• The acid in citrus fruits gives them their tart flavor.Jupiterimages/Photos.com/Getty Images
  
  Fruit is one of nature's greatest gifts. High in vitamins, antioxidants and other nutrients, many fruits are also low in fat and other harmful substances found in foods, making them an ideal snack or addition to a meal. Some fruits have a high acidity level, particularly citric acid. Though it can be rough on tender stomachs, acid gives fruits an intense and often sour taste, adding flavor without adding carbs or calories.
  
  

Lemon

• Lemons can be used for food, pressed for oil and used as an astringent.lemon image by Edsweb from Fotolia.com
  
  High in citric acid, lemons are a common fruit with many uses. According to Purdue University, lemon trees range from 10 to 20 feet in height and have thorny branches which feature white and purple blossoms. The fragrant, tart fruits of the tree are 2 3/4 to 4 3/4 inches in length and have a bright yellow peel lined with pith and dotted with small oil glands. The meat of the fruit is light yellow, extremely sour in taste and divided into several segments containing seeds. Some varieties of lemon may have white peels or be seedless, and there are more than 200 types of the fruit. Lemon can be squirted onto seafood for extra flavor and dried lemon slices make a fragrant addition to potpourri.
  
  

Tomato

• Tomatoes with a higher acid conent have a stronger flavor.tomatoes image by rufar from Fotolia.com
  
  Though some varieties of tomato are low in acid content, others are moderate to high. North Carolina State university says that "low sugar/high acid tomatoes are tart, high sugar/low acid tomatoes are bland and low sugar/low acid tomatoes are tasteless," making more acidic tomatoes a good choice for dishes that need a kick, like pasta sauce or salads. Most red tomatoes contain more acid than yellow, white or other color varieties. A healthy fruit, tomatoes are high in vitamin C, vitamin A and potassium. Tomatoes also contain the antioxidant lycopene, which has been shown to fight cancer-causing free radicals in some studies.
  
  

Limes

• Limes are low in calories and high in vitamin C.limes image by dethchimo from Fotolia.com
  
  Often considered a counterpart to lemons, limes have a round shape and a thin green peel which may be smooth or nobbled, depending on the variety. Purdue University explains that limes grow on evergreen trees which can reach 20 feet in height and are covered in thorns which bear small white blossoms. World's Healthiest Foods states most limes have a diameter of 1 to 2 inches and pale green flesh which derives its tart flavor from citric acid. Limes are also low in calories but high in vitamin C, and their juice can be added to dishes to give them a tart flavor, and the zest from lime peels also imparts a mild, fruity essence. In Asian cuisine, the leaves of lime trees are used to impart a citrus flavor into soups and stews.