Download Innovative Methods of Energy Transfer

Innovative Methods of Energy Transfer
L. E. MCBEE
Rose Acre Farms, Seymour, Indiana 47274
ABSTRACT Energy is utilized in many forms for
processing egg products and other foods. Energy in the
form of heat has commonly been used to kill microorganisms and pasteurize eggs. Transfer of energy by
convection and conduction is limited by the properties
of the egg product. Energy transfer by radiation is being
used to advantage in the development of innovative
methods to kill or inactivate microorganisms. A review
of the electromagnetic spectrum reveals underutilized
forms of energy with unique properties. Specific frequencies and method of application are selected for their
ability to focus energy toward the destruction of
microorganisms and the production of safe food
products for the public.
(Key words: pasteurization, radiation, eggs, microwave, radio waves)
1996 Poultry Science 75:1137-1140
INTRODUCTION
The pasteurization of egg products is mandatory in
the U.S. The purpose of pasteurization is to provide
consumers with safe egg products, free of pathogenic
microorganisms, especially Salmonella. The early work
by Owen Cotterill and associates at the University of
Missouri-Columbia, Garibaldi, Lineweaver, and others
at the USDA Western Regional Laboratory, and many
pioneering researchers established the basis upon which
the USDA developed the pasteurization standards
currently in use. These standards were designed to
minimize the risk of Salmonella while maintaining the
functional properties of egg products. Presently, these
standards are being reevaluated for their adequacy in
meeting current concerns of the public regarding other
pathogens, new product formulations, and alternative
processing methods.
Leaders in the egg products industry have continued
to seek improved processing methods to provide greater
margins of safety to the consumer, improve functional
properties, and reduce costs of operations. Today we
have learned of developments indicating that pasteurization of shell eggs will become a reality. Food
engineers and technologists are adapting unique concepts for the development of improved methods of
pasteurizing eggs and egg products. All of these
methods involve the transfer of energy with the goal of
eliminating Salmonella and other pathogens.
The objective of the following presentation is to
review energy transfer principles, discuss selected recent
developments in egg pasteurization, and stimulate
Received for publication August 16, 1995.
Accepted for publication February 6, 1996.
thought about innovative methods of pasteurizing eggs
and egg products.
THERMODYNAMICS
Food processing operations directly involve mass and
energy. The food product may be considered a mass to
be mixed, blended, separated, heated, cooled, or transformed into a desired form with specific attributes. All
of these processes involve the transfer of mass and
energy by the input of work. Energy is usually
considered to be heat; however, there are many forms of
energy used in food processing. A review of thermodynamics principles reveals limitations and areas of
opportunity for development of innovative food
processing methods.
First Law of Thermodynamics
The total amount of energy in the universe is constant.
Energy can be neither created or destroyed but only
changed from one form to another as shown in the
equation:
E2 = Ei + (q - w)
where: Ei and E2 = total energy of a system; q = heat; and
w = work. In order to transform a food product from one
energy state to another it is necessary to apply energy in
the form of heat with work.
Second Law of Thermodynamics
Any spontaneous change that occurs in the universe
must be accompanied by an increase in the entropy of the
universe. This law may also be applied to a closed system
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or to relationships between defined interactive systems by
the following equation:
AG = AH - T AS (for a system)
where: AG = change in energy; AH = change in heat
content; T = temperature; and AS = change in entropy.
If this equation is applied to changes in biological
systems, we observe that the growth of large ordered
molecules from smaller molecules will have a negative AS
and under isothermal conditions will require the input of
energy. This equation also requires that heat must flow
from higher to lower temperature.
ENERGY TRANSFER APPLICATIONS
Conduction
Energy is conducted through a gas by intermolecular
transfer of kinetic energy from more energetic to less
energetic molecules when they collide. Energy conduction
in liquids is similar to that in gases. The thermal
conductivity of liquids decreases with increasing molecular weight. Energy is conducted in solids by two
mechanisms: migration of free electrons and lattice
vibration. In conductive metals, there is a rapid transfer of
thermal energy by electron transfer, whereas in nonmetallic materials, the lattice vibration transfers energy more
slowly (Keith and Bohn, 1993).
Food products are complex and variable blends of
solids, semi-solids, and liquids having quite slow thermal
transfer. This slow thermal transfer brings in the factor of
interface resistance. There is no single theory or set of data
that fully describes interfacial resistance at surfaces for
food processing. Liquid egg products are usually
homogeneous fluids, so fluids containing particulates will
not be discussed in this presentation.
Convection
When heating fluids with conventional heat exchangers the convection mode is most active. Convection
is a combination of conductive energy transfer due to
molecular motion and the macroscopic motion of fluid
parcels. The motion of the fluid may be due to density
gradients or an external force such as pumps or fans.
Irrespective of the details of the mechanism, the rate of
heat transfer by convection between a surface and a fluid
can be calculated from the relationship:
q c = he A AT
where: q c = rate of heat transfer by convection, Watts
(British thermal units per hour); A = heat transfer area,
square meters (square feet); AT = difference between the
surface temperature T s and a temperature of the fluid J_at
some specified location, degrees Kelvin (Fahrenheit); h c =
average convection heat transfer coefficient over the area
A, Watts per square meter per degrees Kelvin (British
thermal units per hour per square foot per degrees
Fahrenheit).
The rate of heating can be accelerated by increasing the
heat transfer area, increasing the surface temperature, or
improving the heat transfer coefficient; however, there is a
limit to the surface temperature imposed due to the
coagulation temperature of egg. Area is restricted by
economic and physical considerations. To improve the
rate of heat transfer, improvement must be accomplished
by the design of the heat transfer surface.
Electromagnetic Spectrum
The electromagnetic spectrum (Figure 1) may be used
to categorize most energy sources. High frequency
radiation, greater than about 10 - 7 m, is characterized by its
high energy level and ability to penetrate materials easily.
Ultraviolet, visible and infrared radiation will penetrate
only thin layers of selected material. Within the group
comprised of microwave, radio wave and electric power,
penetration decreases with increasing wavelength.
Radiation
Ionizing radiation has long been promoted as an
effective means of destroying microorganisms but has
suffered from poor acceptance by the general public.
Currently, foods are being treated with high energy
electron beams from a linear accelerator (Rice, 1993).
Wong and Herald (1995) compared thermal (57 C for 3.5
min) and irradiation (2.5 to 3.3 kGy for 81 s) treatments of
liquid egg white and found both to destroy Salmonella
typhimurium at 10 7 cfu/mL. Irradiated liquid egg white
exhibited better functional properties, improved
resistance to microbial growth, and reduced required
storage energy by 67% for refrigerated vs frozen storage.
Electric Power
Ohmlc Heating. It is well known that the passage of an
electric current will increase the temperature of materials
due to the electrical resistance of the material. This
process, using 60 Hz alternating current, has been offered
for use by a leading food equipment manufacturer. It has
the advantage of rapid heating of both fluid and solid
particles in the same process stream.
Electroheating. In electroheating the electrical power
is conducted through the product as in ohmic heating;
however, with frequencies in the range of 100 to 450 KHz
there is minimal electrolysis of metallic electrode materials into the food product as described by Reznik (1988).
Reznik and Knipper (1994) and Knipper and Reznik (1995)
improved the process describing equipment and optimum conditions for pasteurization of egg products
utilizing 5,000 to 37,000 V at up to 12 A/cm2 at 150 to 450
KHz. This process is currently approved by the USDA for
the production of extended shelf life refrigerated egg
products.
Pulsed Electric Power. In biology, cell membrane
selective permeability is an advantage to the cell by
SYMPOSIUM: SECOND O. J. COTTERILL EGG AND EGG PRODUCTS SYMPOSIUM
1A
1 nm
1 m
1 km
Wavelength, j Q - 1 4 - i s - I : - n - i o -9 -8 -: -6 -5 -4 -.» -: -1 o i : 3 4
*<m)
» i * t 1 1 I . .I I I I 1 i 1 I 1 I I
Frequency,
Ms* 1 )
1
]Qn
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5 6 7
1 1 1
1 I I I I I I I I I I 1 I I I I I I I I F
21 20 19 is 17 16 15 M 13 12 11 10 9 s 7 6 5 4 3 2 1
1
I I
I
I Ivisibl
Radio
waves
H*— X-rays—*| «
Thermal
Cosmic rays Gamma
radiation
rays
Electric
power
-Hertzian waves*
(a)
Wavelength, X (m) 10" 7
1
Frequency, y d " )
Ultraviolet
10- 4
T
10"
Near
Intermediate
infrared
infrared
io»
Far infrared
llJiJ*
(b)
FIGURE 1. a) Electromagnetic spectrum, b) thermal radiation portion of the electromagnetic spectrum, (Kreith and Bohn, 1993).
preserving the interior of the cell from exogenous
aggression, but a strong limitation to experimental
manipulation of the cytoplasm for genetic modification.
Electropulsation, i.e., submitting cells to strong shortlived
electric field pulses, was pioneered by Neumann and
Rosenheck (1972) to create permeable cell membranes.
Teissie et al. (1992) described a flowthrough device for
electropermeating cells. Under the best of conditions
many cells do not remain viable after electroporation. A
photomicrograph of electroporated cells show orientation
of pores within the electric field and different forms of
pores with different pulse conditions (Tekle et al, 1992). In
food processing, it is desired to select treatment conditions
of greatest detriment to the cell structure of microorganisms leading to death of the cells. Castro et al. (1993)
determined that membrane destruction occurs when a
differential membrane potential exceeds - 1 V in many
cellular systems. An external field strength of - 10 KV is
damaging to Escherichia coli (Sale and Hamilton, 1967).
This effect on cell walls was described as "dielectric
breakdown" by Zimmerman (1986).
Dunn and Pearlman (1987) revealed a method and
apparatus for preserving fluid food products, such as fluid
egg products, by exposure to controlled, pulsed, high
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Bialod, D., 1985. Development of technology for industrial
applications of radio frequencies, in: Radio Frequency/
Radiation and Plasma Processing-Industrial Applications
and Advances. Technomic Publishing Co., Inc., Lancaster,
PA.
Castro, A. J., G. V. Barbosa-Canovas, and B. G, Swanson, 1993.
Microbial inactivation of foods by pulsed electric fields. J.
Food Process. Preserv. 17:47-73.
Decareau, R. V., 1985. Microwaves in the Food Processing
Industry. Academic Press, Inc., Orlando, FL.
Dunn, J. E., and J. S. Pearlman, 1987. Methods and apparatus for
extending the shelf-life of fluid food products. U.S. Patent
4,695,472.
Dunn, J., A. Bushnell, P. Hall, S. Cheng, T. Ott and W. Clark,
1995a. Pulsed electric field pasteurization. Presented at IFT
Annual Meeting, Anaheim, CA.
Dunn, J., A. Bushnell, T. Ott, and W. Clark, 1995b. Pulsed light
for food processing. Presented at IFT Annual Meeting,
Anaheim, CA.
Heinz, V., and D. W. Knorr, 1995. Inactivation of Bacillus subtilus
endospores by ultra-high-pressure in combination with
other treatments. Presented at IFT Annual Meeting, Anaheim, CA.
Huang, F., 1989. Method of treating liquid egg and egg white
with microwave energy to increase refrigerated shelf life.
U.S. Patent 4,853,238.
Knipper, A. J., and D. Reznik, 1995. Producing extended
refrigerated shelf life food without high temperature
heating. U.S. Patent 5,415,882.
Kreith, F., and M. S. Bohn, 1993. Principles of Heat Transfer. West
Publishing Company, St. Paul, MN.
Lentz, R. R., P. S. Peapack, G. R. Anderson, J. DeMare, and T. R.
Peck, 1993. Method of processing food utilizing infrared
radiation. U.S. Patent 5,382,441.
Neumann, E., and K. Rosenheck, 1972. Permeability changes
induced by electric impulses in vesicular membranes. J.
Membr. Biol. 10:279-290.
Reznik, D., 1988. Apparatus and method for electrical heating of
food products. U.S. Patent 4,739,140.
Other Energy
Reznik, D., and A. Knipper, 1994. Method of electroheating
liquid egg and product thereof. U.S. Patent 5,290,583.
Berlin and Hoover (1995), Roberts and Hoover (1995),
Rice, J., 1993. E-B ionization zaps salmonella. Food Process. July,
Aleman et al. (1995), and Heinz and Knorr (1995) recently
p 12.
presented their findings regarding the application of high
Roberts, C. M., and D. G. Hoover, 1995. Tolerance of Bacillus
pressure for inactivating various bacteria and preserving
eoagulans 7050 spores to combinations of high hydrostatic
food products.
pressure, heat, acidity, and nisin. Presented at IFT Annual
Pulsed broad spectrum light with peak emission
Meeting, Anaheim, CA.
Sale, A.J.H., and W. A. Hamilton, 1967. Effect of high electric
between 400 and 500 n m provided high levels of microbial
fields on microorganisms. I. Killing of bacteria and yeast.
kill on simple surfaces (Dunn et al, 1995b). A method of
Biochim. Biophys. Acta 163:37-43.
processing food using a filtered source of infrared
Tekle,
E., P. B. Chock, and R. D. Austumian, 1992. Electric field
radiation for deep heating was described by Lentz et al.
induced asymmetric breakdown of cell membranes, in:
(1993).
Charge and Field Effects in Biosystems-3. Birkhauser,
Boston, MA.
REFERENCES
Teissie, J., S. Sixou, and M. P. Rols. 1992. Large volume cell
electropermeabilization and electrofusion by a flow process.
Aleman, G. D., E. Y. Ting, A Hawes, D. F. Farkas, and J. A. Torres,
in: Charge and Field Effects in Biosystems-3. Birkhauser,
1995. Inactivation of yeasts in pineapple juice by constant
Boston, MA.
and pulsed ultra high pressure. Presented at Institute of
Food Technologists Annual Meeting, Anaheim, CA.
Wong, Y. C, and T. J. Herald, 1995. A comparison study of
thermal and irradiated pasteurization on the functional,
Allen, M. J., S. F. Cleary, A. E. Sowers, and D. D. Shillady, 1992.
Charge and Field Effects in Biosystems-3. Birkauser, Boston,
physical and microbiological properties of liquid egg white
MA.
during refrigerated storage. Presented at IFT Annual
Meeting, Anaheim, CA.
Berlin, D. L., and D. G. Hoover, 1995. Effect of high hydrostatic
pressure on viable and noncultural but viable pathogenic
Zimmerman, U., 1986. Electric breakdown, electropermeabilizaspecies of Vibrio. Presented at IFT Annual Meeting,
tion and electrofusion. Rev. Physiol. Biochem. Pharmacol.
Anaheim, CA.
105:175-256.
voltage electric field treatment. This technology is currently being marketed by PurePulse Technologies tinder
the CoolPure trademark. Dunn et al. (1995a) presented
data on the efficacy of multiple, short duration, high
strength electrical field pulses for providing nonthermal
antimicrobial effects and pasteurization of pumpable
foods.
Radio Waves. Radio frequency energy waves create
heat within the product stream itself rather than by
conduction from heated surfaces. This method results in
the ability to reduce heating time and can heat large
quantities with relatively small processing systems.
Bialod (1985) discussed the development and market
characteristics of radio frequency energy applications.
High frequency installations frequently operate at 27 or 13
MHz. The three major components of the radio wave
system, generator, applicator, and load, must be matched
for optimum efficiency. Although calculating the electrical
characteristics of the system is possible, much experimentation is required for optimum efficiency.
Microwaves. Microwave heating typically uses frequencies from 300 to 3,000 MHz, although the ISM
frequencies permitted are 433, 915, and 2,450 MHz. The
microwave ovens in home use and many commercial
installations use 2,450 MHz. Greater depth of penetration
in food products can be obtained using the 915 MHz
frequency. Few installations use the 433 MHz frequency.
A comprehensive review of microwave technology and
its application to food processing was presented by
Decareau (1985). Huang (1989) patented the use of
microwaves to heat egg white and whole egg at
temperatures up to 83.6 C without significant gelation. He
claimed the treatment provided thermal kill, biological
damage, and alteration of cell membranes and metabolic
function to microorganisms.