Critical Factors Affecting the Destruction of Escherichia coli O157:H7 in Apple Cider Treated with Fumaric Acid and Sodium Benzoate

Destruction of Escherichia coli O157:H7 in apple cider treated with fumaric acid and sodium benzoate (0.15% and 0.05% w/v, respectively) was determined under pH and storage temperatures that commonly occur in apple cider. At 5°C storage, while destruction of E. coli O157:H7 in the presence of preservatives increased with time, there was little decline in E. coli O157:H7 populations in the absence of the preservatives. Increasing storage temperatures to 15°C and 25°C significantly increased the rate of destruction of E. coli O157:H7 in cider with the preservatives (P < 0.05). Increasing the pH of cider (from 3.2 to 4.7) decreased the rate of destruction of E. coli O157:H7.     

Inactivation of different strains of Escherichia coli O157:H7 in various apple ciders treated with dimethyl dicarbonate (DMDC) and sulfur dioxide (SO2) as an alternative method

Escherichia coli has been identified as the causative agent in numerous foodborne illness outbreaks associated with the consumption of fresh apple cider. Apple cider has a pH which is normally below 4.0 and would not be considered a medium capable of supporting the growth of foodborne pathogens. The association of unpasteurized apple cider with foodborne illness due to E. coli O157:H7 has however, led to increased interest in potential alternative methods to produce pathogen free cider. Apple cider was prepared from eight different apple cultivars, inoculated with approximately 10⁶–10⁷ CFU of three strains of E. coli O157:H7 per ml (933, ATCC 43889, and ATCC 43895) and tested to determine the effectiveness of sulfur dioxide (SO₂) and dimethyl dicarbonate (DMDC). Bacterial populations for treated and untreated samples were then enumerated by using non-selective media. Eight different ciders were treated with DMDC (125 and 250 ppm) and SO₂ (25, 50, 75, 100 ppm). Greater than a 5-log reduction was achieved at room temperature with 250 ppm of DMDC and 50 ppm of SO₂ after the incubation time of 6 h and 24 h, respectively. Addition of DMDC and/or SO₂ may offer an inexpensive alternative to thermal pasteurization for the production of safe apple cider for small apple cider producers.     

Inactivation of Escherichia coli O157:H7 and Salmonella in Apple Cider and Orange Juice Treated with Combinations of Ozone, Dimethyl Dicarbonate, and Hydrogen Peroxide

ABSTRACT: Inactivation of Escherichia coli O157:H7 and Salmonella in apple cider and orange juice treated with ozone in combination with antimicrobials was evaluated. E. coli O157:H7 or Salmonella was suspended in cider and orange juice, and ozone was pumped into juices (4°C) containing dimethyl dicarbonate (DMDC; 250 or 500 ppm) or hydrogen peroxide (300 or 600 ppm) for up to 90 min (study 1) or 60 min followed by 24-h storage at 4°C (study 2). Study 1: No combination of treatments resulted in a 5-log colony-forming units (CFU) /mL reduction of either pathogen. Study 2: All combinations of antimicrobials plus ozone treatments, followed by refrigerated storage, caused greater than a 5-log CFU/mL reduction, except ozone/DMDC (250 ppm) treatment in orange juice. Ozone treatment in combination with DMDC or hydrogen peroxide followed by refrigerated storage may provide an alternative to thermal pasteurization to meet the 5-log reduction standard in cider and orange juice.     

Injury,Inhibition and Inactivation ofEscherichia coli O157:H7 by Potassium Sorbate and Sodium Nitrite as Affected by pH and Temperature

The effect of potassium sorbate (0–2 g litre⁻¹) and sodium nitrite (0–1 g litre⁻¹) on the growth of four strains of Escherichia coli O157: H7 in tryptic soya broth at various pH levels (pH 4·0–7·0 for sorbate, pH 5·0–8·0 for nitrite) were determined at 37°C and 4°C. Among the pH levels tested, sorbate and nitrite exhibited the highest antimicrobial activity at pH 4·0 and 5·0, respectively. At pH 5·0 and 37°C, the presence of 500 mg litre⁻¹ sorbate or 200 mg litre⁻¹ nitrite completely inhibited the growth of E coli O157: H7. While at higher pH levels, 2 g litre⁻¹ sorbate or 1 g litre⁻¹, nitrite, the highest concentration tested, did not show significant antimicrobial action against the test organisms. At 4°C and pH 5·0, the inoculated test organisms did not showed any significant growth in preservative-free control media. Different degree of inactivation and injury was observed when E coli O157: H7 strain 933 was stored in TSB (pH 5·0) containing 1 g litre⁻¹ sorbate or nitrite at 37°C. At 4°C, inactivation and injury of E coli O157: H7 cells was not observed in the medium containing sorbate or nitrite throughout the 24 h experimental period.     

Fate of Escherichia coli O157: H7 in Chinese-Style Sausage During the Drying Step of the Manufacturing Process as Affected by the Drying Condition and Curing Agent

In this study, Chinese-style sausage was subjected to three different air-blast drying conditions commonly employed during the manufacturing process. The fate of Escherichia coli O157: H7 during the drying period was determined and compared. The effect of curing agents on the survival of E coli O157: H7 was also identified. Results showed that populations of E coli O157: H7 decreased ca 1.51 Log CFU g^-1 in sausage containing curing agents after a 6-h drying period at 50°C. However, the number of viable cells of E coli O157: H7 increased slightly in sausage without curing agents. When subjected to air-blast drying at 55°C for 6 h or at 55°C for 2·5 h and then 60°C for 3·5 h, a reduction in the number of viable cells of E coli O157: H7 was observed in sausage with or without curing agents. The reduction was more significant in sausage containing curing agents than in those without curing agents. No viable E coli O157: H7 was detected after 6 h of drying in samples containing curing agents, while the control samples still contained a viable E coli O157: H7 population of ca 2·65–4·36 Log CFU g^-1. After drying the sausage at 55°C for 4 h, inactivation of E coli O157: H7 increased in the presence of 30·00 g kg^-1 sodium chloride or 1·50 g kg^-1 sodium sorbate. On the other hand, the presence of 0·07–0·15 g kg^-1 sodium nitrite did not increase the inactivation of E coli O157: H7 compared to that in the control. © 1997 SCI.     

Application of polylactic acid coating with antimicrobials in reduction of Escherichia coli O157:H7 and Salmonella Stanley on apples

Abstract: Survival of Escherichia coli O157:H7 and Salmonella Stanley on apples as affected by application of polylactic acid (PLA) coating with antimicrobials was investigated. Golden Delicious apples were spot inoculated with E. coli O157:H7 or S. Stanley and spray coated with PLA solutions containing lactic acid (LA), disodium ethylenediaminetetraacetic acid (EDTA), sodium benzoate (SB), potassium sorbate (PS), or their combination (LA + EDTA, SB + LA, SB + LA + EDTA). Apples without any coating treatment served as controls. Coating treatments were allowed to dry fully, and the apples were stored at 4 °C for 14 d. Antimicrobial coatings reduced populations of E. coli O157:H7 and S. Stanley by up to 4 log CFU/cm² at 1 d and 4.7 log CFU/cm² at 14 d, compared to controls. SB + LA combination had a similar effectiveness as the SB + LA + EDTA combination against both pathogens and was more effective than other coating treatments. Without antimicrobial treatment, E. coli O157:H7 and S. Stanley were able to survive on apples stored at 4 °C for up to 14 d. The antimicrobial PLA coating provides an alternative intervention to reduce the pathogens on apples. Practical Application: Antimicrobial PLA coatings provide an alternative method to reduce pathogenic contaminations on fruit surface, and therefore, reduce the risk of food‐borne outbreaks.     

Fate of Escherichia coliO157: H7 in Chinese-style sausage subjected to different packaging and storage conditions

In this study, Chinese-style sausages were subjected to air, vacuum or nitrogen packaging and stored at either 5 or 25°C. The survival characteristics of Escherichia coli O157: H7 during the storage period were determined. Results revealed that, when stored at 5°C, the number of viable E coli O157: H7 in sausages decreased slowly as the storage period extended, regardless of packaging methods. E coli O157: H7 in sausages decreased from an initial population of ca 5·97 log CFU g⁻¹ to ca 4·42–4·81 log CFU g⁻¹ after 40 days of storage at 5°C. It was also found that viable cells of E coli O157: H7 declined more rapidly in sausage stored at 25°C than at 5°C. No viable E coli O157: H7 was detected in either vacuum-packed or nitrogen-packed sausage after 40 days of storage at 25°C. On the other hand, the population of E coli O157: H7 reduced to non-detectable levels in air-packed sausages after 20 days of storage. Refrigerated storage and vacuum or nitrogen packaging provided conditions that slowed down the death rate of E coli O157: H7 in sausage. Furthermore, it was noted that, among the curing agents tested, NaCl exerted the most significant lethal effect on E coli O157: H7 in sausage during the storage period. © 1998 Society of Chemical Industry.     

Inactivation of Escherichia coli with Power Ultrasound in Apple Cider

The use of acoustic energy to secure apple cider safety was explored. Inactivation tests were performed with Escherichia coli K12 at 40 °C, 45 °C, 50 °C, 55 °C, and 60 °C with and without ultrasound, followed by a validation test with E. coli O157:H7 at 60 °C. The cell morphology was observed with environmental scanning electron microscopy for samples treated at 40 °C and 60 °C. Physical quality attributes of the apple cider (pH, titratable acidity, °Brix, turbidity, and color) were compared for treated samples. The inactivation tests showed that sonication increased E. coli K12 cell destruction by 5.3‐log, 5.0‐log, and 0.1‐log cycles at 40 °C, 50 °C, and 60 °C, respectively. The additional destruction due to sonication was more pronounced at sublethal temperatures. At the lethal temperature of 60 °C, the rate of death by ultrasound was not significantly different compared with the thermal‐alone treatment. The inactivation of E. coli K12 with heat was described by 1st‐order kinetics, especially at 50 °C and 60 °C. For ultrasound treatments, concave upward survival curves were observed, which had a shape factor in the range of 0.547 to 0.720 for a Weibull distribution model. Extensive damage for ultrasound treated E. coli K12 cells, including cell perforation, was observed. Perforation is a unique phenomenon found on ultrasound‐treated cells that could be caused by liquid jets generated by cavitation. Titratable acidity, pH, and °Brix of the cider were not affected by ultrasound treatment. Minor changes in color and turbidity for ultrasound treated samples, especially for sonication at 40 °C for 17.7 min, were observed.     

Inhibition of Shiga Toxin 2 (Stx2) in Apple Juices and its Resistance to Pasteurization

Abstract: In the present study, we evaluated Shiga toxin (Stx2) activity in apple juices by measuring a decrease in dehydrogenase activity of Vero cells with the microculture tetrazolium (MTT) assay. Freshly prepared juice from Red Delicious apples and Golden Delicious apples inhibited the biological activity of the bacterial toxin Stx2 produced by E. coli O157:H7 strains. Studies with immunomagnetic beads bearing specific antibodies against the toxin revealed that Stx2 activity was restored when removed from the apple juice. SDS gel electrophoresis revealed no difference (P < 0.05) in the densities or molecular weights between Stx2 in either PBS or apple juices. These results suggest that Stx2 may be reversibly bound to small molecular weight constituents in the juice. The Stx2 toxin was not inactivated on exposure to heat programs (63 °C for 30 min, 72 °C for 15 s, 89 °C for 1 s) commonly used to pasteurize apple juice, but lost all activity when exposed to 100 °C for 5 min. The results suggest that pasteurization of apple juice used to inactivate E. coli O157:H7 has no effect on Stx2, and that food-compatible and safe antitoxin compounds can be used to inhibit the biological activity of the Shiga toxin. Practical Application: This study explores the possibility of using naturally occurring antioxidative substances, in this case high phenolic apples juices, to inactivate Shiga toxin (Stx2) produced by E. coli O157:H7 in contaminated foods.     

Sodium Lactate Affects Pathogens in Cooked Beef

Cooked, quartered beef top rounds containing either 1, 2, 3 or 4% sodium lactate were aseptically sampled and slice sections were inoculated with Listeria monocytogenes (ATCC 43256), Staphylococcus aureus (ATCC 27154), Salmonella typhimurium (ATCC 13311), Clostridium perfringens (ATCC 12924), or Escherichia coli O157:H7 (ATCC 43895). Inoculated slices were stored at 10°C for 0. 7. 14. 21 or 28 days.‘Three and 4% sodium lactate generally displayed lim-ited proliferation of S. typhimurium, L. monocytogenes and E. coli O157:H7 when compared with control roasts (0% sodium lactate) and roasts containing 2% sodium lactate.     

Growth patterns of Escherichia coli O157:H7 in ground beef treated with nisin,chelators, organic acids and their combinations immobilized in calcium alginate gels

The effects of antimicrobial substances including nisin, acetic acid, lactic acid, potassium sorbate and chelators (disodium ethylenediamine tetraacetic acid [EDTA] and sodium hexametaphosphate [HMP]), alone or in combination and, with or without immobilization in calcium alginate gels, on the growth of Escherichia coli O157:H7 in ground beef were investigated. Results showed that acetic acid and potassium sorbate could inhibit the growth of E. coli O157:H7 effectively at 10°C and at 30°C. Both EDTA and HMP did not halt the growth of E. coli O157:H7. In an antimicrobial system immobilized with calcium alginate, most of the antimicrobials could not inhibit the growth of E. coli O157:H7 in ground beef at 10°C and at 30°C, with the exception of acetic acid and lactic acid. Immobilization did not enhance the effectiveness of acetic acid against E. coli O157:H7 in ground beef at 10°C and at 30°C (P>0.05) but it did enhance the effectiveness of lactic acid at 10°C. In a system combining different antimicrobials, treatment with nisin /EDTA or nisin/potassium sorbate at 10°C revealed a significantly lower population change of E. coli O157:H7 compared to samples treated with nisin, EDTA or potassium sorbate alone. The use of calcium alginate immobilization further enhanced the effectiveness of the combination system of nisin/EDTA, nisin/acetic acid and nisin/potassium sorbate on the growth of E. coli O157:H7 in ground beef at 10°C but it was not effective at 30°C.     

Detection of Escherichia coli O157:H7 in Food Using Real-Time Multiplex PCR Assays Targeting the stx 1, stx 2, wzy O157, and the fliC h7 or eae Genes

Escherichia coli O157:H7 is an important foodborne pathogen, and foods of bovine origin and fresh produce have been linked to outbreaks. Real-time multiplex PCR assays were developed to detect E. coli O157:H7 in different foods. Apple cider and raw milk (25 ml) and ground beef and lettuce (25 g) were inoculated with 2 or 20 colony-forming units (CFU) of E. coli O157:H7 380-94 and subjected to enrichment in RapidChek E. coli O157:H7 broth at 42°C. One milliliter of the enrichments was removed at 8 and 20 h, and following DNA extraction, real-time multiplex PCR assays targeting the stx ₁, stx ₂, and wzy _O157 genes in combination with probes and primers targeting either the fliC _h7 or the eae genes were performed using OmniMix HS beads and the SmartCycler. The sensitivity of the real-time multiplex PCR assay was about 225 CFU/PCR. E. coli O157:H7 was detected (fluorescent signal generated for all gene targets) in apple cider, raw milk, lettuce and ground beef samples inoculated with 2 or 20 CFU/g or 25 ml after both 8 and 20 h of enrichment. Enrichments of uninoculated food samples were negative using the multiplex PCR targeting the stx ₁, stx ₂, wzy _O157, and eae genes; however, using the assay targeting the stx ₁, stx ₂, wzy _O157, and fliC _h7 gene combination, a positive result was always obtained for the fliC _h7 gene using uninoculated ground beef enrichments. Use of other primer sets targeting the fliC _h7 gene gave similar results. The real-time multiplex PCR assays targeting the stx ₁, stx ₂, eae, and wzy _O157 or the fliC _h7 genes are sensitive and specific and can be used for the detection of E. coli O157:H7 in food, except that the fliC _h7 gene may not be a suitable target for the detection of E. coli O157:H7 in ground beef.     

Thermal Inactivation of Escherichia coli O157:H7 in Strawberry Puree and Its Effect on Anthocyanins and Color

Raw whole strawberries, if contaminated with pathogens, such as Escherichia coli O157:H7, must be pasteurized prior to consumption. Therefore, the objective of this research was to investigate the thermal inactivation kinetics of E. coli O157:H7 in strawberry puree (SP), and evaluate the changes in anthocyanins and color, and the survival of yeasts and molds (YM) after thermal processing. Inoculated with a 5‐strain cocktail, fresh SP, with or without added sugar (20 and 40 °Brix), was heated at 50, 52, 54, 57.5, 60, and 62.5 °C to determine the thermal resistance of E. coli O157:H7. In raw SP, the average D‐values of E. coli O157:H7 were 909.1, 454.6, 212.8, 46.1, and 20.2 s at 50, 52, 54, 57.5, and 60 °C, respectively, with a z‐value of 5.9 °C. While linearly decreasing with temperature, the log D‐values of E. coli O157:H7 increased slightly with sugar concentration. The log degradation rates of anthocyanins increased linearly with temperature, but decreased slightly with sugar concentrations. These results suggest that sugar may provide some protection to both E. coli O157: H7 and anthocyanins in SP. The browning index was not affected by heating at 50 and 52 ºC at low sugar concentrations, but increased by an average of 1.28%, 2.21%, and 10.1% per min when SP was exposed to heating at 54, 57.5, and 60 °C, respectively. YM was also inactivated by heating. This study demonstrated that properly designed thermal processes can effectively inactivate E. coli O157:H7 and YM in contaminated SP, while minimizing the changes in anthocyanins and color.     

Escherichia coli O157:H7 facilitates the penetration of Staphylococcus aureus into table eggs

Abstract: Fresh eggshells collected from a local farm were subjected to different levels of surface contamination with feces containing different levels (3 to 5 log₁₀) of Escherichia coli O157:H7 or Staphylococcus aureus and incubated at 3 different temperatures (10, 25, and 32 °C). The penetration rates of contaminating bacteria were followed throughout the incubation period by tracing bacterial presence in shell, shell membranes, albumen, and yolk. The study revealed the ability of both E. coli O157:H7 and enterotoxigenic S. aureus to grow on shell in feces, penetrate the shell, and move and multiply within egg contents at different rates and periods depending on bacterial type and incubation conditions. High temperatures (25 and 32 °C) increased penetration rate, whereas storage at 10 °C decreased significantly the rate of penetration. High levels of contamination with E. coli O157:H7 also shortened the time needed for the penetration process. Results showed that when eggshells were contaminated with both organisms simultaneously, the penetration of E. coli O157:H7 preceded that of S. aureus and facilitated the invasion of the latter bacteria.     

Modeling the survival of Escherichia coli O157:H7 in apple cider using probability distribution functions for quantitative risk assessment

Outbreaks of foodborne illness from apple cider have prompted research on the survival of Escherichia coli O157:H7 in this food. Published results vary widely, potentially due to differences in E. coli O157:H7 strains, enumeration media, and other experimental considerations. We developed probability distribution functions for the change in concentration of E. coli O157:H7 (log CFU/day) in cider using data from scientific publications for use in a quantitative risk assessment. Six storage conditions (refrigeration [4 to 5 degrees C]; temperature abuse [6 to 10 degrees C]; room temperature [20 to 25 degrees C]; refrigerated with 0.1% sodium benzoate, 0.1% potassium sorbate, or both) were modeled. E. coli survival rate data for all three unpreserved cider storage conditions were highly peaked, and these data were fit to logistic distributions: ideal refrigeration, logistic (-0.061, 0.13); temperature abuse, logistic (-0.0982, 0.23); room temperature, logistic (-0.1, 0.29) and uniform (-4.3, -1.8), to model the very small chance of extremely high log CFU reductions. There were fewer published studies on refrigerated, preserved cider, and these smaller data sets were modeled with beta (4.27, 2.37) x 2.2 - 1.6, normal (-0.2, 0.13), and gamma (1.45, 0.6) distributions, respectively. Simulations were run to show the effect of storage on E. coli O157:H7 during the shelf life of apple cider. Under every storage condition, with and without preservatives, there was an overall decline in E. coli O157:H7 populations in cider, although a small fraction of the time a slight increase was seen.     

Evaluation of Antibacterial Activity of Whey Protein Isolate Coating Incorporated with Nisin,Grape Seed Extract,Malic Acid,and EDTA on a Turkey Frankfurter System

ABSTRACT: The effectiveness of whey protein isolate (WPI) coatings incorporated with grape seed extract (GSE), nisin (N), malic acid (MA), and ethylenediamine tetraacetic acid (EDTA) and their combinations to inhibit the growth of Listeria monocytogenes, E. coli O157:H7, and Salmonella typhimurium were evaluated in a turkey frankfurter system through surface inoculation (approximately 10⁶ CFU/g) of pathogens. The inoculated frankfurters were dipped into WPI film forming solutions both with and without the addition of antimicrobial agents (GSE, MA, or N and EDTA, or combinations). Samples were stored at 4 °C for 28 d. The L. monocytogenes population (5.5 log/g) decreased to 2.3 log/g after 28 d at 4 °C in the samples containing nisin (6000 IU/g) combined with GSE (0.5%) and MA (1.0%). The S. typhimurium population (6.0 log/g) was decreased to approximately 1 log cycles after 28 d at 4 °C in the samples coated with WPI containing a combination of N, MA, GSE, and EDTA. The E. coli O157:H7 population (6.15 log/g) was decreased by 4.6 log cycles after 28 d in samples containing WPI coating incorporated with N, MA, and EDTA. These findings demonstrated that the use of an edible film coating containing nisin, organic acids, and natural extracts is a promising means of controlling the growth and recontamination of L. monocytogenes, S. typhimurium, and E. coli O157:H7 in ready‐to‐eat poultry products.     

Recovery of heat-stressed E. coli O157:H7 from ground beef and survival of E. coli O157:H7 in refrigerated and frozen ground beef and in fermented sausage kept at 7°C and 22°C

A study was undertaken to obtain information on survival of Escherichia coli O157:H7 in ground beef subjected to heat treatment, refrigeration and freezing and on survival of E. coli O157:H7 in fermented sausage kept at 7°C and 22°C. For the challenge test, a mixture of E. coli O157:H7 strains (EH 321, EH 385, EH 302) was used and enumeration was performed on an isolation medium suitable for recovery of stressed organisms: modified Levine's eosin methylene blue agar (mEMB). Heat resistance of E. coli O157:H7 decreased after pre-incubation at a reduced temperature.Escherichia coli O157:H7 was more susceptible to heat inactivation after storage at 7°C and die-off was even more enhanced if cultures were frozen prior to heat inactivation. The enhanced reduction of the pathogen at 56°C after prior storage under refrigeration was confirmed in a test with inoculated ground beef.Escherichia coli O157:H7 was able to survive in ground beef at 7°C for 11 days and at −18°C for 35 days showing maximal one log reduction during the storage period. Thus, ground beef contaminated with E. coli O157:H7 will remain a hazard even if the ground beef is held at low or freezing temperatures. At both 7°C and 22°C, a gradual reduction of E. coli O157:H7 was noticed in fermented sausage over the 35 days storage period resulting in a 2 log decrease of the high inoculum (10⁶cfu 25 g⁻¹). For the low inoculum (10³cfu 25 g⁻¹) a 2·5 log reduction was obtained in 7 and 28 days storage at respectively 22 and 7°C. Application of good hygienic practices and implementation of HACCP in the beef industry are important tools in the control of E. coli O157:H7.     

Kinetics of ultraviolet light inactivation of Escherichia coli O157:H7 in liquid foods

The effects of pH, depth of food medium and ultraviolet (UV) light dose on the inactivation of Escherichia coli O157:H7 in UV‐opaque products such as apple juice (pH 3.5) and egg white (pH 9.1) were investigated. The applied UV dose ranged from 0 to 6.5 mW min cm^?2, while the depths of the medium were 1, 3.5, 5 and 10 mm. The pH of the medium did not affect the inactivation of E coli O157:H7, since similar inactivation characteristics were obtained for both apple juice and liquid egg white. As expected, decreasing the depth of the medium increased the inactivation of E coli O157:H7. More than a 5‐log reduction was obtained when the fluid depth and UV dose were 1 mm and 6.5 mW min cm^?2 respectively. However, less than a 1‐log reduction was obtained when the fluid depth was 10 mm. A two‐phase kinetic model was used to model the inactivation of E coli O157:H7. This model indicated that at higher fluid depths the inactivation rate was controlled by the second, slower inactivation phase, resulting in a lower overall inactivation. The visual appearance of the treated apple juice and egg white did not show any discolouration changes during 4 weeks of storage at ambient temperature (25 °C). Copyright © 2003 Society of Chemical Industry     

Addition of fumaric acid and sodium benzoate as an alternative method to achieve a 5-log reduction of Escherichia coli O157:H7 populations in apple cider

A study was conducted to develop a preservative treatment capable of the Food and Drug Administration-mandated 5-log reduction of Escherichia coli O157:H7 populations in apple cider. Unpreserved apple cider was treated with generally recognized as safe acidulants and preservatives before inoculation with E. coli O157:H7 in test tubes and subjected to mild heat treatments (25, 35, and 45 degrees C) followed by refrigerated storage (4 degrees C). Fumaric acid had significant (P < 0.05) bactericidal effect when added to cider at 0.10% (wt/vol) and adjusted to pH 3.3, but citric and malic acid had no effect. Strong linear correlation (R2 = 0.96) between increasing undissociated fumaric acid concentrations and increasing log reductions of E. coli O157:H7 in apple cider indicated the undissociated acid to be the bactericidal form. The treatment that achieved the 5-log reduction in three commercial ciders was the addition of fumaric acid (0.15%, wt/vol) and sodium benzoate (0.05%, wt/vol) followed by holding at 25 degrees C for 6 h before 24 h of refrigeration at 4 degrees C. Subsequent experiments revealed that the same preservatives added to cider in flasks resulted in a more than 5-log reduction in less than 5 and 2 h when held at 25 and 35 degrees C, respectively. The treatment also significantly (P < 0.05) reduced total aerobic counts in commercial ciders to populations less than those of pasteurized and raw ciders from the same source (after 5 and 21 days of refrigerated storage at 4 degrees C, respectively). Sensory evaluation of the same ciders revealed that consumers found the preservative-treated cider to be acceptable.     

Yeast Inhibition in Grape. Juice Containing Sulfur Dioxide, Sorbic Acid, and Dimethyldicarbonate

Sulfur dioxide (SO₂), sorbic acid (SB), dimethyldicarbonate (DMDC), and their combinations were studied for suppression of fermentation at 21°C or 31°C in grape juice inoculated with 2, 200, or 20,000 colony forming units (CFU)/mL of yeast. The other preservatives did not suppress as well as DMDC. The DMDC (0.8 mM) prevented fermentation at all inoculation levels at both temperatures, except that inoculated with 20,000 CFU/mL at 21°C. The 0.8-mM level of SO₂+DMDC. and SB + DMDC orevented fermentation in samoles inoculated with 2 or 200 CFU/mL at 31°C. Storage at 31°C decreased effectiveness of SO₂, SB, and SO₂+ SB but increased effectiveness of DMDC, SO₂+ DMDC, and SB+DMDC (0.8 mM level).