I love to eat pineapple. [They are] It is sweet and sour at the same time so [they] it is very delicious.
Because a pineapple is a relatively large fruit and you are unlikely to eat a whole one at a time, we would use the singular ' . . eat pineapple'. Other smaller fruits, which you might eat one or more of, are plural e.g. I like to eat apples, plums, strawberries, etc.