Juicing

Fruits and vegetables have cell walls made of cellulose, which is the same material wood is made of. The fluid that travels between the cells -- juice -- serves as the plant’s blood. For softer fruits, such as tomatoes, apples, melons, citrus and berries, you can remove the juice from the flesh by squeezing or reaming; this is known as juicing. What remains afterward is the juice and the remains of fruit’s cellular walls, or pulp.

Blending

The juice for harder fruits and vegetables must be freed by mechanically obliterating the cell walls, usually with a blender. The resulting mass – called puree -- can then be strained to separate the juice or it can be kept together. Use purees to introduce produce into sauces and baked goods or consume purees raw. When used as a sauce, a puree is referred to as coulis.

Differences

Juice is the essence of the fruit. It is mostly water and sugar with the vitamins and minerals the plant used while it was alive. As such, juice is highly nutritional, but it also provides an immediate carbohydrate hit -- particularly, with high-fructose fruits -- as the sugar in the juice is almost immediately absorbed into your bloodstream.

Purees, on the other hand, contain the whole vegetable or fruit in liquid form. Besides being thicker, puree also has the fiber that came from the plant’s cell walls, which will slow down your sugar absorption. As the puree consists of the whole fruit, most purees taste more like the original fruit or vegetable than juice does. The fiber in purees will also help you feel fuller for longer.

Comparisons

According to the U.S. Department of Agriculture, a cup of tomato juice has 41 calories, 1 gram of dietary fiber, 556 milligrams of potassium and 1,094 international units of vitamin A. In comparison, a cup of tomato puree has 95 calories, 4.8 grams of dietary fiber, 1,098 milligrams of potassium and 1,275 IUs of vitamin A.

Juice is sensitive to light, heat and oxidation and will start to lose nutritional value after 15 minutes in direct light. For use in cooking and baking, use blended fruits because they are more heat-stable.