Sorbic acid stability

For a liquid or semi-solid pharmaceutical dosage form, it is crucial to include a preservative in the formulation. Commonly used preservatives in these systems include sodium benzoate, EDTA, sorbic acid, and parabens. A generic HPLC method is also recommended for the preservatives used in liquid formulations for routine monitoring to ensure the stability of the preservative itself and it must be validated specific to its use with the dosage form. (See chapters on Sample Preparation and Method Development.)... 

Potassium sorbate has both antimicrobial and antifungal properties in formulations below pH 6. Generally, it is used at concentrations of 0.1% to 0.2% in oral formulations (solutions, syrup, and suspensions), and is used much more than sorbic acid because of its higher solubility and stability in water. However, some loss of antimicrobial activity occurs in the presence of nonionic surfactants and some plastics. 

Carboxylic Acid Group. Sorbic acid undeigoes the normal acid reactions forming salts, esters, amides, and acid chlorides. Industrially, the most important compound is the potassium salt because of stability and bigb water solubility. Sodium sorbate [7757-81-5] (E E form [42788-83-0]) is less stable and not commercially available. The calcium salt [7492-55-9], which has limited solubility, has use in packaging (qv) materials. 

Sorbic acid and its salts are highly refined to obtain the necessary purity for use in foods. The quahty requirements are defined by the Food Chemicals Codex (Table 3). Codistillation or recrystallization from water, alcoholic solutions, or acetone is used to obtain sorbic acid and potassium sorbate of a purity that passes not only the Codex requirements but is sufficient for long-term storage. Measurement of the peroxide content and heat stability can further determine the presence of low amounts of impurities. The presence of isomers, other than the trans,trans form, causes instability and affects the melting point. 

A variety of additives are incorporated into the dispersions as surfactants (Tween 80, sodium lauryl sulfate, polyoxyethylene nonyl phenyl ether, cetyl alcohol, and Pluronic F-68), plasticizers (dibutyl sebacate, oleic acid, and Myvacet 9-40), pigments, antiadherents (fumed silica), anticoagulant (Myvacet 9-40), preservatives (sorbic acid), and stabilizers (ammonia). ... 

The bacteriological stability of guar gum dispersions may be improved by the addition of a mixture of 0.15% methylpar-aben and 0.02% propylparaben as a preservative. In food applications, benzoic acid, citric acid, sodium benzoate, or sorbic acid may be used. 

Potassium sorbate is used in approximately twice as many pharmaceutical formulations as is sorbic acid owing to its greater solubility and stability in water. Like sorbic acid, potassium sorbate has minimal antibacterial properties in formulations above pH 6. 

Sorbic acid has limited stability and activity against bacteria and is thus frequently used in combination with other antimicrobial preservatives or glycols, when synergistic effects appear to occur see Section 10. 

Sorbic acid is sensitive to oxidation, particularly in the presence of light oxidation occurs more readily in aqueous solution than in the solid form. Sorbic acid may be stabilized by phenolic antioxidants such as 0.02% propyl gallate. ... 

Potassium sorbate is used as a yeast inhibitor for the stabilization of table wines containing residual sugar. When conditions permit the growth of lactic acid bacteria, wines treated with sorbic acid can develop an odor resembling crushed geranium leaves (Burkhardt, 1973 Radler, 1976 Wurdig et al., 1975). This result due to bacterial reduction... 

The use of milk proteins is advantageous in relation to the palatability, flavour and taste stability of the margarine, while it also influences its frying properties (browning, sediment). There is a risk of bacterial infection, which can be minimized by pasteurization of the milk phase. Other measures taken to inhibit the growth of bacteria, moulds and yeasts are a fine water distribution (see Section 5.7.2c) addition of salt (to be effective, more than 13% NaCl in the water phase is desirable which, in many countries, is not appreciated for taste reasons) a low pH (preferably <4.5) use of preservatives (like benzoic or sorbic acid or their sodium salts) hygienic processing. 

Winemakers wishing to stabilize juice with sorbate should also consider the potential presence and activity of LAB. In the absence of alcoholic fermentation and other countermeasures (SO2, filtration, etc.), bacterial reduction of the sorbic acid to sorbyl alcohol may occur. Upon blending... 

Some LAB are known to reduce sorbic acid to sorbyl alcohol, the precursor to geranium tone . As alcohol is not present, the end product is not produced until the juice is added to sweeten the wine at bottling. Subsequendy, geranium tone is produced in the bottled wine chemically and in the absence of viable LAB. Thus, where sorbic acid is used to stabilize stored juice against fermentative yeast activity, SO2 should also be considered to prevent growth of LAB (see section 1.43). 

The solubility of active substances often depends on the pH (see Sect. 5.8.1). By adjusting the pH, a solution or a suspension may be prepared (see Sect. 19.1.1). The pH can affect the stability of an active substance or excipient. For example, the hydrolysis rate of esters depends on the pH (see Sect. 22.2.1). The pH must be taken into account for the preservation of an oral solution. The preservative sorbic acid is only effective at a pH <5.5 and the preservative methyl parahydroxybenzoate undergoes hydrolysis at pH > 8. 

In general methyl parahydroxybenzoate (sometimes combined with propyl parahydroxybenzoate) or sorbic acid are chosen. For stability reasons the pH is adjusted to 5 by the addition of potassium sorbate. If these substances caimot be used, the organic solvents mentioned earlier (ethanol or glycerine) are an alternative to a preparation less susceptible to microbial growth. 

If used to stabilize a sweet wine, sorbic acid should be added just prior to bottling. Additions should be carried out in stainless steel or other containers that can be cleaned and sanitized. Use of wood tanks for pre-botding mixing and storage should be avoided. Here, residual sorbic acid trapped in the wood may be utilized by resident lactic acid bacteria in the production of geranium-tone, which can continually leech into wines subsequently processed through that tank. 

In the 1960s, as early as the first treatments, strange odors and tastes were sometimes noted— especially in red wines treated with sorbic acid. For this reason, its authorization was reconsidered. However, when it is correctly used, experience has shown that in normal storage conditions the evolution and development of bottled wine is not affected. These observations do, however, lead to the problem of the stability of this product in wine. 

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