Effect of pH, temperature, and potassium sorbate on amino acid uptake in Salmonella typhimurium 7136

The effect of sorbate on L-serine and L-histidine uptake in Salmonella typhimurium was studied at various pH levels, temperatures, and amino acid and sorbate concentrations. Low pH had an apparent synergistic effect on amino acid uptake inhibition caused by sorbate. The relationship between sorbate concentration and the amount of amino acid uptake inhibition was not linear. Compared with L-histidine, L-serine uptake was more sensitive to changes in pH, temperature, and sorbate concentration. Various degrees of amino acid uptake inhibition by sorbate may be related to differences between amino acid transport systems. The results of this study suggest that sorbate acts as a noncompetitive inhibitor of amino acid uptake in S. typhimurium.     

Effect of pH, temperature, and potassium sorbate on amino acid uptake in Salmonella typhimurium 7136.

The effect of sorbate on L-serine and L-histidine uptake in Salmonella typhimurium was studied at various pH levels, temperatures, and amino acid and sorbate concentrations. Low pH had an apparent synergistic effect on amino acid uptake inhibition caused by sorbate. The relationship between sorbate concentration and the amount of amino acid uptake inhibition was not linear. Compared with L-histidine, L-serine uptake was more sensitive to changes in pH, temperature, and sorbate concentration. Various degrees of amino acid uptake inhibition by sorbate may be related to differences between amino acid transport systems. The results of this study suggest that sorbate acts as a noncompetitive inhibitor of amino acid uptake in S. typhimurium.     

Comparison of anti-Vibrio activities of potassium sorbate, sodium benzoate, and glycerol and sucrose esters of fatty acids.

The effects of fatty acids and their glycerol and sucrose esters, potassium sorbate, and sodium benzoate on growth of Vibrio parahaemolyticus in laboratory media at pH 6.7 were evaluated. The minimum concentrations at which inhibition by esters of glycerol could be detected were lowest for monolaurin (5 microgram/ml) and monocaprin (40 microgram/ml); these concentrations were lower than those observed for inhibition by lauric and capric acids, respectively. Inhibitory action of sucrose caprylate was detected at 40 microgram/ml, whereas sucrose caprate was effective at 100 microgram/ml; sucrose esters of lauric, myristic, and palmitic acids were ineffective at 100 microgram/ml. Potassium sorbate and sodium benzoate inhibited growth at concentrations as low as 30 and 300 microgram/ml, respectively, and enhanced the rate of thermal inactivation of V. parahaemolyticus at slightly higher concentrations. Fatty acid esters of glycerol and sucrose offer potential as perservatives for slightly acid or alkaline low-fat foods which do not lend themselves to the full antimicrobial action of traditional food preservatives such as potassium sorbate and sodium benzoate.     

Inhibition of growth and patulin synthesis in Penicillium expansum by potassium sorbate and sodium propionate in culture.

Potassium sorbate and sodium propionate brought about a marked inhibition in the growth of Penicillium expansum and a proportionally greater inhibition in the synthesis of patulin by the mold. At inhibitor concentrations used commercially in bakery products, propionate inhibited growth less efficiently than sorbate did but was a more effective inhibitor of patulin synthesis.     

Growth inhibition of putrefactive anaerobe 3679 caused by stringent-type response induced by protonophoric activity of sorbic acid

The inhibitory effects of potassium sorbate on the bioenergetics, phenylalanine uptake, protein synthesis, and certain aspects of cell regulation were examined in putrefactive anaerobe 3679. Undissociated sorbic acid appeared to act as a protonophore by lowering the intracellular pH and dissipating the proton motive force of the membrane. Sorbate inhibited the uptake of phenylalanine, decreased the rate of protein synthesis, and altered patterns of phosphorylated nucleotide accumulation, resulting in increased intracellular concentrations of GTP, ppGpp, and an unidentified compound (possibly pppGpp). The addition of a noninhibitory amount of tetracycline released the inhibition of growth by sorbate. Based on these results, we concluded that the inhibition of putrefactive anaerobe 3679 by sorbate resulted from a stringent-type regulatory response induced by the protonophoric activity of sorbic acid.     

Growth inhibition of putrefactive anaerobe 3679 caused by stringent-type response induced by protonophoric activity of sorbic acid.

The inhibitory effects of potassium sorbate on the bioenergetics, phenylalanine uptake, protein synthesis, and certain aspects of cell regulation were examined in putrefactive anaerobe 3679. Undissociated sorbic acid appeared to act as a protonophore by lowering the intracellular pH and dissipating the proton motive force of the membrane. Sorbate inhibited the uptake of phenylalanine, decreased the rate of protein synthesis, and altered patterns of phosphorylated nucleotide accumulation, resulting in increased intracellular concentrations of GTP, ppGpp, and an unidentified compound (possibly pppGpp). The addition of a noninhibitory amount of tetracycline released the inhibition of growth by sorbate. Based on these results, we concluded that the inhibition of putrefactive anaerobe 3679 by sorbate resulted from a stringent-type regulatory response induced by the protonophoric activity of sorbic acid.     

Inhibition by antimicrobial food additives of ochratoxin A production by Aspergillus sulphureus and Penicillium viridicatum

The effects of antimicrobial food additives on growth and ochratoxin A production by Aspergillus sulphureus NRRL 4077 and Penicillium viridicatum NRRL 3711 were investigated. At pH 4.5, growth and toxin production by both A. sulphureus and P. viridicatum were completely inhibited by 0.02% potassium sorbate, 0.067% methyl paraben, 0.0667% methyl paraben, and 0.2% sodium propionate. At pH 5.5, 0.134% potassium sorbate and 0.067% methyl paraben completely inhibited growth and ochratoxin A production by both fungi. Sodium bisulfite at 0.1%, the maximum level tested, was found to inhibit growth of A. sulphureus and P. viridicatum by 45 and 89%, respectively. Toxin production was inhibited by 97 and 99%, respectively. Sodium propionate (0.64%) at pH 5.5 inhibited growth of A. sulphureus and P. viridicatum by 76 and 90%, respectively. Toxin production was inhibited by greater than 99% for each fungus. Antimicrobial agents were ranked as to effectiveness by comparing the level required for complete inhibition of ochratoxin A production to the highest antimicrobial agent level normally used in food. At pH 4.5, the most effective inhibitor of growth and toxin production was potassium sorbate, followed by sodium propionate, methyl paraben, and sodium bisulfite, respectively, for both fungi. However, at pH 5.5, the most effective antimicrobial agents for inhibiting ochratoxin production were methyl paraben and potassium sorbate, followed by sodium propionate. Sodium bisulfite was not highly inhibitory to these toxigenic fungi at the higher pH value tested.     

Inhibition by antimicrobial food additives of ochratoxin A production by Aspergillus sulphureus and Penicillium viridicatum.

The effects of antimicrobial food additives on growth and ochratoxin A production by Aspergillus sulphureus NRRL 4077 and Penicillium viridicatum NRRL 3711 were investigated. At pH 4.5, growth and toxin production by both A. sulphureus and P. viridicatum were completely inhibited by 0.02% potassium sorbate, 0.067% methyl paraben, 0.0667% methyl paraben, and 0.2% sodium propionate. At pH 5.5, 0.134% potassium sorbate and 0.067% methyl paraben completely inhibited growth and ochratoxin A production by both fungi. Sodium bisulfite at 0.1%, the maximum level tested, was found to inhibit growth of A. sulphureus and P. viridicatum by 45 and 89%, respectively. Toxin production was inhibited by 97 and 99%, respectively. Sodium propionate (0.64%) at pH 5.5 inhibited growth of A. sulphureus and P. viridicatum by 76 and 90%, respectively. Toxin production was inhibited by greater than 99% for each fungus. Antimicrobial agents were ranked as to effectiveness by comparing the level required for complete inhibition of ochratoxin A production to the highest antimicrobial agent level normally used in food. At pH 4.5, the most effective inhibitor of growth and toxin production was potassium sorbate, followed by sodium propionate, methyl paraben, and sodium bisulfite, respectively, for both fungi. However, at pH 5.5, the most effective antimicrobial agents for inhibiting ochratoxin production were methyl paraben and potassium sorbate, followed by sodium propionate. Sodium bisulfite was not highly inhibitory to these toxigenic fungi at the higher pH value tested.     

Use of organic acids and salts to control postharvest diseases of lemon fruits in Egypt

Abstract

Postharvest diseases caused by Geotricum candidum (sour rot), Penicillium digitatum (green mould), and P. italicum (blue mould) are the most important negative factors affecting handling and marketing of citrus fruits in Egypt. The effect of organic acids (ascorbic, benzoic, citric and sorbic) as well as organic salts (potassium sorbate and sodium benzoate) were evaluated on the growth of causal agents and their disease incidence under in vitro and in vivo conditions. Complete inhibition was observed in the linear growth of all tested fungi when exposed to benzoic, citric and sorbic organic acids at concentrations of 4% and 2% of either sodium benzoate or potassium sorbate, respectively. Minimizing the tested concentration of organic acid down to 2%, the tested fungi fluctuated in their response such that only benzoic and sorbic acids could completely inhibit the growth of either P. digitatum or P. italicum only. Different organic acids and salts showed various levels of either protective or therapeutic effect for coated lemon fruits against mould infection whatever the time of their artificial inoculation under in vivo conditions. All treated fruits showed reduction in sour rot and green and blue mould diseases when compared with untreated fruits. Complete inhibition of mould incidence was obtained in coated lemon fruits with 4% of water or wax mixtures of sodium benzoate and potassium sorbate 24 hours before inoculation. Also, high reduction in mould incidence was observed in lemon fruits coated with the same concentration at 48 hours after inoculation under the same conditions. On the other hand, the tested organic acids showed a lesser effect on mould incidence. Moreover, they were more effective against mould incidence when dissolved in water than wax, that only 4% of water mixture of sorbic and benzoic acids showed 100% protection against mould incidence. Furthermore, the severity of infection records followed the same trend. The present findings demonstrate that potassium sorbate and sodium benzoate have potential as environmentally friendly products, nontoxic postharvest fungicides against sour rot, green and blue mould incidence of stored citrus fruits and could be suggested for commercial use in packing-houses in consideration to their wide consumption as safely food preservatives.     

Effectiveness of various food preservatives in controlling the outgrowth of Byssochlamys nivea ascospores

Potassium sorbate, sodium benzoate, sulfur dioxide, and diethylpyrocarbonate (DEPC) were tested for their effectiveness in preventing the outgrowth ofByssochlamys nivea Westling ascospores. Sulfur dioxide was the most inhibitory of the test antimycotics, complete inhibition of colony formation occurring in acidified (pH 3.5) potato dextrose agar containing 50 ppm of the preservative. Complete inhibition ofB. nivea ascospore outgrowth in grape juice stored for 60 days was noted in the presence of 300 ppm sulfur dioxide, 400 ppm potassium sorbate, and 600 ppm DEPC. Growth was observed in grape juice containing 1000 ppm sodium benzoate. The presence of up to 100 ppm potassium sorbate in grape juice during heat activation appears to have a stimulatory effect on breaking dormancy, while the other test preservatives at this concentration decrease the heat resistance ofB. nivea ascospores. The time elapsed between heat shock and exposure to DEPC or sodium benzoate is critical with respect to the sensitivity of ascospores to these preservatives.     

Growth and fumitremorgin production by Neosartorya fischeri as affected by food preservatives and organic acids

The effects of potassium sorbate, sodium benzoate, sulphur dioxide and citric, malic and tartaric acids on growth and fumitremorgin production by a heat-resistant mould, Neosartorya fischeri , cultured on Czapek yeast autolysate agar (CYA) were studied over a 32-day incubation period. Colonies were examined, and extracts of agar and mycelia were analyzed for mycotoxin content using high performance liquid chromatography (HPLC). Growth of N. fischeri always resulted in production of the fumitremorgins verruculogen and fumitremorgin A and C. Growth on CYA (pH 3.5) was highly repressed by potassium sorbate and sodium benzoate; 75 mg/1 completely inhibited germination of ascospores. Sulphur dioxide was less inhibitory; growth occurred on CYA containing 100 but not 200 mg/1. Growth of N. fischeri was significantly reduced when the pH of CYA was reduced from 7.0 to 4.5 to 3.5 to 2.5. Citric, malic and tartaric acids promoted growth and fumitremorgin production when supplemented to CYA (pH 2.5). These observations indicate that growth and fumitremorgin production by N. fischeri are influenced by pH and type of acid present and can be controlled by small amounts of preservatives.     

The ZbYME2 gene from the food spoilage yeast Zygosaccharomyces bailii confers not only YME2 functions in Saccharomyces cerevisiae, but also the capacity for catabolism of sorbate and benzoate, two major weak organic acid preservatives

A factor influencing resistances of food spoilage microbes to sorbate and benzoate is whether these organisms are able to catalyse the degradation of these preservative compounds. Several fungi metabolize benzoic acid by the beta-ketoadipate pathway, involving the hydroxylation of benzoate to 4-hydroxybenzoate. Saccharomyces cerevisiae is unable to use benzoate as a sole carbon source, apparently through the lack of benzoate-4-hydroxylase activity. However a single gene from the food spoilage yeast Zygosaccharomyces bailii, heterologously expressed in S. cerevisiae cells, can enable growth of the latter on benzoate, sorbate and phenylalanine. Although this ZbYME2 gene is essential for benzoate utilization by Z. bailii, its ZbYme2p product has little homology to other fungal benzoate-4-hydroxylases studied to date, all of which appear to be microsomal cytochrome P450s. Instead, ZbYme2p has strong similarity to the matrix domain of the S. cerevisiae mitochondrial protein Yme2p/Rna12p/Prp12p and, when expressed as a functional fusion to green fluorescent protein in S. cerevisiae growing on benzoate, is largely localized to mitochondria. The phenotypes associated with loss of the native Yme2p from S. cerevisiae, mostly apparent in yme1,yme2 cells, may relate to increased detrimental effects of endogenous oxidative stress. Heterologous expression of ZbYME2 complements these phenotypes, yet it also confers a potential for weak acid preservative catabolism that the native S. cerevisiae Yme2p is unable to provide. Benzoate utilization by S. cerevisiae expressing ZbYME2 requires a functional mitochondrial respiratory chain, but not the native Yme1p and Yme2p of the mitochondrion.     

山苍子油对霉菌抗菌性及其与黄曲霉产毒关系的研究

采用平板法比较天然增香剂山苍子油与合成食用防腐剂苯甲酸钠、山梨酸钾对8种霉菌的抗菌效力。结果表明,在培养基pH4．5时山苍子油对多数霉菌的最低抑菌浓度为1．77mg／ml,与山梨酸钾的抑菌强度相近,比苯甲酸钠强;但当培养基pH5．5以上时苯甲酸钠对霉菌几乎无效,山梨酸钾的抗菌效力也有减弱,而山苍子油受影响很小,其活性pH范围为4．5～8．5。山苍子油用脂肪酸蔗糖酯乳化,其抗菌效力增强一倍。同时,从山苍子油与黄曲霉产毒关系的实验中发现,山苍子油对黄曲霉产生黄曲霉毒素有较强的抑制作用。     

Effect of potassium sorbate,sodium benzoate,and sodium nitrite on biosynthesis of cyclopiazonic and mycophenolic acids and citrinin by fungi of the <Emphasis Type="Italic">Penicillium</Emphasis> genus

The effect of potassium sorbate, sodium benzoate, and sodium nitrite used as preservatives in the food industry in the production of such mytotoxins as citrinin cyclopiazonic and mycophenolic acids by the contaminating fungi Penicillium citrinum, P. commune, and P. brevicompactum, respectively, was investigated. It was shown that the effect of preservatives used at concentrations relevant to the food industry on the synthesis of mycotoxins depended on the species-specific biochemical and physiological features of the cultures. The growth of P. brevicompactum was inhibited to the highest degree by sodium nitrite and potassium sorbate, and the growth of P. commune was so inhibited by sodium benzoate. It was established that the introduction of 0.015% sodium nitrite into the medium resulted in 1.3- and 1.4-fold reductions of the production of citrinin and mycophenolic acid, respectively, while the production of cyclopiazonic acid did not change in comparison with the control. The introduction of 0.015% sodium benzoate caused a more than 1.5-fold increase of the concentration of citrinin, cyclopiazonic, and mycophenolic acids, and the addition of 0.02% potassium sorbate increased the production of cyclopiazonic and mycophenolic acids by 1.7 and 2.6 times, respectively.     

Sensitization of thermally injured spores of Bacillus stearothermophilus to sodium benzoate and potassium sorbate

The effects of sodium benzoate and potassium sorbate added to the recovery medium, at different pH values (6·5, 6·0 and 5·0), on the recovery rates and heat resistance of Bacillus stearothermophilus spores (ATCC 12980, 7953, 15951 and 15952) were investigated. Heated spores of strains 12980 and 7953 were inhibited by sorbate concentrations over 0·05%. Potassium sorbate at concentrations as low as 0·025%, and sodium benzoate at 0·1%, were very effective inhibitory agents for heat-damaged spores. Their effectiveness always increased at pH 5·0, at which no growth occurred, with sodium benzoate for strains 7953, 15951 and 15952, and with potassium sorbate for strains 15951 and 15952. Decimal reduction times, whenever recovery was possible, were not significantly ( P  > 0·05) affected. None of these compounds modified the z -values obtained for the spores of the four strains, which had a mean value of 7·53 ± 0·28.     

Weak organic acid stress inhibits aromatic amino acid uptake by yeast, causing a strong influence of amino acid auxotrophies on the phenotypes of membrane transporter mutants.

The ability of yeasts to grow in the presence of weak organic acid preservatives is an important cause of food spoilage. Many of the determinants of acetate resistance in Saccharomyces cerevisiae differ from the determinants of resistance to the more lipophilic sorbate and benzoate. Interestingly, we show in this study that hypersensitivity to both acetate and sorbate results when the cells have auxotrophic requirements for aromatic amino acids. In tryptophan biosynthetic pathway mutants, this weak acid hypersensitivity is suppressed by supplementing the medium with high levels of tryptophan or, in the case of sorbate sensitivity, by overexpressing the Tat2p high affinity tryptophan permease. Weak acid stress therefore inhibits uptake of aromatic amino acids from the medium. This allows auxotrophic requirements for these amino acids to strongly influence the resistance phenotypes of mutant strains. This property must be taken into consideration when using these phenotypes to attribute functional assignments to genes. We show that the acetate sensitivity phenotype previously ascribed to yeast mutants lacking the Pdr12p and Azr1p plasma membrane transporters is an artefact arising from the use of trp1 mutant strains. These transporters do not confer resistance to high acetate levels and, in prototrophs, their presence is actually detrimental for this resistance.     

Kinetics of biodegradation of p-nitrobenzoate and inhibition by benzoate in a pseudomonad.

The degradation of p-nitrobenzoate (p-NBA) by domestic sewage was inhibited by benzoate, and a model for this behavior was found in a soil isolate. The isolate, a pseudomonad, utilized p-NBA and benzoate by separate adaptive enzyme pathways. In oxygen uptake experiments, the degradation of p-NBA was competitively inhibited by benzoate, but the degradation of benzoate was not affected by the presence of p-NBA. 4-Nitrocatechol was not implicated in the inhibition. p-Hydroxybenzoate, which is the p-NBA degradation pathway, also had a decreased rate od degradation when benzoate was present. The growth rate of the isolate on the aromatic substrates and on glucose autoclaved in the medium was 0.3 h-1. When glucose was autoclaved separately, the growth rate was less, about 0.2 h-1. The apparent Km in oxygen uptake experiments was 25 micrometer for p-NBA and benzoate and 5 micrometer for p-hydroxybenzoate.     

Involvement of transport in Rhodobacter sphaeroides chemotaxis.

The chemotactic response to a range of chemicals was investigated in the photosynthetic bacterium Rhodobacter sphaeroides, an organism known to lack conventional methyl-accepting sensory transduction proteins. Strong attractants included monocarboxylic acids and monovalent cations. Results suggest that the chemotactic response required the uptake of the chemoeffector, but not its metabolism. If a chemoeffector could block the uptake of another attractant, it also inhibited chemotaxis to that attractant. Sodium benzoate was not an attractant but was a competitive inhibitor of the propionate uptake system. Binding in an active uptake system was therefore insufficient to cause a chemotactic response. At different concentrations, benzoate either blocked propionate chemotaxis or reduced the sensitivity of propionate chemotaxis, an effect consistent with its role as a competitive inhibitor of uptake. Bacteria only showed chemotaxis to ammonium when grown under ammonia-limited conditions, which derepressed the ammonium transport system. Both chemotaxis and uptake were sensitive to the proton ionophore carbonyl cyanide m-chlorophenylhydrazone, suggesting an involvement of the proton motive force in chemotaxis, at least at the level of transport. There was no evidence for internal pH as a sensory signal. These results suggest a requirement for the uptake of attractants in chemotactic sensing in R. sphaeroides.