G.D. Saravacos’s research while affiliated with Rutgers, The State University of New Jersey and other places

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Publications (74)


Design of Food Processes and Food Processing Plants
  • Article

January 2002

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513 Reads

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4 Citations

George D. Saravacos

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Athanasios E. Kostaropoulos

Process design refers to the design of food processes and manufacturing methods, including process flowsheets, design of processing and control equipment, and economic evaluation of the process. Plant design refers to the design of the whole processing plant, including the processing/control equipment, the utilities, the plant buildings, and the waste treatment units. The two terms are used interchangeably in the technical literature. Both process and plant design are basic parts of feasibility and implementation studies of an industrial project, such as a food processing plant.


Moisture diffusivity data compilation for foodstuffs: Effect of material moisture content and temperature

July 2001

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202 Reads

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52 Citations

There is a wide variation of the reported experimental data of moisture diffusivity of solid food materials, making difficult their utilization in drying and other applications. Published values of moisture diffusivity in various foods were retrieved from the literature, and these were classified and analyzed statistically to reveal the influence of material moisture content and temperature. Empirical models, relating moisture diffusivity to material moisture content and temperature, were fitted to all examined data for each material. The data were screened carefully using residual analysis techniques. The most promising model was proposed, which is based on an Arrhenius-type effect of temperature and it uses a parallel structural model to take into account the effect of material moisture content.



The effect of the method of drying on the color of dehydrated products

January 2001

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5,058 Reads

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311 Citations

Summary We tested the hypothesis that an optimum method of drying fruit could be designed. The effect of the method used for drying on colour of apple, banana, potato and carrot was investigated for five different methods of drying: conventional, vacuum, microwave, freeze and osmotic drying. Colour characteristics were studied by measuring lightness (L), redness (a) and yellowness (b) using a Hunter Lab chromatometer. The method used to dry the material was found to significantly affect the three colour parameters. The changes in redness (a) and yellowness (b) were found to follow a first order kinetic model. Air-, vacuum- and microwave-dried materials caused extensive browning in the fruits and vegetables, this was manifested by a significant drop of the L parameter and an increase of the a and b parameters. Osmotically pretreated samples did not brown as much as the untreated samples and the value for lightness (L) decreased only slightly while a and b increased slightly. Freeze drying seems to prevent colour changes, resulting in products with improved colour characteristics.



Influence of solute temperature and concentration on the combined osmotic and air drying

August 1999

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17 Reads

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46 Citations

The effect of solute concentration (15–45 % sugars) and temperature (10–40 °C) on the osmotic dehydration of apple was investigated. Cylindrical samples of apple were immersed in glucose or sucrose solutions and the water loss, the volume of solids and the porosity were measured as a function of time. Water loss was proportional to the square root of time, while the volume of solids decreased and the porosity increased with time. Sugar gain and water loss decreased the compression stress of the apple samples. Osmotic pre-treatment reduced the shrinkage and the porosity of apple solids during air-drying, compared to the no-treated samples. The results of this investigation are useful in the design of efficient osmotic dehydration processes, and in the evaluation of texture of dehydration of products.


Microwave/vacuum drying of fruit gels

February 1999

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64 Reads

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251 Citations

Journal of Food Engineering

Combined microwave (MW)/vacuum drying of fruit materials has a promising potential for high-quality dehydrated products. A better knowledge of the drying kinetics of fruit products could improve the design and operation of efficient dehydration systems.A laboratory MW/vacuum drier was used for drying kinetics experiments with model fruit gels, simulating orange juice concentrate. The system was operated in the vacuum range of 30–50 mbar and MW power of 640–710 W. The distribution of the electromagnetic field in the cavity of the oven was determined from the drying rate of samples, placed at 5 different locations.The drying rate was determined by periodic weighing of the sample. The rate constant (K) of the single-layer model of drying was estimated by regression analysis of the experimental data. An empirical model is proposed for estimating the drying constant (K) as a function of the absolute pressure and the MW power of the system.


Factors influencing the friction of raisins during processing and handling

August 1997

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13 Reads

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12 Citations

Journal of Food Engineering

Our study on the friction of Sultana and Corinth raisins indicates that there is a linear increase of the static and the kinetic friction force when the sample was loaded with added weights. An increase in the moisture content, up to 18%, reduces the friction of Sultana raisins, but increases that of Corinth raisins. For moistures larger than 30%, the friction of both types of raisins remains constant. Anti-sticking substances, reduce the friction but increase the stick-slip effect. The friction of raisins increases with sugar loss. The friction coefficients of raisins, sliding on Teflon-coated surfaces, are reduced by more than 30%, compared to PVC surfaces.


Thermal diffusivity of granular and porous foods at low moisture content

July 1997

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21 Reads

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64 Citations

Journal of Food Engineering

Thermal diffusivity is an important transport property of foods, which is useful in computations, simulation and control of several unsteady-state food processing operations. Limited data on thermal diffusivity are available, especially at low moistures, which are of interest in drying and storage processes. Experimental values of the thermal diffusivity (α) in the low moisture range were obtained directly for freeze-dried coffee, potato and meat, using the transient method of Dickerson (1965), and indirectly for granular starch, flour, rice, and raisins, using thermal conductivities, obtained by the heated probe method. A nonlinear relationship was found between (α) and moisture content in granular and porous foods in the low moisture region. An evaluation of published data indicates a strong effect of physical structure (especially porosity) on the thermal diffusivity. A similar effect has been observed on the moisture diffusivity. These anomalies may be related to the state of water (adsorbed or capillary) in the porous structure of the low-moisture foods.


Engineering properties in food processing simulation

December 1996

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42 Reads

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27 Citations

Computers & Chemical Engineering

The design, simulation, optimisation and control of food processing operations require basic engineering properties of foods. Due to the complex physical and chemical structure of foods, theoretical prediction is not possible, and experimental data are needed for the thermophysical, transport, and mechanical properties of raw and processed food products. Special consideration is necessary for the quality changes, microbiological / biological safety, and sanitation of food processing. Tables of scattered data and limited databases have been published, but there is a need for more reliable data and models, especially for the transport properties, i.e. the fluid flow, heat and mass transfer properties of food products. Typical experimental values and semi-empirical models for the mechanical properties, the apparent viscosity, the thermal conductivity, and the moisture diffusivity are presented for model foods and fruit / vegetable products. Application of the engineering properties to the simulation of food processing operations, such as thermal processing and drying, is discussed. Reliable pilot-plant and industrial data are essential, since some engineering properties, such as interphase transfer coefficients and fouling factors, are affected strongly by the food product / processing equipment system.


Citations (63)


... handling and processing of agricultural materials. The density can be defined in different ways [3, 4]: true density, substance density, apparent density, bulk density and particle density. Bulk and particle densities are vital parameters in the design, modeling and optimization of food processing operations because they have a direct affect on the thermophysical properties of food materials [3]. ...

Reference:

Influence of Boundary Conditions on Particle Density
Food structure and transport properties
  • Citing Article
  • January 2001

... It has been verified that D eff varies with internal material conditions such as moisture content, temperature, and structure [21,22]. Due to the unfeasible theoretical prediction of D eff in complex materials, the value of D eff is usually obtained from experimental results through computer optimization and the slopes method [23]. The computer optimization method can give D eff at different grid point and time step through the iteration and the discretization [9]. ...

Diffusivity of Moisture in Air Drying of Starch Gels
  • Citing Article
  • January 1984

... Bananas exhibit significant inter-varietal variability in their composition, such as sugars, proteins, or lipids contents [1] , which can impact moisture diffusivity. This variation in moisture diffusivity has been observed in starch-based systems when simple sugars are added to the matrix [50][51][52] . Figure 4(A-C) display the validation data for the strain equation (15). ...

Diffusion of Water in Starch Materials
  • Citing Article
  • December 1992

Developments in Food Science

... These observed D eff values were consistent with published literature such as ð0:2 -10Þ × 10 −9 m 2 /s in potato, carrot, onion, and green pepper at 60-80°C [32,33] and 10 -12 -10 -8 m 2 /s in peas at 60-80°C [34]. These potassium diffusivity values were slightly lower than those of water and NaCl diffusivities (ð8:2 − 12:3Þ × 10 −9 m 2 /s) obtained during osmotic dehydration of potato at 25-55°C [35] but compare favourably with those of KCl (1:82 × 10 −9 m 2 /s) at 25°C [36]. ...

Estimation of the Effective Moisture Diffusivity from Drying Data. Application to Some Vegetables
  • Citing Chapter
  • January 1994

... From Table 2, it is possible to note that D eff ranged from 2.60 Â 10 À6 to 7.65 Â 10 À6 m 2 /s, where the lowest value was obtained at processing conditions of 42.9 C and 3 m/s, and the highest value was obtained at 57.1 C and 3.0 m/s. The results are out of the range presented for vegetables in Saravacos and Maroulis (2001) with a range between 2.20 Â 10 À12 and 3.05 Â 10 À7 m 2 /s but are in the range presented for legumes (2.06 Â 10 À14 to 1.07 Â 10 À6 m 2 /s) and cereal (8.33 Â 10 À12 to 4.04 Â 10 À6 m 2 /s) products (Saravacos and Marouli, 2001). ...

Transport Properties in Food Process Design
  • Citing Chapter
  • September 2013

... It is also considered as an incredible source of many other health promoting components, such as soluble and insoluble dietary fibre, phenolic compounds, minerals and many other functional compounds, which include B-group vitamins (Alagusun daran et al, 2001). Thermal properties of food materials are those characteristics/properties which are functions of temperature or heat (Saravacos and Maroulis, 2001) and therefore the thermal behavior of solids i.e the response of solid material to thermal change which could be increase or decrease of the temperature or heat. In other words, the three major thermal properties are specific heat capacity, thermal conductivity and thermal diffusivity. ...

Thermal conductivity and diffusivity of foods
  • Citing Article

... This method is also used to produce special foods and food ingredients and to process food industry by-products. There is a wide variety of industrial food drying equipment, mainly empirically developed, but continuously improved by recent advances in food drying and engineering technology [26]. The first activity of this teaching experiment offered students information about a radial airflow food drying equipment and also presented them with a mathematical model describing the percentage of moisture removed. ...

Food Engineering Series
  • Citing Chapter
  • January 2002

... Hutchinson et al. ( 1989), Lund ( 1989), Or-ford et al. ( 1 Y 89), Russell & Oliver ( 1989), Shi & Seib ( 1989, Stepto & Dobler ( 1989), Biliaderis ( 1990Biliaderis ( , 199 1 u, 6, 1992a, Biliaderis & Seneviratne ( 199Ou,b), Biliaderis & Zawistowski ( 1990), Ghiasi & Skarra ( 1990) ( 199 lb, 1992a, b), Ollett et al. (1991), Patil(1991), Roos & Karel(1991 d), Scandola etal. (1991),Tomka( 19Yl), Bizot et al. (1992) ( 1992), Huang et al. (1992), Kaletunc & Breslauer (1992), Kalichevsky & Blanshard ( 1992u, c, 1993u), Kalichevsky et al. (19924, h, 1993), Karathanos & Saravacos (1992), Kim & Walker ( 1992), Kokini et ul. (1992u), ...

Water Diffusivity in the Extrusion Cooking of Starch Materials
  • Citing Article

... S. Kannan [28] highlighted challenges and future directions in innovative process measurement and automation. He also discussed the issue of multiple inputs and outputs, the limited nature of industrial processes, and sensor nonlinearity compensation [29]. ...

Handbook of Food Processing Equipment
  • Citing Book
  • January 2002