Hurdle technology is a multi-target preservation process that involves the manipulation of physical and chemical factors to inhibit the microorganism.

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HURDLE
TECHNOLOGY
M.Venkatasami, I.D.No: 2020641005
Ph.D. (Processing and Food Engineering)
Department of Food Process Engineering
AEC&RI, TNAU.
PFE 602 Advances in Food Engineering (2+1)

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INTRODUCTION
Food preservation methods
 Control the growth of microorganisms
 Temperature, water activity(𝑎𝑤), pH, oxidation–reduction potential(Eh), and preservatives
 An optimum to minimum level
 Single factor – reduce nutritional quality
 Preference: fresh, natural, and healthy foods
Hurdle technology
Combination of a
number of milder
preservation factors
Enhanced level of
product quality,
safety, and stability
Limit or prevent
microbial growth

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CONT…
 Factors used for food preservation are called “hurdles”.
 Hurdle groups
Physical
Physical
nonthermal
Physicochemical Microbiological Miscellaneous
hurdles
 Influence the quality, safety and stability of foods
 Improper application: loss of nutrients, texture, and color
 Achieve synergies at low intensity
 Prevent the growth of pathogenic or spoilage microorganisms

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TYPE OF HURDLES EXAMPLES
Physical hurdles Electromagnetic energy (microwave, radiation), high temperature
(blanching, pasteurization, baking), low temperature (chilling, freezing),
packaging (active and vacuum packaging, edible film), and so on
Physical nonthermal
hurdles
High hydrostatic pressure, pulsed electric field, pulsed light, and so on
Physicochemical
hurdles
CO2, O2, O3, ethanol, lactic acid, lacto peroxidase, low pH, low aw, Millard
reaction products, smoking, nitrite/nitrate, sulfite, spices, and so on
Microbiological
hurdles
Competitive flora, protective cultures, microbial products
CONT…

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CONT…
 Food product may require a different combination of hurdles
 The initial microbial number
 Conditions within the product for microbial growth
 Target shelf life
 Types of combined hurdles
 Hurdles is a critical control point
 Different hurdles achieves multi target reliable preservation effects
 Smoked products :
Heating
Reducing moisture
content
Smoking

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 Hurdle technology arose from a number of developments :
CONT…
 Consumer demands for healthier foods that retain their original nutritional
properties
 The shift to ready-to-eat and convenience foods that require little further
processing by consumers
 Consumer preference for more “natural” foods that require less processing and
fewer chemical preservatives.
Desired product quality and microbial stability

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PRINCIPLES OF COMBINED PRESERVATION METHODS
The factors
Major importance
Secondary importance
Heat resistance
𝑎𝑤
Heat resistance
Preservatives
Inhibition
𝐸ℎ
Mild heating Refrigeration
Canned
foods

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CONT…
𝑎𝑤 pH Fermented
sausages
Interaction of different hurdles Improvements in food preservation
 Energy-consuming hurdles
(refrigeration) 𝑎𝑤, pH, Eh
 Hurdle adjustments:

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HURDLE EFFECT
 Microorganisms should not over come (“jump over”) the hurdles;
Start or during
storage
Microbes
Undesirable
Few Sanitation and
aseptic Processing

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CONT…
Different
intensities
Important
Bacterial
spores
Inhibited
Fermented
sausage
Nitrite,
salt
Aerobic microbes
LAB
𝑂2 Strong
Synergistic
effect
Homeostasis,
osmoregulation

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TOTAL QUALITY OF FOODS
 Hurdles of foods can influence,
Stability
Safety
Sensory
Nutritive
Technological
Economic properties
 Hurdles intensity, Negative Positive
 Chilling at low temperature – chilling injury
 Moderate chilling – inhibiting the microbial growth
 pH- inhibits pathogenic bacteria – Taste impairs
(Fermented sausages )
Intensity of
hurdle

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HOMEOSTASIS
 Tendency to maintain uniformity and stability in the internal
microbial cells
Homeostasis
Physiological systems
Operating in balance under unfavorable
environmental condition
 Preservatives - Microbes
 Disturb one or more of the homeostatic mechanisms
 Microorganisms will not multiply
 Remain in the lag phase
 Die before their homeostasis is reestablished
 Metabolic exhaustion
Osmoregulation
 Osmohomeostasis
(tuger - proline and
betaine)

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Stress factor in
environment
Homeostatic response of microbial cell
Low level of nutrients
Low level of metabolism, stationary phase, viable non
culturable forms
Low pH Removal of protons from cell, maintenance of pH gradient
Low water activity
Osmoregulation, accumulation of solutes, reduction of water
loss, maintenance of membrane turgor
Low temperature
“Cold shock” response: change in membrane lipid
composition to maintain fluidity
CONT…

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Stress factor in
environment
Homeostatic response of microbial cell
Raising temperature “Heat shock” response: change in membrane lipid composition
Raising levels of O2 Enzyme protection (production of catalase, peroxidase, and
superoxide dismutase) from H2O2 and oxygen-derived free
radicals
Presence of biocides Phenotypic adaptation, reduction of cell permeability
Ionizing radiation Repair of single-strand breaks in DNA
Competition Aggregation of cells to show symbiosis and produce biofilms
CONT…

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METABOLIC EXHAUSTION
Metabolic exhaustion Auto sterilization of foods
Mild heat treatment
Sausage, high-moisture fruits, and meats
Unrefrigerated storage
(Room temperature, 25°C)
Hurdle factors
(pH, 𝑎𝑤, sorbate, sulfite)
Bacteria, yeasts, and molds
 Salmonella - fermented sausages
 Listeria - water-in-oil-emulsions
 Unrefrigerated storage
 Refrigeration is not always beneficial for the microbial safety and stability of foods
More
hurdles
More metabolic
exhaustion

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STRESS REACTIONS
Cross tolerance  Stressed microorganisms become more tolerant to other stresses
 Escherichia coli O157:H7
 Salmonella enterica subsp. enterica ser. Typhimurium,
 Listeria monocytogenes
 Resistance induced by,
Protective stress shock proteins
(PSSPs)
Bacteria may become more
resistant or more virulent
 Heat
 pH
 𝑎𝑤
 Ethanol
 oxidative compounds
 starvation of nutrients
 Acid-shock or acid-adapted cells tolerant to stresses
 Mild heating of microbial cells may increase acid tolerance

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MULTITARGET PRESERVATION
Synergistic effect Different preservative factors
 Different stresses will sharply reduce energy of microbial cells
 Increase in the antimicrobial effect of each hurdle
 Synthesis of PSSPs avoided
 Individual hurdles at lower intensity improves product quality
 Antimicrobial action on different targets by the hurdles is known as “multitarget
preservation
 Targets Cell membrane DNA Enzyme systems

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APPLICATION
Intermediate-
moisture foods
High-moisture foods Integer foods
 Foods must be differentiated before application of hurdle technology
IMFs HMFs IFs
Fermented Foods Heated Foods Chilled Foods Healthy Foods

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INTERMEDIATE-MOISTURE FOODS
Storable without refrigeration, and cost and energy efficient
𝑎𝑤 0.9–0.60
 𝑎𝑤 is the primary hurdle for microbial stability
Meat Fish Fruits Vegetables
 IMFs
Hurdles IMF’s Stability
 Heating
 Preservatives
 Competitive
microflora
 Redox potential
 Maillard reaction
 pH
 Detection and description of micro stable IMF
 Effective preservative factors
 Preservation and quality of food with hurdle

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HIGH-MOISTURE FOODS
𝑎𝑤 >0.9
 Minimally processed fresh-like products- chilled or frozen
 Low temperature ---- Energy consuming and costly
 Temperature abuse during storage ----- Reduce the stability and safety of HMF
 Additional hurdles besides low temperature
Heating pH Eh 𝑎𝑤 Preservatives Competitive flora
 Hurdle technology is increasingly applied on meat and meat products
HMF Emulsion-type sausage Stored without refrigeration

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 Mild heat treatment
 78°C internal temperature
 𝑎𝑤 (below 0.95) <---- Salt, Sugar, Milk Powder, Drying
<---- Bacterial spores can survive
Emulsion type sausages:
High 𝑎𝑤
Improves the sensory
properties
Decreases microbial
stability and safety
 Glucono-delta-lactone and sodium acetate ---------
 LAB reduces pH
pH 5.5
Vacuum packaging
Reheating at 80°C for
1h in the pouch
Ambient temperature
CONT…

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CONT…
 Heat treatment ------- Eliminates vegetative microorganisms
 The low aw and pH and nitrite ------- Sausage ------- Bacillus and Clostridium spores
 Microbiologically stable and safe ------ Refrigeration not required
 Number of microorganisms decreases faster during storage --- 25°C than at 10°C
 Ambient temperature ---- High metabolic exhaustion
 Highly seasoned chopped or ground pork sausage
 Made with fresh (raw, uncooked) pork/ smoked

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 New technologies for the preservation of high-moisture fruit products (HMFPs) – Based
on GMP
CONT…
 Blanching
for 1–3min
 Steam
Mild heat
treatment
 0.98–0.93
 Glucose or
sucrose
Slight
reduction of 𝑎𝑤
 4.1–3.0
 Citric or
phosphoric
acid
Lowering of pH
 Potassium sorbate
 Sodium benzoate
 Sodium sulfite
 Sodium bisulfite
Antimicrobials
 Reuse of syrup in HMFP processing is recommended after pasteurization
 Zygosaccharomyces bailii and Zygosaccharomyces rouxii

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INTEGER FOODS
 Whole or integer foods---- Consist of large pieces of plant or animal tissue
Coatings
 Contain and maintain inhibitory substances
 Protect the surface of the foods against microbial spoilage
 Dewatering and impregnation process
 Soaking foods in highly concentrated solutions
 Humectants or other food additions
Solid foods Edible coatings and osmotic dehydration
 Soaking of foods Fruits Vegetables Meat Cheese fish
 Concentrated solutions of humectants (sucrose and NaCl

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FERMENTED FOODS
 Fermented sausages, salami, raw hams, ripened cheeses, and pickled vegetables
 Stable, qualitative, and safe at room temperature for extended periods
 Microbial stability - combination of hurdles
 The sequence of hurdles inhibits spoilage and pathogenic :
Clostridium
botulinum
L.
Monocytogenes
Staphylococcus
aureus
Escherichia coli Salmonella
Microstructure
 Influences the ripening process
 Survival of pathogenic bacteria
 Ripening flora only grow in nests
MIXING

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ADVANTAGES AND DISADVANTAGES OF HURDLE TECHNOLOGY
Hurdle Advantage Disadvantage
Low dose irradiation Inactive vegetative
microorganisms
In package treatment
Additional shelf life
Microbial spores resistant
Consumer resistance
Capital costs
Modified atmospheric
packaging
Reduces oxidation and
microbial spoilage
No significant effect on
pathogen
Freezing Longer shelf life Thawing required
Higher costs

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High hydrostatic pressure In- package treatment Spores resistant
Possibility of textural changes
Chemicals (pH, salt, spices) Low cost Impact on sensory quality
Protective cultures Effective against spore
formers
Cost of handling cultures
Heat sensitivity
Bacteriocins Many are heat stable
Effective against spore
formers
Inconsistency of inhibitory
effect
Decompose during storage
CONT…
Hurdle Advantage Disadvantage

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