CHEM215 Lecture Notes - Lecture 16: Electric Field, Lipid Bilayer, Electrical Resistance And Conductance
Lecture 16 – Food Preservation 2
Hurdle Technologies:
• This involves using multiple mild methods of food processing (as opposed to a
single harsh method) to ensure adequate preservation of foodstuff whilst
maintaining quality of the final product.
• Preservative huddles target different aspects of microorganisms
homeostatic mechanisms and act synergistically to prevent microbial growth
• On their own, these methods wouldn’t be suitable or sufficient for adequate
preservation but together they are very effective.
• Hurdles can be classified as physical, physics/chemical and microbial
Physical hurdles:
• temperature
• Pressure
• Light (pulsed light)
• Electromagnetic energy
• Ultrasound
• Packaging (excluding air and limiting oxygen)
• Modified atmosphere (filling with CO2 of NO2)
Physico/chemical hurdles:
• Water activity
• pH
• Redox potential
• Salt —> nitrite, nitrate
• CO2
• O2
• Organic acids (in particular lactic acid)
• Smoke
• Sulphite, phosphates
• Ethanol
• Spices and herbs
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Lecture 16 – Food Preservation 2
• Radiation
Microbial hurdles:
• Competitive flora:
-Starter cultures —> Lactic acid bacteria give rise to reduced pH and hinder
the growth of other bacteria eg. Fermented dairy products such as yoghurt and
cheese. Lactic acid ferments sugars as produces a low pH environment as it does so
which is not favourable for other bacterial growth.
-Bacteriocins —> toxins (proteins) produced by bacteria that inhibit the growth
of closely related species/strains. They can be considered narrow spectrum
antibiotics.
-Antibiotics —> produced by competitive flora (or are artificially added). They
have a brand spectrum of antimicrobial activity.
• Difference between bacteriocins and antibiotics:
-Bacteriocins are proteins
-Bacteriocins are high molecular weight and antibiotics are low molecular weight.
Hurdle technology example: Fermented (used) meat products
1. Add salts to mixture —> Sodium nitrate inhibits the growth of certain microbes.
2. Oxygen levels decrease so aerobic bacteria die off
3. Other bacteria that are anaerobic (lactic acid) thrive and lower the pH
4. Low pH inhibits the growth of other microbes as well.
• Hurdles in this process:
-Salt and nitrite —> Physico/chemical hurdles
-Change in redox potential —> O2 drops
-Competitie microflora
-pH —> acidification from lactic acid
-Water activity decreases
Non-thermal Preservation technologies - modern methods
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Document Summary
Physical hurdles: temperature: pressure, light (pulsed light, electromagnetic energy, ultrasound, packaging (excluding air and limiting oxygen, modified atmosphere (filling with co2 of no2) Physico/chemical hurdles: water activity, ph, redox potential, salt > nitrite, nitrate, co2, o2, organic acids (in particular lactic acid, smoke, sulphite, phosphates, ethanol, spices and herbs. Lecture 16 food preservation 2: radiation. Starter cultures > lactic acid bacteria give rise to reduced ph and hinder the growth of other bacteria eg. fermented dairy products such as yoghurt and cheese. Lactic acid ferments sugars as produces a low ph environment as it does so which is not favourable for other bacterial growth. Bacteriocins > toxins (proteins) produced by bacteria that inhibit the growth of closely related species/strains. Antibiotics > produced by competitive flora (or are artificially added). They have a brand spectrum of antimicrobial activity: difference between bacteriocins and antibiotics: Bacteriocins are high molecular weight and antibiotics are low molecular weight.
