Concept 04 / 05Chemistry in Everyday Life
Chemicals in Food: Preservatives, Artificial Sweeteners and Antioxidants
Why chemicals are added to food, food preservatives (salt, sugar, oil, sodium benzoate, salts of sorbic and propanoic acids), artificial sweeteners (saccharin, aspartame, sucralose, alitame) with relative sweetness and stability, and antioxidants (BHT, BHA, sulfur dioxide and sulfite).
Chemicals are added to food for preservation, to improve appeal and to add nutritive value. Such additives include colouring and flavouring agents, sweeteners, fat emulsifiers and stabilisers, flour improvers (antistaling agents and bleaches), antioxidants, preservatives, and nutritional supplements (minerals, vitamins and amino acids). Except for the nutritional supplements, none of these has nutritive value.
Food preservatives prevent spoilage due to microbial growth. Table salt, sugar and vegetable oils are traditional preservatives (salt and sugar work by osmotically dehydrating microbes). Sodium benzoate, , is used in limited quantities and is metabolised in the body by conversion to hippuric acid, , which is excreted in urine. Salts of sorbic acid and propanoic acid are also used.
Artificial sweetening agents. Natural sweeteners such as sucrose add to calorie intake, so artificial sweeteners are widely used, especially by diabetics.
Saccharin (o-sulfobenzimide): about 550 times as sweet as cane sugar. It is excreted unchanged in urine, inert and non-toxic, and was the first popular artificial sweetener; valuable for diabetics.
Aspartame: about 100 times as sweet; it is the methyl ester of a dipeptide of aspartic acid and phenylalanine. It is unstable at cooking temperatures, so its use is limited to cold foods and soft drinks.
Sucralose: a trichloro derivative of sucrose, about 600 times as sweet. Its appearance and taste are like sugar, it is stable at cooking temperatures, and it provides no calories.
Alitame: a high-potency sweetener, about 2000 times as sweet; because it is so potent, controlling the sweetness of food is difficult.
Antioxidants retard the action of oxygen on food, preventing rancidity of fats and oils. They are more reactive towards oxygen than the food, so they are oxidised first (they react with the free radicals that propagate oxidation). The most common are butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA). Adding BHA to butter increases its shelf life from months to years. BHT and BHA are sometimes combined with citric or ascorbic acid for a more active effect. Sulfur dioxide and sulfite are antioxidants for wine and beer, sugar syrups and cut, peeled or dried fruits and vegetables.
Key Takeaways:
- Sodium benzoate is metabolised to hippuric acid; sorbates and propanoates are also preservatives.
- Relative sweetness: aspartame 100, saccharin 550, sucralose 600, alitame 2000.
- Aspartame is not heat-stable; sucralose is.
- BHT and BHA are antioxidants; and sulfite protect wine and fruit products.
- Pitfall: except for nutritional supplements, food additives have no nutritive value.
Brain-Teaser 1: A recipe needs of cane sugar. What mass of saccharin would give the same sweetness?
Solution: Saccharin is about 550 times sweeter, so is needed, with essentially zero calories since it passes out unchanged.
Brain-Teaser 2: Why is aspartame avoided in baked sweets but sucralose is used?
Solution: Aspartame is a dipeptide ester; at baking temperatures its ester and peptide links break down, so its sweetness is lost. Sucralose, a chlorinated sucrose, is stable at cooking temperatures and keeps its sweetness.
Brain-Teaser 3: How does BHA protect butter from going rancid?
Solution: Rancidity is autoxidation, a free-radical chain reaction of unsaturated fats with oxygen. BHA, a hindered phenol, gives up its O-H hydrogen to the chain-carrying radicals, forming a stable, unreactive phenoxy radical. This breaks the chain, so the fat is spared.
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