Summary:
This article provides a comprehensive overview of the principles, major types, and industrial applications of food acidulants. The sensation of sourness originates from the stimulation of taste bud membranes by hydrogen ions, with its intensity influenced by factors such as pH value, the type of acid anion, and buffering effects. In today’s food industry, commonly used acidulants include organic acids such as citric acid, malic acid, lactic acid, tartaric acid, and acetic acid, as well as inorganic acids like phosphoric acid. Among these, citric acid dominates the organic acid market with over 70% share. Beyond enhancing flavor, acidulants also help preserve color, extend shelf life, and prevent microbial growth. This article explores the specific applications of major acidulants across different food categories and highlights the trend toward blending acidulants and using them in conjunction with other additives—offering valuable technical insights for the food industry.
01. The Principle Behind Sourness
Sourness is triggered when hydrogen ions (H⁺) stimulate the membranes of taste buds. Thus, any compound that can release hydrogen ions in a solution will typically taste sour. However, the relationship between the concentration of acid and the intensity of sourness is not linear. Different acids produce distinct sour sensations due to variations in their anions, pH levels, titratable acidity, buffering capacity, and interactions with other ingredients—especially sugars.
Even at the same pH level, organic acids tend to produce a stronger sour sensation than inorganic ones. Moreover, the perception of sourness in aqueous solutions may differ from that in actual foods. Buffering plays a key role: at equal pH, weak organic acids often feel more sour than mineral acids. This is partly because components in saliva and food can buffer the acids, altering the perceived sourness.
The type of anion associated with an acid also impacts the flavor. Most organic acids provide a clean, refreshing sourness, whereas many inorganic acids (like hydrochloric acid) may taste harsh or bitter, negatively affecting food flavor. This effect, often referred to as an “off-taste,” is primarily due to the accompanying anions. Substances like ethanol and sugars can mask or reduce the sourness. In fact, the balance of sweetness and acidity is essential for the characteristic flavor of fruit-based beverages.
02. Types of Food Acidulants
Currently, around 20 types of acidulants are commonly used worldwide, with annual demand growing at a rate of 3% to 5%. Food acidulants can be broadly categorized into organic and inorganic types. In addition, certain organic and inorganic salts may also serve as acidulants.
Organic acidulants are the most common in modern food processing. These include citric acid, malic acid, lactic acid, tartaric acid, and acetic acid—among which citric acid is the most widely used, accounting for over 70% of the global organic acid market. Among inorganic acids, phosphoric acid is the most frequently used in food products.
Sour-tasting substances in food are typically water-soluble organic or inorganic acids. In fruits, vegetables, and their derivatives, the primary acids are malic, citric, tartaric, succinic, and acetic acids. In meat and seafood products, lactic acid is more prevalent. These acids come from various sources: some occur naturally in food—such as tartaric acid in grapes and malic acid in apples—while others are added during processing, like citric acid in soft drinks. Some acids, like lactic acid in yogurt, are produced through fermentation.
03. Functions of Food Acidulants
1. Flavor Enhancer
Regardless of how they are derived, acidic compounds are important flavor enhancers in food and play a significant role in shaping the overall taste profile. Most organic acids carry a strong fruity aroma that can stimulate the appetite and aid digestion. Additionally, they contribute to maintaining the body's acid-base balance.
2. Color Stabilizer
Acidulants also help stabilize the color of food by affecting its pH level. In fruit processing, adding acid to lower the pH can suppress enzymatic browning. Similarly, blanching vegetables in boiling water with a pH of 6.5 to 7.2 helps preserve their natural green color, especially in leafy greens.
3. Preservative Effect
Acidulants contribute to food preservation as well. When the pH of a food product drops below 2.5, the growth of most microorganisms—except for certain molds—is effectively inhibited. For example, controlling acetic acid concentration at around 6% can significantly suppress the growth of spoilage bacteria.
04. Applications of Common Acidulants in Food
Food acidulants are widely used across various sectors of the food industry, particularly in beverage and fermentation applications. In beverages, acidulants not only enhance flavor but also serve as preservatives, making them essential ingredients in production. In the fermentation industry, acidulants are used in products such as fermented chili and lactic acid beverages. Some acidulants also offer functional benefits—for example, malic acid is known for its health-promoting properties and is currently one of the most widely used and promising organic acids in the global food industry.
1. Citric Acid in Food Applications
Citric acid is the most widely distributed organic acid found in fruits and vegetables and is also the most commonly used acidulant in the food industry. It was first discovered and extracted from lemons, which is how it got its name. According to statistics, about 99% of the global citric acid supply is produced through microbial fermentation.
Citric acid typically exists as a monoclinic crystal containing one molecule of water of crystallization. It is highly soluble in water and ethanol, but poorly soluble in ether. At 20°C, its solubility in water reaches 100%. It has a strong sour taste. When it contains crystal water, it melts between 10°C and 133°C, and it tends to lose water if exposed to air for a long time. The anhydrous form melts at 153°C and readily absorbs moisture from humid air, forming crystals again. Interestingly, citric acid is more soluble in cold water than in hot water.
Citrus fruits and berries contain the highest concentrations of citric acid, often coexisting with malic acid. In some cases, citric acid can account for 6%–8% of the fruit’s dry weight. Its flavor is clean, pleasant, and well-rounded, with a quick onset of sourness but a short aftertaste. Typical usage levels range from 0.1% to 1.0%.
Citric acid is also commonly used in pastry making. Besides enhancing flavor, it helps prevent spoilage. In food processing, it serves multiple functions—acting as a sucrose inversion agent, a color stabilizer for fruits and vegetables, and a synergist for antioxidants. Moreover, its functional potential goes beyond flavoring. Studies by Liao Lan and others have shown that citric acid can effectively unfold wheat protein structures, making it a viable alternative to hydrochloric acid for deamidation. This expands the application scope of wheat gluten proteins.
2. Malic Acid in Food Applications
Malic acid appears as white, needle-like crystals that typically clump into spherical shapes. It readily absorbs moisture from the air and dissolves easily in both water and ethanol, with a solubility of 55.2% in water at 20°C. Naturally occurring malic acid is in the L-form and is found in nearly all fruits, with pome fruits containing the highest levels.
Compared to citric acid, malic acid has a stronger and longer-lasting sourness with a slightly astringent aftertaste. When used together with citric acid, it can significantly enhance the overall sour flavor. Industrial-grade malic acid is typically produced synthetically, and it is generally used at concentrations between 0.05% and 0.5%.
Malic acid also plays a role in fermentation industries, particularly in secondary fermentation of wine. Research has shown that L-malic acid can promote the growth of Oenococcus oeni, a lactic acid bacterium crucial for malolactic fermentation, thereby contributing to the production of high-quality wine.
3. Lactic Acid in Food Applications
Lactic acid is a key organic acidulant with an important role in the food industry. It imparts a distinct sour taste to food and serves multiple functions such as adjusting pH, preventing spoilage, and extending shelf life. It is widely used in beverages, fermented foods, grain processing, and the production of certain seasonings. Lactic acid is produced in large quantities through the fermentation of lactic acid bacteria, which also contributes to human health.
A research team from Japan’s Ministry of Health, Labour and Welfare found that regular consumption of lactic acid bacteria-based foods may help alleviate symptoms of allergic rhinitis to some extent. The U.S. FDA has classified lactic acid as Generally Recognized as Safe (GRAS), and it is widely used as a preservative and pickling agent in the production of soft drinks, candy, and pastries. Lactic acid solutions can also extend the shelf life of meat products, making it a promising ingredient for future food preservation technologies.
In beer production, U.S. regulations prohibit the use of inorganic acids such as phosphoric acid to adjust pH levels, favoring lactic acid instead. Additionally, lactic acid can modify the structure and properties of rice starch and is used in glutinous rice flour to improve anti-aging properties at a usage level of around 1%. It also has certain applications in the baking industry.
4. Vinegar
Vinegar is a traditional and commonly used sour seasoning in China. It typically contains 3% to 5% acetic acid, along with other organic acids, amino acids, sugars, alcohols, esters, and more. Vinegar is made from starch- or sugar-rich raw materials through fermentation.
Because of its mild acidity, vinegar is used not only as a seasoning in cooking but also to eliminate unpleasant odors. For example, adding vinegar when cooking fish helps reduce the fishy smell, and using vinegar when braising beef or lamb can make the meat more tender. In everyday life, Chinese households have developed many creative and practical uses for vinegar beyond cooking.
5. Acetic Acid
Also known as ethanoic acid, acetic acid is a colorless liquid with a pungent odor. It has a boiling point of 118.2°C and a melting point of 16°C. When its concentration exceeds 98%, it solidifies into a crystalline substance known as glacial acetic acid. It is fully miscible with water, ethanol, ether, and glycerol in any proportion, and it is corrosive to the skin with antibacterial properties. Acetic acid is used to produce synthetic vinegar and is commonly applied in food preservation and flavoring.
6. Blended Applications of Food Acidulants
The combined use of acidulants falls into two categories: blending multiple acidulants and combining acidulants with other food additives. For instance, in experiments with fermented chili peppers, researcher Zhang Yusong found that using a blend of various common acidulants significantly enhanced the chili’s flavor. The study showed that a single acidulant often fails to achieve the desired sour profile in fermented products, making combinations necessary.
Mixing acidulants with other food additives is also widely practiced in the food industry. It not only improves the sensory characteristics of the product but also enhances antimicrobial and preservative effects. Acidulants and sweeteners often work in opposition to each other, so the right balance between sweetness and sourness—especially in beverages and candies—can lead to superior flavor outcomes.
Experts point out that achieving harmony between sourness and other taste profiles in food or beverages remains a challenging task. While consumers are open to bold and complex flavors, manufacturers must strive to develop balanced and approachable taste combinations. Going forward, consumer interest is expected to increase in products that creatively blend sourness with other flavor profiles.
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