Paper No.: 03

Paper Title: MICROBIOLOGY Module – 35: Application of

in

(e-Text and Learn More)

Component-I (A) - Personal Details:

Role Name Affiliation

National Coordinator Professor R.C. Kuhad University of Delhi South Campus New Delhi Subject Coordinator Professor Vijayakhader Former Dean, Acharya N.G. Ranga Agricultural University, Hyderabad Paper Coordinator Professor A. K. Puniya National Dairy Research Institute (NDRI), Karnal Content Writer/Author Dr. Pradip Behare

Content Reviewer

Language Editor (LE)

Technical Conversion

FOOD APPLICATION OF HURDLE TECHNOLOGY IN FOOD INDUSTRY MICROBIOLOGY

Component-I (A) - Module Structure: Structure of Module/Syllabus of a module (Define Topic of module and its subtopic) Introduction, Principle of hurdle technology, Hurdle, Basic Aspects of Application of Hurdle Hurdle Technology, Homeostasis, Metabolic exhaustion, Stress Technology in Food Industry reactions, Multitarget preservation, Individual Hurdles, Microbiocidla Hurdles Reduces Microbial Load, Microbiostatic Hurdles (Chemical Hurdles), Microbiostatic Hurdles (physical Hurdles), Hrudles that prevent contamination, Application of hurdle technology in .

Component-II - Description of Module Description of Module Subject Name

Paper Name

Module Name Application of Hurdle Technology in Food Industry Module Id FT/FM/35

Pre-requisites Hurdles, Concept, Hurlde technology in dairy and food products

Objectives To study about types of hurdles and their application in food industry

Keywords Hurdles, dairy foods, salt, , high-pressure, hurdle concept

FOOD APPLICATION OF HURDLE TECHNOLOGY IN FOOD INDUSTRY MICROBIOLOGY

TABLE OF CONTENTS

Table No. Description

Table 2.1 Examples of hurdles used to preserve foods Table 3.1 Role of Microbiocidla Hurdles

Table 3.2 Role of Microbiostatic hurdles

Table 3.3 Role of Microbiostatic Hurdles

Table 3.4 Role of Hurdels in Preventing Contamination

Table 4.1 Application of Hurdle Technology in Dairy and Food Products

FIGURES OF CONTENTS

Table No. Description Figure 2.1 Basic concept of bacterial inhibition by hurdles

Figure 4.1 Preservation of food by individual and combined hurdles

FOOD APPLICATION OF HURDLE TECHNOLOGY IN FOOD INDUSTRY MICROBIOLOGY

1. Introduction

2. Principle of hurdle technology

2.1 Hurdle

2.2 Basic Aspects of Hurdle Technology

2.2.1. Homeostasis

2.2.2. Metabolic exhaustion

2.2.3 Stress reactions

2.3 Multitarget preservation 3. Individual Hurdles

3.1 Microbiocidla Hurdles Reduces Microbial Load

3.2. Microbiostatic Hurdles (Chemical Hurdles)

3.3. Microbiostatic Hurdles (physical Hurdles)

3.4. Hrudles that prevent contamination

4. Application of hurdle technology in foods

5. Summary

FOOD APPLICATION OF HURDLE TECHNOLOGY IN FOOD INDUSTRY MICROBIOLOGY

1. INTRODUCTION

The primary objective of traditional and newly developed processes is the inhibition or inactivation of that ultimately helps to improve shelf stability of food. Every food has

certain inherent preservation factors such as extent of heat treatment received (F), (aw), low temperature storage (t), redox potential (Eh), pH, etc. which may be termed as hurdles, because microorganisms will have to 'jump' these hurdles in order to grow and spoil the product. The stability of the product depends upon the intensity of hurdles present in it. More the intensity or height of these hurdle, or more the number of these hurdles, more difficult it will be for microorganisms to overcome these hurdles. In conventional preservation method the intensity of one or two of these hurdle is exceptionally increased making it extremely difficult for microorganisms to overcome that hurdle. For example, in sterilization process F-value (i.e. the amount of heat treatment given) is increased to 3 to 15. Or in dehydration the water

activity (aw) is decreased to a very low value i.e. 0.85. Such increase or decrease in the intensities of these parameters adversely affects the quality of certain products. Microbial stability and safety, as well as the sensory and nutritional quality of most preserved foods, are based on a combination of several empirically applied factors (hurdles), and more recently on knowingly employed hurdle technology. Deliberate and intelligent application of hurdle technology allows a gentle, efficient preservation of foods, which is advancing worldwide. Many foods can not be preserved by a single hurdle alone without affecting their sensory and nutritional properties. Therefore, hurdle Technology is the combination of selected hurdles, which can keep microbiological hazards and other microorganisms under control, with or without combinations with microbial steps, so as to obtain and retain end product safety or suitability.

2. PRINCIPLE OF HURDLE TECHNOLOGY

The most important hurdles commonly used in food preservation are temperature (high or low), water activity (aw), acidity (pH), redox potential (Eh), (nitrite, sorbate, sulfite, etc.), and competitive micro-organisms (e.g., bacteria). More than 60 potential hurdles for foods of animal or plant origin, which improve the microbial stability and/or the sensory quality of these products, have been already studied, and the list of possible hurdles for food preservation is by no means complete. At present, physical, non-thermal processes (high hydrostatic pressure, oscillating magnetic fields, pulsed electric fields, light pulses, etc.) receive considerable attention (Non-thermal Processing), since in combination with other conventional hurdles they are of potential use for the microbial stabilization of fresh-like food products, with little degeneration of nutritional and sensory properties. Another group of hurdles, of special interest in industrialized and developing countries at present, would be „natural preservatives‟ (spices and their extracts, lysozyme, chitosan, pectin hydrolysate, etc.). In most countries, these „green preservatives‟ are preferred because they are not synthetic chemicals, but in some developing countries, they are given preference, since

FOOD APPLICATION OF HURDLE TECHNOLOGY IN FOOD INDUSTRY MICROBIOLOGY

spices are readily available and cheaper than imported chemicals. The critical values of many preservative factors for the death, survival, or growth of micro-organisms in foods have been determined in recent decades and are now the basis of food preservation. However, the critical value of a particular parameter changes if additional preservative factors are present in the food. For instance, it is well known that the heat resistance of bacteria increases at low aw and decreases at low pH or in the presence of preservatives, whereas low Eh increases the inhibition of micro-organisms due to reduced aw. The simultaneous effect of different preservative factors (hurdles) could be additive or even synergistic. In food preservation, the combined effect of preservative factors must be taken into account, which is illustrated by the hurdle effect.

2.1 Hurdles

Microbial growth is dependent upon many conditions in the organism‟s environment such as ingredients; nutrients, water activity, pH, presence of preservatives, competitive microorganisms, gas atmosphere, redox- potential, storage temperature and time (Table 2.1). Control of these conditions can therefore be used to limit, retard or prevent microbial growth.

One major use of hurdles is to prevent or restrict the growth and/or to reduce the concentration of microorganisms, including target pathogens in milk, intermediate and final milk products. Most milk products need the use of hurdles to become safe and suitable and/or to retain such quality.

Table 2.1. Examples of hurdles used to preserve foods

Type of hurdle Examples

Physical hurdles Aseptic packaging, electromagnetic energy (microwave, radio frequency, pulsed magnetic fields, high electric fields), high temperatures (, , sterilization, evaporation, extrusion, , ), ionic radiation, low temperature (chilling freezing), modified atmospheres, packaging films (including , edible coatings), photodynamic inactivation, ultra-high pressures, ultrasonication, ultraviolet radiation

Chemical hurdles Carbon dioxide, ethanol, lactic acid, lactoperoxidase, low pH, low redox potential, low water activity, Maillard reaction products, organic acids, oxygen, ozone, phenols, phosphates, salt, , sodium nitrite/nitrate, sodium or potassium sulphite, spices and herbs, surface treatment agents

Microbial derived Antibiotics, bacteriocins, competitive flora, protective cultures

FOOD APPLICATION OF HURDLE TECHNOLOGY IN FOOD INDUSTRY MICROBIOLOGY

hurdles

2.2 Basic aspects of hurdle technology

The strength or intensity of a hurdle will normally not be sufficient to render the food as safe, but in combination with other hurdles the desired effect can be achieved. Therefore, to ensure the safety and suitability and or to extend the of milk products, generally more than one hurdle is needed to control microbial content and or growth, to inhibit spoilage and to help prevent food borne diseases. Suitable combinations of hurdles can be devised so that the organisms of concern can be reduced in number and or no longer grow/survive in the product. Such suitable combinations are called “Hurdle Technology”.

Many hurdles act by interfering with the homeostasis mechanisms that microorganisms have evolved in order to survive environmental stresses. Maintaining a constant internal environment requires significant energy and material resources of the , and when a hurdle disturbs the homeostasis there will be less energy left for the microorganism to multiply. Consequently, the organisms will remain in the lag phase and some may even die out before the homeostasis is re-established. Hurdle Technology is most efficient when it is multi-targeted that is, when various individual hurdles are selected so that different systems of the microorganism are targeted, such as the cell wall, membrane transport, receptor functions, signal transduction, control of gene expression, enzyme system, etc. In many cases, a multi-targeted hurdle technology using hurdles with low intensity may be more effective than one single hurdle (treatment or factor) with high intensity.

The presence of number of hurdles inhibiting or reducing the number of microorganisms may also be synergistic. Some hurdles rely on a change of the physiological status of microorganisms, which leads to stress. Consequently, other subsequently hurdles can become more efficient. Therefore, the utilization of synergistic effects can allow for combating hurdles of less intensity to control growth than would be otherwise expected from each hurdle individually. Similarly, when the microbiocidal hurdles used are of sufficient intensity, the necessary performance may be less or the shelf life may become longer.

2.2.1. Homeostasis

Homeostasis is the tendency to uniformity and stability in the internal status of organisms. For instance, the maintenance of a defined pH is a prerequisite and feature of living cells, and this applies to higher organisms as well as to microorganismsm. In food preservation the homeosta-sis of microorganisms is a key phenomenon, because if the homeostasis of these microorganisms is disturbed by preservative factors (hurdles) in foods, they will not multiply, i.e. they remain in the lag-phase or even die, before homeostasis is repaired (re-established). Therefore, food preservation is achieved by disturbing the homeostasis of microorganisms in a food temporarily or permanently.

FOOD APPLICATION OF HURDLE TECHNOLOGY IN FOOD INDUSTRY MICROBIOLOGY

2.2.2.Metabolic exhaustion

Another phenomenon of practical importance is metabolic exhaustion of microorganisms, which could cause „autosterilization‟ of a food. This was first observed in experiments with mildly heated (95°C core temperature) liver sausage adjusted to different water activities by the addition of salt and fat, and the product was inoculated with sporogenes and stored at 37°C. Clostridial spores surviving the heat treatment vanished in the product during storage.

The most likely ex-planation is that bacterial spores which survive the heat treatment are able to germinate in these foods under less favourable conditions than those under which vegetative bacteria are able to multiply. Thus, the spore counts in stable hurdle-technology foods actually decrease during storage of the products, especially in unrefrigerated foods. A general explanation for this surprising behaviour might be that vegetative microorganisms which cannot grow will die, and they die more quickly if the stability is close to the threshold for growth, storage temperature is elevated, antimicrobials are present, and the microorganisms are sublethally injured. Apparently, microorganisms in stable hurdle-technology foods strain every possible repair mechanisms for their homeostasis to overcome the hostile environment, by doing this they completely use up their energy and die, if they become metabolically exhausted. This leads to an autosterilization of such foods. Due to autosterilization hurdle-technology foods, which are microbiologically stable, become more safe during storage, especially at ambient tempera-tures. For example, salmonellae that survive the ripening process in fermented sausages will vanish more quickly if the products are stored at ambient temperature, and they will survive longer and possibly cause foodborne illness if the products are stored under refrigeration. It is also well known that salmonellae survive in mayonnaise at chill temperatures much better than at ambient temperatures.

2.2.3 Stress reactions

Some bacteria become more resistant or even more virulent under stress, since they generate stress shock proteins. The synthesis of protective stress shock proteins is induced by heat, pH, aw, ethanol, oxidative compounds, etc. as well as by starvation. The various responses of microorganisms under stress might hamper food preservation and could turn out to be problematic for the application of hurdle technology. On the other hand, the activation of genes for the synthesis of stress shock proteins, which help organisms to cope with stress situations, should be more difficult if different stresses are received at the same time. Simultaneous exposure to different stresses will require energy-consuming synthesis of several or at least much more protective stress shock proteins, which in turn may cause the microorganisms to become metabolically exhausted. Therefore, multi-target preservation of foods could be the key to avoiding synthesis of stress shock proteins, which otherwise could jeopardize the microbial stability and safety of hurdle- technology foods.

FOOD APPLICATION OF HURDLE TECHNOLOGY IN FOOD INDUSTRY MICROBIOLOGY

Figure 2.1 Basic concept of bacterial inhibition by hurdles

2.3 Multitarget preservation

Multitarget preservation of foods should be the ambitious goal for a gentle but most effective preservation of foods. It has been suspected for some time that different hurdles in a food might not have just an additive effect on microbial stability, but they could act synergistically. A synergistic effect could be achieved if the hurdles in a food hit, at the same time, different targets (e.g., cell membrane, DNA, enzyme systems, pH, aw, Eh) within the microbial cells and thus disturb the homeostasis of the microorganisms present in several respects. If so, the repair of homeostasis as well as the activation of stress shock proteins become more difficult. Therefore, employing simultaneously different hurdles in the preservation of a particular food should lead to optimal microbial stability. In practical terms, this could mean that it is more effective to employ different preservative factors (hurdles) of small intensity than one preservative factor of larger intensity, because different preservative factors might have a synergistic effect. It is anticipated that the targets in microorganisms of different preservative factors for foods will be elucidated, and that hurdles could then be grouped in classes according to their targets. A mild and effective preservation of foods, i.e. a synergistic effect of hurdles, is likely if the preservation measures are based on intelligent selection and combination of hurdles taken from different target classes. This approach is probably not only valid for traditional food-preservation procedures, but as well for modern processes such as , ultra- ´high pressure, pulsed technologies. Food microbiologists could learn from pharmacologists, because the mechanisms of action of biocides have been studied extensively in the medical field. At least 12 classes of

FOOD APPLICATION OF HURDLE TECHNOLOGY IN FOOD INDUSTRY MICROBIOLOGY

biocides are already known which have different targets, and sometimes more than one, within the microbial cell. Often the cell membrane is the primary target, becoming leaky and disrupting the organism, but biocides also impair the synthesis of enzymes, proteins, and DNA. Multi-drug attack has proven successful in the medical field to fight bacterial infections (e.g., tuberculosis) as well as viral infections (e.g., AIDS), and thus a multi-target attack on microorganisms should also be a promising approach in food microbiology.

3 . INDIVIDUAL HURDLES

Individual hurdles can be grouped according to primary function as follows:

 Microbiocidla hurdles that reduce the microbial load, for instance by killing, inactivation or removal.  Microbiostatic hurdles that prevent or limit growth of microorganism by chemicla or physical means.  Hrudles that prevent contamination of product; for instance by closed circuits or protecting the product.

Many hrudles have multiple functions. The above grouping of hurldes should therefore not be regarded as a rigid classification of the functions of the hurdles belonging to each group. Many microstatic hurdles have as well microbiocidal effects, the degree often depending upon the intensity at which they are applied (eg. pH reduction, refrigeration, freezing, preservatives and indigenous antimicrobial systems).

3.1 Microbiocidla hurdles reduces microbial load

The principles of the most commont hurdles with in this categary are shown in table 3.1.

Table 3.1 Role of Microbiocidla Hurdles

The removal of cells of high density from milk using high Bacteriofugataion centrifugal forces.

The reduction of the number of undesrible microorganisms by lowering the pH, consumption of nutrients and production of Competitive microflora antimicrobial substance (such as nisin, other bacteriocins and hydrogen peroxide), usually this hurdle is applied by choice of starter culture.

Removal of microbial cells, clumps and somatic cells by Microfiltration recircualtion over a microfilter.

Ripening (ageing) The holding of such time, at such temperature and under such

FOOD APPLICATION OF HURDLE TECHNOLOGY IN FOOD INDUSTRY MICROBIOLOGY

conditions as will result in the necessary biochemical and physical changes characterizing the cheese in question. When applied as a hurdle, the multifactoral, complex system developing in cheese (pH, antagonistic flora, decreased water activity, of bacterocins and organic acids) is utilized to influence the microenvironment in and on the food and consequently the consumption of the microflora present.

The application to milk of a heat treatment of a lower intensity than pasteurization that aims at reducing the number of microorganisms. Thermized milk is alkaline phosphatase positive.

Application of high hydrostatic pressures(>3000 bar) to High-pressure treatment irreversibly damage the membranes of vegetative cells.

The application of high intensity ultrasound (18-500MHz) that cause cycles of comression and expansion as well as cavitation Ultrasonication in microbial cells. Implosion of microscopic bubbles generates spots with very high pressure and temperature able to destroy cells.

Electromagnetic energy result from high voltage electrical fields which alternate their frequency millions of times per second (<108MHz). Examples are microwave energy (thermal Electromagnetic energy treatment effect).radio-frequency (non-thermal effects) of high electric field pulses (10-50 kV/cm. non- thermal effects). The treatment destroys cells by establishing pores in the cell walls due to the build up of electrical charges at the cell membrane.

The submission of beams pf photons/electroms to destory Low intensity irradiation viable microorganisms.

3.2. Microbiostatic hurdles (Chemical hurdles)

FOOD APPLICATION OF HURDLE TECHNOLOGY IN FOOD INDUSTRY MICROBIOLOGY

The principles of the most common hurdles with in this catogory are summarized in table 3.2.

Table 3.2 Role of Microbiostatic hurdles

The creation of extra-cellular acid conditions that enables hydrogen ions to be imported in to the cytoplasma of microorganisms, thus distrubing the homeostasis mechanism of pH reduction key cell components vital for continuing growth and viability low pH values are obtained by frementation or addition of acids (inorganic or organic).

The addition and/or formation of carbonic acid to obtain a multiple hurdle effect, including the creation of anaerobic conditions by replacing oxygen, reducting, pH, inhibiting Carbond doxide (CO2) certain intracellular enzymes (decarboxylation) and inhibiting the transport of water-soluble nutrients across the membrane (by dehydrating the cellular membrane).

The addition of certain additives to echance keeping quality and stability through direct or indirect antimicrobial and/or Use of preservatives fungicidal activity. Most preservatives are rather specific and have effect only on certain microorganisms.

The establishing of gaseous environment (either low in oxygen and/ or high in carbon dioxide or nitrogen) to limit growth of aerobic microoranisms by impairing biochemical pathways. Modified atmosphere packaging (MAP) means that a modification of the gas atmosphere in the packaging is created.

Redox potential (Eh) is a measure of the oxidizing or reducing potential of food systems that determines whether aerobic or Redox potential control anaeroic miroorganisms are able to grow. Eh is influenced by removal of oxygen and/ or addition of reducing substanes (e.g. ascorbic acid, sucrose, etc.).

Lactoferrins The utilization of naturally present glycoproteins (highest

FOOD APPLICATION OF HURDLE TECHNOLOGY IN FOOD INDUSTRY MICROBIOLOGY

concentration in colostrum) to prolong the lag phases of bacteria for 12-14 hours, by binding iron in the presence of bicarbonates.

The lactoperoxidase system The activation of the lactoperoxidase/thiocyanate/hydrogen peroxide system (indigenous system in milk) to inactivation

several vital metablic bacterial enzymes, consequently blocking

their metabolism and ability to multiply.

The application of two interrelated steps, as follows: The hydrogen peroxide- catalase  Additon of hydrogen peroxide to the milk, e.g. at method collection centers by trained personnel, and

 Addition of catalase at the dairy plant (after heat treatment) with subsequent period of inhibition.

FOOD APPLICATION OF HURDLE TECHNOLOGY IN FOOD INDUSTRY MICROBIOLOGY

3.3. Microbiostatic hurdles (Physical hurdles)

The principles of the most common hurdles with in this category are given table 3.3.

Table 3.3 Role of Microbiostatic Hurdles

Refrigeration Lowering of product temperature to reduce microbial activity.

The contorl of the water activity in the product (the accessibility of water for microorganism, not the water content in the food), expressed as the ratio of water vapour pressure of the food to that of pure water. Water activity can be controlled by:

 Concentration, evaporation and drying, which also incresas the buffering capacity of milk. Water activity control  (addition of sodium chloride), which also reduces the cell resistance against carbon doxide and in the solubility of oxygen .

 Sweetening (addition of ), which at aw below 0.9.- 0.95 also results in an antimicrobial effect, depending on the type of sugar.

The lowering of temperature below the freezing point of the Freezing product combined with a reduction of the water activity. Freezing has microbiostatic as well as microbiocidal effects.

The practice of applying very short collection/storage periods, limitin the shelf life of products or immediate processing of raw Time milk to ensure that all microorganisms present are in the lag phase, and therefore not active and more susceptible to other hurdles.

3.4. Hrudles that prevent contamination

A large number of control measures are preventive measures. Preventive measures are generally not regarded as hurdles, however, a few are used in the production lines to obtain hurdle effects.

FOOD APPLICATION OF HURDLE TECHNOLOGY IN FOOD INDUSTRY MICROBIOLOGY

The principles of the most common hurdles within this category are shon in table 3.4.

Table 3.4 Role of Hurdels in Preventing Contamination

The application of (on eg. Packging materils, equipment and water) high intensity broadband light pulses of wavelengths in Pulsed high-intesnity light: the ultraviolet, visible and infradred spectrum (20000 times sunlight) to destory microorganisms

The introduction of a physical barrier against contamination, with or with out antimicrobial substance implemented in to it Coatings (immobilized) to obtain a slowly migration of these from the surface.

Packaging provides a physical barrier that protects against access of microorganisms from the surroundings. Aseptic packaging as the process of packaging a product in to sterilized Packaging containers followed by hermetic sealing with a sterilized closure in a manner that prevents microbiological recontamination of the product.

4. APPLICATION OF HURDLE TECHNOLOGY IN FOODS

The hurdle technology approach is currently of most interest because;  For minimally processed foods which are mildly heated or fermented.  For underpinning the microbial stability and safety of foods coming from future lines, e.g., healthful foods with less fat and/or salt.  For advanced hurdle-technology requiring only minimal packaging.  For refrigerated foods chill temperatures are the major and sometimes the only hurdle.  If exposed to temperature abuse during distribution of the foods, this hurdle breaks down, and spoilage or food poisoning could happen.  Additional hurdles should be incorporated as safeguards into chilled foods, using an approach called „invisible technology‟ Foods can be preserved and kept safe for long duration by applying individual or combination of hurdles (Figure 4.1)

In developing countries

FOOD APPLICATION OF HURDLE TECHNOLOGY IN FOOD INDUSTRY MICROBIOLOGY

The application of hurdle technology is of paramount importance for foods

 remain stable, safe, and tasty if stored without refrigeration  novel minimally processed, high-moisture fruit products especially in Latin America  for meat products in China  for dairy products in India.

There is a general trend to move gradually away from intermediate-moisture foods because

 too salty or too sweet  have a less appealing texture and appearance than high-moisture foods.

Hurdle technology has two main functions:

 During manufacture: providing assurance that the levels of the pathogens of concern where present, are kept at or reduced to tolerable levels (Table 4.1).  During packaging, distribution and storage: providing assurance that the tolerable levels of the pathogens of concern that have been achieved during manufacture are kept under control throughout shelf life.

Figure 4.1 Preservation of food by individual and combined hurdles

FOOD APPLICATION OF HURDLE TECHNOLOGY IN FOOD INDUSTRY MICROBIOLOGY

Table 4.1 Application of Hurdle Technology in Dairy and Food Products

Sr. Hurdles Role Target Organisms Foods No.

A. Physical Hurdles

1. Bactofugation Remove bacterial cells of high Clostridium Spores, Cheese milk density (Bacterial spores and spoilage causing Somatic Cells), Remove organisms bacterial load about 1.3 decimal reduction and 90-95% of cells removal

2. Pulsed electric fields Inhibitory action against L. innocua Whey pathogens (PEF)

3. Thermization Make microorganisms All microorganisms are Milk vulnerable to subsequent affected (especially hurdles psychotropic)

4. High Pressure Treatment High pressure kills organism Yersinia enterolitica, Milk and milk products

5. Microfilteration Filter of normal size about , Salmonella, Milk,cheese 0.6-1.4 µm is sufficient to Spores separate most bacteria

6. Sonication Create stress for the Salmonella, Liquid microorganisms Streptococci, products Staph.aureus

7. Pulsed Electric field Electric current is used to kill Effective against Gram Milk organisms positive bacteria than Gram negative bacteria

FOOD APPLICATION OF HURDLE TECHNOLOGY IN FOOD INDUSTRY MICROBIOLOGY

8. Freezing Inhibit bacterial growth, No Some pathogenic and Dairy bacterial growth occurs below spoilage causing products, 10 C , killing of 50% bacteria microorganisms fruits, during freezing storage vegetables depending on composition etc

B. Chemical Hurdles

1. Sodium citrate and Killing of organisms Arcobacter butzleri on Butter, food chicken products sodium lactate

2. Hydrogen Peroxide- Inhibitory action Salmonella, Coliforms Milk and catalase and Clostridia milk products

3. pH Reduction Suppress the growth of Listeria Milk and Pathogenic bacteria monocytogenes, Cheese Staph.aureus

4. Carbon dioxide Inhibits the growth of bacteria E.coli Milk and cheeses

5. Lysozyme destruction of outgrowing Clostridium Cheese cells Tyrobutyricum

6. Propionates Block the metabolism due to Yeasts and Moulds Butter, enzyme inhibition and cheese, bacterial development vegetables

7. Water Activity Reduction of aw suppress the Almost all types of Milk powder, growth of pathogenic bacteria microorganisms khoa, condensed milk, cereals etc

FOOD APPLICATION OF HURDLE TECHNOLOGY IN FOOD INDUSTRY MICROBIOLOGY

C. Microbial derived hurdles

1. Competitive Microflora Reduction of the no. of Almost all potential Dairy microbes by lowering pH, pathogenic organisms products and consumption of nutrients and other foods production of antimicrobial substances

2. Ripenining agents Killing of pathogens by Salmonella Cheddar (Lactobacilli) production of antimicrobial typhimurium, S. cheese, compounds aureus, E. coli, Emmental cereus, cheese Listeria

monocytogenes

3. Nisin Inhibits gram positive bacteria Bacillus, Clostridium, Cheeses, Streptococcus, S. buttermilk, aureus fermented milks

4. Pediocins, helvetin J Inhibitory action Listeria Cheeses, monocytogenes fermented milks

D. Combined Hurdles

1. Nisin With HHP Inhibitory action against S. carnosus and B. Cheese pathogens, effective to subtilis spores inactivate cheese indigenous

Microbiota

2. pH and low Inhibitory action against significant reduction in liquid pathogens L. innocua products, temperature cheese,

whey

FOOD APPLICATION OF HURDLE TECHNOLOGY IN FOOD INDUSTRY MICROBIOLOGY

3. acid, salt, and heating Inhibitory action against E. coli O157:H7 pickled pathogens products

4. Salt and nitrite Killing effect Many bacteria Meat products

5. Summary

Food preservation implies putting microorganisms in a hostile environment, in order to inhibit their growth or shorten their survival or cause their death. The feasible responses of microorganisms to this hostile environment determine whether they may grow or die. More research is needed in view of these responses; however, recent advances have been made by considering the homeostasis, metabolic exhaustion, and stress reactions of microorganisms in relation to hurdle technology, as well as by intro-ducing the novel concept of multitarget preservation for a gentel but most effective preservation of hurdle-technology foods.

FOOD APPLICATION OF HURDLE TECHNOLOGY IN FOOD INDUSTRY MICROBIOLOGY