Why do they put mint in toothpaste? Would garlic be better?

GCSE: Chemistry

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Biological Knowledge:
Plants are susceptible to infections by bacteria and fungi; they do everything to repel one another. Several plants are known to or even thought to inhibit the growth of certain bacteria. A plant with such properties is known as an antibacterial. Chemicals within them are toxic to bacteria and interfere with the metabolism in some way. In order to protect themselves they produce anti-bacterial and anti-fungi agents. Garlic is said to be used to treat infections with bacteria, yeast, fungi, and parasites, and can be used to treat high blood sugar levels. They also say it has properties that may help stomach and abdominal problems. The use of garlic has also been claimed to reduce risk of heart disease, lower serum cholesterol, and reduce blood pressure.
Toothpastes have flavours to make them more palatable. Mint is the most common flavour used because it imparts a feeling of freshness. This feeling of freshness is the result of long term conditioning by the toothpaste industry. The American public associates mint with freshness. There may be a basis for this in fact; mint flavours contain oils that volatize in the mouth's warm environment. This volatizing action imparts a cooling sensation in the mouth. The most common toothpaste flavours are spearmint, peppermint, wintergreen, and cinnamon. Some of the more exotic toothpaste flavours include bourbon, rye, anise, clove, caraway, coriander, eucalyptus, nutmeg, and thyme.
Variables:
Dependent - amount of bacteria killed
Independent - plant material on the Whatman antibiotics assay paper disc.
Controls - Temperature of incubator, volume of plant material used, time left to kill bacteria.





Method:

1 Agar plates seeded with suitable bacteria need to be prepared. This may have been done for
you in advance; if not, follow the instructions below Pouring agar plates. The
Practical Support has a sheet on plate pouring and aseptic technique.
2 Obtain a plant extract by crushing 3 g of plant material with 10 cm3 of industrial methylated
spirit and shake it from time to time for 10 minutes. The advantage of using methylated spirits
instead of water is that it kills any bacteria that might otherwise contaminate the extract.
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