Acids are substances that can neutralize alkalis to form salts. When dissolved in water, they release protons (hydrogen ions), reducing the pH and driving it lower than the neutral point of 7.1
They perform a variety of functions in foods and bake systems including acidification, buffering, preservation, gel setting, flavor development, leavening and many others. There are two classes:
Organic acids: referred to as weak acids which are composed of carbon, hydrogen and oxygen such as citric, ascorbic, lactic, malic, tartaric, and fumaric.
Inorganic acids: referred to as strong acids which contain minerals and include phosphoric, hydrochloric, and sulfuric acids.
Acids are abundant in nature with organic acids being the most common in food applications. Commercially, many are produced by microbes and fermentation processes. Citric acid, for example, is naturally present in citrus and other fruits but is produced on large-scale from Aspergillus niger.2 Tartaric acid is derived from wine by-products but is commercially prepared from xylose using racemic resolution processes. Inorganic varieties such as phosphoric, sulfuric and hydrochloric are produced using chemical processes.
In baked goods, they serve several purposes, such as:
Preservation and shelf life extension: In many bakery products, acids help in extending the finished product’s shelf life by lowering pH. Moreover, under those conditions preservatives such as calcium propionate and potassium sorbate are in their most active form. Fermentation-based reactions using cultured wheat flour/starch/dextrose can produce organic acids of powerful antimicrobial activities.
Chemical leavening: typically, organic acids react with sodium bicarbonate or other alkalis to produce carbon dioxide gas, essential for volume building in cakes, biscuits and many bakery products according to the following reaction:
HX + NaHCO3 → NaX + H2O + CO2
HX: non-metal leavening acid3
Flavor enhancement and balancing: organic acids, as acidulants, can add desirable sour notes, sharpen taste and/or balance flavors and sweetness in products like sourdough breads, raisin bread, artisan breads/bread mixes, turnovers, or pastries. Traditionally, sour milk products, lemon juice, and fruit products are acid sources used for that purpose.
Organic acids play a significant role in intracellular metabolic pathways such as catabolism of amino acids, the tricarboxylic acid cycle (TCA) as well as various neurotransmitter functions.
Organic acids can be obtained using various processes, mainly:
Chemical oxidation of aldehydes under controlled parameters to form carboxylic acids.
Biotechnological process: Vinegar and citric acid, for example, are commercially obtained by fermentation. Acetobacter aceti converts ethanol to acetic acid under aerobic conditions.
Typical applications and neutralization values (NV*) of organic acids in various baked products are listed in the following table: