Microbes and food 1. Menu - you are what you eat
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Tomatoes photo
Picture 1.19a Although you might not immediately think so, tomatoes are a fruit.

1.19 Fruit
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What are they?
Fruits are the parts of a plant which produce seeds. They include citrus fruits, apples, pears, plums and compound fruits such as berries. Tomatoes, cucumbers and olives are really fruits, although they are often classed as vegetables. Fruits are often eaten raw, although they can be canned, frozen or dried to extend storage life. Fruits carry a natural flora of micro-organisms acquired from their environment.
How do they spoil?
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Fruits can be contaminated with microbes from the soil, the air, water or animal wastes. The high water content and acidity (low pH) favour the growth of fungiyeasts and moulds.

Whilst still on the plant, fruits can be infected by pathogenic microbes which cause wilts, blotching and browning. Once harvested care has to be taken in handling as bruising can allow the entry of harmful organisms, particularly fungi, which soon rot the product. The green mould sometimes seen on oranges is a type of Penicillium; Botrytis causes the fuzzy grey growth on strawberries.

Mouldy peach photo
Picture 1.19b A mouldy peach.

Washing, dipping or wrapping fruit in paper that has been impregnated with preservative is sometimes used to prolong storage life. Refrigeration and controlled atmosphere packaging also allow fruit to be kept for several months before being sold – this is how fruit from all around the world can appear on our supermarket shelves.

Dishes such as fresh fruit salad contain sugar syrup. If not eaten quickly, yeasts from the air soon get to work and ferment it.

Can it be harmful?
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Food poisoning is rarely caused by eating fruit, although pathogenic bacteria can sometimes get on them from the soil and manure. Some intestinal virus diseases have been spread on fruit due to contamination from human faeces either during or after harvesting. Washing and good hygienic practices should prevent this.

Mould growth can produce poisons known as aflatoxins in certain fruits. For example Penicillium expansum and other fungi on apples cause the formation of patulin which can get into the fresh juice. It is not a good idea to eat mouldy fruit.