Sorbic acid

Distinct effects of sorbic acid and acetic acid on the electrophysiology and metabolism of Bacillus subtilis.[Pubmed: 25038097]

Appl Environ Microbiol. 2014 Oct;80(19):5918-26.

Sorbic acid and acetic acid are among the weak organic acid preservatives most commonly used to improve the microbiological stability of foods. They have similar pKa values, but Sorbic acid is a far more potent preservative. Weak organic acids are most effective at low pH. Under these circumstances, they are assumed to diffuse across the membrane as neutral undissociated acids.
METHODS AND RESULTS:
We show here that the level of initial intracellular acidification depends on the concentration of undissociated acid and less on the nature of the acid. Recovery of the internal pH depends on the presence of an energy source, but acidification of the cytosol causes a decrease in glucose flux. Furthermore, Sorbic acid is a more potent uncoupler of the membrane potential than acetic acid.
CONCLUSIONS:
Together these effects may also slow the rate of ATP synthesis significantly and may thus (partially) explain Sorbic acid's effectiveness.

Impact of sorbic acid on germination and outgrowth heterogeneity of Bacillus cereus ATCC 14579 spores.[Pubmed: 23001664]

Appl Environ Microbiol. 2012 Dec;78(23):8477-80.

Population heterogeneity complicates the predictability of the outgrowth kinetics of individual spores.
METHODS AND RESULTS:
Flow cytometry sorting and monitoring of the germination and outgrowth of single dormant spores allowed the quantification of acid-induced spore population heterogeneity at pH 5.5 and in the presence of Sorbic acid.
CONCLUSIONS:
This showed that germination efficiency was not a good predictor for heterogeneity in final outgrowth.

Effect of sorbic acid on the storage quality of Kaladhi -an acid coagulated milk product[Pubmed: 25477678]

J Food Sci Technol. 2014 Dec;51(12):4040-6.

The present study was conducted to determine the effect of three different levels of Sorbic acid (0.1 %, 0.2 % and 0.3 %) on the shelf life and storage quality of Kaladhi.
METHODS AND RESULTS:
Kaladhi was prepared from pasteurized buffalo milk standardized to 6 % fat and 9 % SNF with coagulation at 40 °C using 5 % lactic acid as a coagulant. Kaladhi prepared without Sorbic acid served as control and was compared with the products treated with different levels of Sorbic acid for a storage period of 35 days at ambient temperature. The results showed a significant (P < 0.05) effect of Sorbic acid on most of the physicochemical parameters i.e. titratable acidity, free fatty acid content (% oleic acid) and thiobarbituric acid value which showed a decreasing trend with increasing concentration of Sorbic acid. However, a non-significant (P > 0.05) effect of Sorbic acid was observed on pH and proximate parameters of the product. Kaladhi treated with 0.3 % Sorbic acid retained most desirable physicochemical and sensory properties throughout the storage period hence, was considered the best.

Sorbic acid stress activates the Candida glabrata high osmolarity glycerol MAP kinase pathway.[Pubmed: 24324463]

Front Microbiol. 2013 Nov 26;4:350.

Weak organic acids such as Sorbic acid are important food preservatives and powerful fungistatic agents.
METHODS AND RESULTS:
These compounds accumulate in the cytosol and disturb the cellular pH and energy homeostasis. Candida glabrata is in many aspects similar to Saccharomyces cerevisiae. However, with regard to confrontation to Sorbic acid, two of the principal response pathways behave differently in C. glabrata. In yeast, Sorbic acid stress causes activation of many genes via the transcription factors Msn2 and Msn4. The C. glabrata homologs CgMsn2 and CgMsn4 are apparently not activated by Sorbic acid. In contrast, in C. glabrata the high osmolarity glycerol (HOG) pathway is activated by Sorbic acid. Here we show that the MAP kinase of the HOG pathway, CgHog1, becomes phosphorylated and has a function for weak acid stress resistance. Transcript profiling of weak acid treated C. glabrata cells suggests a broad and very similar response pattern of cells lacking CgHog1 compared to wild type which is over lapping with but distinct from S. cerevisiae. The PDR12 gene was the highest induced gene in both species and it required CgHog1 for full expression.
CONCLUSIONS:
Our results support flexibility of the response cues for general stress signaling pathways, even between closely related yeasts, and functional extension of a specific response pathway.