Acidulants are food additives that can act as flavor enhancers, preservatives, stabilizers, or antioxidants. This article compares five common acidulants.
Acidulants are acidity regulators. They are substances (organic or inorganic) that release hydrogen and a salt part in water solutions. When the concentration of hydrogen ions increases, the acidity of the whole system increases, while the pH decreases.
Acidulants are used as food additives. They play an important role in flavoring, adding bright, fresh, or sour notes, and enhancing other flavor ingredients. They also act as a preservative to increase shelf life and ensure food safety. Some acidifiers also act as stabilizers, while others serve as antioxidants or emulsifiers or assist in color retention.
Can be isolated from wine, and the principal component of wine crystals
Can be isolated from whey
Chemical Synthesis
Can be synthetically produced (isolated) using citrus juices
Cavita process (carbonylation of methanol), oxidation of aldehyde and oxidation of ethylene
Chemical hydration of maleic or fumaric acid at high temperature (180–220°C) and high pressure (14–18 bar), yielding a racemic mixture of dl-malic acid
Chemical treatment of potassium tartrate, a by-product of the wine industry
Hydrogen cyanide is added to liquid acetaldehyde in the presence of a base catalyst under high pressure to obtain lactonitrile, which is hydrolyzed using sulfuric acid to get lactic acid
Microbial Synthesis
Commonly produced by fermentation with the filamentous fungus Aspergillus nigerby one of three different processes: submerged, surface, and solid fermentations
Acetobacter and Gluconacetobacter are the most commonly used species. Surface fermentation processes are used for the production: the Orleans, the Boerhaave, the generator, and the Schutzenbach/ submerged process.
Microorganisms with high fumarase (fumarate hydratase) activity are used. Gene promoters can be used to amplify the enzyme for maximal production of malic acid.
Achromobacter and Alcaligenes are used.Microbial conversion of cis-epoxysuccinic acid is subjected to asymmetrical hydrolysis by the catalytic action of a microorganism.
Lactic acid bacteria are the main bacteria used.These bacteria convert different carbohydrate sources into lactic acid.
Acidulant Usage in Food
Acidulants are used in the food industry for the following purposes:
Flavoring: Acidulants add a “tang” or “tartness” to obtain the desired taste profile.
pH Control (Acidification): Adding acidulants to food decreases the pH of the final product. This is desirable for obtaining desired texture, color, taste, shelf life, and stability in food products.
Preservation: Acidulants create unfavorable conditions for microbial growth by decreasing the pH. Acids are canning powerhouses, reducing the energy needed to sterilize by lowering the pH. They also extend the shelf life of raw foods.
Anti-Microbial Activity: Some acidulants have intrinsic anti-microbial properties that inhibit microbes’ growth.
Flavor Masking: Acids can mask the flavor of existing ingredients, saccharine. Malic and citric acid remove saccharine’s unsatisfactory aftertaste.
Antioxidant Activity: Some acidulants sequester metal cations which are pro-oxidants. For this reason, they act as antioxidant synergists in the food system, retaining the taste and color of food products that would have been lost due to oxidation.
Raising Action: Acids react with bases to release carbon dioxide. This property is utilized for a leavening or raising action in multiple acid-leavened foods.
Functions of Various Acidulants
Citric Acid
Flavor Enhancer, pH Control, Microbial Control, Chelating Agent, Antioxidant Synergist, Sequestrant, Color Retention Aid
Molar enthalpy of solution (298.15 K, 0.03 mol · kg -1)
29061 ± 123 J · mol−1
–
21846 ± 86 J · mol−1
15705 ± 29 J · mol−1
–
pKa
2.79
4.74
pKa1 = 3.40pKa2 = 5.20
pKa1 = 2.98pKa2 = 4.34
3.86
Formulation Considerations
Stability
Stability
Citric Acid
Acetic Acid
Malic Acid
Tartaric Acid
Lactic Acid
Heat
Decomposes at > 175°C
Decomposes at > 230°C
Decomposes at > 140°C
Decomposes at > 210°C
Decomposes at > 299°C
Oxidation
Stable
Stable
Stable
Stable
Stable
Moisture (Hygroscopicity)
Hygroscopic
Hygroscopic
Hygroscopic
Hygroscopic
Hygroscopic
Interaction
Reacts with oxidizing agents, bases, reducing agents, and metal nitrates.
Reacts with oxidizing agents, bases, and reducing agents.
Reacts with oxidizing agents, bases, alkali metals, and reducing agents.
Reacts with oxidizing agents, bases, and reducing agents.
Reacts with oxidizing agents, bases, and reducing agents.
Storage Conditions
Can be stored in dry form at ambient temperature. High humidity and elevated temperatures should be avoided to prevent caking.
Can be stored at ambient temperature. High humidity and elevated temperatures should be avoided. Keep in a well-ventilated room.
Can be stored in dry form at ambient temperature. High humidity and elevated temperatures should be avoided to prevent caking.
Can be stored in dry form at ambient temperature. High humidity and elevated temperatures should be avoided to prevent caking.
Can be stored at ambient temperature. High humidity and elevated temperatures should be avoided. Keep in a well-ventilated room.
Sensory Properties
Citric Acid
Acetic Acid
Malic Acid
Tartaric Acid
Lactic Acid
Taste Profile
Sharp and pronounced acid tasteSudden onset
Vinegar like tastePungency
Strong acidic tasteSubtle onset & long residence time
Strong & sharp acidic tart taste
Balanced & less sharp sour tasteSofter & rounder sourness
Odor
Odorless
Vinegar-like pungent odor
Odorless
Odorless
Odorless
Color
White or colorless
Clear
White or colorless
White or colorless
Colorless to pale yellow
Resemblance
Sour element of citrus juices
Vinegar
Sour element of unripe apple
Sour element of wine
Primary flavor associated with lacto-fermentation
Compatibility & Culinary Uses
Citric Acid
Acetic Acid
Malic Acid
Tartaric Acid
Lactic Acid
Can be used with fruit flavors to provide a refreshing effectUsed with sweeteners to enhance flavorUsed to bring out flavors that are more reminiscent of a vegetable in its raw form
Goes well with food of savory profilesFoods with high-fat content complement acetic acid for sourness
Boosts fruit flavors, especially citrus Used mostly in combination with citric acidBoosts the impact of high-intensity sweetenersProgressive release of the acid creates sustained juiciness and flavor during chewing.
Adds a tart taste and used in combination with other acidulantsGoes well with sugary & savory foods
Goes well with milky, bakery, and pickled notes (acetic acid)Used in dishes that need an uplifting sourness that does not distract from other flavors
Mechanism of Sour Taste
Sour taste is the key element in the flavor profile of food acidulants. Human saliva is slightly acidic (with a pH of approximately 6.8), so when we consume sour food or drink, our taste receptors interact with the acids present, and this sensation is recognized as sourness.
However, there is a poor correlation between the sour taste of organic acids and stimulus pH, derived using acid-induced salivary secretion as an index of response. The pH of various organic acid solutions is considerably different at their observed threshold concentrations. Together, these results indicate that in addition to hydrogen ions, anions and/or protonated (undissociated) acid species play a role in determining the sour taste intensity of organic acids.
Here is the relative sourness, in arbitrary units, of organic acids compared to citric acid:
Citric acid: 100
Fumaric acid: 55
Tartaric acid: 70
Malic acid: 75
Succinic acid: 87
Lactic acid: 107
Glucono-delta-lactone: 310
Effect on Properties of Food
Citric Acid
Acetic Acid
Malic Acid
Tartaric Acid
Lactic Acid
Texture
Gelling
Used to improve gel formation in pectin gels
–
Used to improve gel formation in pectin gels
Used to improve gel formation in pectin gels
–
Raising
Used as a raising agent
Used as a raising agent
Used as a raising agent
Used as a raising agent
Used as a raising agent
Consistency
Emulsifying ability
Emulsifying ability
Emulsifying ability
Color Stability
Improves color stability andcolor retention (pH induced)
Color retention (pH induced)
Improves color stability and color retention (pH induced)
Improves color stability and color retention (pH induced)
Color retention (pH induced)
Antimicrobial Activity & Preservation
The survival and reproduction of microbes depend on their ability to produce appropriate responses to their immediate environmental conditions. One of the most significant environmental parameters impacting growth and survival is pH. Microbes typically respond to acid stress by preventing a damaging drop in intracellular pH (pHi) below a threshold level necessary for viability.
Microbial cells use different strategies to respond to acid stress, including enzyme-catalyzed reactions to consume protons, production of basic components for counteracting acidity, proton elimination by refluxing, or even modification of membrane permeability to protons for an improved protective system.
Two acids equilibrated to an identical pH can achieve different inhibitory effects on microorganisms. This indicates that not only the hydrogen ion concentration of the environment but also the undissociated molecule also plays a role in the inhibition of the microbe.
The following table describes the preservative properties of various types of acidulants.
Citric Acid
Acetic Acid
Malic Acid
Tartaric Acid
Lactic Acid
pH of 1% Aqueous Solution
2.3
2.7
2.34
2.1
2.4
Antimicrobial Activity
– More effective in the inhibition of thermophilic bacteria, Salmonella typhimurium, lactic acid bacteria such as Streptococcus agalactiae, and S. anatum and S. oranienburg than lactic & acetic acid – 0.3% concentration is effective in decreasing native levels of salmonellae on poultry carcassesEffective in reducing mesophilic and thermophilic spoilage.
– Has bactericidal and fungicidal properties – Lactic acetic bacteria, propionic acid bacteria and butyric acid bacteria are tolerant to inhibition by acetic acid. Used primarily to limit bacterial and yeast growth rather than mold growth – Effective antifungal agent at pH 3.5 against the black bread molds, particularly Aspergillus niger and Rhizopus nigrificans
No unusual antimicrobial action is attributed to malic acid other than that associated with pH effects.
The antimicrobial use of tartaric acid is limited.
– More extensively known for its sensory qualities than antimicrobial properties – Psychrotrophic gram negative bacteria are the most sensitive to lactic – Lactates are promising in inhibition of microbial growth
Substance added directly to human food affirmed as generally recognized as safe (GRAS)
Substance added directly to human food affirmed as generally recognized as safe (GRAS)
Substance added directly to human food affirmed as generally recognized as safe (GRAS)
Substance added directly to human food affirmed as generally recognized as safe (GRAS)
Substance added directly to human food affirmed as generally recognized as safe (GRAS)
EU
Approved Food Additive E 330
Approved Food Additive E 260
Approved Food AdditiveE 296
Approved Food AdditiveE 334
Approved Food AdditiveE 334
ADI (as per WHO/ JECFA)
Not limited
No safety concern at current levels of intake when used as a flavoring agent
No safety concern at current levels of intake when used as a flavoring agent
0-30 mg/kg bwGroup ADI for tartaric acid and its salts
No safety concern at current levels of intake when used as a flavoring agent
Maximum Usage Level
Citric Acid
Acetic Acid
Malic Acid
Tartaric Acid
Lactic Acid
EU
quantum satis
quantum satis
quantum satis
quantum satis
quantum satis
FAO/ GSFA
GMP in given food categories except 5000 mg/kg in complementary foods for infants and young children, fruit nectars, fruit nectar concentrates)3000 mg/kg in fruit juice & fruit juice concentrates
No limitations other than GMP; exempted to be used in infant foods & formulas.
Identification
Citric Acid
Acetic Acid
Malic Acid
Tartaric Acid
Lactic Acid
Chemical Name
2-hydroxypropane-1,2,3-tricarboxylic acid
acetic acid
2-hydroxybutanedioic acid
2,3-dihydroxybutanedioic acid
2-hydroxypropanoic acid
CAS Number
77-92-9
64-19-7
97-67-6
87-69-4
50-21-5
EC Number
201-069-1
200-580-7
230-022-8
201-766-0
200-018-0
INS No. (Food Additive)
INS 330
INS 260
INS 296
INS 334
INS 270
E Number (Food Additive)
E 330
E 260
E 296
E 334
E 270
FEMA Number
2306
2006
2655
3044
2611
JECFA Number
218
81
619
621
930
How to Choose the Right Acidulant
In general, acidulants play a very similar role in food formulations. But choosing the right acid or a combination of acids depends on several important factors and understanding the differences between acidulants.
Physical Form of the Acid: The physical form of the acid affects the choice of acid since the end application may require acid in a specific physical form. For example, tablets, instant beverages, and powder blends require powder acidulants, whereas liquid formulations can use both liquid and powder acidulants (where solubility matters).
Solubility: The amount of acid required to achieve the desired pH and taste profile is a factor to consider while working with less soluble acidulants.
Antimicrobial Activity: The antimicrobial activity of an acidulant plays an important role in the selection as a mere reduction in pH is sometimes not required.
Taste Profile and Interaction with Flavors: Most acidulants impact the overall taste profile and have synergies with various flavors and sweetening systems.
Fun Facts about Acidulants
Acidulants can be derived from various natural and synthetic sources. For example, citric acid comes from citrus fruits, while lactic acid can be found in dairy products.
Acidulants can act as preservatives by creating an environment that is hostile to certain bacteria and molds. Lowering a food product’s pH helps preserve its shelf life and keep it safe to consume.
Acidulants are commonly used to enhance or balance flavors in food products. They can intensify the perceived sweetness or mask undesirable flavors, improving the overall taste profile.
Acidulants play a crucial role in cheese production. They help in coagulating the proteins, a key step in forming the curds.
Acidulants can influence the solubility and stability of certain vitamins and minerals. They may enhance or inhibit the absorption of these nutrients in the body.
Alginates are available as calcium, sodium, potassium, or ammonium salts. They have several uses in the food industry, including as a thickener and gelling agent.
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