This document discusses criteria for evaluating alternative food processing technologies to reduce E. coli contamination. The essential criteria that must be met are: 1) the ability to process solid foods, 2) achieve at least a 5-log reduction of E. coli, 3) not increase food temperature above 150°C, and 4) maintain the base shelf-life of foods. Desirable criteria include high throughput of 500 lbs per hour to meet commercial-scale needs. Several technologies - ozone, irradiation, high pressure processing, pulsed electric fields, and antimicrobial films - are evaluated against these criteria. Antimicrobial films are recommended as they can prevent outbreaks during large-scale production while meeting all essential criteria.
2. 1
ABSTRACT
The USDA’s Safety and Inspection Service drafted a report from data collected over multiple years on the
contamination level for the human pathogen Escherichia coli O157:H7 in ground beef patties.It was found that in
2000, 0.86% of patties were contaminated, as compared to 0.84% in 2001, 0.78% in 2002, 0.30% in 2003 and 0.17%
in 2004. Then, between 2003 and 2006, there were 22 ground beef patty recalls due to the presence of E. coli
O157:H7. Efforts to prevent the continuation of such outbreaks including heavier surveillance, hazard analysis and
critical control point plans have helped, but not abolished, contamination by E. coli in meat, poultry and other
produce. Still, two out of every thousand beefpatties contain traces of E. coli, which is only required in a small dose
to induce severe infection in a human. Over the last two decades,the largest produce manufacturers spent billions of
dollars fighting E. coli. Even with cleaner handling today, the risk of infection for large-scale producers is
astronomical, which is why steps must be taken to block the bacteria’s every chance of infesting consumable goods.
This has given rise to a new era of food processing technology.Methods developed overthe last century such as
high hydrostatic pressure and irradiation are currently being challenged by potentially better techniques like ozone
and antimicrobial films treatment. It is the aim of this paper to select a processing technology for a plant with
commercial-scale throughput (on the order of 500 pounds per hour[226.8 kg/hr]) based on multiple acceptance
criteria. These criteria include ability to reduce E. coli populations by 5 log10 reductions,preservation of quality,
solid food aptitude, induced temperature changes as well as throughput capacity,shelf-life extension, compliance
with regulation and public approval rating. The final recommendation is for antimicrobial films, which possessthe
ability to prevent outbreak throughout large-scale commercial production of fruits, vegetables,and meats. This is
also accompanied by a potential problem analysis and suggestions forfuture work with this technology.
4. 3
Table 14: Evaluation of Throughput for Antimicrobial Films.....................................................26
Table 15: Percent ofUntrained Consumers Who Favor Processed Food over Non-processed
(2009)..........................................................................................................................................26
RECOMMENDATION ....................................................................................................................27
FUTURE WORK.............................................................................................................................27
REFERENCES.................................................................................................................................28
5. 4
INTRODUCTION
Consumer’s life habits and an increase in demand for healthier foods are driving a revolution in the food
industry to betterpreserve products. With the help of fast transportation and refrigeration, a healthier and more
widespread market is developing for suppliers, meaning food will travel hundreds or thousands ofmiles before
reaching the consumer. This also presents an opportunity for microorganisms to hitch a ride and spread disease,
making preservation techniques all the more relevant. Beginning in the 1970s, health and safety organizations
established the role of microbes in food poisoning outbreaks and their ability to grow in adverse environments, such
as in refrigerated goods.Species like Escherichia coli,amongst many other pathogens,when present in food are
found to propagate and spoil the product. The number of illnesses caused by the consumption of fresh produce is an
ongoing concern and there is an emergent need to reduce the incidence of pathogens.
Conveniently, some products can be pasteurized before refrigerated storage,which can lead to multiple log
reductions of pathogenic members like E. coli and inactivation of the enzymes responsible for spoilage. However,
the heat treatment in this process is not proper for all foods and can damage goods by modifying nutritional and
sensory properties.Such losses render the products unacceptable as compared to otheravailable fresh foods.
Furthermore, pasteurization is suited only for liquid foods – an exception which bars most household food items
from protection. And while in theory, the application of preservatives and chemical treatment renders fresh food
contaminant-free, in practice there is a great deal of public scrutiny due to the dangerous health effects of chemical
preservatives.
In response to the need for alternative methods for the treatment of heat-sensitive food products,new
technologies have arisen that minimize the effect of preservation on the final good and assure safety and reliability.
Ideas range from irradiation to the formation of synthetic skins on the surfaces of food. With approximately two out
of every thousand ground beefpatties infected with E. coli O157:H7 (Sommers & Xuetong,2011), one certainty is
clear: there is a serious need for the removal of contamination prior to packaging. This paper will examine the
different criteria that must be met to qualify a technique as advantageous to sanitization against E. coli on solid food
surfaces,followed by an evaluation of alternative technologies.
6. 5
BACKGROUND
Food product quality considers a number of factors. Sensorial quality defines what the consumer sees,
feels, smells and tastes.It is well established that the average consumer, when evaluating fresh produce, looks for
the item with the least blemishes. Firmness, aroma and color are all inspected with reasonable attention paid to
detail. Blotching, discoloration, soft spots in fruits and vegetables and odors are all related to senescence and are
negative qualities. Senescence is the natural process by which a food product ages and decays.The sensorial quality
of a product is therefore directly related to the rate of moisture loss, oxygenation and enzymatic activation, as they
each change the composition of the produce. Bacteria, fungi and various other microorganisms accelerate this
process as they use their digestive enzymes to consume the food. E. coli, for example, forms patches or colonies on
the surface of the food which may not be seen by the naked eye, but are marked by discoloration as a result of the
decomposition taking place. Decomposition also leads to the depletion of nutritional matter. Minerals, vitamins and
aromatic compounds are healthy to the consumer but very sensitive to changes in chemistry. The physical effects of
nutritional decay are recognizable by the average consumer. The health and wellness effects are also noticeable as a
lack of certain vitamins, for instance, often manifests itself through deficiencies associated with those vitamins.
Microbes present on a product are frequently associated with toxins and other infectious agents which they
release to keep competing organisms out. As a colony of E. coli in a ground beef patty grows, so too does the toxic
waste which it creates. While many strains of E. coli are harmless, strains like O157:H7 cause serious illness, and
even death in individuals with weakened immune systems. If consumed in large enough concentrations,E. coli
O157:H7 will render a human being dangerously ill with a wide range of severe symptoms from vomiting to bloody
diarrhea. Immunization against E. coli O157:H7 is impossible due to its ability to adapt to living systems.Hence,
culling the incidence of dangerous illness by E. coli infection must be performed in the processing stage.The current
industry standard calls for a 5 log10 (99.999%) reduction in microbial content in post-processing produce (Gutsol &
Niemira, 2011). It is believed that inactivation of this degree minimizes the probability of infection by E. coli
O157:H7.
7. 6
It is microbial diversity and the ability to adapt that pose the greatest obstacle for food processing
technologies.The bacteria of interest are classified into two categories: vegetative cells, which have an active
metabolism, and spores, which exhibit no metabolic activity and present elevated resistance to all forms of treatment
(Cebrian, Condon, & Manas,2011). Amongst the vegetative cells, there are two sub-categories:gram-negative and
gram-positive cells. Gram-positive bacteria possess a thick peptidoglycan cell wall which acts as a strong barrier to
disinfecting agents.Gram-negative bacteria do not have a dense cell wall but instead have a thin wall surrounded by
an outer membrane, which allows for increased intra- and extracellular regulation. The majority of the inactivation
technologies that inhibit bacteria do so through structuralor physiological changes in the microbial cells that may
have crippling effects or lead to increased sensitivity. The most common target is the cellular membrane, which
controls the influx and efflux of extracellular contents and manages pH levels. Loss of function in the lipid bilayer
membrane undermines a cell’s ability to control its own equilibrium, which very often results in cellular destruction.
E. coli O157:H7 is a gram-negative bacterium. It is also a facultative anaerobe, meaning that it can survive in an
environment regardless of the presence of oxygen.
Processing of food begins at the source, which may be at a farm or a slaughterhouse.At this early stage,it
is required that a conscientious effort is made to provide food products with preliminary cleaning. For example, all
cuts made from a beef carcass must undergo washing with clean water and all tools used to cut meat must be
sterilized before and after each use. It is at this stage of processing where the largest reduction in pathogenic
contamination occurs (Rodriguez-Romo, Vurma, & Yousef, 2011). At the processing stage,some techniques
involve the use of heat treatment. High temperatures target critical enzymes vital to microbial metabolic pathways.
The heat energy required for such inactivation, however, is high enough to alter the sensorial and nutritional
qualities of produce. For example, the heat may fry an egg, cook beef or brown an apple. Chemical alternatives also
represent a frequently used cleaning option, such as in the use of aqueous chlorine to wash fresh produce. These
chemical agents are poisonous forthe microbes and pose no threat to the consumer. Like heat treatment, however,
many chemical disinfectants currently in use cause sensorialand nutritional deficits in the food. Newer approaches
focus on the use of various forms of energy to attack microbial cells while leaving the product unaffected. This is
done by taking advantage of a range of optimum dosage levels.
8. 7
Some definitions in this paper include terms that are related to various alternative processes in food
preservation. The D-value refers to the amount of ionizing radiation required to kill 90% of microbial cells in a
sample and is expressed in kiloGrays (kGy). The afore-mentioned radiation is provided by a radiation source.
Spores are defined as dormant bacterial cells with a very resistant outer cell wall which renders nearly all
disinfecting agents ineffective. Throughput refers to the amount of product treated with a specific dose within a
defined period of time. Units for throughput vary according to each method but are typically taken as pound per
hour or kilograms per hour. Throughput for batch processes is limited by the time it takes to remove a load and
begin a new cycle. Throughput for continuous processes is limited by mechanical constraints such as the speed of
the conveyorbelt carrying the product in and out of the unit operator. Process duration, for the food product,is the
time it takes to reach a desired log10 reduction in a given process.And finally, compliance with food regulations
refers to the design of the processing method, in that it agrees with good manufacturing practices and with
government food processing regulations.
CRITERIA
A total of eight selection criteria will be considered for the analysis of alternative food processing
technologies.These eight are categorized into two sections:essentialcriteria, which set the threshold values and
desirable criteria, which refer to optimum quantities or what is preferable. From the combined analysis of all criteria
and alternatives, it is possible to make an educated recommendation on which processing method should be
preferred by the large-scale processing plant in question.The superior method would be one which satisfies all
essentialcriteria and is the best fit for the desirable criteria.
ESSENTIAL
1. The need for alternative food processing methods stems from the current method’s inadequacy with
certain types of food, namely solids. Pasteurization is frequently used to eliminate foodborne
pathogens in liquids, but cannot process solid products due to incompatibility in its design. Therefore,
9. 8
it is necessary that an alternative has the ability to process solid food, as this is where the need for
treatment is greatest.While no numerical quantity can be put upon this, an alternative method’s
capacity to handle solid foods is given as a percentage representing the fraction of solid food types
than can be processed compared to all solid food options.The current heat treatment method can
process only about 40% of solid foods.All others are too sensitive to large temperature increases (on
the order of 150°C) for heat treatment to be an effective method.
2. The main focus of food treatment is the elimination of viable levels of E. coli O157:H7 present on or
within the food product. Industrial standards hold that tolerable reduction levels for pathogenic
material is on the order of 5 log10 for natural or artificial inoculations. Therefore, it is absolutely
necessary that alternative methods of treatment inhibit the growth of E. coli O157:H7 by 99.999% for
various food products.The reduction percentage is determined from sampling and analysis via either a
plate count, viable cell count or through the turbidity method. Current heat treating methods are able to
achieve a 5 log10 reduction of E. coli O157:H7. Simple washing, i.e. without processing,leads to only
about a 2 – 3 log10 reduction for most solid food types.
3. As part of measuring a method’s effect on food quality, the temperature changes induced by the
method are taken into consideration. Temperature largely influences the structure and composition of
solid food products.While heat is effective for inactivating E. coli O157:H7, the treated produce may
not be of adequate quality for sale to consumers if the treatment has changed its desired chemical or
physical nature. The most noticeable side effect of heat treatment is discoloration and cooking of flesh.
For heat treatment methods, the typical increase in temperature for a product occurs in a flash instance
(1 – 2 seconds)and is between 125°C and 150°C. Alternatives therefore must not produce heat that
raises the temperature of the product above this level.
4. Part of the purpose of replacing heat treatment as the current method is that food products treated with
heat often have different texture, gloss,odor, taste and nutritional quality. An adequate replacement
10. 9
should therefore confer little to no physical or chemical change upon the processed product.Retention
of sensorial and nutritive quality is measured in terms of shelf-life. A fresh product that has not
undergone processing treatment has a base shelf-life, usually between two days and a week for most
food types,though this is further specified by food type in the tables to follow. Decreases in sensorial
qualities such as discoloration, spotting or losses in moisture content after treatment are unacceptable
in a final product as they indicate a shorter shelf-life. Loss of nutritional value including the leaching
of minerals or the volatilization of aromatics results in peculiar odors and is also deemed unappealing
to consumers and has no shelf-life. For a processing method to qualify as a satisfactory replacement for
heat treatment, the food product must retain the base shelf-life.
DESIRABLE
1. Of the criteria that must be met in order to validate the appropriateness of each process,there are also
parameters that are based on preferred product quality and economic sensibility. One of these desired
criteria is taken from a manufacturing efficiency standpoint,which is that high throughput and ease of
production are favorable to slower and more cumbersome operations.Therefore, throughput should be
on the order of 500 pounds perday or 226 kg per day for all solid food types to meet the scale desired
by a large food producer. Equipment that is simple to clean, easy to replace in the event of wear and
which avoids frequent interruption is also preferable. This criterion has the highest relative importance
compared to otherdesirable criteria. This is because the selection for an alternative must rely on the
cost effectiveness of the alternative. A process which produces the most treated product at lowest cost
is favored over other alternatives.
2. Certain techniques in sanitation,in addition to reducing E. coli O157:H7 counts,also confer improved
product quality. This can be defined as better sensorial value or nutritional content,such as increased
gloss,as well as slowed transpiration and oxygenation. Improvements in quality are measured in terms
of shelf-life; any enhancement to a product’s preservation leads to a longer shelf-life than the standard,
untreated product. Increased shelf-life is a desirable outcome of a processing method.
11. 10
3. Reputation plays a significant role in the marketing of any product. In the United States and most
westernized markets, it is required that producers include labels of the processing method used on the
product.Thus, a product that is processed using a method that is generally regarded as safe by the
uninformed public will fare much better on the shelf than a product that is processed using a
controversial method. This will be taken into account in the decision making process,as the ability to
market the final product has a major effect in choosing the appropriate processing technology.
4. There are numerous agencies across the world that regulate safety standards for consumer products,
especially within the food industry.In the United States,the FDA and USDA set the bar for which
processing techniques are acceptable. It is generally preferred in making a selection to choose an
alternative that requires the least amount of regulatory hurdles. Technology not approved by the
government that is used to process food cannot be sold to consumers. The FDA, for example, has a
long list of requirements that a processing method must meet before it can be applied to production,
and anotherlist of all the experimental parameters that a supplier must provide in order to claim that a
product has certain attributes. These experiments and approval requirements take time and delay
production substantially.The patents for the technology must also be checked, as certain
manufacturers of food processing equipment may forbid alterations to equipment specific to a certain
process.It is a desirable quality that a food processing technology is government-approved and
reliable.
12. 11
THE SUBSTITUTES
Ozone Sanitization
Ozone is a triatomic molecule (O3) and is extremely reactive and unstable.It is produced through molecular
oxygen (O2) interactions with chemicals, electrical discharges or ultraviolet radiation. It possesses a limited
solubility in water which makes it usefulfor food applications as a surface sanitizer. Treatment processes that utilize
chlorine dissolved in water are gradually being converted to ozone in the water-treatment industry only (Zorlugenc
& Zorlugenc, 2012). The relationship between temperature and ozone solubility is given in Table 1.
Table 1: Ozone Solubility in Water
Temperature (°C) Solubility (L ozone/L water)
0 0.641
15 0.456
27 0.270
40 0.112
60 0.000
First introduced as a disinfectant in the treatment of drinking water, ozone inactivates microbial cells
through a mechanism involving the oxidation of cellular constituents. Typicalreactions between ozone and
microbial cells occur on unsaturated lipids in the cellular membrane, intracellular enzymes and genetic material
(Rodriguez-Romo, Vurma, & Yousef, 2011). Enzymes are inactivated through the oxidation of sulfhydryl groups.
Ozone can be generated with high-purity oxygen or dry air coming into contact with an energy source like
a corona discharge generator. Due to its instability, ozone cannot be packaged and must be generated at the
processing facility (Rodriguez-Romo, Vurma, & Yousef, 2011). Ozone detectors are therefore required for worker
safety, as ozone can be lethal at doses above 25.0 ppm (Zorlugenc & Zorlugenc, 2012).
Ozone is known to strongly inhibit the growth of all microbial life, including E. coli O157:H7. It acts at the
cell surface, degrading the bacterial cell wall and membrane until the E. coli cell lyses.Ozone, through its
antimicrobial action, also extends the shelf-life of food products and has application over a wider range of solid
products than heat treatment. Due to its oxidative nature, however, ozone is not recommended for meat products as
13. 12
it very quickly changes the composition of fresh produce like beef and poultry. Ozone dissolved in water has no
effect on heat generation, and thus can be trusted with heat-sensitive foods.
Because it is dissolved in water and produced on-site, scaling up issues can be avoided. The treatment time
required for different products is relatively small, allowing for high throughput in continuous processes assisted by a
conveyorbelt. Ozone use in the treatment of food is also an approved process by all regulatory agencies. While it is
not well-known amongst consumers, food processed by ozone treatment is generally preferred above standard
untreated food items.
Table 2: Ozone Effectiveness for Selected Food Products
Product:
Treatment
Conditions
Shelf-life
(refrigerated):
Inhibition of E.
coli O157:H7:
Temperature
change due to
exposure:
Apple
21 - 25 mg O3
/ L for 3
minutes
4 - 6 months
3.7 log10
reductions
negligible
Tomato
21 - 25 mg O3
/ L for 3
minutes
3 - 4 weeks
4.2 log10
reductions
negligible
Lettuce
21 - 25 mg O3
/ L for 3
minutes
2 - 3 weeks
3.6 log10
reductions
negligible
Potatoes
21 - 25 mg O3
/ L for 3
minutes
3 - 4 months
4.7 log10
reductions
negligible
14. 13
Irradiation (IR)
Ionizing radiation causes genetic damage in microorganisms, primarily in the form of single- and double-
stranded DNA strand-breaks.This results in various sorts of mutations that either kill the pathogenic bacteria or
make them incapable of propagation. There are two mechanisms by which ionizing radiation effects DNA: one is
photon-induced breakage of the phosphodiesterbackbone of DNA and the other is the creation of hydroxyl radicals
which strip DNA of its molecules. Formation of radicals accounts formore than 70% of the genetic damage caused
by exposure to a radioactive source (Sommers & Xuetong,2011).
Survival of ionizing radiation is dependent on the organism’s sensitivity to a radiation source. Some cells
have zero tolerance to radiation and are eliminated quickly at small doses,while others have resistive qualities due
to chemical and physical structure as well as genetic repair attributes.The effectiveness of irradiation also depends
on the composition of the medium, the moisture content,temperature, oxygen levels and fresh or frozen food state.
A microbe’s resistance to ionizing radiation is determined by its inherent D-value. Larger D-values infer that a
microorganism can withstand photon bombardment to a greater extent. Therefore larger doses ofradiation are
required to induce inactivation.
Irradiation techniques have been proven to cause at least a 5 log10 reduction in E. coli O157:H7 numbers
for all forms of solid foods.Consequently,there is no visible damage done to a product at the required dosage and
nutrition values are not effected. Heat effects of irradiation are negligible, ranging no more than 0.1˚C per 1 kGy of
radiation. This amounts to less than a single degree Celsius increase in temperature, which is inconsequentialto the
quality of the food. The shelf-life of irradiated food products is on average one of the longest, particularly when
combined with effective packaging or refrigeration.
Irradiation of food is a scalable process and it is possible to reach very high throughput levels in a
continuous process with the aid of a conveyorbelt. Maintenance requirements are low, as mandatory replacement of
the radiation source is no more than once every six months. Irradiation techniques are also approved by food
regulatory agencies and a wide variety of methods are available depending on the dosage requirements for certain
foods.Irradiation does not impart any new qualities on to the processed food,but is capable of extending shelf-life
by a factor of up to four or five. Consumer opinion is improving as well. In 1993, only 29% of consumers answered
15. 14
positively on a survey that they would consume ground beef treated with irradiation technology.By 2003, this
number had risen to 67% (Sommers & Xuetong, 2011).
Table 3: IR Effectiveness for Selected Food Products
Product:
Dosage (at 10°C,
atmospheric pressure):
Shelf-life
(refrigerated):
Inhibition of E. coli
O157:H7:
Temperature
changes due to
energy increase:
Frozen ground beef 0.30 - 0.98 kGy 1 - 2 months 7 log10 reductions 0.1°C per kGy
Non-frozen ground beef 0.24 - 0.43 kGy 36 - 48 days 6.5 log10 reductions 0.1°C per kGy
Frozen poultry 0.3 - 0.98 kGy 1 - 2 months 7 log10 reductions 0.1°C per kGy
Non-frozen poultry 0.24 - 0.43 kGy 24 - 36 days 7 log10 reductions 0.1°C per kGy
Apple 1.0 - 2.0 kGy 1 year 8 log10 reductions ˂ 0.1°C per kGy
Non-frozen pork 0.422 - 0.447 kGy 36 - 48 days 6.5 log10 reductions 0.1°C per kGy
Tomato 0.80 - 2.0 kGy 4 - 6 weeks 8 log10 reductions ˂ 0.1°C per kGy
Cauliflower 0.564 kGy 6 - 7 weeks 7 log10 reductions ˂ 0.1°C per kGy
Roast beef 0.569 kGy 2 - 3 months 6 log10 reductions ˂ 0.1°C per kGy
Skim milk 1.0 - 2.0 kGy 9 - 12 months 6 log10 reductions 0.1°C per kGy
High hydrostatic pressure (HHP)
HHP is a method used in the food processing industry that subjects food to elevated pressures (up to 6000
atmospheres)to inactivate microorganisms or to alter food attributes.This is achieved with a minimal side effect on
the quality of freshness and without the addition of heat. Pressure distribution throughout the product is rapid and
uniform, hence there is no change in the physical structure of foods.The isostatic compression generated by HHP
has critical effects on the structure of microorganisms like E. coli O157:H7. Produce treated using HPP is generally
16. 15
packaged to maintain a separation between the pressurized fluid and the food contents.The pressurizing fluid is
compressed and exerts a force on the package that is transferred to the food. A typical pressure-transmitting fluid is
water, as the compression heating characteristic of water is analogous to that of most food materials. Pressure is held
for a number of minutes in order to ensure the desired inactivation. Inactivation of E. coli O157:H7 is related to the
compressive heat that is generated during compression and damage is generally directed at the cell membrane.
In addition to reducing E. coli O157:H7 counts on the surfaces of food, HHP confers longer shelf-life. It is
limited in the types of foods that it can process due to physical constraints ofthe vesseland the structure of certain
foods,such as whole eggs, which may crack. HHP is a batch process and involves a small amount of down-time for
transfers in between cycles. Throughput sizes are also limited as containment becomes increasing difficult in larger
vessels due to the increase in pressure to surface area ratio. HHP is approved by all regulatory agencies and in
general has a positive consumer outlook.
Table 4: HHP Effectiveness for Selected Food Products
Product:
Required
Pressure:
Shelf-life
(refrigerated):
Inhibition of E. coli
O157:H7:
Temperature
changes due to
pressure increase:
Skim Milk 500 MPa 6 - 9 months 6.5 log10 reductions 3°C per 100 Mpa
Cheese 400 MPa 2 - 4 months 7 log10 reductions 3°C per 100 MPa
Pork 300 MPa 3 - 6 weeks 6 log10 reductions 5°C per 100 MPa
Poultry 375 MPa 2 - 4 weeks 2 log10 reductions 4.5°C per 100 MPa
17. 16
Cooked Ham 500 MPa 10 - 12 weeks 4 log10 reductions 4.5°C per 100 MPa
Oyster 300 MPa 3 - 7 days 4 log10 reductions 3.2°C per 100 MPa
Beef 350 MPa 1 - 3 weeks 5 log10 reductions 6.3°C per 100 MPa
Apple 400 MPa 4 - 6 months 6.5 log10 reductions 3°C per 100 MPa
Tomato 300 MPa 2 - 5 weeks 6 log10 reductions 3.1°C per 100 MPa
Pulsed electric fields
Pulsed electric fields (PEF) is a non-thermal method of treatment for microbial inactivation in food
products; however, it is only relevant for solid foods.High-voltage pulses (between 20-80 kV) are applied for short
periods of time (µs to ms) to a product located between two electrodes (Elez-Martinez, Martin-Belloso, & Pena,
2011). PEF facilitates microbial inactivation by causing damage to the cell membrane through electroporation.
Differences in charge across the bacterial membrane cause the expansion of existing pores and the creation of new
pores. The introduction of these pores renders the cell permeable to small molecules, which eventually causes
swelling and rupture of the cell.
PEF is effective in causing reductions in E. coli O157:H7 of up to 5 log10 in liquid food media. It
subsequently increases shelf-life due to the inactivation of enzymes responsible for spoilage. There is also no
noticeable increase in internal temperature of the product,as the electric pulses are typically not sustained beyond a
few microseconds. And despite its ability to process large volumes in a continuous process,PEF cannot process
solid foods. It has attained approval by government regulatory agencies and its products are favored to untreated
products.
18. 17
Table 5: PEF Effectiveness for Selected Food Products
Product:
Treatment
Conditions:
Shelf-life
(refrigerated):
Inhibition of E.
coli O157:H7:
Temperature
changes due to
energy increase:
Skim milk
Batch, 45 kV/cm,
150 pulses, 8 µs,
40°C
6 - 9 months
3 log10
Reductions
Negligible
Liquid egg yolk
Continuous, 30
kV/cm, 105
pulses, 2 µs,
40°C
2 - 3 months
5 log10
Reductions
Negligible
Pea soup
Continuous, 33
kV/cm, 30
pulses, 2 µs,
40°C
1 year
5.3 - 6.5 log10
Reductions
Negligible
Apple juice
Continuous, 30
kV/cm, 43
pulses, 4 µs,
25°C
1 year
5 log10
Reductions
Negligible
Melon juice
Continuous, 35
kV/cm, 400
pulses, 4 µs,
39°C
1 year
3.8 - 4.3 log10
Reductions
Negligible
Antimicrobial films and coatings (AF)
Antimicrobial films and coatings are an environmentally-safe technology that creates a selectively-
permeable barrier to water vapor, oxygen and carbon dioxide. Films are a stand-alone layer surrounding the produce
with mechanical and tensile properties similar to that of the food product.Coating formation occurs directly on the
surface of the product and provides protection and enhancement. A layer of film or coating effectively blocks all E.
coli O157:H7 contaminants from growing on the surface of produce. The mechanism is simple: the skin is not
penetrable by E. coli and contains antimicrobial agents derived from nature that prevent growth. Some of these
19. 18
antimicrobial agents may be fruit-based, protein-based or lipid-based. Given any solid surface, there exists an
effective treatment by antimicrobial films and coatings.
Products treated with films and coatings exhibit longer shelf-life than standard untreated items. There is
also no heat generation associated with the binding of films to surfaces.The mechanical and structuralproperties of
the product remain the same as before treatment; however, films and coatings create the possibility of conferring
new properties onto the skin of the product such as novel flavors or preserving compounds.The coating process is
semi-batch and therefore slightly slower than continuous production,but with more control over the input and output
of the system. Because the vessels used for coating of products can be made quite large, and therefore able to
process many items at once,throughput is not negatively affected by the discontinuous nature of the spray-coating
process.Antimicrobial films and coatings are being sought afterby numerous producers across the world, though
they still require government testing.Consumer opinion, on the other hand,is hopeful.
Table 6: Antimicrobial Film Effectiveness for Selected Food Products
Product: Treatment Conditions
Shelf-life
(refrigerated)
Inhibition of E.
coli O157:H7:
Temperature
changes due to
exposure:
Non-frozen beef
Whey-protein isolated
matrix with oregano and
pimento oils
10 - 12 weeks
6 log10
reductions
none
Non-frozen turkey
Gelatin matrix with
0.50% nisin
10 - 12 weeks
6 log10
reductions
none
Apple
Chitosan matrix with
0.50% nisin
16 - 20 weeks
8.7 log10
reductions
none
Tomato
Chitosan matrix with
0.50% nisin
10 - 12 weeks
7.5 log10
reductions
none
Orange Chitosan matrix only 12 - 14 weeks
8.2 log10
reductions
none
20. 19
Melon Chitosan matrix only 12 - 14 weeks
8 log10
reductions
none
Grapes
Chitosan matrix with
0.50% nisin
8 - 9 weeks
7.5 log10
reductions
none
Strawberry
Chitosan matrix with
0.50% nisin
8 - 9 weeks
6 log10
reductions
none
Squash
Chitosan matrix with
0.50% nisin
10 - 12 weeks
7 log10
reductions
none
AN ANALYSIS OF SUBSTITUTES
Acceptable Alternatives
Ozone induces a moderate-to-high log reduction of E. coli O157:H7 for fruits and vegetables at cool
temperatures. This reduction leads to a subsequently longershelf-life for the product than if it had been only treated
by washing with water. However, ozone treatment has proven to be difficult and overly complicated when dealing
with meat products,which comprise a large portion of total processed foods.The ozone molecules oxidize the meat,
causing discoloration, deterioration and drastic reductions in nutritional content.Therefore, ozone treatment is not a
satisfactory alternative to heat treatment.
Pulsed electric field technologies are entirely incapable of processing solid food and cannot be considered
as an acceptable alternative – this criterion is the single most relevant in selecting a method to replace heat
treatment. While this technology is efficient in creating an absence of E. coli in liquid foods, the main interest of this
analysis is solid foods.
Irradiation causes enormous reductions in E. coli O157:H7 levels for all types of solid foods,ranging from
meats to fruits and vegetables. This inactivation does not come at the cost of increased heating,as irradiation does
not cook produce at the low doses required for multiple log reductions of E. coli. The shelf-life extension of
21. 20
products treated by irradiation is also unparalleled by any other method besides antimicrobial films. Sensorial and
nutritional quality do not differ noticeably from untreated fresh products.It is therefore an acceptable alternative
according to the essential criteria.
High hydrostatic pressure processing lacks the flexibility of irradiation in that more energy is required to
cause meaningful reductions of E. coli. However, HHP is applicable for many different solid food types and
eliminates E. coli O157:H7 by up to 5 log10 reductions in most of these types.HHP is also good for maintaining the
sensorial and nutritional quality of processed foods,thus meeting shelf-life requirements. The heat generated by
HHP processing may be problematic for a limited range of products,but for the most part, temperature rises are
inconsequentialto the quality of the final product.Heat treatment typically induces heating in the range of 125 –
150°C. HHP causes temperature increases proportional to the amount of pressure,which for most cases is no more
than 600 MPa, corresponding to an 18°C increase. HHP therefore meets the heating requirements.
Antimicrobial films are a rival only to irradiation as far as log10 reductions of E. coli numbers. The majority
of products treated with films and coatings experience a reduction of over 5 log10.Films and coatings are applicable
for all solid food types,ranging from meat to fruits and vegetables and maintain the sensorialand nutritional quality
of fresh, untreated produce.Temperature increases are also completely eliminated by this process,therefore making
it a suitable alternative according to the essentialcriteria.
Desirable Alternatives
Irradiation of food is often associated with negative connotation,likely because its name implies the need
for a radioactive source.It is commonplace to believe that some of the essence ofthis radioactive source is
transferred to the food being treated, where in reality only the E. coli cells are affected by the radiation. Despite the
mixed opinions from consumers, food irradiation technologies have undergone rigorous testing by various U.S.
regulatory agencies and have been approved for use.It is acknowledged by the FDA and USDA that irradiation of
food in fact vastly improves quality over untreated or heat treated products by extending shelf-life to four to five
times the untreated product.Irradiation technologies also boast a very high throughput – about 500 pounds per hour
(226.8 kg/hr) – making application on the desired scale possible and economically beneficial.
22. 21
High hydrostatic pressure processing is typically employed by producers within a local but not regional
market. This is because the pressure vessels used to achieve reduction in E. coli O157:H7 are not built above a
certain volume due to design limitations associated with the high pressures needed to attain significant reduction. As
a result, throughput is lower than for othercompeting methods like irradiation and antimicrobial films, on the order
of 100 – 150 pounds perhour, maximum. The shelf-life conferred to treated products is also substantially shorter
than either irradiation or antimicrobial films, as log reductions are not as numerable. HHP technologies are
government approved and draw a reasonable amount of good reputation from consumers (between a 43 – 80%
approval rating for various foods).
Antimicrobial films are a progressive alternative to older techniques like pressure, heat and radiation
treatment that currently lacks extensive government and consumer testing.Designs for coating processes take into
account large-scale operations such as that which is the focus of this paper, but they are not continuous.Their semi-
batch mechanism allows for greater control over conditions for different types of food, and the same processing
chamber can be used for multiple products in different cycles. The process is also fairly quick, with the products
only requiring a minute or less inside the coating chamber, which permits multiple cycles per hour. The materials
needed for the coatings and films are inexpensive, mostly comprising isolated salts and proteins that effectively
block the growth of E. coli O157:H7. Antimicrobial films offer a property that other processing technologies do not,
which is the enhancement of produce with additives contained in the surface. This not only extends shelf-life but can
lead to dramatic improvements in overall sensorial and nutritional quality. Compared to irradiation and high
hydrostatic pressure processing,antimicrobial films boast the best reputation from consumer testing,though the
technology is not yet mature. Antimicrobial films virtually have the largest application for solid foods sold by
grocers.
Potential Problem Analysis
Irradiation techniques,though they offer feasibly high throughput,exceptional protection from E. coli
O157:H7 and extremely long shelf-life, face problems in the public sector.Consumers are not entirely convinced of
the safety of irradiated food. For all food categories, consumer approval trails behind alternatives like antimicrobial
films and HHP. For example, 75% and 72% of consumers preferred non-frozen beef treated by antimicrobial films
23. 22
and HHP, respectively, while only 59% approved the beef processed using irradiation. Outside of the scope of the
criteria, as a side note, the presence of a radiation source in a food processing plant is of substantialconcern. While
the design of the process does not involve any produce coming in contact with the radiation source,errors in the
systemor in mishandling can create opportunities for exposure. This would have catastrophic consequences forthe
plant if the contaminated food is consumed. The radiation source must also be disposed when it has been exhausted ;
however, it is still radioactive even once its use period has been finished.
HHP has the disadvantage ofscaling-up problems, as the pressure vessels cannot be built above a certain
volume and are capable of a limited number of cycles per day. There is also the down-time associated with transfer
between cycles. As HHP is dealing with very high pressures,there is a risk of explosion. The equipment is under
constant compressive and decompressive strain and the metal comprising the pressure vesselexperiences wear each
time a cycle is run. Safety measures have been built into pressure vessels to gage the amount of wear a unit has
taken; there is a design which leaks instead of undergoing rapid failure all at once. Even with this feature, however,
the HHP unit would be under heavy usage in the plant being considered and fracture would be an imminent threat
for the process and for workers.
Antimicrobial films, like irradiation, support a very high throughput; however,this efficiency comes at the
cost of uniformity. The coatings are sprayed onto the product from sprayers within the chamber. Due to the large
number of products being processed percycle, food items will be put into the chamber in layers. There is a high
probability that not all surfaces of the products will be exposed to the spray due to impediments such as other
products in the chamber and uneven spraying. This would result in a patchy or incomplete surface coating.
Additionally, the chamber must be cleaned prior to the start of every new cycle, particularly in the case where the
same chamber is used for different foods.This creates a down-time that must be considered in throughput
calculations. Such a down-time adds to the time that it takes to remove a load of produce and replace it with a new
untreated load. Lastly, if films and coatings of different compositions are to be used,there is anotherdown -time
associated with replacing the feed storage tank.
24. 23
TABLES OF COMPARISON
Table 7: Application of Methods
Process:
% of solid foods in
which treatment is
viable
Heat
Treatment
40.00
HHP 70.00
IR 90.00
PEF 2.00
Ozone 60.00
Films 95.00
Table 8: Comparison of Quality/Shelf-life
Process
Product:
Pre-process
cleaning only HPP IR PEF Ozone Films
Beef (non-frozen) 2 - 3 days 1 - 3 weeks 6 - 7 weeks N/A N/A 10 - 12 weeks
Poultry (non-frozen) 2 - 3 days 2 - 4 weeks 4 - 6 weeks N/A N/A 10 - 12 weeks
Apple 14 - 20 days 4 - 6 months 1 year N/A 4 - 6 months 4 - 5 months
Tomato 8 - 12 days 2 - 5 weeks 4 - 6 weeks N/A 3 - 4 weeks ~ 3 months
25. 24
Table 9: Comparison of Inhibition Abilities for E. coli O157:H7
Process
Product:
Pre-process
cleaning
only HPP IR PEF Ozone Films
Beef (non-frozen)
2.9 log10
reductions
5 log10
reductions
6.5 log10
reductions
N/A N/A
6 log10
reductions
Poultry (non-frozen)
2.5 log10
reductions
2 log10
reductions
7 log10
reductions
N/A N/A
6 log10
reductions
Apple
2.4 log10
reductions
6.5 log10
reductions
8 log10
reductions
N/A
3.7 log10
reductions
8.7 log10
reductions
Tomato
2.6 log10
reductions
6 log10
reductions
8 log10
reductions
N/A
4.2 log10
reductions
7.5 log10
reductions
Table 10: Comparison of Heating
Process
Product:
Heat
treatment HPP IR PEF Ozone Films
Beef (non-frozen) 150˚C
6.3°C per
100 Mpa
0.1°C per
kGy
negligible negligible none
Poultry (non-frozen) 150˚C
4.5°C per
100 MPa
0.1°C per
kGy
negligible negligible none
Apple 150˚C
3°C per 100
MPa
˂ 0.1°C per
kGy
negligible negligible none
Tomato 150˚C
3.1°C per
100 MPa
˂ 0.1°C per
kGy
negligible negligible none
Table 11: Evaluation of Throughput for HHP
Product: Process type:
Equivalent
working days:
Cycles per 12-
hr day:
Volume per
cycle:
Beef (non-frozen) Batch 256 12 250 L
26. 25
Poultry (non-frozen) Batch 316 12 250 L
Apple Batch 328 16 1000 L
Tomato Batch 322 15 1000 L
Table 12: Evaluation of Throughput for IR
Product: Process type:
Equivalent
working days:
Process
Duration:
Throughput
(per day):
Beef (non-frozen) Continuous 324 0.5 min. 2700 kg
Poultry (non-frozen) Continuous 330 0.5 min. 2700 kg
Apple Continuous 344 2 min. 2700 kg
Tomato Continuous 335 2 min. 2700 kg
Table 13: Evaluation of Throughput for Ozone
Product: Process type:
Equivalent
working days:
Process
Duration:
Throughput
(per day):
Beef (non-frozen) N/A
Poultry (non-frozen) N/A
Apple Continuous 330 3 min. 2700 kg
Tomato Continuous 320 3 min. 2700 kg
27. 26
Table 14: Evaluation of Throughput for Antimicrobial Films
Product: Process type:
Equivalent
working days:
Process
Duration:
Throughput
(per cycle):
Throughput
(per day):
Beef (non-frozen) Semi-batch 286 1 min. 18 kg 720 kg
Poultry (non-frozen) Semi-batch 313 1 min. 18 kg 720 kg
Apple Semi-batch 324 1 min. 20 kg 800 kg
Tomato Semi-batch 316 1 min. 20 kg 800 kg
Table 15: Percent of Untrained Consumers Who Favor Processed Food over Non-processed (2009)
Process
Product: HPP IR PEF Ozone Films
Beef (frozen): 68% 48% N/A N/A 72%
Beef (non-frozen): 72% 59% N/A N/A 75%
Poultry (frozen): 69% 42% N/A N/A 69%
Poultry (non-frozen): 64% 60% N/A N/A 71%
Apple: 80% 52% N/A 52% 83%
Tomato: 43% 61% N/A 47% 90%
28. 27
RECOMMENDATION
Antimicrobial films and coatings are best suited for the non-thermal treatment of solid food products.This
method is designed to support all types of solid foods and is fairly simple as far as operation and the mechanism of
E. coli reduction. Films and coatings also provide extended protection,where techniques such as irradiation and
HHP eliminate bacteria in only one instance,which is at the processing stage.The surfaces created by antimicrobial
films are designed to last and provide a continuous barrier against exposures to E. coli O157:H7. E. coli can neither
grow on the film nor penetrate it. Large-scale production on the order of hundreds of kilograms per hour is limited
but not abated by the throughput capacity of the coating unit. In addition to increased shelf-life, antimicrobial films
also create the possibility for new products that combine different salts, lipids, proteins and minerals for enhanced
smell, flavor, appearance or nutritional value. It is suggested that the down-time can be diminished and the
throughput increased by the operation of multiple spraying units. The units are simple and inexpensive, and the
necessary materials are easy to attain and non-toxic to store.There is no heating associated with films and coatings
and complete inhibition is guaranteed,especially when multiple coatings are applied.
FUTURE WORK
Antimicrobial films and coatings have not yet reached the full approval stage by the FDA or USDA. Their
presence elsewhere in the world is limited and is not on a large commercial scale. Therefore, the technology must be
made scalable so that the larger volumes of produce required by the concerned plant can be treated in an efficient
and economically sensible manner. Most of the validation that remains for films and coatings lies in repeatability
and reproducibility of their experiments. Once approval has been gained, however, throughput can be further
enhanced by the design of a continuous process,which may be possible with the use of sprayers assisted by a
conveyorbelt. Further along, once the technology has been established and found to be effective, there is a strong
possibility of further development of films and coatings for the post-processing packaging stage.In lieu of plastic
packaging, which is dangerous to the environment, thick films or coatings that can be eaten or peeled off and
composted can be used to protect food during transportation and storage.Such technology is not far from reality
considering the success already found by current antimicrobial films and coatings.
29. 28
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![1
ABSTRACT
The USDA’s Safety and Inspection Service drafted a report from data collected over multiple years on the
contamination level for the human pathogen Escherichia coli O157:H7 in ground beef patties.It was found that in
2000, 0.86% of patties were contaminated, as compared to 0.84% in 2001, 0.78% in 2002, 0.30% in 2003 and 0.17%
in 2004. Then, between 2003 and 2006, there were 22 ground beef patty recalls due to the presence of E. coli
O157:H7. Efforts to prevent the continuation of such outbreaks including heavier surveillance, hazard analysis and
critical control point plans have helped, but not abolished, contamination by E. coli in meat, poultry and other
produce. Still, two out of every thousand beefpatties contain traces of E. coli, which is only required in a small dose
to induce severe infection in a human. Over the last two decades,the largest produce manufacturers spent billions of
dollars fighting E. coli. Even with cleaner handling today, the risk of infection for large-scale producers is
astronomical, which is why steps must be taken to block the bacteria’s every chance of infesting consumable goods.
This has given rise to a new era of food processing technology.Methods developed overthe last century such as
high hydrostatic pressure and irradiation are currently being challenged by potentially better techniques like ozone
and antimicrobial films treatment. It is the aim of this paper to select a processing technology for a plant with
commercial-scale throughput (on the order of 500 pounds per hour[226.8 kg/hr]) based on multiple acceptance
criteria. These criteria include ability to reduce E. coli populations by 5 log10 reductions,preservation of quality,
solid food aptitude, induced temperature changes as well as throughput capacity,shelf-life extension, compliance
with regulation and public approval rating. The final recommendation is for antimicrobial films, which possessthe
ability to prevent outbreak throughout large-scale commercial production of fruits, vegetables,and meats. This is
also accompanied by a potential problem analysis and suggestions forfuture work with this technology.](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)