Hao Feng

DIELECTRIC PROPERTIES OF DEHYDRATED APPLES AS AFFECTED BY MOISTURE AND TEMPERATURE

Dielectric properties directly influence microwave drying characteristics of food products. A knowledge of ndielectric properties of foods as a function of moisture content and temperature is essential in the design and control of nmicrowave drying systems. Dielectric constant x01 nx01 nand loss factor x01 nx02 nof Red Delicious apples (Malus domestica Borkh.) were nmeasured over a moisture content range of 4% to 87.5% at 22 nx03 nC and 60 nx03 nC. At high moisture content (>70%), free water ndispersion and ionic conduction accounted for the dielectric behavior. At medium moisture ( nx01 n23%), ionic conduction played na major role. At low moisture contents ( nx01 n4%), bound water accounted for the major dispersion mechanism. A decrease in nmoisture content resulted in a decrease in x01 nx01 nand x01 nx02 n. Based on this study, we expect a strong moisture leveling effect when ndrying apples from 50% to 4% at elevated temperatures in 915 MHz or 2.45 GHz microwave drying systems.

Power ultrasound treatment of Listeria monocytogenes in apple cider

Inactivation experiments with Listeria monocytogenes 10403S, an ultrasound-resistant strain, were conducted at sublethal (20, 30, and 40 degrees C) and lethal (50, 55, and 60 degrees C) temperatures in saline solution (pH 7.0), acidified saline solution (pH 3.4), and apple cider (pH 3.4) with and without application of ultrasound (20 kHz, 457 mW.ml(-l)). The survival of recoverable L. monocytogenes 10403S in apple cider was evaluated, and the effects of temperature, ultrasound, pH, and food matrix on inactivation were studied. Application of ultrasound increased the inactivation rate at both sublethal and lethal temperatures. Additional death of L. monocytogenes 10403S was due to low acidity at the lethal temperatures. The reduction in surviving L. monocytogenes 10403S followed first order kinetics at sublethal temperatures, but at lethal temperatures, a two-section linear model described the inactivation behavior. The bactericidal effect of thermosonication was additive in apple cider. The survival tests of L. monocytogenes 10403S in apple cider indicated the possibility of using a mild treatment condition in combination with ultrasound to achieve a 5-log reduction in number of listerial cells.

Dielectric properties of cottage cheese and surface treatment using microwaves

Abstract This research determines the dielectric properties of cottage cheese and explores the application of microwave treatment to reduce surface spoilage microorganisms, extending the shelf-life of cottage cheese in sealed plastic containers. Dielectric properties of cottage cheese of 0, 2 and 4% fat content were measured at temperatures between 5 and 65 °C. The penetration depths of microwaves of 2450 and 915 MHz were estimated to be between 1.2 and 3.2 cm. Microwaves were then used to treat the surface of the cheese in containers shielded on the sides and the bottom. Temperature distribution followed an exponential decay along the depth, as described by a model derived from Lamberts law. Microbiological, sensory and pH analyses of samples after treatment and 1–4 weeks after storage at 3 °C showed that microwave surface treatment could contribute to extending the shelf-life of cottage cheese, but further studies are necessary to identify optimum conditions that would maintain appearance and texture.

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...

Analysis of microwave assisted fluidized-bed drying of particulate product with a simplified heat and mass transfer model

Drying characteristics of particulates in a fluidized bed with microwave energy were studied with a simplified heat and mass transfer model. In the model, the temperature equation considered the air flow conditions while in the moisture equation, a diffusion equation was employed. The resulting equations were solved with an implicit finite difference scheme. The model simulation was checked against the experimental results of diced apples. The model prediction for product moisture agreed well with the experimental result. Predicted product temperature was slightly lower than the measured. This may be caused by error in the estimation of the microwave power term. The development and validation of the model will provide a relatively simple means of simulating the drying kinetics of microwave assisted convective drying in a fluidized bed.

DETERMINATION OF MOISTURE DIFFUSIVITY OF RED DELICIOUS APPLE TISSUES BY THERMOGRAVIMETRIC ANALYSIS

ABSTRACT Moisture diffusivity is an important parameter needed in the analysis, design and optimization of drying processes for food and other materials. Published data on moisture diffusivities of food materials are scarce and, sometimes, inconsistent due to a lack of a precise and repeatable experimental technique. Most experimental data are limited to low and moderate drying temperature (<70°C), whereas in the food industry hot air of up to 100°C is usually used in the falling rate period to speed up the drying processes. In this study, the effective moisture diffusivities of Red Delicious apple tissues were determined from drying curves produced with a Perkin Elmer thermogravimetric analyzer, using the slope method. The experiments were conducted at lour temperatures 60, 80, 100 and 120°C. Two well defined falling rate periods were observed. The effective moisture diffusivity, for the four temperature levels ranged from 3.2 × 10−7 to 7.9 × 10−8 m2/s for the first falling rate period and 3.8 × 10−8 to 4.7 × 10−8 m2/s for the second falling rate period. The temperature dependence of the effective diffusivity can be described with an Arrhenius-type equation.

Intrinsic and relative permeability for flow of humid air in unsaturated apple tissues

Abstract Knowledge of intrinsic and relative permeabilities is important when studying pressure driven mass transport in unsaturated porous media. Little information is available on intrinsic and relative permeabilities of biomaterials. In this study, an experimental procedure was developed to determine intrinsic and relative permeabilities for the flow of humid air in porous apple tissues. Experiments were completed in two steps. In the first step, apple tissues were freeze-dried to remove moisture without changing the sample’s original pore structure. Dry air was passed through the sample and Darcy’s law was used to determine intrinsic permeability, K , as a function of porosity. In the second step, moist air was forced through partially saturated apple tissues to determine the air permeability, K g . The humid air was in thermodynamic equilibrium with the apple tissues to obtain an equivalent immiscible condition. The air relative permeability k rg was then calculated based on the value of the air permeability K g and the intrinsic permeability K . The intrinsic permeability for apple tissue varied from 8.89xa0×xa010 −13 to 4.57xa0×xa010 −11 m 2 for porosity ranging from 0.33 to 0.77. The porosity dependency of intrinsic permeability can be described by the Kozeny–Carman model. The gas relative permeability k rg was correlated to saturation by an empirical model.

Starch recovery from degermed corn flour and hominy feed using power ultrasound

Power ultrasound is sound waves in the frequency range of 20– 100 kHz with a sound intensity of 10–1,000 W/cm. It has been studied for use in a number of food-processing applications. The ultrasound mode of action is attributed to a phenomenon called cavitation, which is the formation, growth, and implosion of tiny gas bubbles or cavities in a liquid. Implosion of cavities results in micro-streaming and localized high shear that can be used to perform various physical or biochemical operations or to enhance biological and biochemical separations. Mason et al (1996), Salisova et al (1997), and Vinatoru et al (1997) studied the efficacy of ultrasound on extracting low molecular weight substances from plant materials. They postulated that the enhanced extraction of organic compounds was due to disruption of cell walls and enhanced mass transfer between interfaces of biocomponents. Ebringerova et al (1998) extracted immunologically active xylan from corncobs and heteroxylan from corn hulls with ultrasound and did not observe noticeable changes in functional properties of the biopolymers. The physical effect of ultrasound is also utilized in food emulsification and homogenization applications (Mason 1998). Few studies have documented the effects of power ultrasound on starch physicochemical properties or the use of ultrasound in corn processing. Jackson et al (1988, 1989) used ultrasound to dissolve corn and sorghum starch granules after heating instead of solubilizing in alkali or dimethyl sulfoxide for the analysis of molecular structures. They reported that ultrasonic vibrations disrupt swollen granules, thereby releasing amylose and amylopectin from the granules, and resulting in an increase in water solubility of starch. Chung et al (2002) treated mung bean, potato, and rice starches with ultrasound after heating and reported that the average degree of polymerization did not change after sonication. They also proposed that the changes in starch properties were induced by disruption of swollen granules rather than a breakage of glucosidic linkages. There are no studies in the literature on the effect of sonication on native or raw corn starches. In a study on rice starch isolation, Wang et al (2003) found that power ultrasound treatment resulted in a high starch recovery but a slightly higher residual protein content. Yang et al (2002a,b) used ultrasound to treat corn kernels in steeping water. They found that the affinity between pericarp and endosperm was reduced, indicating an enhanced separation of corn components by ultrasound treatment. Corn dry milling often produces process streams, which due to market conditions go to animal feed. Hominy feed, which contains corn bran, germ, and some starchy portion of the corn kernel, is a by-product of dry milling and is sold as feed. Degermed corn flour is a prime product that has an inelastic demand. Frequently, processing conditions and product mix result in overproduction of degermed flour. Both products are reasonably high in starch and may be a source of nonsulfate-treated starch. The objectives of this study were to test power ultrasound as a means to recover starch from degermed corn flour and hominy feed, and to study the properties of the resulting starches.

Image analysis and dynamic modeling of thin layer drying of osmotically dehydrated pumpkin

This study was conducted to investigate the effect of osmotic dehydration as a pretreatment on hot-air drying kinetics of pumpkin, to evaluate the best model for hot-air drying of pumpkin and to apply a computer vision system to study the color changes during drying. Pumpkin cubes were treated in 50% w/w sorbitol or sucrose solutions at 50C for up to 6 h, followed by hot-air drying at 60C and air velocity of 1 m/s. Drying data were fitted to 11 drying kinetic models. The goodness of fit was determined using the coefficient of determination (R), reduced chi square (c), root mean square error (RMSE) and percent mean relative deviation modulus (E%). Hot-air dried samples pretreated with sorbitol had an improved lightness (higher L* values) compared to the hot-air drying while that pretreated with sucrose exhibited lower L* values. The total color changes (DE* values) increased during drying in a sequence of DE*sucrose solution < DE*sorbitol solution < DE*sucrose+hot air & < DE*sorbitol+hot air. 5 Corresponding author. TEL: +98-21-240-3045; FAX: +98-21-240-2082; EMAIL: mshafafiz@ gmail.com Journal of Food Processing and Preservation 32 (2008) 88–102. All Rights Reserved.

Improvement of Fermentation of Dried Distillers’ Grains and Solubles (DDGS) Hydrolysates to Acetone Butanol and Ethanol (ABE) with Hydrolysate-adapted Clostridium beijerinckii BA 101

Formation of compounds that are toxic to fermenting organisms during pretreatment and hydrolysis of lignocellulosic biomass has long been identified as one of the key factors affecting bioconversion of biomass to biofuels. In this study, fermentation was carried out to convert electrolyzed water pretreated dried distillers’ grains and solubles (DDGS) hydrolysates to acetone butanol ethanol (ABE) using the hyper-butanol producing Clostridium beijerinckii BA 101. The presence of inhibitors in the DDGS hydrolysates resulted in a 40 h adjustment phase before the initiation of fermentation while the mixed sugar control fermentation was completed in less than 16 hours. While the ABE yield (ABE produced per unit of sugar utilized) obtained from the fermentation of DDGS hydrolysates was comparable to the yield obtained from the mixed sugar control fermentation, ABE productivity (ABE produced per unit of fermentation time) from the DDGS hydrolysates was lower than that of the mixed sugar control due to the long adjustment time experienced by C. beijerinckii BA101 in DGGS hydrolysates fermentation.