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PubMedDate not supplied

Fungal metabolites of sorbic acid.

A number of fungal detoxification reactions of sorbic acid have been reviewed. These include decarboxylation to give trans-1,3-pentadiene, esterification to give ethyl sorbate, reduction to give 4-hexenol and 4-hexenoic acid. It was shown that seven Penicillium species could convert sorbic acid into 1,3-pentadiene whilst P. bilaii, P. fellutanum and P. glabrum did not. However, most Eurotium species were unable to bring about this conversion. Considerable differences in the resistance of two isolates of P. crustosum to sorbic acid were found. An isolate from coconut was more resistant than one isolated from hazelnuts. Both sorbic acid and caproic acid (hexanoic) brought about disorganization of the mitochondrial membranes in P. crustosum. It is suggested that these lipophilic acids inhibit growth by interfering with the electrochemical membrane potential across the mitochondrial membranes.

Alcohols↗
PubMed1989

Spectrophotometric method for the determination of sorbic acid in various food samples with iron(III) and 2-thiobarbituric acid as reagents.

A simple, rapid and accurate spectrophotometric method has been developed for the determination of sorbic acid in various food samples based on the oxidation of sorbic acid by iron(III) at 100 degrees C to malonaldehyde, which then reacts with 2-thiobarbituric acid to form a reddish brown product. The optimum experimental conditions for colour development have been assessed. Absorbance measurements were made at 529 nm in the presence of 0.4% m/V citric acid. The calibration graph was linear for 0-6 micrograms ml-1 of sorbic acid with a slope of 0.131 A micrograms-1 ml. The recoveries of sorbic acid at concentrations of 164-557 micrograms ml-1 ranged from 96 to 103%. The relative standard deviations of ten replicate determinations of sorbic acid in a synthetic cream soda sample spiked with 573 micrograms ml-1 of sorbic acid and in an onion juice sample containing 82 micrograms ml-1 of sorbic acid were 1.6 and 1.9%, respectively. Interferences from several common food additives can be minimised by extracting sorbic acid with diethyl ether and then back-extracting the acid with sodium hydrogen carbonate. The method has been applied successfully to the determination of sorbic acid in a wide range of food samples including beverages, cake, cake mate, garlic bread sprinkle, onion juice, oyster flavoured sauce and grenadine syrup.

Fatty Acids, Unsaturated↗
PubMed2006

NMR analysis of ion pair formation between timolol and sorbic acid in ophthalmic preparations.

Ion pair formation between timolol and sorbic acid was investigated using NMR spectroscopy in order to clarify their interactions within ophthalmic preparation. (13)C and (1)H NMR spectra of timolol, sorbic acid, and a mixture of the two were obtained, and the signal changes induced by pairing were observed. The carbon signals of the butylaminopropanol moiety of timolol were markedly shifted in the mixture, as were the carboxyl and conjugated carbons assigned to sorbic acid. The localizations of the changes in each molecule revealed the binding sites. The profiles of butylaminopropanol carbon chemical shifts plotted against a molar ratio of sorbate were synchronized, which suggested a single type of interaction with sorbic acid. The Job plot showed a typical pattern with a single-maximum at a mole function of 0.5, indicating the presence of a 1:1 complex of timolol and sorbic acid. The stability constants (K) of the timolol-sorbate and timolol-maleate pairs were 1.9x10(1) and 2.2x10(2)M(-1), respectively. The higher K value of the timolol-maleate interaction suggested that it was dominant to the timolol-sorbate interaction when maleate and sorbate coexisted within a timolol solution. Here, we demonstrated evidence of an interaction between timolol and sorbic acid using simple NMR measurements, which suggested the existence of ion pair formation derived from charge neutralization. Our analysis using NMR spectroscopy should advance the understanding and optimization of formulations that are based on ion pair.

Chromatography, High Pressure Liquid↗
PubMed2001

Controlled release of water-soluble polymeric complexes of sorbic acid with antifungal activities.

We synthesized six water-soluble polymeric complexes of sorbic acid with polyvinylpyrrolidone of different molecular weight (mol wt). As shown by infrared absorption spectrum analysis, the complexes were formed by hydrogen bonding. The complexes (SC1, with mol wt=10 kDa, SC2 with mol wt=25 kDa, SC3 with mol wt=30 kDa, SC4 with mol wt=40 kDa, SC5 with mol wt=90 kDa, and SC6 with mol wt=360 kDa) were characterized as low mol wt (SC1, SC2, and SC3) and high mol wt (SC4, SC5, and SC6). The antifungal potencies of the complexes were tested by the macrodilution susceptibility method against environmental and clinically important fungi. Sorbic acid as well as the complexes exhibited minimum inhibitory concentrations (MICs) lower than potassium sorbate against all the strains tested. MICs of SC1, SC2, and SC3 were shown to be 2- to 4-fold lower for yeast and 1.5- to 3-fold lower than those of sorbic acid for moulds, respectively. The MICs of SC4 and SC5 against both of the Candida species tested ranged from 500 to 800 microg/ml, whereas for SC6 and sorbic acid they were about 1 mg/ml. The potencies of the high mol wt complexes against moulds were decreased by increasing the mol wt. For both of the moulds tested, the MICs of SC4 were slightly lower than those of sorbate. The MICs of sorbic acid and SC5 were equal to 300 microg/ml and 500 microg/ml respectively for Aspergillus parasiticus and for Penicillum viridicatum. The susceptibility to SC6 of all of the hyphomycetes tested was higher than that to sorbic acid. The low mol wt complexes and the sorbic acid exhibited minimal fungicidal concentrations (MFCs) 2 and 3 times higher respectively than the MICs. Sorbic acid and SC3 at a concentration of 2.5 mg/ml in an in vitro time kill curve study of Candida tropicalis were shown to be fungistatic, whereas SC1 and SC2 were fungicidal at the same concentrations. For Aspergillus parasiticus sorbic acid at 2.5 mg/ml was fungistatic for a 24-h period, whereas SC1, SC2, and SC3 were fungicidal.

Antifungal Agents↗
PubMed1980

Ultraviolet spectrophotometric determination of sorbic acid in dry fermented sausage.

A rapid and reliable method is described for determining sorbic acid in dry fermented Italian salami (moisture < 50%, fat > 25%). Sorbic acid was extracted from the homogenized sample with metaphosphoric acid and partitioned into isooctane. The absorbance of the extract was read at 255 nm. Background UV-absorbing materials were determined by their absorbance at 255 nm after permanganate oxidation of sorbic acid. Unexpectedly, spice components contributed to the UV absorbance of permanganate-labile substances, and sorbic acid was at first overestimated. Interference caused by spice components was calculated by measuring the difference in absorbance before and after permanganate treatment of a sample extract from a salami which had not been treated with sorbic acid. Recovery of added sorbic acid (50--600 ppm) was between 92 and 98.7%.

Animals↗
PubMedDate not supplied

Reaction of sorbic acid in wheat flour doughs: reaction with thiols.

The general characteristics of the reaction between sorbic acid and thiols are reviewed. Cysteine adds to the conjugated diene in position 5 to form the substituted 3-hexenoic acid. This is labile in acid solution, yielding a quantitative amount of sorbic acid. When wheat flour doughs are treated with sorbic acid and heated, a significant amount of the sorbic acid is not recovered on extraction with methanol. The use of acidified methanol leads to a quantitative recovery of the preservation and evidence is presented to suggest that sorbic acid-thiol adducts are formed. This is the first report of 'reversibly bound' sorbic acid in a food.

Cysteine↗
PubMed1990

[Use of gas chromatography for determining benzoic and sorbic acid levels in orange beverage and tomato concentrate].

Conditions of simultaneous determination of benzoic and sorbic acid in orange drink and tomato concentrate by gas chromatography method were developed and tested. Preservatives were isolated by extraction of the samples with diethyl ether in acidic media, and then converted into methyl esters with thionyl chloride. Methyl esters were separated on column packed with 15% EGA coated on 80-100 mesh Chromosorb W AW DMCS. The smallest amount of preservatives detectable on chromatography column is 20 ng for benzoic acid and 16 ng for sorbic acid. The recovery rate of the method ranged from 96-97% for benzoic acid and 89-92% for sorbic acid, while the variability coefficient was from 1.7-3.5% for benzoic acid and 4.5-6% for sorbic acid.

Benzoates↗
PubMed1986

Sorbic acid revisited.

135 patients wearing hydrogel lenses were prescribed a care system of sorbic acid preserved surfactant, Lensept and Bausch and Lomb Sensitive Eyes Saline (sorbic acid 0.10%). Fifteen percent of patients presented with an adverse ocular response to their care system. The etiology was attributed to sorbic acid as the use of nonpreserved saline eliminated the signs and symptoms. This incidence of reaction is similar to those published earlier on thimerosal preserved saline and sorbic acid preserved saline.

Contact Lenses↗
PubMed1998

Comparison of the inhibitory effect of sorbic acid and amphotericin B on Saccharomyces cerevisiae: is growth inhibition dependent on reduced intracellular pH?

The effects of sorbic acid and amphotericin B on the growth and intracellular pH (pHi) of Saccharomyces cerevisiae were studied and compared. Past evidence has suggested that the inhibitory action of sorbic acid on yeast is due to reduction of pHi per se. However, using a novel method to measure pHi in growing cells, little correlation was found between reduced growth rate on exposure to sorbic acid and reduction of pHi. In fact, growth inhibition correlated with an increase in the intracellular ADP/ATP ratio due to increased ATP consumption by the cells. This was partly attributed to the activation of protective mechanisms, such as increased proton pumping by the membrane H(+)-ATPase, which ensured that pHi did not decline when cells were exposed to sorbic acid. Therefore, the available evidence suggested that the inhibitory action of sorbic acid was due to the induction of an energetically expensive protective mechanism that compensated for any disruption of pHi homeostasis but resulted in less available energy for normal growth. In contrast to sorbic acid, with amphotericin B there was a direct correlation between growth inhibition and reduction of pHi due to the uncoupling effect of this compound on the plasma membrane. The inhibitory effect of amphotericin B was consistent with membrane disruption, or 'proton-uncoupling' leading to growth inhibition due to proton influx, decline in pHi and partial dissipation of the proton gradient.

Adenosine Diphosphate↗
PubMed1998

Evidence that sorbic acid does not inhibit yeast as a classic 'weak acid preservative'.

Weak-acid preservatives are widely used to maintain microbial stability in foods and beverages. Classical weak-acid theory proposes that undissociated acid molecules pass through the plasma membrane, dissociate in the neutral pH of the cytoplasm, release protons and inhibit growth through acidification of the cytoplasm. Inhibitory concentrations of sorbic acid are shown to liberate fewer protons than other weak-acid preservatives. Sorbic acid shows similar inhibition to other six-carbon acids, alcohols and aldehydes, the latter being unable to act as weak acids. A survey of 22 yeasts showed high correlation between sorbate resistance and ethanol tolerance. Inhibition by short-chain acids or alcohols showed strong correlation with lipophilicity. It is proposed that sorbic acid acts as a membrane-active substance rather than as a weak-acid preservative.

Benzoic Acid↗
PubMed2006

High Pdr12 levels in spoilage yeast (Saccharomyces cerevisiae) correlate directly with sorbic acid levels in the culture medium but are not sufficient to provide cells with acquired resistance to the food preservative.

Sorbic acid is a commonly used food preservative against yeast and fungal food spoilage. Understanding its effect on the molecular physiology of yeast cells will allow the food industry to develop knowledge-based strategies to make more optimal use of its preservative action. Here we show that the yeast membrane protein Pdr12, previously shown to be prominently involved in sorbic acid resistance development in laboratory strains, was strongly induced by the presence of sorbic acid in the culture medium in Saccharomyces strains isolated from spoiled foods. Induction of Pdr12 expression was seen both under laboratory conditions and upon growth in a commercial soft drink. Induction was rapid and maintained for the duration of the stress. No Pdr12-like protein induction was seen in Zygosaccharomyces bailii or Zygosaccharomyces lentus, two well-known beverages spoilage organisms. Finally, unexpectedly, our studies showed for the first time that pre-inducing Pdr12p to maximal levels by subjecting cells to a mild sorbic acid stress did not lead to cells with an acquired resistance. Neither more rapid growth in the presence of the acid nor growth at higher sorbic acid concentrations at a given environmental pH was observed. Thus we have shown that while important in resistance development against sorbic acid, by itself induction of the pump is not sufficient to acquire resistance to the preservative.

ATP-Binding Cassette Transporters↗
PubMedDate not supplied

Reaction of sorbic acid in millet and sorghum doughs: reaction with thiols.

The fate of sorbic acid in pearl millet and sorghum doughs on cooking and storage is reported. A solution of sorbic acid added to the cereal flours gave a dough, which was cooked to give the product 'fura'. A significant amount (40%) of the sorbic acid was not recovered from the dough and fura on extraction with methanol. The use of acidified methanol leads to a quantitative recovery of that proportion of the preservative which otherwise becomes unavailable during the cooking of the dough and evidence is presented to suggest that sorbic acid-thiol adducts are formed at that stage.

Bread↗
PubMed2000

Chemical and toxicological studies of products resulting from sorbic acid and methylamine interaction in food conditions.

Sorbic acid has a system of conjugated double bonds which makes it able to undergo nucleophilic addition reactions with certain functions. The interactions between sorbic acid and an amine present in the endogenous constituents of food were quantified. We demonstrated the formation of new products and studied the underlying mechanisms using ethyl sorbate and various amines. HPLC, GC, GC-SM and NMR analyses of the reaction mixes enabled the isolation and identification of the products. The addition reactions led, at 20 degrees C, to linear monoadducts and, at 50 degrees C, to cyclic derivatives resulting from double addition. Mutagenesis studies, involving Ames test and genotoxicity studies with HeLa cells and on plasmid DNA, in cyclic interaction products, showed that none of the products studied presented neither mutagenic nor genotoxic activities.

Chromatography, Gas↗
PubMedDate not supplied

Kinetics of the reaction of sorbic acid with sulphite species.

Under aerobic conditions, the reaction of sorbic acid with sulphite species, S(IV), involves a pH-dependent oxidative mechanism with the loss of S(IV). Sorbic acid is essential to the process. In the absence of air, a much slower nucleophilic addition of sulphite ion to undissociated sorbic acid takes place.

Aerobiosis↗