Acids

Origin

Acids are abundant in nature in both organic and inorganic forms. Organic acids made up of only Carbon, Hydrogen and Oxygen are mostly used in food applications.

Organic acids such as fumaric acid, a powerful antimicrobial agent and acidulant, and inorganic acids such as phosphoric acid, can be artificially synthesized under controlled reaction parameters in chemical plants. Inorganic acids are also found in nature.

Citric acid, an organic compound, is naturally present in all citrus fruits such as grapefruit, pineapples, peaches, oranges, lemons, and limes.

Function

If an acidic ingredient is included in a recipe, an alkali ingredients known as a base must balance out the acid. The addition of an acidic substance into a primarily basic substance causes the basic substance to weaken or to become neutralized. In baking, neutralization of leavening acids occurs according to the following reaction:

HX + NaHCO3 → NaX + H2O + CO2     X: non-metal or hydrocarbon chain

Leavening acid + baking soda (in the presence of moisture and release of heat) will produce neutral salt + water + carbon dioxide.¹

Acids play a vital role in baking. In the production of cakes, the carbon dioxide produced during leavening is responsible for the expansion of the batter resulting in the cellular structure of the baked product. In bread, acids in sufficient amounts boost yeast fermentation rate, and extend shelf life of baked products.

Commercial production

Organic acids can be obtained from the following processes:

• Chemical oxidation of aldehydes under controlled parameters. When obtained, they are referred as carboxylic acids, and are identified by containing a carboxyl group which is a combination of a carbonyl group and a hydroxyl group.
• Biotechnological synthesis. Vinegar and citric acid are commercially obtained by fermentation. Acetobacter aceti converts ethanol to acetic acid under aerobic conditions, and citric acid is produced by microbial fermentation of molasses by fungi Aspergillus niger.

Application

Acids add a sour note when such flavors are desired. Sour milk products, lemon juice, and fruit products are acids used in the baking industry to enhance flavor and add a sharp taste, or balance flavors of sweetness such as in sourdough bread, raisin bread, and turnovers or pastries.

• Tartaric acid is a naturally occurring inorganic product obtained as a by-product from winemaking. It is commonly added in confectioneries to regulate the pH in the food. In bakery products, it may be used in icings and fillings as a chelating agent. It is also found in cream of tartar, a leavening acid.
• Citric acid, a three-carbon, three-carboxylic acid, is used primarily as a flavoring agent or acidulant. Citric acid and its salts are also used in the production of sourdough bread, helping create the distinct sourdough flavor.
• Lactic acid, a three-carbon compound, is present in appreciable quantities in sour or fermented milk. Also used in bakery formulations.

The following table presents some acids used in baking as leavening acids:

*Neutralizing value: Parts by weight of baking soda (sodium bicarbonate) from which 100 parts by weight of leavening acid will release all the available CO2, achieving neutralization.

References

1. Miller, R. “Leavening Agents” Encyclopedia of Food and Health, Elsevier Ltd., 2016, pp. 523–528.
2. Delcour, J.A, and Hoseney, R.C. “Chemically Leavened Products” Principles of Cereal Science and Technology, 3rd edition, AACC International, Inc., 2010, pp. 177–180.
3. U.S. Food and Drug Administration. “21 CFR 184 – Direct Food Substances Affirmed As Generally Recognized As Safe.” 1 Apr. 2017, https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?CFRPart=184. Accessed 16 May 2018.
4. U.S. Food and Drug Administration. “21 CFR 182 – Direct Food Substances Affirmed As Generally Recognized As Safe.” 1 Apr. 2017, https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?CFRPart=182. Accessed 16 May 2018.