values suggest that the proposed TTIs have the potential to assess pasteurization processes that target microorganism such as Listeria monocytogenes and Escherichia coli O157:H7.

Amperometric Enzyme Biosensor Optimization Using Mathematical Modeling

A mathematical model for glucose oxidase immobilized in an electrochemically-generated polymer is proposed. The model uses previously reported diffusion coefficients and kinetic parameters and the two-substrate ping-pong mechanism for the enzyme kinetic reaction term. This model however, accounts for an inner catalytic film where the enzyme is immobilized and an outer non-catalytic layer. The boundary value problem consisting of non-homogeneous, non-linear partial differential equations was solved using the MATLAB bvp4c finite difference subroutine implementing a continuation procedure. Sensor sensitivity, linearity and operational life are calculated as functions of the experimentally adjustable parameters: enzyme-polymer film thickness, enzyme load, and noncatalytic outer film thickness. Such parameters were varied in ranges slightly beyond normally feasible limits. Kinetic and diffusion controlling regimes are presented. The trade-off between sensitivity, linearity and operational life is addressed. From this theoretical approach, strategies for sensor optimization are proposed. Electrochemically generated non-conducting polymers result in very thin films (l < 30 nm) that operate in strongly kinetic-controlled regimes. The amperometric response of such sensors is therefore strongly dependent on active enzyme concentration and their linearity is dictated by Michaelis-Menten kinetic parameters. Increased stability and linearity are achieved by using thicker films( l > 250 nm) of conducting polymers or by using a non-catalytic diffusion barrier. However, both cases are accompanied by a decrease in sensitivity.

Objective Assessment of Apple Maturity Based on Starch Location

ABSTRACT PHYSIOLOGICAL maturity is a critical criterion in determining the suitability of an apple for long term storage. A test based on the location of starch in the apple is commonly used as one measure of maturity. In an effort to remove operator subjectivity and errors in grading, a computer based image processing system was developed to determine starch location and estimate maturity grade. Three algorithms were tested. One related the starch maturity index (SMI) to the ratio of starch-cleared to starch-filled cross-sectional areas in the apple. A second algorithm estimated the SMI based on the amount of starch-cleared area with respect to the apple core line and vascular bundles. A third algorithm graded the maturity of the apple with respect to SMI predicted storability. Although the first two algorithms did not predict the starch maturity index, the storability algorithm was able to classify Red Delicious, Golden Delicious and Granny Smith cultivars as to the suitability for long term storage.

Prototype Instruments for Laboratory and On-line Measurement of Lipoxygenase Activity

A laboratory bench-top and a continuous prototype for measurement of lipoxygenase activity was developed. Lipoxygenase activity determination was based on the measurement of the rate of oxygen consumption by the enzyme using a polarographic sensor for the bench-top prototype and fibre optic sensors for the continuous prototype. The bench-top and the continuous sensors were compared against the standard spectrophotometric method. The range of LOX activity according to the spectrophotometric assay was from 0 to 0.163 μmol/L s. Accuracy and precision were 0.009 and 0.005 μmol/L s respectively for the bench top prototype and 0.007 and 0.006 μmol/L s for the on-line prototype. Correlation coefficients (R 2) were 0.99 for both prototypes with respect to the spectrophotometric method.