Ramaswamy C. Anantheswaran

Handbook of microwave technology for food applications

Part 1 Fundamental physical aspects of microwave absorption and heating: electromagnetics - fundamental aspects and numerical modelling electromagnetics of microwave heating - magnitude and uniformity of energy absorption in an oven dielectric properties of food materials and electric field interactions fundamentals of heat and moisture transport for microwavable food product and process development. Part 2 Chemical and biological changes due to heating: generation and release of food aromas under microwave heating bacterial destruction and enzyme inactivation during microwave heating. Part 3 Processing systems and instrumentation: consumer, commercial and industrial microwave ovens and heating systems measurement and instrumentation. Part 4 Processes at industry and home: microwave processes for the food industry basic principles for using a home microwave oven. Part 5 Product and process development: ingredient interactions in microwave heating packaging techniques for microwavable foods. Part 6 Safety: safety in microwave processing.

Finite element modeling of heat and mass transfer in food materials during microwave heating — Model development and validation

Abstract A three-dimensional finite element model (FEM) was developed to predict temperature and moisture distributions in food materials during microwave heating. The FEM was tested with analytical solutions and commercial software (TWODEPEP, ANSYS) calculated values. The FEM predictions compared favorably with analytical solutions (within 0.066% of maximum temperature) and values calculated from commercial softwares (within 0.14% of maximum temperature). The three-dimensional FEM was also verified using experimental data from microwave oven heated cylinder- and slab-shaped potato specimens. A fluoroptic temperature measurement system and the near infrared (NIR) technique were used to measure temperature and moisture distributions, respectively. The FEM predicted temperature in potato samples agreed with measured results. The absolute maximum difference for slab geometry after 60 s of heating was 8.1 °C (or relative difference of 15.5% from the measured value), whereas, for the cylindrical geometry, it was 8.7 °C (or relative difference of 11.4%). The absolute moisture differences after 60 s of heating between FEM predictions and measured values for potato slab and cylinder were within 1.97% wet basis (or relative difference of 2.4%) and 1.85% wet basis (or relative difference of 2.1%), respectively.

Fat, Moisture, and Ethanol Migration through Chocolates and Confectionary Coatings

The migration of fat, moisture, and ethanol is a common problem with chocolate-coated confectionery products. Migration of one of these components into the coating leads to visual and sensory defects such as sugar or fat bloom, making the product unacceptable to the consumer. The migration rate depends on the structure and composition of the coating. The migration of each of these species can be slowed to a certain extent by proper tempering of the coating, because proper tempering will give a structure that resists migration. In the continuous lipid phase, these chemical species migrate mainly through the liquid portion. Thus, the migration rate depends on the amount of liquid oil present in the product. Migration can be delayed either by reducing the liquid fat content or by immobilizing the liquid phase. The actual mechanisms for the migration processes are speculative, and a more thorough understanding is necessary to better abate quality deterioration. Armed with this understanding, a manufacturer would know a priori the effect of changing the ingredient or process. A few methods for control have been suggested, but have found limited application. Mathematical models have been proposed to predict the migration behavior, but their application is hindered because of the simplified assumptions employed. There is a need for developing better models that combine mass transfer with the phase behavior to be able to accurately predict the migration process. This review discusses the current understanding of fat, moisture, and ethanol migration through chocolate coatings and also includes a brief description of the theoretical aspects governing migration.

Finite element analysis of microwave heating of solid foods

Abstract Microwave heating of solid food with rectangular and cylindrical geometries were analysed using TWODEPEP, a two-dimensional commercial finite element software. Absorbed microwave power density at any location in the test material was derived as a function of dielectric properties and geometry of the material. The model was experimentally validated by using sodium alginate gel as a test material. The temperature predictions by finite element analysis and the experimental measurements were very similar in slab-shaped samples. In cylindrical samples, the experimental data and the finite element predicted values of temperatures were close to each other at all regions except at the central region. Sensitivity analyses showed that variation in thermal diffusivity, dielectric properties, and incident microwave power resulted in significant variation in the temperatures as predicted by the finite element method.

Heat transfer to model non-Newtonian liquid foods in cans during end-over-end rotation

Abstract Heat transfer coefficients were determined for aqueous guar gum solutions (0·3%, 0·4%, 0·5%, and 0·75%) during end-over-end rotation in copper cans. The variables investigated were size of can, speed of rotation and radius of rotation. The centre temperature within the can was found to oscillate. Over the range of variables studied, the heat transfer coefficient was found to be independent of the radius of rotation and the size of the can. The heat transfer data for non-Newtonian fluids were correlated in terms of Nusselt (Nu), generalised Reynolds (GRe), and generalised Prandtl (GPr) numbers: Nu = 1.41GRe 0.482 GPr 0.355 The correlation was found to be similar to that developed earlier for Newtonian liquids.

Convective Heat Transfer to Fluid Foods in Cans

Publisher Summary The chapter explains about the convection heating of foods in cans. Canning is the effective means to preserve large part of food supply. Heating characteristics of food products based on conduction and convection are illustrated. Conduction heated products exhibit slower heating rates and longer lag times and convection-heated products exhibit faster heating rates and shorter lag times. Methodologies to study convective heat transfer to foods are explained. The heat transfer rates to liquid foods are influenced by flow conditions such as viscosity, geometry, velocity of flow, and physical and thermal properties of liquid. Flow properties of Non-Newtonian fluids and viscoelastic fluids are also discussed. Heat transfer by natural convection takes place by conduction through a stagnant film of liquid on the inside surface of the can. Various factors affecting heat transfer by forced convection are explained in details. Methods of heat transfer in orbitor retorts, spin cooker, flame sterilization etc. are clearly illustrated. The process of heat transfer by convection in the presence of particulate matter is explained in detail. Heat is first transferred to the fluid and then to the particle. The presence of particulate matter will alter the flow patterns and contribute to the mixing of the cans contents due to their motion. The chapter also emphases the need for experimental studies that are applicable to non-Newtonian foods. It also illustrates the importance of dimensionless correlation in the field of heat transfer.

Ascorbic acid degradation in a model apple juice system and in apple juice during ultraviolet processing and storage.

UNLABELLED Ultraviolet radiation induced degradation of ascorbic acid in a model apple juice system and in apple juice was studied using a collimated beam batch UV reactor. In the model system, ascorbic acid degradation was more rapid at higher dose levels and the reaction accelerated with increasing exposure time. Ascorbic acid degradation significantly (P < 0.05) increased as the pH was raised from 2.4 to 5.5, although no difference was observed between 2.4 and 3.3. Increasing malic acid concentration between 0.1 and 1%, increased ascorbic acid degradation (P < 0.05) although there was no difference between 0.5 and 1.0%. Solution absorbance, varied by addition of tannic acid, decreased ascorbic acid degradation with increasing concentration due to absorption of UV radiation. Fructose at levels found in apple juice significantly increased ascorbic acid degradation while glucose and sucrose did not. Factors identified that accelerate ascorbic acid degradation may at least partially explain why ascorbic acid degradation occurred more rapidly in UV-treated apple juice than in the 0.5% malic acid model system. Ascorbic acid degradation continued after UV treatments during dark storage. Storage decreases were faster at higher initial UV dose levels and higher storage temperature. PRACTICAL APPLICATION The present study shows the effect of UV processing on ascorbic acid, a key vitamin found in many fruit juices. Process developers and researchers can use this study as a model for designing experiments to identify factors that influence the stability of vitamin C and other bioactive compounds during UV processing.

CHANGES IN BAROTOLERANCE, THERMOTOLERANCE AND CELLULAR MORPHOLOGY THROUGHOUT THE LIFE CYCLE OF LISTERIA MONOCYTOGENES

ABSTRACT Changes in barotolerance, thermotolerance, and cellular morphology throughout the life cycle of Listeria monocytogenes were investigated. For part 1 of this analysis, L. monocytogenes ATCC 19115 was grown to log, stationary, death, and long-term-survival phases at 35°C in tryptic soy broth with yeast extract (TSBYE). Cells were diluted in whole milk that had been subjected to ultrahigh temperatures (UHT whole milk) and then high-pressure processed (HPP) at 400 MPa for 180 s or thermally processed at 62.8°C for 30 s. As cells transitioned from the log to the long-term-survival phase, the D400 MPa and D62.8°C values increased 10- and 19-fold, respectively. Cells decreased in size as they transitioned from the log to the long-term-survival phase. Rod-shaped cells transitioned to cocci as they entered the late-death and long-term-survival phases. L. monocytogenes strains F5069 and Scott A showed similar results. For part 2 of the analysis, cells in long-term-survival phase were centrifuged, suspended in fresh TSBYE, and incubated at 35°C. As cells transitioned from the long-term-survival phase to log and the stationary phase, they increased in size and log reductions increased following HPP or heat treatment. In part 3 of this analysis, cells in long-term-survival phase were centrifuged, suspended in UHT whole milk, and incubated at 4°C. After HPP or heat treatment, similar results were observed as for part 2. We hypothesize that cells of L. monocytogenes enter a dormant, long-term-survival phase and become more barotolerant and thermotolerant due to cytoplasmic condensation when they transition from rods to cocci. Further research is needed to test this hypothesis and to determine the practical significance of these findings.

Effect of water activity on inactivation of Listeria monocytogenes and lactate dehydrogenase during high pressure processing

The aim of this study was to investigate the effect of water activity (aw) on the inactivation of Listeria monocytogenes and lactate dehydrogenase (LDH) during high pressure processing (HPP). For microbial inactivation lyophilized cells of L. monocytogenes 19,115 were left dry or were suspended in 10 ml of 0.1% peptone water, 10 ml of glycerol, or mixtures of glycerol and peptone water. All samples of various aws were high pressure (HP) processed at ambient temperature at 600 MPa for 300 s. Following HPP, samples were serially diluted in 0.1% peptone and spread-plated on Tryptic Soy agar supplemented with Yeast Extract. For enzyme inactivation, 4.2 mg of lyophilized LDH was suspended in 2 ml of 100 mM phosphate buffer (pH 7.4), 2 ml of peptone water or glycerol, or in 2 ml mixtures of glycerol and peptone water. A lyophilized sample with no added liquid was also included. All enzyme samples were subjected to HPP as described above. After HPP, LDH was diluted to 0.28 microg/ml in 100 mM phosphate buffer (pH 7.4). LDH activity was assessed by measuring the change in concentration of beta-NADH as a function of time. Dynamic light scattering analysis (DLS) was performed to examine the size distribution, polydispersity, and hydrodynamic radius of LDH before and after HPP. No significant difference in CFU/g was observed between lyophilized cells not subjected to HPP and lyophilized cells subjected to 600 MPa for 300 s (P<0.05). However, lyophilized cells that were suspended in 100% to 60% peptone water showed a approximately 7.5-log(10) reduction when subjected to HPP. Survival of L. monocytogenes following HPP significantly increased (P<0.05) when the peptone water concentration was decreased below 60% (aw approximately 0.8). DLS results revealed that LDH suspended in buffer underwent aggregation following HPP (600 MPa, 300 s). Inactivation rate constants obtained using a first-order kinetic model indicated that untreated and HP processed lyophilized LDH had similar activities. When LDH was subject to HPP in solutions containing glycerol, enzyme activity decreased as the water content increased (r2=0.95). Lyophilization completely protected L. monocytogenes and LDH from inactivation by high pressure. Furthermore, enzyme activity and cell survival increased as water activity was decreased. We postulate low aw results in protein stabilization, which prevents protein denaturation and cell death during HPP.

Penetration of Salmonella enteritidis into Eggs Subjected to Rapid Cooling

Eggs were cooled to 0°C using two different cooling rates, natural convection, and forced convection at an air speed of 30.5 m/min. Upon rapid cooling using forced convection and when brought back to room temperature, eggs were more prone to penetration by Salmonella enteritidis (strain PS8NSR). Eggs cooled using forced convection had 100% penetration by PS8NSR; eggs cooled using natural convection had 91.3% penetration; and uncooled eggs had 48% penetration. Scanning electron microscopy revealed that shells of both cooled and uncooled eggs had microscopic cracks; however, cracks were more numerous and larger in shells of cooled eggs.