Drinking fruit juice daily helps you stay fit and healthy and boost your immune system. Here's a list of the best manual citrus juicers that make juicing easy. When you hear citrus fruits- what comes to mind are? Oranges, grapefruits, limes, tangerines, and lemons. These fruits are an excellent source of vitamin C that greatly boosts the immune system, other outstanding health benefits of these fruits includes; good source of soluble fibers, which is known to lower cholesterol.