260353823_technical paper 1 final draft

NONTHERMAL

TECHNOLOGIES FOR THE

PROCESSING OF FOOD

AND THE PREVENTION OF

INFECTION BY E. COLI

O157:H7 Technical Paper I

NOVEMBER 25, 2013 MICHAEL GARIBALDI

260353823

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 beef patties 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 over the 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 log 10 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 possess the

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 for future work with this technology.

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CONTENTS

ABSTRACT ......................................................................................................................................1

CONTENTS ......................................................................................................................................2

INTRODUCTION ..............................................................................................................................4

BACKGROUND................................................................................................................................5

CRITERIA.........................................................................................................................................7

ESSENTIAL ..................................................................................................................................7

DESIRABLE..................................................................................................................................9

THE SUBSTITUTES........................................................................................................................ 11

Ozone Sanitization ........................................................................................................................ 11

Table 1: Ozone Solubility in Water ............................................................................................. 11

Table 2: Ozone Effectiveness for Selected Food Products............................................................ 12

Irradiation (IR) ............................................................................................................................. 13

Table 3: IR Effectiveness for Selected Food Products ................................................................. 14

High hydrostatic pressure (HHP) ................................................................................................... 14

Table 4: HHP Effectiveness for Selected Food Products.............................................................. 15

Pulsed electric fields ..................................................................................................................... 16

Table 5: PEF Effectiveness for Selected Food Products............................................................... 17

Antimicrobial films and coatings (AF) ........................................................................................... 17

Table 6: Antimicrobial Film Effectiveness for Selected Food Products ....................................... 18

AN ANALYSIS OF SUBSTITUTES................................................................................................. 19

Acceptable Alternatives................................................................................................................. 19

Desirable Alternatives ................................................................................................................... 20

Potential Problem Analysis ............................................................................................................ 21

TABLES OF COMPARISON ........................................................................................................... 23

Table 8: Comparison of Quality/Shelf-life ................................................................................... 23

Table 9: Comparison of Inhibition Abilities for E. coli O157:H7................................................. 24

Table 10: Comparison of Heating ............................................................................................... 24

Table 11: Evaluation of Throughput for HHP............................................................................. 24

Table 12: Evaluation of Throughput for IR ................................................................................ 25

Table 13: Evaluation of Throughput for Ozone .......................................................................... 25

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Table 14: Evaluation of Throughput for Antimicrobial Films ..................................................... 26

Table 15: Percent of Untrained Consumers Who Favor Processed Food over Non-processed

(2009) .......................................................................................................................................... 26

RECOMMENDATION .................................................................................................................... 27

FUTURE WORK ............................................................................................................................. 27

REFERENCES................................................................................................................................. 28

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INTRODUCTION

Consumer’s life habits and an increase in demand for healthier foods are driving a revolution in the food

industry to better preserve 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 of miles 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 other available 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 pres ervation 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 beef patties 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.

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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.

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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 structural or 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 for the microbes and pose no threat to the consumer. Like heat treatment, however,

many chemical disinfectants currently in use cause sensorial and 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.

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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 conveyor belt 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: essential criteria, 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

essential criteria 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,

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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

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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 per day 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 other desirable 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.

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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 another list 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.

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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 useful for 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. Typical reactions 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

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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

conveyor belt. 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


Lettuce

21 - 25 mg O3

/ L for 3

minutes

2 - 3 weeks 3.6 log10


Potatoes

21 - 25 mg O3

/ L for 3

minutes

3 - 4 months 4.7 log10


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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 phosphodiester backbone of DNA and the other is the creation of hydroxyl radicals

which strip DNA of its molecules . Formation of radicals accounts for more 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 of radiation are

required to induce inactivation.

Irradiation techniques have been proven to cause at least a 5 log 10 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 temperatu re, which is inconsequential to 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 conveyor belt. 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

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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

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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 of the vessel and 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

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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 cau ses

swelling and rupture of the cell.

PEF is effective in causing reductions in E. coli O157:H7 of up to 5 log 10 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.

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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


Pea soup

Continuous, 33

kV/cm, 30

pulses, 2 µs,

40°C

1 year 5.3 - 6.5 log10


Apple juice

Continuous, 30

kV/cm, 43

pulses, 4 µs,

25°C

1 year 5 log10


Melon juice

Continuous, 35

kV/cm, 400

pulses, 4 µs,

39°C

1 year 3.8 - 4.3 log10


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

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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 s helf-life than standard untreated items. There is

also no heat generation associated with the binding of films to surfaces. The mechanical and structural properties 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 after by 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


8.7 log10

reductions none

Tomato Chitosan matrix with


7.5 log10

reductions none

Orange Chitosan matrix only 12 - 14 weeks 8.2 log10

reductions none

19

Melon Chitosan matrix only 12 - 14 weeks 8 log10

reductions none

Grapes Chitosan matrix with


7.5 log10

reductions none

Strawberry Chitosan matrix with


6 log10

reductions none

Squash Chitosan matrix with


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 longer shelf-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

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 acceptab le 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 foo d 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

inconsequential to 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 log 10. Films and coatings are applicable

for all solid food types, ranging from meat to fruits and vegetables and maintain the sen sorial and nutritional quality

of fresh, untreated produce. Temperature increases are also completely eliminated by this process, therefore making

it a suitable alternative according to the essential criteria.

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 of this 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.

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 other competing methods like irradiation and antimicro bial films, on the order

of 100 – 150 pounds per hour, 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 mult iple 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

22

and HHP, respectively, while only 59% approved the beef process ed 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 substantial concern. While

the design of the process does not involve any produce coming in contact with the rad iation source, errors in the

system or in mishandling can create opportunities for exposure. This would have catastrophic consequences for the

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 of scaling-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 vessel experien ces 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 per cycle, 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 another down -time

associated with replacing the feed storage tank.

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

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


Apple 150˚C 3°C per 100

MPa

˂ 0.1°C per


Tomato 150˚C 3.1°C per

100 MPa

˂ 0.1°C per


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

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


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


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

26

Table 14: Evaluation of Throughput for Antimicrobial Films


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%

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 coat ings 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

conveyor belt. 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 tech nology is not far from reality

considering the success already found by current antimicrobial films and coatings.

28

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