Food Preservation Flashcards
Define food preservation?
The treatment of food to prevent or delay spoilage and inhibit growth of pathogenic organisms which would render food unfit.
List and define the principles of food preservation.
- Inhibition: this involves the prevention of the growth of microorganisms that can spoil food
- Inactivation: involves destroying microorganisms that can spoil food.
- Avoid recontamination: involves preventing the growth of microorganisms that can contaminate food after preservation.
What are some examples of the different methods that fall under the preservation principles?
- Inhibition: low temp storage, reduction of water activity (Aw), decrease O2 increase CO2 vaccum, acidification, fermentation, freezing
- Inactivation: sterilization, pasteurization, radiation, high pressure, blanching, cooking
- Avoid recontamination: packaging, hygienic processing, hygienic storage, aseptic processing
What are the different ways foods can be preserved?
- Chemical
- Biological
- Physical
What does chemical preservation involve?
Chemical preservation inhibits, retards or slows food decomposition (both chemical or microbiological deterioration)
Chemical preservation involves microbial inhibitors, antioxidants, acidulants and sequestrants
Discuss organic acids and the ways they are used as preservatives.
- Occur widely in nature
- Several are permitted in foods such as Benzoic, propionic, sorbic, citric, lactic and acetic acid
- these are inhibitors of yeast and moulds in cheeses, bakery products, fruit juices etc
- Undissociated acid has a greater inhibitory effect. Undissociated acids cross cell membrane, dissociate inside due to shift in pH and decrease cellular pH and electrochemical gradient.
- The disruption of cell membrane activity inhibit uptake of substrate molecules and especially amino acids
What are the advantages and limitations of organic acids?
Advantages:
- Compatible with other preservatives
- Some combinations are synergistic (sorbic acid or benzoic acid + NaCl or sucrose)
Limitations:
- Ineffective at high microbial levels
- Many microbes are capable of metabolizing them
- Some microorganisms are resistant to acids
Discuss Benzoic Acid & Parabens used as preservatives.
- Benzoic Acids ( C6H5COOH):
- Occurs naturally in some foods like cranberries
- used to inhibit the growth of yeast and mould in high acid foods such as fruit juices, pickles, soft drinks, dressings etc.
- It is most effective between pH 2.5 - 4.0
- Maximum level of 0.1% because used in excess it causes unpleasant burning taste.
-Parabens:
*These are esters of benzoic acid
* Antibiotic activity less sensitive to pH (effective up to pH 8.0)
Discuss how nitrates and nitrites are used as preservatives.
- both used in curing meats
- Adds to the flavour and it stabilizes the red meat colour.
- plays a role in the inhibition of spoilage and pathogenic bacteria, especially Clostridium botulinum.
- Other processes are used in conjunction with nitrates and nitrites such as fermentation, smoking, drying etc.
What is the most important attribute of nitrites?
The inhibition of C. botulinum
What are the effects of nitrates and nitrites on C. botulinum?
- Inhibits cell growth and prevent germination and growth of spores.
- This inhibition is an interaction of sodium chloride, sodium nitrite, pH , degree of cooking, initial number of spores present and storage temperature
- Nitrate interferes with iron sulphur enzymes such as ferredoxin and prevents synthesis of ATP
What is the Perigo Effect?
The Perigo Effect has to do with when nitrite is heated in a lab medium and the substance created was 10x more inhibitory to Clostridia than the nitrite level present alone.
What are the limitations/disadvantages of nitrates and nitrites?
- Reactions with secondary amines to form carcinogenic nitroso amines
- Can be toxic in high concentration so levels kept to minimum
- Gradually disappear during storage
Sulphur dioxides are normally present is what forms?
- Gaseous
- Liquid
- Salts
List the foods that sulphur dioxides are used in.
- Dried fruits
- Lemon juice
- Molasses
- Wines
- Fruit juices
Why/How is sulphur dioxide/sulphite used in food preservation?
- Sulphur dioxide has antimicrobial as well as antioxidant properties
- Used in dehydration of some foods to prevent enzymatic browing
- Active against bacteria such as salmonella and moulds
- The actual mechanism of action is unknown
Describe chemical preservation using sugar and salt.
- These preservation techniques reduces the available water for growth
- Sugar acts in a similar way to salt but needs about six times more to have the same effect.
- The effectiveness depends on concentration and are also affected by:
1. Water content
2. Contamination levels
3. pH
4. Temperature
5. Protein content
6. Presence of other inhibitory substance
What are food sanitizers?
- These are not food additives, but aid in preservation by reducing bacterial load.
- The desirable objective is to effect a 5-log reduction of pathogen
What are some food sanitizers used in food preservation?
- Acidified sodium chlorite - citric or phosphoric acid + NaCl
- Electrolyzed oxidizing water - 2-5 log reduction achieved by extreme oxidation reduction potential of water
- Activated Lactoferrin (ALF, Activin) - Lactoferrin immobilized on polysaccharide in citric bicarbonate buffer; chelate Fe2+, binds to cell surface proteins of gram neg. bacteria, interact with nucleic acids, inhibits growth and neutralizes endotoxins
- Ozone - Powerful oxidant, no residue left after treatment
- Hydrogen Peroxide (H2O2) - Strong oxidant
- Chlorine and other agents - Strong oxidant
How are Ethylene and Propylene oxides used?
- used as fumigants for foods
- Foods such as dried fruits, nuts, spices
- Mainly used as antifungal compounds. The hydroxyl ethyl radicals are formed which blocks reactive groups in proteins (this disrupts biological processes and microbial activity thereby extending shelf life of products)
- Effective against vegetative and endospores
