In the plant world 4-hydroxybenzoic acid and its derivatives are commonly found in various vegetable foods, such as barley, strawberries, black currants, peaches, carrots, onions, cocoa-beans, vanilla; further in foods prepared from fruit plants such as grapes and fruit juices, yeast extract, wine vinegar and also in cheeses. The distribution of the acid in plants, as derivatives of alkaloids, natural colourings etc. was reviewed by Banfield 1. Tomaszewski 2 investigated 122 plant species and found the acid present in all the plants. Billek 3 concluded that 4-hydroxybenzoic acid is the most widely distributed aromatic organic acid in the vegetable kingdom. Baardseth 4 showed that the Scandinavian cloudberry contained benzoic acid, sorbic acid, salicylic acid, 2-hydroxybenzoic acid, as well as methyl and propyl parabens, which accounted for the superior resistance of cloudberries to microbial spoilage.
The total organic acids were present at a level of 600 ppm.
Recently, Schafers 5 reported an elegant technique (GC/MS) for the detection of methyl and ethyl esters of hydroxybenzoic acid in vegetable and potato peelings.
In the animal kingdom, Schildknecht 6 found Dytiscus marginalis, the yellow beetle, produced in the secretion of its glands a disinfecting mixture of benzoic acid, 4-hydroxybenzoic acid, 4-hydroxybenzaldehyde and methyl paraben, which protected the glands from bacterial infection. Staddon 7 likewise found methyl paraben in the stink gland secretions of the British water bug, Ilyocoris cimicoides.
The presence of 4-hydroxybenzoic acid in urine of healthy, normally fed human beings 8,9 has been known for many years and is due to the decomposition of the amino acid, tyrosine, and from dietary sources.
Goodwin 10 identified methylparaben in the vaginal secretions of female dogs in oestrus. It was proposed that methylparaben was an essential part of the complex odour profile generated by the secretions of the vaginal glands. It is more likely, as in the water bug and yellow beetle examples, that methylparaben was produced as antimicrobial protection 11 of the microbiologically labile odoriferous components of the secretions.
Research worker suspected a vital role for 4-hydroxybenzoic acid. Davis 12 found it an essential growth factor (bacterial vitamin) for E. coli and as sulphonamides were an antagonist to 4-aminobenzoic acid (bacterial vitamin H), so methyl paraben was to its parent acid. Many other workers 13 supported these findings, culminating in Simonart & Wiaux 14 detecting the occurrence of 4-hydroxybenzoic acid in Penicillium griseofulvum which emphasized the fundamental importance of this acid in biochemistry.
It was eventually resolved 3,5-19 that 4-hydroxybenzoic acid was the precursor building block for ubiquinones (coenzyme-Q) which is essential for the oxidative phosphorylative process in all respiring organisms. Ubiquinones were found in microbes, in the heart muscle and in the normal skin 20. It was concluded that:-
"All respiring vegetable and animal species require 4-hydroxybenzoic acid. Without it there are no ubiquinones and hence no respiration. 4-hydroxybenzoic acid is a natural vital ingredient of aerobic life, it is no foreign substance to them."
Bose 21 reported that 4-hydroxybenzoic acid exhibited marked synergy with auxins, in promoting root growth of chrysanthemums, tomatoes and marigolds. Another interesting report by Kickuth 22 isolated and identified nine aromatic compounds from the rhizomes of bullrushes S. lacustris which had microbiocidal activity (especially against E. coli and Salmonella spp.) and therefore would make these plants important in maintaining water quality and protecting against pollution from disease producing organisms. The nine compounds identified were derivatives of benzaldehyde, 4-hydroxybenzoic acid and cinnamic acid (0.025 wt % of rhizomes). The aromatic acid function had the greatest activity and had bactericidal activity against E. coli at concentrations as low as single ppm levels.
Da & Vialle 23 studied the flavour components of natural vanilla extracts. They showed that, unlike the Bourbon vanilla, the Tahiti vanilla contained methyl paraben as one of the four major flavour components. Harbourne 24 found methyl paraben a constituent of lignin in some gymnosperms and woody dicotyledons.
Aldrich 25,26, studying the 7th-8th ventral abdominal gland secretions of adult males of the leaf-footed bugs, Leptoglossus and related species, found a preponderance of aromatic compounds, contrasting sharply with the aliphatic compounds which comprise the metathoracic gland defensive secretions of male and female leaf-footed bugs. It was later found that methyl paraben was a major component of the ventral abdominal gland secretion.
Perkins 27, investigating the major components of the rectal glandular secretions of male fruit flies found methyl, ethyl and propyl parabens. He found that the glandular extracts of the S.E. Asian fruit fly (Dacus albistrigatus) was rich in methyl paraben. In another Dacus zeugodacus sp. (a large unidentified Malaysian fruit fly) the glandular extract contained 66% ethyl paraben. Dacus cucurbitae, the melon fly, is the major fruit fly pest of melon and other cucurbits. Analysis of the rectal gland secretions showed ethyl paraben as the major component and propyl paraben as a minor one. Hancock 28, studying African cucurbit pests, found Dacus vertebratus Bezzi to be highly attracted to methyl paraben. This discovery was initially observed when the fly was attracted to a locally manufactured cosmetic product.
Methyl paraben has now joined three other previously identified fruit fly attractants, "Cue-lure" [4-(4-acetoxyphenyl)butan-2-one], "Willison's lure" [4-(4-hydroxyphenyl) buutan-2-one] and methyl eugenol. Methyl paraben has been called "Vert-lure".
The article continues with a discussion of the biodegradability and the 4-hydroxybenzoic acid biocycle.
It was concluded that 4-hydroxybenzoic acid and derivatives have a well reported and proven biocycle and are intrinsic and fundamental to all respiring and anaerobic life.
See the reference list in the data sheet.