The organic acids in food, particularly acids in fruits and vegetables, vary enormously. However, a few principal acids act as the key players in producing unique flavor and even contribute to an increased chance of kidney stones, so awareness is essential.
Acids in Fruits
Some of the most common organic acids in food are found within fruits. Many people are already aware that citric acid occurs in citrus fruits such as oranges, lemons and limes, but there are lesser known acids in fruits that you may not have heard of. These include malic acid, which is found in apples, and tartaric acid found in grapes.
The pH scale is used to measure the acidity of food, with one end of the spectrum reading "acidic" and the other "alkaline." It counts from zero to 14, with zero being the most acidic and 14 the most alkaline. Foods that rest at 7 on the scale are considered neutral, whereas foods that feature a pH less than this are considered acidic.
These acids provide these fruits with that distinctive, sharp taste. The mixture of acid and sugar is what gives fruits their unique flavor, so foods will often be deliberately fermented in particular acids to retain or increase the flavor.
In addition to taste, acids in fruits are also used as preservatives due to their ability to reduce the onset of bacterial degradation. High acidity helps to kill bacteria so food doesn't spoil as quickly. Maintaining an ideal pH level within the food keeps it fresher for longer.
Many of the acids in fruits can provide benefits to your body if consumed in moderation, but some of the more specific benefits of each include:
- Citric acid: Found in the highest amounts in lemons and limes, it also occurs in many other citrus fruits such as oranges and grapefruits. However, what may be surprising is that a number of berries also include citric acid, including strawberries, raspberries and gooseberries. Due to its strong, sharp taste and high acidity, it is often used independently as a flavoring in various foods and drinks. Its key role in the body is the appropriately named citric acid cycle (or Krebs cycle) which occurs in all cells and is the process of releasing energy broken down from fats, carbohydrates and sugars.
- Malic acid: Predominantly found in apples, malic acid is also in a variety of fruits with stones at their center. This includes cherries, apricots, peaches and watermelon, despite watermelon being classed as an alkaline fruit. While all acids mentioned in this list feature a sharp taste, malic acid may have the strongest — for this reason, it is actually used to flavor the sour candies that are designed to overwhelm your palate. It is also used to give salt and vinegar-flavored products that distinctive taste. Similarly to citric acid, the body uses malic acid for a variety of cellular processes and as such, salts of malic acid are found in the cells of most living things.
- Tartaric acid: Though not as common as its counterparts citric and malic, tartaric is still a common acid found in foods, particularly in grapes and avocados. As with malic acid, it is sometimes used as sharp flavoring in sour candies, but its predominant use is in wine. Manufacturers include tartaric acid in their wines to increase the tartness of the wine's taste, thus providing it with a stronger and more distinctive flavor.
These are just three of the more predominant acids in fruits, but there are many others that play smaller roles in the body such as succinic, oxalic, benzoic, isocitric and quinic acid. A February 2018 study published in Horticulture Reviews found that fleshier fruits (such as berries, watermelon, peaches and other soft fruits) have the highest levels of key acids compared to their harder counterparts.
Acids in Vegetables
Many of the acids present in vegetables are also present in fruits — the key difference is that vegetables do not tend to be as acidic in their makeup, making them a potentially safer source of key acids if you struggle with acid reflux or high stomach acidity.
There is some crossover in the organic acids found in food. Both fruits and vegetables include citric acid (found in tomatoes, cayenne peppers and even lettuce), oxalic acid and benzoic acid (the oldest known food preservative).
Vegetables that are naturally low in pH acidity include:
- Green beans
- Greens (lettuce, kale, collards, spinach, etc.)
- Squash (summer or winter varieties)
Oxalic acid, also known by its chemical name ethanedioic acid, is a naturally occurring acid found in a wide range of vegetables. In its purest form, oxalic acid appears as a colorless, crystalized powder. When consumed in high doses, it imparts corrosive, bleach-like properties.
Luckily, it is found only in trace amounts in vegetables, so you don't need to worry about bleaching your stomach with a green veggie, but even in low amounts, oxalic acid forms into oxalates, which can have a distinct effect on your body.
Oxalates are known for binding to almost any mineral in the body, which does not ordinarily pose an issue due to the water solubility of these compounds. However, when oxalates bind with calcium, it is nearly impossible for the body to move the calcium oxalate through the system due to its close-to-insoluble state.
Oxalates build up insoluble compounds that can lead to kidney stones if precautions aren't taken. According to the Cleveland Clinic, adjusting your diet to eat less foods high in oxalic acid is the first step for reducing the risk of adverse effects.
Vegetables high in oxalic acid include:
The highest concentrations occur in dark, leafy vegetables such as spinach, kale and broccoli.
Acids in Dairy Products
Read more: Is Milk Alkaline or Acidic?
Cow milk produces a complex range of fatty acids, with over 400 individual fatty acids comprising its unique makeup. The flavor of dairy products is directly related to its content of fatty acids, similarly to the way lemons get their distinct taste from citric acid, and sour candies are flavored with malic acid. This correlation is especially true in the fermentation process to create stronger cheeses.
Despite dairy products' potentially high-fat content, when it comes to acidity, they are not so bad. An October 2011 study published in the Journal of the American College of Nutrition found that milk and dairy products neither produce acid upon metabolism nor cause metabolic acidosis. The study also found that the consumption of dairy products does not make the body acidic as a whole.
- Food and Agriculture Organization of the United Nations: "Chemical Composition"
- CK12: "Krebs Cycle"
- Compound Interest: "A Guide to Common Fruit Acids"
- Elmhurst College: "The pH Scale"
- Horticultural Reviews: "Oragnic Acids in Fruits"
- Greenend: "Citric Acid Intolerance"
- Food and Agriculture Organization of the United Nations: "Preservatives"
- Acidpedia: "Oxalic Acid"
- Cleveland Clinic: "Kidney Stones: Oxalate-Controlled Diet"
- Journal of the American College of Nutrition: "Milk and Acid-Base Balance: Proposed Hypothesis Versus Scientific Evidence"
- Physicians Committee for Responsible Medicine: "Health Concerns About Dairy"
- Nutrition Facts: "Dairy"
- Agriculture New York: "Acidity/Alkalinity (pH) Values of Various Foods"
- Vegetarian Society: "Protein"
- National Kidney Foundation: "Calcium Oxalate Stones"
- Journal of Animal and Veterinary Advances: "Changes of Lactic and Benzoic Acid Concentrations in Milk During Post-Collection Period"
- Separations: "Total and Free Fatty Acids Analysis in Milk and Dairy Fat"