“moulds are not that dangerous to human health, mainly because large colonies make them easy to spot”
Science
Why food decomposes
Take a closer look at the microscopic world of food spoilage now Micro-organisms are one of the biggest culprits for the spoilage of food; they feed on the nutrients, breaking them down into small molecules that can be absorbed across their cell walls. This destroys the structure of the food and produces by-products that smell and taste unappetising and – eventually – makes the food unfit for human consumption. Mould produces the most visible changes to food. The branching filaments of mould are called hyphae, and their growing tips make enzymes, which break down tough molecules like cellulose and starch, converting them to mushier material. This causes the spongy feeling of decaying fruit and vegetables. The spots of mould seen on food represent huge colonies of interconnected hyphae, which advance over the surface seeking nutrients. Moulds are actually not that dangerous to human health, mainly because their large colonies make them very easy to spot and avoid. The real danger comes from bacteria, which replicate virtually unseen. Signs of bacterial infection of food include discolouration, odour and a surface slime, but even before these changes are detectable, harmful numbers of bacteria can be present. Not all decomposition is down to microorganisms though. Foods contain natural enzymes used during the lifetime of the plant or animal to catalyse reactions. Even after death the enzymes are still functional and contribute to the gradual breakdown of the product. This is particularly obvious in fruit like apples and bananas, which go brown when cut surfaces are exposed to oxygen; this is the result of an enzymatic reaction that produces the brown pigment melanin. Some foods are so hostile to microbial growth that they do not go off at all. This is often down to water content and osmosis. Microbes require relatively moist environments to thrive, so dried foods, or foods very high in salt or sugar, usually remain good for much longer periods of time. Indeed, honey that’s still technically edible has been retrieved from the tombs of Ancient Egyptian pharaohs buried around 5,000 years ago.
022 | How It Works
When food turns bad… What happens to a lemon as it goes mouldy?
1. Waxed The skin of lemons is often waxed to prevent evaporation. It provides a barrier that inhibits gas exchange and also helps to protect the fruit from mould.
3. Feeding The tips of the mould hyphae secrete digestive enzymes, which break down the nutrients in the lemon.
5. Penicillium Green moulds are usually of the Penicillium family – the moulds responsible for making the antibiotic penicillin.
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