Inhibition of alcoholic fermentation by sorbic acid

Antibacterial Effect of Melanoidins Derived From Xylose and Phenylalanine Against Bacillus cereus and Clostridium perfringens

Melanoidins produced from the combination of D-xylose and L-phenylalanine have been reported to exhibit strong antibacterial effects. This study investigated the influence of environmental factors, such as temperatures (10, 15, 20, 25, 30, 35, 40, and 45°C), pH (5.5, 6.0, 6.5, 7.0, 7.5, and 8.0), and water activity (aw: 0.99, 0.96, and 0.93), on the antibacterial effect of the melanoidins produced from the combination of D-xylose with L-phenylalanine against Bacillus cereus and Clostridium perfringens in culture media. Furthermore, freeze-dried powdered melanoidin was used to determine the minimum concentration for growth inhibition, to compare the antibacterial effect of the melanoidin with conventional food preservatives. The liquid melanoidins significantly inhibited the growth of B. cereus (up to 4 log CFU/mL at the maximum) and C. perfringens (up to 6.5 log CFU/mL at the maximum) regardless of the incubation temperatures. However, the remarkable difference between the presence and absence of the melanoidins was demonstrated in the range of 20-35°C as 4 log-cycle lower in B. cereus and 2 log-cycle lower in C. perfringens than those without the melanoidins. The antibacterial effect of the melanoidin on B. cereus was not influenced by pH from 5.5 to 7.0, which exhibited 2-3 log-cycle lower viable counts than those without the melanoidin. Only one log-cycle difference between with and without the melanoidin was shown in C. perfringens growth under the pH range of 5.5-7.0. Although there was no significant difference in the growth of B. cereus between three aw conditions, the melanoidin exhibited a significant antibacterial effect at aw 0.99 demonstrating 4 log-cycle lower viable numbers than those without the melanoidin. Minimum inhibitory concentration of the melanoidin powder for B. cereus and C. perfringens was 7 mg/mL and 15 mg/mL, respectively, regardless of the kind of foods. Furthermore, the melanoidin exhibited comparable antibacterial effect on B. cereus and C. perfringens to potassium sorbate and sodium benzoate under the same concentration as the minimum inhibitory concentration of the melanoidin, demonstrating 2 log-cycle reduction during 3 days of incubation period at 25°C. The results presented here suggest that the xylose- and phenylalanine-based melanoidin demonstrates the possibility to be an alternative food preservative.

Valorisation of food and beverage waste via saccharification for sugars recovery

Valorisation of mixed food and beverage (F&B) waste was studied for the recovery of sugars via saccharification. Glucoamylase and sucrase were employed to hydrolyse the starch and sucrose present in the mixed F&B waste because of the high cost-effectiveness for such recovery. The Michaelis-Menten kinetics model suggests that preservatives and additives in beverages did not inhibit glucoamylase and sucrase during saccharification. High levels of glucose (228.1 g L^-1) and fructose (55.7 g L^-1) were efficiently produced within 12 h at a solid-to-liquid ratio of 37.5% (w/v) in 2.5 L bioreactors. An overall conversion yield of 0.17 g sugars per g of mixed F&B waste was obtained in mass balance analysis. Lastly, possible industrial applications of the sugar-rich hydrolysate and by-products are discussed. This study is believed to cast insights into F&B waste recycling via biotechnology to produce high-value added products to promote the establishment of a circular bio-economy.

RodZ and PgsA Play Intertwined Roles in Membrane Homeostasis of Bacillus subtilis and Resistance to Weak Organic Acid Stress

Weak organic acids like sorbic and acetic acid are widely used to prevent growth of spoilage organisms such as Bacilli. To identify genes involved in weak acid stress tolerance we screened a transposon mutant library of Bacillus subtilis for sorbic acid sensitivity. Mutants of the rodZ (ymfM) gene were found to be hypersensitive to the lipophilic weak organic acid. RodZ is involved in determining the cell's rod-shape and believed to interact with the bacterial actin-like MreB cytoskeleton. Since rodZ lies upstream in the genome of the essential gene pgsA (phosphatidylglycerol phosphate synthase) we hypothesized that expression of the latter might also be affected in rodZ mutants and hence contribute to the phenotype observed. We show that both genes are co-transcribed and that both the rodZ::mini-Tn10 mutant and a conditional pgsA mutant, under conditions of minimal pgsA expression, were sensitive to sorbic and acetic acid. Both strains displayed a severely altered membrane composition. Compared to the wild-type strain, phosphatidylglycerol and cardiolipin levels were lowered and the average acyl chain length was elongated. Induction of rodZ expression from a plasmid in our transposon mutant led to no recovery of weak acid susceptibility comparable to wild-type levels. However, pgsA overexpression in the same mutant partly restored sorbic acid susceptibility and fully restored acetic acid sensitivity. A construct containing both rodZ and pgsA as on the genome led to some restored growth as well. We propose that RodZ and PgsA play intertwined roles in membrane homeostasis and tolerance to weak organic acid stress.

4: Final Report on the Safety Assessment of Sorbic Acid and Potassium Sorbate

Sorbic acid is a straight-chain monocarboxylic acid used in cosmetic formulations as a preservative at concentrations up to 1.0%.

Sorbic acid and potassium sorbate were practically nontoxic to rats and mice in acute oral toxicity studies. In subchronic studies no significant adverse effects were observed in rats, mice, or dogs when 10% sorbic acid was included in the diet.

Sorbic acid and potassium sorbate at concentrations up to 10% were practically nonirritating to the rabbit eye. Both ingredients at concentrations up to 10% were at most only slightly irritating.

Sorbic acid and potassium sorbate have been tested for mutagenic effects using the Ames test, genetic recombination tests, reversion assays, rec assays, tests for chromosomal aberrations, sister chromatid exchanges, and gene mutations. Results have been both positive and negative.

Potassium sorbate at 0.1% in the diet or 0.3% in drinking water of rats for up to 100 weeks produced no neoplasms. In other chronic studies, no carcinogenic effect was demonstrated by sorbic acid in rats or mice fed diets containing up to 10% sorbic acid.

No teratogenic effects have been observed in pregnant mice and rats administered potassium sorbate.

In three repeat insult patch tests, sorbic acid had overall sensitization rates of 0, 0.33, and 0.8%. All of the subjects sensitized were inducted with 20% sorbic acid and challenged with 5% sorbic acid. Formulations containing up to 0.5% sorbic acid and or potassium sorbate were not significant primary or cumulative irritants and not sensitizers at this test concentration. A formulation containing 0.01% sorbic acid was not a photosensitizer.

On the basis of the available data, it is concluded that sorbic acid and potassium sorbate are safe as cosmetic ingredients in the present practices of use and concentration.

Growth response of Escherichia coli ATCC 35218 adapted to several concentrations of sodium benzoate and potassium sorbate

Escherichia coli ATCC 35218 growth response was evaluated after repetitive cultivation in stepwise increasing antimicrobial agent concentrations (potassium sorbate or sodium benzoate) to observe its adaptation process to high weak-acid concentrations. The effect of antimicrobial (potassium sorbate or sodium benzoate) concentration (0 to 7,000 ppm) was tested using laboratory media. Cells adapted at 1,000 ppm were inoculated in media containing the same concentration of the antimicrobial; after that, cells were transferred to media containing a higher concentration, followed by repetitive cultivations. In every case, viable cells were determined by surface plating every hour up to 48 h. Logarithmic representations of survival or growing fraction were modeled using the Gompertz equation. Adapted and nonadapted cells were analyzed for plasmid presence as well as phosphofructokinase and succinate dehydrogenase activity. Bacterial growth was observed after adaptation processes in media formulated up to 7,000 ppm of potassium sorbate or sodium benzoate. Analyses of variance demonstrated that no significant difference (P > 0.05) in lag time or growth rate was observed among adapted cells cultured in media containing the studied concentrations for each of the antimicrobials tested. These results suggest that E. coli can be adapted to high weak-acid concentrations if the exposure is performed under sublethal conditions. Furthermore, there was demonstrated inhibition of the enzymes phosphofructokinase and succinate dehydrogenase by action of sodium benzoate and potassium sorbate, respectively. E. coli adaptation to antimicrobial agents was not related to plasmid presence but appears to be due to other action mechanisms.

Transcriptome analysis of sorbic acid-stressed Bacillus subtilis reveals a nutrient limitation response and indicates plasma membrane remodeling

The weak organic acid sorbic acid is a commonly used food preservative, as it inhibits the growth of bacteria, yeasts, and molds. We have used genome-wide transcriptional profiling of Bacillus subtilis cells during mild sorbic acid stress to reveal the growth-inhibitory activity of this preservative and to identify potential resistance mechanisms. Our analysis demonstrated that sorbic acid-stressed cells induce responses normally seen upon nutrient limitation. This is indicated by the strong derepression of the CcpA, CodY, and Fur regulon and the induction of tricarboxylic acid cycle genes, SigL- and SigH-mediated genes, and the stringent response. Intriguingly, these conditions did not lead to the activation of sporulation, competence, or the general stress response. The fatty acid biosynthesis (fab) genes and BkdR-regulated genes are upregulated, which may indicate plasma membrane remodeling. This was further supported by the reduced sensitivity toward the fab inhibitor cerulenin upon sorbic acid stress. We are the first to present a comprehensive analysis of the transcriptional response of B. subtilis to sorbic acid stress.

Mechanisms of Fatty Acid Toxicity for Yeast

Neal, A. L. (Rutgers, The State University, New Brunswick, N.J.), Joan O. Weinstock, and J. Oliver Lampen. Mechanisms of fatty acid toxicity for yeast. J. Bacteriol. 90:126-131. 1965.-The internal pH of stationary- and log-phase yeast cells dropped quite rapidly when the cells were exposed to acetate buffers at pH 4 and 3, whereas no, or much less, acidification occurred with pyruvate or phosphate. Although inhibition of respiration and glycolysis was almost instantaneous when the cells were exposed to 0.2 m acetate at pH 4, the effect was not permanent and could be reversed by washing them with water or phosphate buffer. Irreversible inhibition did occur, however, at 0.5 m acetate under the same conditions; there was a marked decrease in several glycolytic enzyme systems, which undoubtedly contributed to the irreversible nature of the inhibition. In cell-free homogenates, various low-molecular-weight monocarboxylic acids exhibited about the same inhibitory effect on glycolysis; structural differences such as branching or unsaturation did not cause a marked change in their inhibitory effect. Also, glycolysis was much more sensitive to dicarboxylic acids such as succinate and phthalate than to acetate; phthalate was more inhibitory than succinate. This is in contrast with the noninhibitory nature of succinate and phthalate to whole cells, even at pH 4. Pyruvic acid decarboxylation was inhibited by phthalate but not by succinate. The greater toxic effect of phthalic acid may be due to the fixed steric configuration of its carboxyl groups, as compared with those of succinic acid.

Weak-acid preservatives: modelling microbial inhibition and response

Weak-acid preservatives are widely used to prevent microbial spoilage of acidic foods and beverages. Characteristically, weak-acid preservatives do not kill micro-organisms but inhibit growth, causing very extended lag phases. Preservatives are more effective at low pH values where solutions contain increased concentrations of undissociated acids. Inhibition by weak-acids involves rapid diffusion of undissociated molecules through the plasma membrane; dissociation of these molecules within cells liberates protons, thus acidifying the cytoplasm and preventing growth. By modelling preservative action in yeast, using a thermodynamic and kinetic approach, it was possible to demonstrate that: (i) inhibition depends more on the degree to which individual preservatives are concentrated within cells, rather than on undissociated acid concentration per se; (ii) it is entirely feasible for microbes to pump protons out of the cell during extended lag phase and raise internal pH (pHi), despite further influx of preservatives; (iii) the duration of the lag phase can be predicted from the model, using a Gaussian fit of proton-pumping H(+)-ATPase activity against pHi; (iv) theoretical ATP consumption for proton pumping can be directly correlated with the reduction in cell yield observed in glucose-limited cultures.

MECHANISMS IN THE INHIBITION OF MICROORGANISMS BY SORBIC ACID

York, George K. (University of California, Davis), and Reese H. Vaughn. Mechanisms in the inhibition of microorganisms by sorbic acid. J. Bacteriol. 88:411-417. 1964.-Oxidative assimilation of glucose, acetate, succinate, and fumarate by washed cells of Escherichia coli, Pseudomonas aeruginosa, and Saccharomyces cerevisiae was inhibited by concentrations of sorbic acid ranging from 15 to 105 mg per 100 ml. At higher concentrations, the oxidation of these substrates was inhibited. Oxidative phosphorylation by submicroscopic particles of E. coli was reduced by about 30% by 37 mg per 100 ml of sorbic acid. The sulfhydryl enzymes fumarase, aspartase, and succinic dehydrogenase were inhibited by sorbic acid. The loss of activity of sorbic acid after reacting with cysteine suggested that a thiol addition occurred, which is believed to be the mechanism of action against sulfhydryl enzymes or cofactors.

Growth characteristics of Saccharomyces rouxii isolated from chocolate syrup

We investigated the growth parameters of Saccharomyces rouxii isolated from spoiled chocolate syrup. The optimum pH range for S. rouxii was 3.5 to 5.5, whereas the minimum and maximum pH values that permitted growth were 1.5 and 10.5, respectively. For cells grown in 0 and 60% sucrose the optimum water activity (aw) values were 0.97 and 0.96, respectively. The optimum temperature for S. rouxii increased with a decreasing aw regardless of whether glucose or sucrose was used as the humectant. The optimum temperatures for S. rouxii were 28 degrees C at an aw of greater than 0.995 and 35 degrees C at an aw of 0.96 to 0.90 in 2 X potato dextrose broth with sucrose. Increasing the sorbate concentration (from 0.03 to 0.10%) caused the growth of S. rouxii to become more inhibited between aws of greater than 0.995 and 0.82. S. rouxii did not grow when the sorbate level was 0.12% (wt/vol). At lower sorbate levels, the effect of sorbate on the growth of S. rouxii depended on the aw level. Lowering the aw enhanced the resistance of S. rouxii to increasing concentrations of potassium sorbate. Permeability and polyol production are discussed with respect to sorbate tolerance of S. rouxii at different aw levels.

Nitrite, nitrite alternatives, and the control of Clostridium botulinum in cured meats

Historically, nitrite has been a component of meat-curing additives for several centuries. In recent years the safety of nitrite as an additive in cured meats has been questioned mainly because of the possible formation of carcinogenic nitrosamines. Nitrite has many important functions in meat curing including its role in color development, flavor, antioxidant properties, and antimicrobial activity. The inhibition of Clostridium botulinum growth and toxin production is an especially important antimicrobial property of nitrite. This review discusses the effects of processing, curing ingredients (especially nitrite), and storage of cured meats in relation to the control of C. botulinum. If nitrite is eliminated from cured meats or the level of usage decreased, then alternatives for the antibotulinal function of nitrite need to be considered. Several potential alternatives including sorbates, parabens, and biological acidulants are discussed.