1. Searching for the Most Acidic Citrus

    Every citrus fruit contains organic acids, such as citric acid and ascorbic acid, also known as vitamin C. Yet limes or lemons taste quite acidic while oranges or mandarins are on the sweet side. Which among citrus fruits is the "world champion" in acidity? Is there a correlation between acid taste and pH-levels? Are there variations in pH for the same citrus fruit grown in various countries, regions or climate zones. Those questions will be explored in this activity.

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    Searching for the Most Acidic Citrus

    Limes, lemons, grapefruit, oranges, mandarins and many similar plants belong to the plant genus Citrus. These plants were cultivated since ancient times, mostly in hot climate. One of the many uses of citrus fruits is medicinal, as they have high levels of vitamin C, ascorbic acid – a powerful chemical that does many important things for our health. A deficiency in ascorbic acid is called scurvy.

    No one doubts that lemons are sour. It is likely that all lemons in the world taste acidic. Are there acidity champions among them? Their taste is hardly the right way to judge. Taste can be misleading. To find a champion requires a special instrument: the best suited instrument is a digital probe. In this project we will work together to identify the most acid among citrus fruits. 

    While you are searching for an "acidity champion", it would be interesting to hear your thoughts on why it might be useful for a citrus fruit, e.g., lemon, to taste sour. After all, it is generally thought that the fruits of various plants attract animals with their sweet taste so that the animals eat the fruit, and release and scatter the seeds enclosed in the fruit. Is it possible for a sour taste to be attractive to some animals, so they actually eat them for the sour taste?

    Think what could be the evolutionary role for lemons that no one wants to eat them. Maybe in their homeland in dry climates lemons should not be eaten, but instead retain moisture so that their seeds can germinate.  Let's run the Acidity World Cup in search for the most acid citrus!

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