Food Process Design and Evaluation

Rakesh K. Singh

• Publisher: CRC Press
• Year: 2019
• Print ISBN: 9781566762304
• eBook ISBN: 9781351447584
• Topic: Technology & Engineering
• Subtopic: Nutrition, Dietics & Bariatrics
• Index: Technology & Engineering

This book provides detailed illustrated reports on important recent advances in processing of foods including separation, mixing, preservation, and extrusion. The authors are specialists in food processing from North America and Europe. The reports were originally presented at the Conference of Food Engineering sponsored by the American Institute of Chemical Engineers in 1992 and 1993; they were selected, rewritten and updated for this book.

—————— 1 ——————

Electrically Assisted Membrane Separation Processes

IOANNIS VRADIS and JOHN D. FLOROS

Purdue University
Department of Food Science
West Lafayette, IN 47907, U.S.A.

---

INTRODUCTION

LIFE IS PARTIALLY sustained by the ability of organisms to organize and control the flow and concentration of certain materials. This increased or decreased localization of materials in specific spaces is a phenomenon called separation. Examples of separation are abundant in nature. They include simple natural phenomena, such as evaporation of sea water, or more complex events, such as selective absorption of nutrients in the digestive tract of animals.

Competition for survival drove primitive man to develop methods of separating certain materials. Preserving food by sun drying was an early attempt to speed up a naturally occurring separation process. More complex separation applications have been developed, and current efforts are concentrating on (a) developing new separation processes and (b) improving the performance of existing processes.

A group of separation processes, developed during the last quarter of this century, is called membrane separations (MS). Membrane separations are based on the selective transport of materials through membranes. They use molecular weight as the main criterion for separation and pressure difference as the driving force. Membrane separations have certain advantages over other separation techniques, especially in biochemical applications (Knorr, 1987; Meares, 1976). Membrane separations do not involve excessive heat or organic solvents, which are harmful to many biomaterials. On the other hand, two important problems associated with membrane separations are concentration polarization and fouling (Porter, 1972). Both are related to material accumulation and buildup inside pores and on surfaces of membranes and eventually result in reduction of flux through the membrane.

Several attempts have been made to reduce concentration polarization and fouling and to increase the performance of membrane separation processes. Some techniques involve the use of abrasive materials, diatomaceous earths (as filtration aids), pulsated flows, ultrasonic fields, and electric fields (Wakeman and Talerton, 1991). This chapter focuses on the theory and methods of applying electric fields during membrane separations to reduce concentration polarization and fouling. The effect of electric fields is manifested by forces exerted on charged particles present in the field. These forces can be used to move matter away from a membrane and, therefore, reduce material buildup.

The objectives of this work are to (a) obtain a better understanding of electrically assisted membrane separation processes, (b) link equations of membrane separations and electrodynamics and propose combined theoretical models, and (c) explore some applications of electrically assisted membrane separations in the food and biochemical industries.

SEPARATION UNDER APPLICATION OF EXTERNAL FIELDS

The aim of separation processes is to increase the concentration of one or more compounds in a well-defined space. If a mixture with components 1 and 2, occupied a space a, the aim of a separation process will be to retain one component, say 1, in the space a, while moving the other (i.e., 2) into a different space b. This will increase the concentration of components in the respective areas. The effectiveness of a separation process can be expressed by a separation factor, SF, which is defined as (Giddings, 1991):

where 1 and 2 are the components to be separated, a and b are regions of space, and c is the component concentration in each region. High separation factors indicate effective separation.

In general, separation processes perform two tasks. The first is to increase the concentration of components in a solution by removing solvents. An example is the concentration of milk by removing water. The second task is to separate and purify a specific component (i.e., isolation of an enzyme from a broth).

Separation processes are divided according to their applications into analytical and preparative. Analytical separations are used in laboratories to analyze and quantify certain constituents of solutions. Preparative separations are used industrially either to separate and purify one or more components of a solution or to increase the concentration by removing solvents.

Separation processes, as all processes, are based on flow of energy. This energy is expressed by thermodynamic variables such as entropy, chemical potential, and Gibbs function.

Chemical Potential and Gibbs Function

According to the second law of thermodynamics, a spontaneously occurring process is always accompanied by an increase of entropy. In general, natural changes occurring in a system at equilibrium with its surroundings are controlled by two criteria (Atkins, 1990):

where S is entropy, U is internal energy, and V is volume. Equation (2) states that, in an isolated system of constant volume, the entropy increases spontaneously. Equation (3) stat...

Table of contents

• Cover Page
• Half Title
• Title Page
• Copyright Page
• Contents
• Preface
• 1 / Electrically Assisted Membrane Separation Processes—IOANNIS VRADIS and JOHN D. FLOROS
• 2 / Review and Advances in Apple Juice Processing—E. ORTEGA-RIVAS
• 3 / An Appraisal of the Characteristics of Food Mixing—K. NIRANJAN
• 4 / An Economical Method for the Dispersion of Powders into Liquids—GREGORY STURICZ
• 5 / Hygienic Design and Evaluation of a NIMIX Mixer for Particulate Suspension Duties—G J. POLLARD and M. H. K. GHOVANLOU
• 6 / Design Considerations in Aseptic Processing of Foods—S. BHAMIDIPATI and R. K. SINGH
• 7 / Flow Diversion Valve Practices in Plants Designed for Aseptic Processing—STEVEN G. GRALL
• 8 / Electrical Control and Monitoring Systems for an Aseptic Packaging Line—V. E. CAUDILL
• 9 / Advances in High-Pressure Food Preservation Methods—DIETRICH KNOOR
• 10 / Recent Developments in the Commercial Applications of High-Pressure Technology in Food Processing—REY A. EUZONDO
• 11 / Extruded Cereals and Snacks—MASSOUD KAZEMZADEH
• 12 / Current Automated Control Approaches to Twin Screw Extrusion Systems—MASSOUD KAZEMZADEH
• Index