FOOD CHEMISTRY: FOOD ADDITIVES
Diagram
Two ways to keep food longer
Antioxidant
Stops oxidation. It protects fats and oils from attack by oxygen, so they do not go rancid.
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Preservative
Stops microbes. It inhibits the growth of bacteria, yeasts and moulds, so the food does not spoil or become unsafe.
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The key point
Both extend shelf life, but they fight different enemies: oxygen and microbes.
Figure 1: Antioxidants fight oxygen; preservatives fight microbes. Drawn in our own style from Hudson, Food Antioxidants, and the preservatives chapter of Coultate, Food: The Chemistry of Its Components. Note: this pair was flagged as chapter level and not yet verified in a dedicated search, and it was re-checked at build time through the Google Books pages for Hudson and Coultate, which cover the two roles separately.
Introduction
Antioxidants and preservatives both extend shelf life, but they fight different enemies. An antioxidant stops oxidation: it protects fats, oils and other food parts from attack by oxygen, so the food does not go rancid or lose colour and flavour. A preservative stops microbes: it inhibits the growth of bacteria, yeasts and moulds, so the food does not spoil and does not become unsafe. A food that needs both kinds of protection needs both kinds of additive.
Hudson covers antioxidants in Food Antioxidants, and Coultate covers preservatives among the minor components of food. This article follows those two books, and it states plainly where the books give no shared detail.
Quick comparison
Table 1: Antioxidant compared with preservative
| Aspect | Antioxidant | Preservative |
|---|---|---|
| Enemy | Oxygen and oxidation | Bacteria, yeasts and moulds |
| What it stops | Rancidity, off flavours, colour loss from oxidation | Spoilage and microbial growth |
| How it works | Intervenes in the oxidation chain, as Hudson describes, so oxidation is slowed or stopped | Inhibits microbial growth, by damaging the microbe or blocking its growth |
| Where it acts | In fats, oils and other parts that oxidise | Through the food and on its surface, where microbes grow |
| Typical level | Very small quantities, typically about 0.01 percent or less, as Hudson states | Small quantities, set by law for each preservative and each food |
| Natural examples | Tocopherols, ascorbic acid, phenolic compounds from plants | Salt, sugar, vinegar and smoke, in traditional preserving |
| Added examples | Butylated hydroxyanisole, butylated hydroxytoluene, tocopherols | Benzoates, sorbates, sulphites, nitrites |
| Effect on safety | Protects quality, not safety from microbes | Protects safety, by holding microbes back |
| Effect on flavour | Stops rancid and stale flavours from oxidation | Can add its own flavour, as with smoke or vinegar |
| If it is left out | Fat goes rancid and flavour and colour are lost | Microbes grow and the food spoils or becomes unsafe |
Scientific explanation
Definition
An antioxidant is a substance that slows or stops oxidation in food. Hudson states that antioxidants are present naturally in almost all food commodities, giving them protection against oxidative attack, and that they work in very small quantities, typically about 0.01 percent or less. A preservative is a substance that inhibits the growth of microorganisms in food. Coultate lists preservatives among the minor components of food, alongside colours, flavours and vitamins. The two are different in target, in mechanism, and in what happens when they are left out.
Working principle
Oxidation runs as a chain: oxygen attacks a fat molecule, makes a free radical, and that radical attacks the next fat molecule, so rancidity spreads. An antioxidant breaks the chain, as Hudson describes in the chapter on the mechanism of antioxidant action, so the spread stops. A preservative works differently: it enters the microbial cell or changes the food around it so the microbe cannot grow. The two mechanisms do not overlap, which is why a food can be protected from rancidity and still go mouldy, or be protected from microbes and still go rancid.
Apparatus
The books used here name no laboratory apparatus for telling the two apart, so no apparatus list is given.
Measurement procedure
The books used here name no single standard laboratory procedure for telling an antioxidant from a preservative. The distinction is made from the target: oxidation is followed by measuring rancidity and peroxide value, and microbial growth is followed by plate counts. The books give no worked food example with numbers for this comparison, so none is given.
Factors affecting readings
Light, heat, air and metals speed oxidation, so they raise the need for an antioxidant. Temperature, pH, water activity and the starting microbial load change how well a preservative works. Processing can deplete natural antioxidants, as Hudson states, so processed food usually keeps less well than the commodity it came from.
Formulas and calculations
The books used here give no formula for this comparison, so no formula or worked calculation is given.
Industrial applications
- Antioxidants are used in oils, fats, snacks and fried foods to stop rancidity.
- Preservatives are used in jams, sauces, drinks and cured meats to stop microbial spoilage.
- Antioxidants are used in dried foods and nuts, where fat oxidation is the main spoilage.
- Preservatives are used in bread and cakes to stop mould.
- Both are used together in processed foods that face both oxidation and microbes.
Advantages and limitations
- Antioxidant: advantage: stops rancidity and keeps flavour and colour. Limitation: does nothing against microbes, so the food can still spoil.
- Preservative: advantage: holds microbes back and keeps food safe. Limitation: does nothing against oxidation, so fat can still go rancid.
- Antioxidant: advantage: works at very small levels, about 0.01 percent or less. Limitation: natural antioxidants are depleted by processing, as Hudson states.
FAQ
Does an antioxidant kill bacteria?
No. An antioxidant stops oxidation. Only a preservative, or another antimicrobial step, holds microbes back.
Does a preservative stop rancidity?
No. A preservative stops microbes. Only an antioxidant, or keeping air out, slows oxidation.
Are salt and sugar preservatives?
Yes, in the traditional sense. They hold microbes back by lowering water activity, and they are not antioxidants.
Why does processed food need added antioxidants?
Hudson states that processing depletes natural antioxidants, so processed food usually keeps less well than the commodity it came from.
