Potassium Sorbate Concentration Research Articles

Evaluation of the indirect conductance method for the detection of yeasts in laboratory media and apple juice

The technique of indirect conductimetry was examined to asses growth of seven yeast species (Candida glabrata, C. parapsilosis, Debaryomyces hansenii, Pichia membranaefaciens, Rhodotorula glutinis, Saccharomyces cerevisiae, Zygosaccharomyces bailii) in terms of detection time, maximum rate of change in conductance and maximum change in conductance in laboratory media and apple juice. Conductance parameters were dependent on the species, population density, temperature, pH, aw and potassium sorbate concentration. Indirect conductimetry can be applied to detect yeasts at populations as low as 101 cfu ml-1 within 48 h at 30°C. A defined medium is not required to enhance conductivity. Measurements can be done directly in apple juice without interference of juice constituents with conductance signals. Compared to direct conductimetry, the indirect method is more sensitive, giving shorter detection times and higher rates of change in conductance. Conductance responses measured by the indirect method correlated well with viable yeast populations determined by conventional plate count techniques. Indirect conductimetry has potential as a rapid, convenient and reliable method to evaluate product quality and stability, and it may also have application in developing model systems to predict shelf-life of foods subject to yeast spoilage.

Effects of potassium sorbate on growth patterns, morphology, and heat resistance of Zygosaccharomyces rouxii at reduced water activity.

A study was made of the effects of potassium sorbate on growth, morphology, and heat sensitivity of an osmotolerant yeast, Zygosaccharomyces rouxii, grown in media (water activity (aw) 0.93) supplemented with glucose and sucrose. Growth patterns of Z. rouxii in YM broth supplemented with glucose (YMBG) and sucrose (YMBS) were similar, although increased potassium sorbate concentration in both media resulted in decreased growth rates. Growth in YMBS containing potassium sorbate was not as prolific as that in YMBG containing potassium sorbate. Inhibition of growth was indicated by decreased absorbance (at 600 nm) of cells grown in YMBS and in YMBG and YMBS supplemented with potassium sorbate at 600 or 1000 micrograms/mL. Slight decreases in cell size and alteration of cellular morphology were associated with increased potassium sorbate concentration. Plasmolysis increased as potassium sorbate concentration was elevated in YMBS but not in YMBG. Tolerance of Z. rouxii to potassium sorbate was enhanced by previous adaptation of cells in media with elevated potassium sorbate concentrations. Heat resistance of cells unadapted to potassium sorbate showed little or no increase regardless of culture age, but increased substantially in cells grown in media containing potassium sorbate, particularly YMBS.

Inhibition, Injury, and Inactivation of Four Psychrotrophic Foodborne Bacteria by the Preservatives Methyl ρ-Hydroxybenzoate and Potassium Sorbate

The minimum inhibitory concentrations (MICs) of methyl ρ-hydroxybenzoate (methyl paraben) and potassium sorbate for four psychrotrophic bacteria were compared at pH 5 and 6 and at 5 and 30°C. The bacteria tested were Listeria monocytogenes, Pseudomonas putida, Yersinia enterocolitica, and Aeromonas hydrophila. L. monocytogenes was generally the most resistant and A. hydrophila the least resistant to the preservatives. The differences between the bacteria were substantial. The MICs of the two preservatives were similar at pH 5, but at pH 6 the MICs of paraben were well below those of sorbate, except in the case of A. hydrophila. The MICs at 5°C were much lower than those observed at 30°C for all of the bacteria except P. putida. All four bacteria were inhibited by 1000 mg methyl paraben per L at 5°C. Exposure of the bacteria to concentrations of preservative that permitted growth at 30°C did not lead to adaptation to the preservative. The death rates of the bacteria in media containing 1000 mg methyl paraben per L varied over a wide range. At 5°C, a 3 log10 decrease in viable counts of L. monocytogenes and A. hydrophila took >4 months and a few days, respectively. Injury of L. monocytogenes, Y. enterocolitica, and A. hydrophila was detected under these conditions. Repair of the injury was demonstrated, with up to 24 h required for complete recovery. The type of buffer in which the test medium was prepared affected the preservative MICs and rate of injury of L. monocytogenes.

Control of fermentation problems in a gas packaged bakery product using a response surface methodology approach

English style crumpets of a w 0·98 and pH of 6·0 were packaged in a CO 2:N 2 (60:40) gas mixture, stored at 25°C and 30°C monitored for changes in package volume. For packages stored at 25°C, package volume decreased during the initial storage period. Subsequent in-package C0 2 production resulted in all packages having a blown appearance when a critical volume of 1700 ml was reached after 16–20 days storage at 30°C and 25°C respectively. Effects of water activity (a w ), pH, storage temperature, concentration of potassium sorbate, C0 2: air ratio and inoculum level on the growth of, and C0 2 production by Leuconostoc mesenteroides, the major spoilage isolate of gas packaged crumpets, were studied in agar and broth model systems using an experimental design termed Response Surface Methodology (RSM). The preliminary screening design indicated that a w , pH and storage temperature were the most significant variables influencing growth of L. mesenteroides in an agar model system. Further study to evaluate the effects of the three variables on C0 2 production by L. mesenteroides in a broth model system generated a second order polynomial equation which was used to predict levels of C0 2 production under various combinations of these variables. Based on this and previous studies, it was found that crumpets reformulated to a w 0·965–0·97 and pH 5·25–7·25 and packaged in 60% C0 2 could be stored at ambient temperature for 25–30 days without visible mold growth, or C0 2 production and swelling of packages. This study demonstrated RSM as a powerful and useful research tool when several variables are to be studied simultaneously.

Influence of Potassium Sorbate on the Growth of Yersinia enterocolitica

The growth and survival of Yersinia enterocolitica 0:3 and 0:8 were determined using Brain Heart Infusion Broth at pH 5.5 or 6.5, with 0, 250, 500, 1000, 1500, 2500, or 5000 ppm potassium sorbate, and incubated at 25 or 3°C. Results showed that Y. enterocolitica was susceptible to the antimicrobial activity of potassium sorbate. At 25°C and pH 5.5, a population increase of 6.8 and 6.9 log CFU/ml was noted for Y. enterocolitica serotypes 0:3 and 0:8, respectively, in broth without potassium sorbate. The presence of 1000–1500 ppm potassium sorbate in broth retarded the growth of the inoculated Y. enterocolitica cells or partially or completely inactivated them. At 25°C and pH 6.5, potassium sorbate at a concentration as high as 5000 ppm did not inactivate this pathogen. All the concentrations of potassium sorbate tested only retarded the growth of Y. enterocolitica. A 3°C and pH 5.5, Y. enterocolitica grew slightly in the control broth. The presence of 250–500 ppm or more potassium sorbate in broth completely inhibited the growth of Y. enterocolitica or reduced the number of viable cells. At 3°C and pH 6.5, a slight increase in the population of Y. enterocolitica was observed in the broth with or without potassium sorbate, but the increase slacked off as the amount of potassium sorbate was increased.

Inhibition and Inactivation of Listeria monocytogenes by Sorbic Acid

Inhibition and inactivation of Listeria monocytogenes by sorbic acid were studied using tryptose broth supplemented with 0, 0.05, 0.1, 0.15, 0.2, 0.25 or 0.3% potassium sorbate; adjusted to pH 5.6 or 5.0; and incubated at 4, 13, 21 or 35°C. The bacterium grew in sorbate-free controls under all conditions except at 4°C and pH 5.0. At pH 5.6 and 4°C, the bacterium was inactivated by 0.25 or 0.3% of potassium sorbate after 66 and 60 d. Other concentrations permitted slight growth followed by decreases in populations. At 4°C and pH 5.0, concentrations of 0.15 to 0.3% potassium sorbate completely inactivated the pathogen in 60 to 36 d, whereas the other concentrations caused a gradual decrease in populations during the incubation period. At 13°C and pH 5.6, L. monocytogenes grew at all test concentrations of potassium sorbate, but the maximum populations were directly related to the concentration of potassium sorbate added to the medium - the higher the concentration, the lower the ultimate maximum population. At 13°C and pH 5.0, concentrations of 0.2, 0.25 or 0.3% potassium sorbate completely inhibited growth and caused complete inactivation of the pathogen, whereas presence of 0.15% or less potassium sorbate allowed growth of the pathogen. At 21 and 35°C and pH 5.6, appreciable growth of L. monocytogenes occurred at all test concentrations of sorbate. Reducing the pH to 5.0 allowed limited growth of the pathogen at 21 and 35°C when the medium contained 0.05, 0.1 or 0.15% potassium sorbate. Higher concentrations caused either complete inhibition or inhibition plus partial or complete inactivation of L. monocytogenes.

Use of response surface methodology in shelf life extension studies of a bakery product

Effects of water activity, pH, storage temperature, concentration of potassium sorbate, CO 2 concentration in the package headspace and inoculum level on growth of Aspergillus niger, the major spoilage isolate of English style crumpets, was studied on an agar model system using an experimental design termed Response Surface Methodology. The initial screening design indicated that a w, pH, levels of potassium sorbate, CO 2 and storage temperature were significant variables. When a central composite rotatable design was subsequently applied to four variables with pH held constant at pH 6.5 only a w, storage temperature and CO 2 level were found to have a significant effect on mold growth. Using multiple regression analysis, a second order polynomial model was derived and used to predict the number of days to visible mold growth under various combinations of the remaining three variables. Generation of contour plots enabled selection of levels for each variable to give a product with a desired mold free shelf life. Typically, crumpets with an a w of 0.96, packaged in 62% CO 2 had a mold free shelf life of 20 d when stored at 20°C. The observed shelf life results agreed well with predicted values on Potato Dextrose Agar and demonstrated RSM as a powerful and elegant research tool when several variables are to be evaluated simultaneously.

Resistance of Sporolactobacillus to potassium sorbate and sodium nitrite

The resistance of Sporolactobacillus to different concentrations of potassium sorbate and sodium nitrite in autoclaved glucose yeast-extract peptone broth, pH 6.0, was determined. The minimum inhibitory concentration of potassium sorbate that completely inhibited outgrowth of endospores and vegetative growth of Sporolactobacillus inulinus ATCC 15538 was 4000 μg/ml and 5000 μg/ml, respectively. For twelve isolates of Sporolactobacillus the average minimum inhibitory concentrations of potassium sorbate that completely inhibited outgrowth of endospores and vegetative growth were 5000 μg/ml and 7000 μg/ml, respectively. Resistance of endospores of Sporolactobacillus to different sodium nitrite concentrations was high. Outgrowth of spores took place at sodium nitrite concentrations as high as 2000 μg/ml.

Growth and Aflatoxin Production by Aspergillus parasiticus NRRL 2999 in the Presence of Potassium Benzoate or Potassium Sorbate and at Different Initial pH Values

Experiments were done to determine how different concentrations of potassium benzoate or potassium sorbate in a glucose-yeast extract-salts medium with an initial pH value of 3.5, 4.5 or 5.5 affected growth and aflatoxin production by Aspergillus parasiticus NRRL 2999. The pH of the medium, weight of mycelium and amount of aflatoxin produced were determined after 3 and 7 d of incubation. Aflatoxin was determined using reversed-phase high-performance liquid chromatography. Maximum concentrations of potassium sorbate and potassium benzoate that permitted growth were 0.2% and 0.4%, respectively, in a medium with an initial pH of 5.5. When the initial pH was 4.5, the maximum concentrations of potassium sorbate and potassium benzoate that permitted growth were 0.05% and 0.10%, respectively, but there was an extended lag phase. Increasing concentrations of potassium benzoate or potassium sorbate decreased amounts of aflatoxin B1 and G1 produced after 3 d in a medium with initial pH values of 5.5 or 4.5. Cultures growing in the medium containing 0.1, 0.15 or 0.20% potassium benzoate or potassium sorbate and with an initial pH of 5.5 were somewhat inhibited at 3 d of incubation, which was characterized by a slow decrease in pH, low mycelium dry weight and small amounts of accumulated aflatoxins. After 7 d these cultures overcame the initial inhibition and produced substantial amounts of aflatoxins and mycelium. This was also true for cultures growing in a medium with an initial pH of 4.5 and containing potassium benzoate or potassium sorbate. By decreasing the initial pH of the medium from 5.5 to 4.5, amounts of potassium benzoate or potassium sorbate required to achieve inhibition decreased by a factor of 10.

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)

Potassium Sorbate Inhibition of Microorganisms Growing on Refrigerated Packaged Beef

ABSTRACTThe influence of potassium sorbate concentration (27–1325 ppm of sorbic acid) on the growth of natural flora in raw beef samples wrapped in plastic films of different oxygen permeability was studied at 0° and 4°C. Changes in aerobic plate counts, Pseudomonas spp., Brochothrix thermosphacta, Lactobacillus spp., Enterobacteriaceae and yeasts were monitored. Sorbate treatment effect on percentage increment of lag phase and reduction of growth rate during exponential phase for the different microorganisms were analyzed and antimicrobial action was evaluated by the Inhibition Index. A significant increase in the time to reach aerobic counts of 106.5 CFU/cm2 was observed at low storage temperatures and pH values in vacuum packaged treated samples.

INFLUENCE OF POTASSIUM SORBATE AND SELECTED ANTIOXIDANTS ON GROWTH OF Salmonella senftenberg1

ABSTRACT The effect of potassium sorbate alone and in combination with butyl hydroxyanisole (BHA), tertiary butylhydroquinone (TBHQ), or propyl gallate (PG) on the growth of Salmonella senftenberg was studied. Growth studies were first made using trypticase soy broth (pH5.5) at 37°C. Certain combinations of sorbate with BHA, TBHQ and PG resulted in synergistic inhibition of growth of the test microorganisms. Concentrations of 0.2% potassium sorbate and 200 ppm BHA was the most effective in inhibition of growth of S. senftenberg. The concentrations of potassium sorbate, combined with BHA, TBHQ or PG, that were the most effective in synergistic inhibition of growth of S. senftenberg in media were used to study the effectiveness of sorbate/antioxident combinations in a food system. Fresh ground beef was employed as the food system and held at elevated abuse temperature (30°C). All the sorbate/antioxidant combinations tested resulted in destruction or suppressed final growth of S. senftenberg. The antimicrobial effectiveness of sorbate/antioxidant combinations in fresh ground beef was markedly diminished, compared to media studies. The diminished effectiveness can probably be attributed to autoxidation of the ground beef lipid content and the antioxidant being used up to prevent the autoxidation. Potassium sorbate alone in ground beef was found to be effective in the limitations of S. senftenberg growth. All potassium sorbate/antioxidant and potassium sorbate alone treatments in ground beef were found to significantly inhibit (P>0.05) growth of the test organism when compared to control samples.

Effect of Anti-oxidants on Growth and Lactic Acid Production by Streptococcus mutans

The effects of three anti-oxidants--tertiary butylhydroquinone (TBHQ), butylated hydroxyanisole (BHA), and butylated hydroxytoluene (BHT)--on both growth and lactic acid production by eight cariogenic strains of Streptococcus mutans were investigated. Synergistic inhibitory effects of potassium sorbate on lactic acid production were also determined. All three anti-oxidants are phenolic derivatives and are commonly used in food systems due to their excellent "carry-through" properties during processing. Growth inhibition was determined by turbidity measurements at 600 nm. Lactic acid was assayed by gas chromatography, and bacterial DNA was assayed by the diphenylamine reaction. There were reduced growth levels of S. mutans due to the anti-oxidants and potassium sorbate for at least 12 hr, with TBHQ and BHA still inhibiting growth at 24 hr. Nearly all concentrations of anti-oxidants and potassium sorbate reduced lactic acid production by S. mutans, but only TBHQ significantly inhibited lactic acid production when the amount of acid per microgram DNA was calculated. A synergistic reduction of lactic acid production by S. mutans does occur in most combinations of potassium sorbate with anti-oxidants.

Inhibition of Penicillia and Aspergilli by Potassium Sorbate

Cultures of molds from the genera Penicillium (25 isolates) and Aspergillus (18 isolates) were inoculated onto YM agar fortified with different concentrations of potassium sorbate to determine their abilities to grow in the presence of this compound. Molds were incubated for up to 30 d at 25 or 4°C. Nine of the penicillia grew in the presence of 3000 ppm or more of sorbate at both temperatures. All of these molds were isolated from sorbate-treated cheeses. None of the aspergilli grew in the presence of 2000 ppm or more of sorbate and only three strains grew in the presence of 1000 ppm of sorbate at 25°C. None of the aspergilli grew in the presence of 500 ppm of sorbate at 4°C.

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.

Influence of Potassium Sorbate and Reduced pH on the Growth of Vegetative Cells of Four Strains of Type A and B Clostridium botulinum

ABSTRACTGrowth of vegetative cells of four strains of Clostridium botulinum was measured as the average A630nm of five replicate peptone‐yeast extract broth cultures at 37°C. Media pH values ranged from 7.1 to 5.5 and potassium sorbate concentrations of 0 or 0.26%. Growth ratios (GR = treatment/control) based on the time to reach an A = 0.35 were calculated. Predicted GR's from the linear regression of log (GR) vs log (undissociated sorbic acid concentration) were used to compare strains. Reduced pH (>5.5) had minimal effects on GR. Sorbate inhibited the growth of all strains at 250 mg/L undissociated sorbic acid. This was indicated by predicted GR's of 2.3‐3.4. Responses of cells derived from different spore suspensions of the same strain were similar.

Potassium Sorbate Inhibition of Microorganisms Isolated from Seafood

Microorganisms isolated from seafood showed various degrees of sensitivity toward potassium sorbate (PS). At pH 7.0, PS concentration of 0.53% completely inhibited growth of Moraxella sp., while 2.73% was needed to inhibit Arthrobacter sp. Pseudomonas I sp., which was relatively resistant to PS (inhibitory concentration = 1.62%), was not affected by 0.3% PS after freeze-thaw treatment (−78°C for 8 min and 20°C for 20 min), but showed a delay in onset of logarithmic growth for up to 20 h after heating at 50°C for 5 min. The inhibitory effect of PS on sub-lethally injured Pseudomonas I was greater in basal medium (Minimum Broth, Davis) than in a rich medium (tryptone-peptone-extract, TPE). Alteromonas putrefaciens, which was sensitive to PS (inhibitory concentration = 0.74%), was also sensitive to freeze-thaw and mild heat. The lag period for quick-frozen cells was extended by 14 h in the presence of 0.05% PS. Heating at 45°C for 10 sec was sufficient to cause complete inhibition of growth by 0.05% PS in MBD, and 8 h delay in the onset of logarithmic growth in TPE. Selective and inhibitory effects of PS, therefore, could be further enhanced in frozen or heat-treated seafood.

Influence of Potassium Sorbate and pH on Ten Strains of Type A and B Clostridium botulinum

ABSTRACTGrowth of each of ten strains of C. botulinum was measured as the average A630nm of five replicate peptone‐yeast extract‐glucose (PYEG) broth cultures at 37°C. Media ranged in pH from 7.10–5.10 with potassium sorbate concentrations of 0–0.26%. Growth Ratios [GR = treatment/control] based on time to reach A630=0.35 were calculated. The linear regressions of log [GR] vs log [undissociated sorbic acid in mg/L] or [1/GR] vs [pH] were used to predict GR's at 250 mg/L undissociated sorbic acid (pH 5.65 and 0.26% sorbate) and at pH 5.65 (0% sorbate) respectively. Among the ten strains examined, statistically significant differences (P<0.05) in resistance to pH and sorbate among strains and for the same strain from different spore suspensions were discovered. Resistance to pH and sorbate appeared to be correlated.

EFFECTS OF VARIOUS CONCENTRATIONS OF SODIUM NITRITE AND POTASSIUM SORBATE ON COLOR AND SENSORY QUALITIES OF COMMERCIALLY PREPARED BACON

ABSTRACTPork bellies (270) were processed under regular commercial conditions utilizing various concentrations (five treatments) of sodium nitrite and potassium sorbate. Sliced bacon was stored at 4°C under vacuum and nonvacuum packaged conditions and evaluated by consumers for uncooked color at 7, 14, 21, 35, and 49 days after slicing. Fried bacon slices were evaluated for flavor, texture, appearance, and overall desirability by a taste panel on a nine‐point hedonic scale during 63 days storage at 4°C under vacuum‐packaged conditions. Bacon samples formulated with sodium nitrite (40, 80, and 120 ppm) were similar in fresh color desirability during storage and were significantly more desirable than bacon formulated without sodium nitrite. Bacon formulated with 0.26% potassium sorbate in combination with 40 or 80 ppm sodium nitrite was not significantly different (p < 0.05) from bacon formulated with 120 ppm of sodium nitrite and no potassium sorbate for color and sensory qualities.

EFFECTS OF VARIOUS CONCENTRATIONS OF SODIUM NITRITE AND POTASSIUM SORBATE ON NITROSAMINE FORMATION IN COMMERCIALLY PREPARED BACON

ABSTRACTPork bellies (270) were processed under regular commercial conditions using various concentrations (five treatments) of sodium nitrite and potassium sorbate. The bacon produced was stored at 3°C, then fried and tested for nitrosamines by GC‐TEA (Thermal Energy Analyzer) at 0 and 21 days after slicing. Nitrite and sorbate concentrations were determined weekly during a 49‐day period of 3°C storage. Bacon processed without sodium nitrite, regardless of sorbate concentration, contained low (<4.4 ppb) levels of N‐nitroso‐pyrrolidine (NPYR) after being fried at 171°C for 3 min on each side. Bacon processed with 40 ppm nitrite and 0.26% potassium sorbate contained an average of 8.7 ppb NPYR at zero time (after slicing) and 5.4 ppb after 21 days of 3°C storage under vacuum packaged conditions. Bacon with 80 ppm nitrite and 0.26% potassium sorbate had average NPYR levels of 14.3 ppb at zero time and 11.4 ppb after 21 days of refrigerated storage. Bacon made with 120 ppm nitrite contained an average of 28.1 ppb NYPR at zero time and 16.2 ppb after 21 days at 3°C. After frying the bacon, 61‐71% of the potassium sorbate remained in the product. Methods for nitrosamine analysis (CC‐TEA) and sorbate determination are described.