Trends in Thermal Processing Pasteurization and Commercial Sterilization

Transcription

1 Trends in Thermal Processing Pasteurization and Commercial Sterilization Hosahalli S. Ramaswamy Professor, Department of Food Science McGill University, Canada Food Processing and Safety Food Industry Meeting MAC Campus, June 8, 2012

2 Presentation Outline Public Safety Food Microbiological Issues Thermal Processing Principles Focus on pasteurization and sterilization Novel approaches in thermal processing Non-Thermal Processing Conclusions

3 Micro-organisms & Food Food Pathogens public health concern because they enter the human system through food and cause various disease Food Poisoning Micro-organisms these are not pathogens but produce toxins in foods which when ingested cause harm to public health Food Spoilage Microorganisms these are not of public health concern, but they cause spoilage of foods

4 Common Food Pathogens Clostridium perfringens Salmonella, Bacillus cereus Escherichia coli O157:H7 Listeria monocytogenes Shigella Staphylococcus Streptococcus faecalis, faecium Vibrio; Yersinia Clostridium botulinum (proteoletic)

5 Micro-organisms of Safety Concern Bacteria Producing Exotoxins Clostridium botulinum Clostridium perfringens Staphylococcus aureus Bacillus cereus

6 Food Processing Objectives Primary Objectives Safety and Stability (Preservation) Safety Concern Eliminate or Disable Pathogens Stability Eliminate or Disable Spoilage Organisms Inactivate enzymes Suppress chemical reactions

7 Thermal Processing Good Old Technology, Old is Gold To make the product safe & shelf-stable Objective is to reduce microorganisms of public health concern to a statistically small level Most serious & heat resistant (low acid) Clostridium botulinum Level: Survivor probability 1 in Botulinum Cook Create conditions that prevents the activity of spoilage bacteria

8 Thermal Processing Principle Overview Vacuum Sealed Cans/Pouches (Prevents the growth of Obligate Aerobes ph < 4.5 High Acid Foods ph ph > 4.5 Low Acid Foods Pasteurization: mild treatment < 100 o C Pasteurization: mild treatment < 100 o C Sterilization: severe treatment >110 o C Controls pathogenic & Only pathogens Spooilage vegetative forms. controlled. Spore formers in-active. Spores are active Shelf-stable products for Provides Short-term fruits & acidified storage at refrigerated foods conditions Spores killed: Public health concern: Clostridium botulinum; Bot Cook - 12D Process is implemented. Spoilage: Mesophiles are killed. Heat resistant thermophiles are not killed but controlled by storing the product below 30 o C

9 Pasteurization vs Sterilization Pasteurization Mild heat treatment Destruction of pathogenic microorganims Temporary shelf-life extension Product refrigerated to control spoilage Sterilization or Appertisation More severe heat treatment Control of pathogenic and spoilage bacteria Shelf life extension & safety Long term preservation Product not fully sterile it is a misnomer Considered to be practically sterile because of stability

10 Pasteurization (CFIA) The processes is normally developed by a process authority. The target organism depends on the product storage temperature and safety parameters. Targeting L. monocytogenes prevents the growth of other non-spore formers but does not prevent growth of spore formers. Targeting non-proteolytic Clostridium botulinum will control both spore and non-spore formers in a refrigerated product. The pasteurization must result in one of the following (CFIA): a) A 5 log reduction of Listeria monocytogenes where: D value at 65 C=1.18 minutes and; Z value = 6.7 C, or; b) A 6 log reduction of non-proteolytic Clostridium botulinum where: F value at 90 C = 10 minutes and; Z value = 10 C (F90 10 min process)

11 Comparison of Criteria Sterilization Target micro-organism Clostridium botulinum Reference temperature = 121 C Characteristics: D 121 = 0.25 min and z = 10 C Estimated number of micro-organisms N o = 1/g Number desired in final product N = 1/10 12 g = /g Treatment effectiveness n = log (1/10-12 ) = 12 Minimum sterilization value at 121 C F o = n x D = 12 x 0.25 = 3 min Pasteurization Target micro-organism Streptococcus faecalis Reference temperature = 70 C Characteristics: D 70 = 2.95 min and z = 10 C Estimated number of micro-organisms N o = 10 7 /g Number desired in final product N = 1/10 6 g = 10-6 /g Treatment effectiveness n = log (10 7 /10-6 ) = 13 Minimum pasteurization value at 70 C Pm = n x D = 13 x 2.95 = 38 min

12 Thermal Processing Objectives Safety vs Quality FROM A SAFETY ASPECT Need to monitor the temperature and establish the process at: coldest point in the container placed at the coldest location in the retort. FROM A QUALITY POINT OF VIEW Need to minimize the bulk cooking. Product near or at the surface of the container will be cooked more than the product near the centre.

13 Retort Temperature Distribution - Very important as it affects the retort performance - It can compromise safety - It can compromise quality - Must be assessed by a process authority Large temperature fluctuations warrant modifications to the retort equipment or loading practice Two major issues in temperature distribution 1) Temperature stability with respect to Time Controller / System limitations 2) Temperature stability with respect to Space Distribution / Loading pattern limitations

14 Spatial Retort Temperature Distribution Local mean temperatures during cook time

15 Transient Temperature Distribution T e m p Time Average local retort temperatures as a function of time

16 Quality Optimization in Thermal Processing All techniques used improve the heat transfer to the product which reduces the cooking time and hence improve the quality in thermally processed foods q ka x T q = h A

17 Relative D value Quality Optimization: 1) Increase T Nutrient Microbial Spore Vegitative bacteria Temperature

18 Relative time Illustration of high temperature short time (HTST) heating principle Nutrient Destruction t1 90% 50% t2 Bot cook t3 10% t4 5% T1 T2 T3 T4 3% Temperature (C )

19 Rotary Processing Two modes of agitation/rotation q = h A mg Axial Rotation (Continuous Operation) End over end rotation (Batch Operation)

20 Steristar rotary retort (Courtesy Malo Inc.) End-overend Agitation processing, steam/air or steam

21 A cutaway view of the continuous rotary turbo cooker (FMC)

22 Aseptic processing q = h A Aseptic Environment Sterilization Sterilization Filling & Sealing Aseptic Product

23 Middle layer Thin Profile Process Retort Pouch Outer layer: strength and printability Middle layer: barrier properties Inner layer: heat sealing, food contact Outer layer q ka x T Inner layer

24 Semi-Rigid Plastic Containers Light weight, easy storability, thin profile, easy end use preparation and disposal, microwavable Slow filling and sealing, labor intensive

25 Novel Methods of Heating Microwave Heating: Two Modes Ionic Polarization Dipole Rotation

26 Applications Heating, Reheating and Cooking Pasteurization and Sterilization MW Tempering and Thawing MW Blanching Enhancing reaction kinetics Microwave assisted extraction

27 Novel Heating Techniques. Ohmic heating Electrode Also called R V Direct resistance heating Joule effect heating Electro-conductive heating Electro-resistive heating Principle Electrode Food Product An electrical circuit analogue Heat generation occurs when an electric current is passed through an electrically conducting food product.

28 Temperature ( o C) Typical Time Temperature Profiles under Ohmic Heating Conditions ~ v 60v 70v 80v 100v Time (min)

29 Advantages of Ohmic Heating Very rapid heating No need for a heat transfer surface Gentle handling of particulates No moving parts Quiet operation Easy process control Better energy conservation than MW Easier tailoring of particle/liquid heating Easy adaptability to Aseptic Processing of Particulates

30 High Pressure Processing l An emerging and Novel technology l Gaining tremendous popularity

31 HP Characteristics and Advantages Can destroy microorganisms and inactivate enzymes Results in fresh-like product Environmentally friendly (less wastage) Process Independent of product shape and size

32 High Pressure Application Areas Pasteurization: Sterilization: Juices, milk High and low acid foods Texture modification: Fish, egg, proteins, starches Functional changes: Cheese, yogurt, surimi Specialty processes: Freezing, thawing, fat crystallization, enhancing reaction kinetics

33 Equipment HP Dynamics Inc Avure STANSTED NC Hyperbaric ACB

34 High Pressure Pilot Plant at McGill

35 High Pressure Processing Pasteurization and Sterilization

36 HP Pasteurization Well studied Guidelines have been developed (USDA - FDA) Processes now must demonstrate 5 log reduction in pressure resistant pathogens Examples: Listeria monocytogenes, E. coli 0157:H7, Salmonella sp. 1 min at MPa adequate for juices Safe - shelf stable high quality product

37 HP Sterilization Shelf-stable product Spores of both spoilage and public health concern need to destroyed, requires high pressure and high temperature High pressure accelerates the destruction kinetics. Permits the use of lower processing temperatures: Quality advantage Most unique feature: Adiabatic heating

38 Temperature change ( T) due to adiabatic compression Substance (25 C) T ( C) per 100MPa Water ~ 3 Mashed potato ~ 3 Orange juice ~ 3 2%-fat milk ~ 3 30%-fat Cheese ~ 5 ^ Salmon ~ 3.2 Water/glycol (50/50) 4.8 ~ 3.7 * Beef fat ~ 6.3 Olive oil 8.7 ~ 6.3 * Soy oil 9.1 ~ 6.2 * ^ Observed by Shao and Zhu (2002). * T decreases as pressure increase. T 3-5 C/100MPa for high moisture foods Large T for fat-rich foods

39 HP sterilization: Principle Pack and Bring initial temperature to 90C Delivery of target lethality - Safe product Rapid heating & cooling - High quality product Load sample and quickly pressurize chamber to 700 MPa Depressurize. Sample cools to 90C instantaneously Compression heating increases sample temperature to 125C Hold until sterility is achieved: 1-5 min

40 Effect on HP treatment on quality Salami, before and after

41 Effect on HP treatment on quality Milk and strawberry, before and after

42 Effect on HP treatment on quality Cheese and Milk, before and after

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44 Effect on HP treatment on quality Salmon, Chicken, beef and pork before and after

45 Thank you