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Week 4: Thermal Preservation - Coggle Diagram

- - - - heated to >100℃ in pressure cookers (retort). The foods should reach at least 110-121℃ and kept for a defined period of time
        
        Retort Technology
        
        Typical industrial practice
        
        12 D process – for low acid canned foods (pH > 4.6) to reduce Cl. botulinum spore population by 12 log cycle
        
        5D process – for acid canned foods (pH < 4.6) to reduce B. sterothermophilus population by 5 log cycle
        
        Containers for heat preserved foods must be hermetically sealed and air tight to prevent recontamination from airborne microbes.
        
        Common types of heat sterilizable containers
        
        Metal cans
        
        Glass jar/bottles
        
        Flexible pouches/ rigid trays
        
        Characteristics of retort
        
        Operate under pressure
        
        Use a heating medium (pure steam, hot water, steam/air mixture) to transfer heat to products
        
        (Moist heat is more effective than dry heat)
        
        2 Types
        
        Stationary (still) or rotated (agitated) configuration
        
        Batch / Continuous method
      - Commercial sterility refers to the degree of sterilization whereby all pathogenic and toxin forming microorganisms are destroyed and those remaining are incapable to grow and result in spoilage under normal storage conditions.
      - Two types
        
        In package sterilization – product is packed into container and sealed followed by sterilization. E.g. Canned foods, retort pouches
        
        UHT or aseptically processed products – Sterilisation of foods before packaging followed by filling into pre-sterilized containers and sealed in a sterile environment. E.g. UHT products
  - - - 2 aims
        
        Inactivate natural oxidative enzymes (e.g. polyphenol oxidase, lipoxygenase) in fruits and vegetables
        
        Purge gas from plant tissues to prevent chemical reactions during storage
      - Common pre-treatment before freezing, canning and dehydration to prevent loss of colour, flavour and nutrients during handling and storage.
      - ranges from 1 to 15 mins dependent on
        
        Factors
        
        Type and size of Vegetables
        
        Methods of heating
        
        Water is better conductor than steam but causes more nutrients to be lost
        
        Blanching Temperature
        
        Under-blanching and over-blanching should be avoided.
      - Methods
        
        Hot Water Blancher
        
        Conventional method to hold foods in hot water for specific time
        
        Steam Blancher
        
        Foods pass thorough steam in controlled residence time
        
        Fluidized Bed Blancher
        
        Foods pass through a mixture of gas & steam for specific time
        
        Microwave Blancher
        
        Uses microwave for blanching
      - Peroxidase test is a chemical test used as blanching adequacy index to detect the inactivation of peroxidase.
        Adding guaiacol solution and hydrogen peroxide solution
        Observe for development of brown colour which indicates peroxidase activity. No colour change indicates enzymes have been inactivated.
    - - Pros
        
        Superior Product Reproducibility
        E.g. better control of doneness
        
        Extension of Product Shelf Life
        E.g. reduction of pathogen, prevent growth of aerobic microbes, prevent recontamination
        
        Higher Product Quality
        Eg: Reduce loss of nutrient/flavor/moisture to cooking medium, minimize oxidation
      - Cons
        
        Potential Food Safety Risk
        E.g. food spends longer time in danger zone, increase risk of anaerobic microbes
        
        Capital Investment
        E.g. cost of equipment & pouches
        
        Long Processing Time & Impractical for some foods
        E.g. 45 mins to 4 hrs @ 54-57℃ for middle-rare tenderloin. Degradation of chlorophyll & retention of alcohol
    - - Purposes
        
        Inactivate enzymes
        
        Eliminate selected heat sensitive pathogenic microorganisms
      - Severity of heat treatment and shelf life
        
        pH of foods (low acid foods pH>4.6, acid foods pH <4.6)
        
        Heat resistance of microorganisms (D value of most heat resistance microorganism and enzyme)
        
        Type of heat application (steam-air, hot water)
        
        Heat sensitivity of foods
      - sensory characteristic and nutritional value of food are minimally affected.
      - Often use in combination with other preservation methods to minimize microbial growth.
      - Methods
        
        Batch pasteurizer
        E.g. milk heated to at least 63℃ & hold for at least 30 mins
        
        High Temperature Short Time (HTST) continuous pasteurizer (E.g. milk heated to at least 72℃ & hold for at least 15 secs)
        
        Tunnel Pasteurizer (E.g. steam tunnel with preheating, heating and cooling zones)
      - Alkaline Phosphatase Test: Alkaline phosphatase is naturally occurring enzyme in raw milk with D value higher than target pathogens (e.g. Mycobacterium tuberculosis). If their activity is detected, it is assumed that pasteurization is inadequate.