1	Evaluation of the Hurdle Concept P. Michael Davidson Dept. Food Science & Technology University of Tennessee Knoxville, Tennessee
2	Outline History of the Hurdle Concept Definition Characteristics Targets, Hurdle Types, Examples Strengths/Weaknesses Appropriate Application Potential Failure Modes
3	Frazier (1958) “Only rarely is a single method effective…usually several are combined.” “When preservative methods are combined, the required intensity of each usually is reduced to less than that for preservation by one [agent] alone.”
4	Hurdle Concept - History Empirical application Semi-Systematic Approach – Hurdle Concept Lothar Leistner Federal Meat Research Center 1978 Leon G.M. Gorris, Netherlands Hurdle technology Utilization of multiple barriers or hurdles to preserve foods
5	Hurdle Technology Definition Utilization of existing and/or novel preservation methods to establish a series of preservation factors (hurdles) that any microorganism should not be able to overcome Shelf stable foods Extended to other foods
6	Hurdle Technology - aka Combined methods Combined processes Combined preservation Combination techniques Barrier technology Intervention technology
7	Hurdle Technology - Targets Pathogenic microorganisms Spoilage microorganisms Fermentative microorganisms Quality attributes Sensory Nutritive value
8	Hurdles Physical Physicochemical Microbial Miscellaneous “Over 60 potential hurdles” (Leistner, 2000) Inhibition and Inactivation Some are multiple – sensory, inhibitory
9	Physical Hurdles Temperature – high & low Process Storage Packaging MAP Composition Aseptic Irradiation Non-Thermal processes
10	Physicochemical Hurdles Water Activity Low pH Low Redox potential (E_h) Low? Salt
11	Physicochemical Hurdles Preservatives Organic Acids, Acetate, Lactate, Sorbate Carbon Dioxide, Chlorine, Ethanol, Lysozyme, Monolaurin, Natamycin, Nitrite, Nitrate, Ozone, Parabens, Phosphates, Spices, Sulfite Questionable or very limited: Ascorbate, Chitosan, Glucon-delta-lactone, Hop Extracts, Lactoperoxidase, Maillard reaction products, Pectin Hydrolysate, Propylene Glycol, Protamin
12	Microbial Hurdles Competitive microflora Lactic acid bacteria Microbially derived inhibitors Nisin Other Bacteriocins
13	Hurdles (Interventions) for Meats Fresh Lactic and Acetic acid Chlorine, Peroxyacetic Acid, Phosphate, Ozonated Water Hot Water, Steam Sodium Chlorite, CPC Processed Salt, pH, Water Activity, Nitrite Lactate, Diacetate
14
15
16
17
18	Example Salami-type fermented sausages Stable at ambient temperature for extended periods Early ripening Salt, nitrite Inhibit many microorganisms in meat batter Microorganisms resistant to nitrite, salt Grow and reduce Eh by using oxygen Growth of Lactic Acid Bacteria Increase acidity (reduce pH)
19	Example (cont’d.) Salami-type fermented sausages Long term Decrease nitrite, lactic acid bacteria Increase pH, Eh BUT decreased Water activity Preservation
20	Hurdle Concept – Weaknesses and Strengths Weaknesses Generally qualitative Systems too complex to be fully described quantitatively? Strengths Holistic approach Potential for synergistic interaction
21	Hurdle Concept - Problems Generally Not Quantitative Numerous Factors Affecting Growth Often little known concerning effects Numerous Target Microorganisms
22	Factors Affecting Growth and Control of Microorganisms Microbial - Intrinsic Extrinsic - Environment Intrinsic – Food Related Process - Applied
23	Intrinsic Microbial Factors Form Vegetative Cells Spores Types Bacteria, Molds, Yeasts Genus, Species, Strains
24	Extrinsic and Intrinsic Factors Extrinsic Storage Temperature Atmosphere Intrinsic pH Oxidation-Reduction Potential Water Activity Microstructure Natural Inhibitory Substances
25	Hurdle Concept - Problems Little known about the precise effect of many process-related hurdles
26	Limited Data Food Processes Inactivation Irradiation, High Pressure, Pulsed Electric Fields, others Inhibition Naturally Occurring Antimicrobials
27	Hurdle Concept - Problems Factors Change Over Time Hurdle Concept does recognize to some extent Examples Aerobic growth Reduces Redox potential pH changes with microbial growth Mold effect on Clostridium botulinum No Quantitative Treatment
28	Hurdle Concept - Strength Use of Multiple Factors or Control Methods Sequential Potential for simultaneous and therefore interactive effects Difficult to predict
29
30	Definitions - Combinations Additive - combined antimicrobials are equivalent to the sum of each antimicrobial acting independently Antagonistic - reduced efficacy of the combined agents Synergistic - enhancement of activity compared to the sum of individuals
31	Multi-Target Preservation Application of hurdles targeted to specific and different cellular processes Targets Metabolic processes (enzymes) Critical enzymatic processes Cell membrane function Genetic mechanisms To Achieve Synergistic Activity Different processes must be inhibited
32	Antimicrobial Combinations Selection of Antimicrobials and Concentrations Trial and Error Based upon Mechanism of Action Evaluation of Results
33
34
35
36
37	Modeling for Quantitative Hurdle Technology Application Viability Growth/No growth Interface Inactivation
38	Value of Hurdle Technology Holistic approach If appropriately designed and applied Not an easy process Requires extensive knowledge of: All microorganisms important in a particular food Limiting or stress conditions associated with food Appropriate processing methods and chemical antimicrobials Effect of changes on food quality
39	Steps for Product Development Using Hurdle Technology Decisions Desired sensory traits Shelflife Appropriate processing objective and methods Inhibition Inactivation
40	Steps for Product Development Using Hurdle Technology Analyze processed food for inhibitory factors and modify to produce hurdles or interventions Utilize predictive microbiology Keep in mind multi-target preservation Challenge tests Pathogens and spoilage microorganisms Inoculum higher than bioburden
41	Steps for Product Development Using Hurdle Technology Modify hurdles if necessary Challenge study II Modify again if necessary Establish hurdles precisely, including tolerances Determine methods for monitoring Validate (full-scale industrial conditions) Determine CCP’s and develop HACCP program
42	Can Hurdle Technology Fail? Initial Contamination Improper Design Improper Application Antimicrobial potency Post-Process or Post-Application Contamination Resistance Development
43	Summary The use of multiple barriers, whether they be stresses to growth factors or process applications, is a sound method for controlling growth of or inactivating pathogenic and spoilage microorganisms The design of these multiple barriers can be complex and requires extensive knowledge of microorganisms, their growth factors and preservation methods
44	Summary Research Needs Define the quantitative effects on microorganisms of combinations of growth factor stresses and preservation techniques Determine the mechanisms of antimicrobial action of all preservation processes
45
46