P-hydroxybenzoic acid esters

Fig. 6.2 Separation of benzoic acid, sorbic acid and p-hydroxybenzoic acid esters by...

Several wholly aromatic polyesters are available. As expected, they are more difficult to process, stiffer, and less soluble, but are employed because of their good high-thermal performance. Ekonol is the homopolymer formed from p-hydroxybenzoic acid ester (structure 4.51). Ekonol has a Tg in excess of 500°C. It is highly crystalline and offers good strength ... 

Uekama, K., Ikeda, Y., Hirayama, F., Otagiri, M., and Shibata, M. 1980. Inclusion complexation of p-hydroxybenzoic acid esters with andfS-cyclodextrins dissolution behaviors and antimicrobial activities.Yakugaku Zasshi, 100 994-1003. 

Acidic preservatives are the most widely used for oral preparations, such as the p-Hydroxybenzoic acid esters and salts of benzoic acid. These are adequately soluble in aqueous systems and possess both antifungal and antibacterial properties. Methyl and propyl p-hydroxybenzoic acid are often used together in a 10 1 ratio. Concomitant use of multiple esters makes possible a higher total preservative concentration owing to the independent solubilities of each and, according to some researchers, maximizes the antimicrobial effect. 

Aalto TR, Firman MC, Rigler NE. p-Hydroxybenzoic acid esters as preservatives I uses, antibacterial and antifungal studies, properties and determination. ] Am Pharm Assoc (Sci) 1953 42 449-457. 

Kamada A, Yata N, Kubo K, Arakawa M. Stability of p-hydroxybenzoic acid esters in acidic medium. Chem Pharm Bull 1973 21 2073-2076. 

Aoki M, Kameta A, Yoshioka I, Matsuzaki T. Application of surface active agents to pharmaceutical preparations I effect of Tween 20 upon the antifungal activities of p-hydroxybenzoic acid esters in solubilized preparations [in Japanese]. / Pharm Soc Jpn 1956 76 939-943. 

Lehner SJ, Muller BW, Seydel JK. Interactions between p-hydroxybenzoic acid esters and hydroxypropyl-P-cyclodextrin and their antimicrobial effect against Candida albicans. Int J Pharm 1993 93 201-208. 

Matthews C, Davidson J, Bauer E, et al. p-Hydroxybenzoic acid esters as preservatives II acute and chronic toxicity in dogs, rats and mice. / Am Pharm Assoc Sci) 1956 45 260—267. 

W G Tammilehto S and Buchi J, p-Hydroxybenzoic acid esters (Nipagins). I. Physicochemical properties, Pharm. Acta Helv., 43, 726-738 (1968). 

Econol Poly(p-hydroxybenzoic acid ester) Sumitomo Chem. 

The ADI-level for every p-hydroxybenzoic acid ester is temporarily fixed to a maximum of 0 - lOmg/kg body weight/day by the Joint expert committees of the WHO/FAO. 

Antimicrobial action. All p-hydroxybenzoic acid esters have principally a fungistatic action. The p-hydroxy-benzoic acid esters destroy the cell membrane and lead to a protein denaturation in the interior of the cell besides competitive reactions occur with coenzymes (Tatsuguchi, et ah 1991). Under aerobic conditions Paraben is hydrolysed to p-hydroxybenzoic acid. The following decarboxylation of which leads to phenol, [II, 7.1.] (Valkova, et ah, 2001). 

As p-hydroxybenzoic acid esters present a relatively high pKa value (approx. 8.5), their antimicrobial action is less dependent on the pH value of the type of food to be preserved. In this respect they are superior to the organic preservative acids. Unfavourably, as in the case of phenol, p-hydroxybenzoic acid esters may be linked to some extent to proteins, emulsifiers or other food components on account of their phenolic hydroxylic-group and thus be inactivated. The antimicrobial action of the p-hydroxybenzoic acid esters is proportional to the alkyl chain length. Thus the antimicrobial action of the methyl ester is some 3 to 4 times, that of the ethyl ester some 5 to 8 times, that of the propyl ester about 25 times as powerful as phenol (Thompson, 1994). However, superimposed on this effect may be the water solubility of the esters, which is inversely proportional to the alkyl chain length. Since the activity spectra of the individual p-hydroxybenzoic acid esters are different, the application of mixtures can be profitable. 

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