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.     

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。     

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.     

Effects of potassium sorbate and other antibotulinal agents on germination and outgrowth of Clostridium botulinum type E spores in microcultures.

The effects of potassium sorbate, sodium hypophosphite, sodium tripolyphosphate, sodium nitrite, and linoleic acid on the germination and outgrowth of Clostridium botulinum type E spores were studied in microcultures. At pH 5.8 to 6.0 in liver veal agar, the germination rate was decreased to nearly zero with 1.0, 1.5, or 2.0% sorbate. At pH 7.0 t 7.2, these levels of sorbate afforded germination and outgrowth of abnormally shaped cells that were defective in cell division. At the high pH range, 0.5 or 1.0% hypophosphite had effects similar to those of sorbate. The use of 0.05% sodium nitrite with sorbate enhanced the lysis of outgrowing cells at pH 7.2 or lower. Emergence and elongation were inhibited by 0.05% linoleic acid with or without 1.0% sorbate at pH 7.0 to 7.2. The addition of 0.5% tripolyphosphate to media containing 1.5% sorbate at pH 7.1 prevented normal cell growth to an extent greater than with sorbate alone.     

Susceptibility of food-borne bacteria to binary combinations of antimicrobials at selected a(w) and pH

AIM: To evaluate the antibacterial susceptibilities of food-borne bacteria to individual and binary mixtures of a synthetic antimicrobial agent with a natural phenolic compound. METHODS AND RESULTS: Antibacterial susceptibilities of Escherichia coli, Listeria innocua, Salmonella Typhimurium and Staphylococcus aureus to individual and binary mixtures of potassium sorbate with a phenolic compound (thymol, carvacrol, or eugenol) were evaluated, at selected water activity (a(w); 0.99 or 0.97) and pH (5.5 or 4.5). The bacteria studied were susceptible to the action of the antimicrobials individually with minimal inhibitory concentrations that varied from 800-ppm potassium sorbate for Staph. aureus at a(w) 0.99, and pH 5.5 to 100-ppm thymol or carvacrol for the four studied bacteria at a(w) 0.97 and pH 4.5. Several binary mixtures of potassium sorbate with thymol, carvacrol or eugenol inhibited bacterial growth. Antimicrobial agent inhibitory concentrations in the mixture varied among bacteria, additionally depending on the a(w) and the pH tested. CONCLUSIONS: Synergistic binary mixtures with fractional inhibitory concentration index <0.6 include 100- or 200-ppm potassium sorbate with 50- or 100-ppm thymol, carvacrol or eugenol. SIGNIFICANCE AND IMPACT OF THE STUDY: The synergistic combinations could be useful in reducing the amounts of antimicrobials needed to inhibit growth, thus diminishing consumer concerns regarding chemical preservatives.     

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.     

Bioproduction of [14C]ochratoxin A in submerged culture.

A number of Aspergillus and Penicillium species were tested for production of ochratoxin A (OA) in several media. After 8 days of static incubations of submerged cultures at 28 degrees C, toxin yields of 25 and 30 micrograms/ml were obtained with Aspergillus alliaceus NRRL 4181 in Ferreirás and 2% yeast extract-4% sucrose media, respectively. However, the largest production observed in the preliminary screening was 54 micrograms/ml; this highest level was produced by A. sulphureus NRRL 4077 in a modified Czapek solution. The medium contained the basal salts and sucrose of Czapek plus urea (3%) and corn steep liquor (0.5% solids). A time study of toxin production demonstrated maximum yield of 350 micrograms/ml by the A. sulphureus isolate in the modified Czapek medium after 11 days of static incubation at 28 degrees C. The optimal production conditions were employed in additional tests designed to measure the efficiency of 14C incorporation from sodium [1-14C]-acetate into OA. Samples (20 microCi) of sodium acetate were added to separate culture flasks at 24-h intervals during the initial 9 days of the fermentation. Addition of [14C]acetate on day 4 of incubation provided the maximum yield of labeled OA. The highest specific activity of labeled toxin obtained was 0.07 microCi/mg of OA and the maximum incorporation rate of labeled acetate was 5.3%.     

Ochratoxin A production by Aspergillus ochraceus Wilhelm grown under controlled atmospheres.

When Aspergillus ochraceus NRRL 3174 was grown under controlled atmospheres with 1 and 5% O2 and without CO2, the amount of ochratoxin produced was the same as that produced by the control colonies. Increasing the O2 level up to 40% reduced ochratoxin production by 75%, whereas at 60% O2, ochratoxin production was enhanced. In atmospheres enriched with 10 or 20% CO2, ochratoxin production was reduced when O2 concentrations were below 20% and enhanced when the O2 concentration was 40 or 60% O2. Ochratoxin production was completely inhibited at 30% CO2 and above, regardless of the O2 level. Colony growth was partially inhibited at 60% CO2, and no growth occurred at 80% CO2 or above. However, when colonies inhibited by 60% CO2 or above were subsequently exposed to air, radial growth, number of sclerotia formed, and the amount of ochratoxin produced were the same as in the control colonies. The results indicate that A. ochraceus is tolerant to CO2 concentrations higher than those required to control storage insects.     

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.     

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.     

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.     

Staphylococcus aureus growth boundaries: moving towards mechanistic predictive models based on solute-specific effects

The formulation of shelf-stable intermediate-moisture products is a critical food safety issue. Therefore, knowing the precise boundary for the growth-no-growth interface of Staphylococcus aureus is necessary for food safety risk assessment. This study was designed to examine the effects of various humectants and to produce growth boundary models as tools for risk assessment. The molecular mobility and the effects of various physical properties of humectants, such as their glass transition temperatures, their membrane permeability, and their ionic and nonionic properties, on S. aureus growth were investigated. The effects of relative humidity (RH; 84 to 95%, adjusted by sucrose plus fructose, glycerol, or NaCl), initial pH (4.5 to 7.0, adjusted by HCl), and potassium sorbate concentration (0 or 1,000 ppm) on the growth of S. aureus were determined. Growth was monitored by turbidity over a 24-week period. Toxin production was determined by enterotoxin assay. The 1,792 data points generated were analyzed by LIFEREG procedures (SAS Institute, Inc., Cary, N.C.), which showed that all parameters studied significantly affected the growth responses of S. aureus. Differences were observed in the growth-no-growth boundary when different humectants were used to achieve the desired RH values in both the absence and the presence of potassium sorbate. Sucrose plus fructose was most inhibitory at neutral pH values, while NaCl was most inhibitory at low pH values. The addition of potassium sorbate greatly increased the no-growth regions, particularly when pH was <6.0. Published kinetic growth and survival models were compared with boundary models developed in this work. The effects of solutes and differences in modeling approaches are discussed.     

Postharvest production of ochratoxin A by Aspergillus ochraceus and Penicillium viridicatum in barley with different protein levels.

The production of ochratoxin A (OA) in barley by Aspergillus ochraceus and Penicillium viridicatum was measured at 12 and 25 degrees C. The grain had been fertilized with various amounts of nitrogen fertilizer (0, 90, or 240 kg/ha) and contained (at crop maturity) 9.1, 10.4, or 12.0% protein, respectively. The production of OA by both fungi increased as the protein concentration increased. Glutamic acid and proline were enriched relative to other amino acids as the protein concentration increased. The differences in OA production could not be explained by a differential effect of protein or amino acids on fungal growth in barley. However, glutamic acid and proline enhanced OA production in liquid cultures of both A. ochraceus and P. viridicatum.     

Effects of natamycin and potassium sorbate on growth and aflatoxin production in olives

Aspergillus flavus NRRL 6555 was inoculated onto whole olives and olive paste samples containing variable amounts of either natamycin or potassium sorbate and incubated at 15 degrees, 25 degrees, and 35 degrees C for 7, 14 and 21 days for whole olives and at 15 degrees and 25 degrees C for 8 and 16 days for olive pastes. The initiation time of growth was parallel to the concentrations of either preservatives applied. However, at 15 degrees C, natamycin at 160 and 320 micrograms/g (ppm) completely inhibited the growth of mold on whole olives for 21 days and olive paste for 7 and 15 days, respectively. All levels of potassium sorbate inhibited mold growth at 15 degrees C, but at 25 degrees C, 6000 micrograms/g (ppm) only, delayed growth for 15 days. The extent of growth at the end of the incubation periods was parallel to the temperatures of incubation. The analyses for aflatoxin B1 production in all samples at all levels of preservatives and control were negative.     

Evaluation of Inhibitory Effect of Organic and Inorganic Salts Against Ilyonectria liriodendri,The Causal Agent of Root Rot Disease of Kiwifruit

This study evaluated efficacy of 42 organic and inorganic salts as possible alternatives to synthetic fungicides for the control of Ilyonectria root rot of kiwifruit. Preliminary in vitro tests showed that ammonium bicarbonate, ammonium carbonate, potassium benzoate, potassium sorbate, sodium benzoate and sodium metabisulphite at 2% completely inhibited mycelial growth of the fungus. No significant differences were observed among these salts and disodium EDTA (P ≤ 0.05). However, the ED₅₀, minimum inhibition concentration (MIC), and minimum fungicidal concentration (MFC) values indicated that sodium metabisulphite was more toxic to Ilyonectria liriodendri than these other six salts. Soil bioassays showed that sodium metabisulphite, sodium benzoate and potassium sorbate at 0.25% completely inhibited mycelial growth of the fungus, whereas potassium benzoate reduced the mycelial growth of fungus by 90.30%; however, the differences in inhibitory effects were statistically insignificant (P ≤ 0.05). Moreover, there was no significant difference between 0.1% sodium metabisulphite and 0.5% ammonium carbonate, 0.75% ammonium bicarbonate and 1.5–2.0% disodium EDTA (P ≤ 0.05). Unlike disodium EDTA, complete inhibitory was observed with ammonium carbonate and ammonium bicarbonate at higher concentrations. However, in root bioassays, applications of 2% ammonium bicarbonate, 1.5% ammonium carbonate and 2% disodium EDTA were phytotoxic to kiwifruit seedlings, but 0.25% four other salts were neither phytotoxic to kiwifruit seedlings nor did it adversely affect root length, root fresh weight and root dry weight of seedling. This study also showed I. liriodendri to be capable of growth in both acidic and basic environments. However, while the fungus showed uninhibited growth at pH values of 5–11, growth decreased significantly at both higher and lower pH values (P ≤ 0.05) and was completely inhibited at pH 12.     

Staphylococcus aureus Growth Boundaries: Moving towards Mechanistic Predictive Models Based on Solute-Specific Effects

The formulation of shelf-stable intermediate-moisture products is a critical food safety issue. Therefore, knowing the precise boundary for the growth-no-growth interface of Staphylococcus aureus is necessary for food safety risk assessment. This study was designed to examine the effects of various humectants and to produce growth boundary models as tools for risk assessment. The molecular mobility and the effects of various physical properties of humectants, such as their glass transition temperatures, their membrane permeability, and their ionic and nonionic properties, on S. aureus growth were investigated. The effects of relative humidity (RH; 84 to 95%, adjusted by sucrose plus fructose, glycerol, or NaCl), initial pH (4.5 to 7.0, adjusted by HCl), and potassium sorbate concentration (0 or 1,000 ppm) on the growth of S. aureus were determined. Growth was monitored by turbidity over a 24-week period. Toxin production was determined by enterotoxin assay. The 1,792 data points generated were analyzed by LIFEREG procedures (SAS Institute, Inc., Cary, N.C.), which showed that all parameters studied significantly affected the growth responses of S. aureus. Differences were observed in the growth-no-growth boundary when different humectants were used to achieve the desired RH values in both the absence and the presence of potassium sorbate. Sucrose plus fructose was most inhibitory at neutral pH values, while NaCl was most inhibitory at low pH values. The addition of potassium sorbate greatly increased the no-growth regions, particularly when pH was <6.0. Published kinetic growth and survival models were compared with boundary models developed in this work. The effects of solutes and differences in modeling approaches are discussed.     

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.     

The effect of potassium sorbate, NaCl and pH on the growth of food spoilage fungi

In this study, the hurdle technology approach was used to prevent fungal growth of common spoilage fungi in naturally fermented black olives (Alternaria alternata, Aspergillus niger, Fusarium semitectum andPenicillium roqueforti). The factors studied included a combination of different concentrations of potassium sorbate (100 up to 1000 mg/L), a range of pH values (4.5, 5, 5.5, 6, and 6.5) and levels of NaCl (0, 3.5, 5, 7.5, and 10%).Alternaria alternata was the most sensitive fungus whereasP. roqueforti was the most resistant fungi against all hurdle factors. The combination of all hurdles completely inhibitedA. alternata andF. semitectum by lowest inhibitory factors, such as 100 mg/L potassium sorbate with 3.5% NaCl at pH 5. On the other hand, at pH 5, A.niger andP. roqueforti were totally prevented by a combination of 300 mg/L potassium sorbate with 10% NaCl and 400 mg/L potassium sorbate with 7.5% NaCl, respectively. Potassium sorbate and 5–10% NaCl interaction had significant stimulation effect onp. roqueforti andA. niger (p<0.05). This study indicates that potassium sorbate is a suitable preserving agent to inhibit growth of fungi in fermented products of pH near 4.5 regardless levels of NaCl. For products of slightly higher pH, the addition of potassium sorbate is suggested in combination with NaCl.     

Inhibition of type A and type B (proteolytic) Clostridium botulinum by sorbic acid

The effect of sorbic acid in the pH range 4.9 to 7.0 on the probability P of growth of a single vegetative bacterium of proteolytic strains of Clostridium botulinum has been determined by comparison of the most probable number count of the bacteria in media at pH 4.9 to 7.0 containing a series of concentrations of potassium sorbate and in a nutrient medium at pH 6.8 to 7.0. The media were maintained under strictly anaerobic conditions at a redox potential equivalent to lower than -350 mV at pH 7. In medium adjusted to the required pH with HCl, P for strain ZK3 (type A) at pH 5.1 or 5.5 after 2 days at 30 degrees C was similar to that at pH 6.8 to 7.0 but was slightly lower at pH 4.9. Potassium sorbate inhibited growth, the inhibition being a function of the concentration of undissociated sorbic acid. A calculated undissociated sorbic acid concentration of 156 mg/liter delayed growth of strain ZK3 (type A) but did not result in a significant decrease in P after an incubation time of 14 days. Higher concentrations of undissociated sorbic acid caused longer delays before maximum most probable number counts developed, and a calculated undissociated sorbic acid concentration of 282 mg/liter decreased log P for strain ZK3 after an incubation time of 14 days by a factor of 5.5 to 7.5. Four additional type A strains and five type B strains were inhibited to an extent comparable to inhibition of strain ZK3.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibition of type A and type B (proteolytic) Clostridium botulinum by sorbic acid.

The effect of sorbic acid in the pH range 4.9 to 7.0 on the probability P of growth of a single vegetative bacterium of proteolytic strains of Clostridium botulinum has been determined by comparison of the most probable number count of the bacteria in media at pH 4.9 to 7.0 containing a series of concentrations of potassium sorbate and in a nutrient medium at pH 6.8 to 7.0. The media were maintained under strictly anaerobic conditions at a redox potential equivalent to lower than -350 mV at pH 7. In medium adjusted to the required pH with HCl, P for strain ZK3 (type A) at pH 5.1 or 5.5 after 2 days at 30 degrees C was similar to that at pH 6.8 to 7.0 but was slightly lower at pH 4.9. Potassium sorbate inhibited growth, the inhibition being a function of the concentration of undissociated sorbic acid. A calculated undissociated sorbic acid concentration of 156 mg/liter delayed growth of strain ZK3 (type A) but did not result in a significant decrease in P after an incubation time of 14 days. Higher concentrations of undissociated sorbic acid caused longer delays before maximum most probable number counts developed, and a calculated undissociated sorbic acid concentration of 282 mg/liter decreased log P for strain ZK3 after an incubation time of 14 days by a factor of 5.5 to 7.5. Four additional type A strains and five type B strains were inhibited to an extent comparable to inhibition of strain ZK3.(ABSTRACT TRUNCATED AT 250 WORDS)