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Week 11: Antimicrobial Agents (AMA) & Acidulants - Coggle Diagram
Week 11: Antimicrobial Agents (AMA) & Acidulants
Antimicrobial Agents (AMA)
deploys other “Agents” too :check:
Processing Agents
Heating
Freezing
Packaging Agents
MAP
Aseptic
Generally Bacteriostatic rather than Bacteriocidal
Bacteriostatic: stops bacteria from reproducing
Bacteriocidal: kills bacteria
Consist of both acid & non-acid types
Acidic AMAs most common
Factors Affecting Microbial Growth :check:
F00d - Nutrients
Food rich in proteins and carbohydrates offer more nutrients for microbes to grow
Food high in fat may have less nutrients for mcirobes
Acidity - pH
Usually pH 4-5 or below to inhibit most microbial growth
Temperature
5-60 Cel is the danger zone where food deterioriation is fast when microbial growth is favourable.
Time
Usually, food cannot be stored at ambient temperature for more than 4 hours or below. Beyond the time limit, microbial load will be too high. Microbes can double their population for approximately every 20 minutes
Oxygen
Most microbes need oxygen and moisture, exposure allows them to grow.
Moisture
Factors Affecting The Selection of AMA :check:
AMA activity against different organisms
Some AMAs affect specific microbial types such as yeasts.while some affect a wide range of microbial species
Initial microbial load in product
With small load, it may not be suitable to add AMA. Otherwise, with high initial load, it may be suitable to add AMA
pKa of the AMA - acid dissociation constant at logarithmic scale
pH of the food product
Food composition
Includes the nutritional value of food
Processing, and storage conditions
AMA is not needed for products processed by UHT or retort sterilization. There is no need to add AMA for products meant to be stored in freezers or chillers.
Solubility of AMA
If not soluble in water, it can form residues in the product. Alternatively, It can be in the form of sodium/ potassium salts to aid in solubility
Flavor
Does it impart flavour?
Cost
Price varies with different AMAs
Marketing impact
Consumers are concern about use of preservatives. They are more likely to purchase prodcts without them
Procedure In Selecting A Suitable AMA :check:
Must know
what organism the AMA
is effective in and
the initial load
of the product.
pKa and solubility of the AMA & pH of the food must be known.
Interaction with other processes to ensure AMA is functional over time.
Condition of storage of the product.
Freezing products usually do not need AMAs because they cannot reproduce at all, they also have long shelf life. AMAs may be added in chilled products
Includes high temperature and pressure. Does AMA remain functional, interact with these processes and cause unwanted changes? (eg precipitation, discolouration of product...)
Principles For Using AMA :check:
Most agents are weak acids: partially ionised in water
They are usually not corrosive, thus less harmful
Most work when in the unionized form.
Most are not effective above their pKa's.
Most affect flavour.
Most are affected by processing, order of addition – distribution between oil and aqueous phase
Order of addition: It is usually added early. AMA need water to solubilize. If it is added as one of the last ingredients, AMA may not dissolved due to inadequate free water.
Much water is bound to ingredients such as proteins added earlier on
Processing: AMA must be thermally processed with the other ingredients. It should not be added after pasteurization.
Henderson-Hasselbach
Modified
Self-Made “Rules”
This is a log relationship so a little change can mean a lot.
AMA are only used when pH is at or below to their pKa. (pH < pKa)
At pH = pKa, only 50% of the AMA will be effective.
When the pH is 1 unit less than the pKa, then about 90% is in the effective form.
When the pH is 1 unit more than the pKa, only about 10% is in the effective form. Forget about it!
Commercial examples
Most Common AMA’s :check:
Sorbic Acid and Sorbate
pKa = 4.8
Usage level limited to 0.1%.
Broad spectrum against yeast and molds, lactic acid bacteria at low pH.
Major usage in salad dressings, fruit juices, cottage cheese.
Available forms:
Calcium/Potassium/Sodium sorbate
Potassium salt is the most widely used form.
Sorbic acid
Acetic Acid
pKa = 4.76
Usage level limited by taste.
More effective against yeast and bacteria.
Major usage in “pickled" foods
Preservative labeling may not be required
Common types:
Sodium acetate
Sodium diacetate in some bread
Propionic Acid And Propionates
pKa = 4.87
Usage limited to 0.1%.
Effective against molds, but not on yeast.
Major usage in bread and baked goods.
Common types
Calcium propionate/Sodium propionate
Calcium salt most used form, especially in breads
Sodium salt is usually used in products high in oil such as cakes and cookies
Propionic acid
Sulphur Dioxide And Sulphate
pKa = 1.89, 7.0
Effective against moulds, yeast, bacteria.
Yeast are more resistant than lactics
Major usage in wines.
Used often for its anti-browning & color stabilization characteristics.
Flavour problem, hypersensitivity.
May trigger asthma and some respiratory issues
Common types
Potassium bisulfite
Sodium metabisulfite
Sodium sulfite
Sodium bisulfite
Sulphur dioxide
Nitrite
Effective against Clostridium botulinum.
Used in cured meat products.
However, when the meat are barbecued, the compounds can become carcinogenic
Reacts with myoglobin to give cured meat color
Nitrate is not an anti-microbial agent unless it is converted to nitrite
Common types:
Potassium nitrate/Sodium nitrate
Sodium nitrite
Parabens (Methyl-, Propyl-, Heptyl-)
pKa = 8.47
Usage level limited to 0.1%.
Effective against yeast and molds, gram (+) bacteria.
Longer chain esters are more effective.
Heptyl > Propyl > Ethyl > Methyl.
Usage is not usually shown by food labels.
Found in artificial sweeteners, baked goods, some salad dressings, beer.
Common types
Heptylparaben
Methylparaben
Propylparaben
Benzoic Acid and Benzoate
pKa = 4.2
Most active against yeast and molds.
Usage level limited to less than 0.1% by regulation.
Major uses in beverages, juices, jellies, margarine, sauces
Common types
Benzoic acid
Acid form relatively Insoluble and not used much.
Sodium benzoate
Other AMA’s :check:
Acidulants eg. Citric/Malic/Lactic acid.
Chlorine dioxide.
Dimethyl dicarbonate - yeast spoilage in wine
Nisin produced by bacterium Lactococcus lactis, effective against Gram (+) bacteria.
Ozone (O3)
Lysozyme (enzyme) - Gram (+) bacteria
Inappropriate Uses of AMA :check:
Addition to frozen products
Addition to dried products
Addition to heat sterilized products
Addition to cover-up poor sanitation
Addition to foods with the wrong pH
Acidulants
widely used in food both modern and of yesterdays.
2 types
Organic acid – acetic, citric, fumaric, lactic, malic, succinic and tartaric acid.
Inorganic acid – phosphoric acid (coke).
Functions :check:
Flavour modification :check:
Intensify flavours
Citric acid / malic acid in fruit juices
Butyric acid
High concentration → rancid flavour
Low concentration → cheese/butter flavour
Sucrose sweetness is increased by lactic, malic & citric acid.
Add sour or tartness taste
To balance the excessive sweetness in confectionary.
A good balance achieves full potential of the flavour.
The ratio of sweetness to tartness = Brix acid ratio.
Different acids give different levels and type of tartness
Tartaric acid in grape flavoured foods
Phosphoric acid in cola drinks.
Interaction of NaCl2 reduces sourness of acetic & citric acid
Buffering / pH control: Control pH of foods during processing and finished product. :check:
Essential in optimum development of gel character & strength in gelatine desserts, jams, jellies and candy e.g. citric acid in jelly making.
Pectin
Certain pH is needed to prevent watery texture in jams. Aid in solubilisation of hydrocolloids that contribute to the gel texture
Leavening :check:
Chemical leaveners are mixtures that releases CO2 gases when they react with moisture and heat.
In baked products, beverages and effervescent tablets, the leavening agents depend on the acidity to interact with alkali which gives off gas.
Preservation :check:
Prevents growth of microbes and germination of spores in foods by lowering the pH of food product.
Acid is needed for AMAs e.g. benzoates, sorbates and propionates to be effective.
AMA works well in acidic conditions
As sterilising acid (shorten sterilising time)
As anti-browning agents / antioxidant to maintain flavour, colour and texture of canned fruits.
As a chelating agent by binding to metal ions
Antioxidant / chelating agents :check:
Prevents undesirable reactions eg. discolouration, rancidity and instability of nutrients by chelating with free metal ions in food products or during processing eg. citrates and phosphates
Viscosity modification :check:
Alters softening, melting points and texture of cheese, margarine and hard candy mixtures.
Rich in proteins. Acid reacts with proteins to denature and coagulate, affecting texture
Influences rheological properties of dough by reacting with gluten proteins e.g. succinates and acetates
Lowers the pH to 3.0. Increased hydration of gluten for a more tender bread
Applications
Beverages
Applications: alcoholic, carbonated, still, powdered and nutritional.
Functions
Balance flavour and impart tartness
Inhibit microbial spoilage
Chelate metal ions that could catalyse harmful reactions.
Cereal & baked products
Functions
Act as leavening aid
pH control
dough conditioning
Applications
Baking powders
Prepared baking mixes
Refrigerated dough. (tend to be dry and hard)
Confectionery
To enhance the flavouring in candy, gums and jellies.
Commonly added acids:
citric and malic acids due to their solubility and tartness
tartaric acid for grape flavoured products.
Dairy products
Interact with milk proteins
Rate of gelation of milk (for yoghurt, cheese, condensed and evaporated milk) directly proportional to Calcium ions concentration and milk-solids-non-fat content.
Desserts
Functions
To control pH in for optimum setting
impart tartness,
applicable for gelatine desserts, jams, jellies and preserves.
Pectin, a hydrocolloid. Citric acid + Pectin. The acids must be added after cooking to prevent sucrose inversion and acid hydrolysis.
Meat & seafood products
Processing
Increase meat tenderness
Improve protein binding
Retain moisture
Preservation
Retain flavour and colour
Prevent microbial spoilage
Enhance the action of antioxidant.
