does food relly give electricity

Does food really give electricity? what i will be testing is a lime, lemons, and potato's. I think that the lime will give the most electricity. The reason why i think the lime will give more electricity is because it has a lot more aside and fumes then the other foods i'M testing. What I will do is I will grab a lime a potato a lemon and I will grab a couple nails and then copper wire and a volt meter the copper around the nails and then a teach the meter to the copper wire and then see what gives more electricity. For my vinegar I got .61 for my apple .30 and for my banana .46 that is my project for the science fair thank you.