The effects of different technologies on<Emphasis Type="Italic"> Alicyclobacillus acidoterrestris</Emphasis> during apple juice production

In this study, the effects of various processing steps applied during apple juice processing on Alicyclobacillus acidoterrestris were investigated. Raw apple juice was inoculated with A. acidoterrestris spores at two inoculum levels of 1×10³ cfu/ml and 1×10⁶ cfu/ml. Following enzymatic treatment, the raw juice was processed into clear juice using either conventional clarification or ultrafiltration. The number of A. acidoterrestris spores in the final product was determined to be dependent on both initial contamination level and processing conditions. Increasing temperature to 50 °C during depectinization resulted in a higher spore counts at both inoculum levels. Even if the ultrafiltration process was found to be much more convenient for the retention of A. acidoterrestris when compared to conventional clarification, the spores could penetrate the ultrafiltration membranes having both 20 and 50 kDa. Increasing membrane pore size and initial spore counts in the feed solution also increased the number of spores penetrating the membrane during ultrafiltration.     

Determination of guaiacol produced by Alicyclobacillus acidoterrestris in apple juice by using HPLC and spectrophotometric methods, and mathematical modeling of guaiacol production

In this study, easy detection of Alicyclobacillus acidoterrestris was performed by determination of guaiacol in apple juice. Guaiacol produced by A. acidoterrestris was determined by using HPLC, UV-Vis spectrophotometer, and Minolta spectrophotometer. Statistical analysis showed that the methods used for measuring the guaiacol concentrations were not significantly different (p > 0.05). Guaiacol formation in apple juice spiked with different levels of A. acidoterrestris spores was also analyzed using Gompertz, Logistic, and Richards models. In all cases, a good agreement between experimental data and fitted values was obtained. Using the modified Gompertz model, the derived biological parameters were calculated. Guaiacol formation rates (μ) and final guaiacol concentrations (A) were very similar in all cases, regardless of the initial A. acidoterrestris spore counts. However, lag phase durations (λ) were found to be dependent on the initial bacterial counts, and increased from 28.4 to 37.6 h, when initial inoculation level decreased from ∼10³ to ∼10¹ cfu/mL.     

Isolation of Alicyclobacillus and the influence of different growth parameters

Alicyclobacillus species are thermo-acidophilic, endospore-forming bacteria that are able to survive pasteurisation and have been implicated in a number of spoilage incidents involving acidic foods and beverages. The aim of this study was to compare three isolation methods used for the detection of Alicyclobacillus acidoterrestris and to investigate the influence of incubation temperature on the growth of A. acidoterrestris and A. acidocaldarius. Peach juice samples inoculated with A. acidoterrestris K47 were analysed using either the International Federation of Fruit Juice Producers (IFU) Method No. 12 (Method A), which involved spread plating onto Bacillus acidoterrestris (BAT) agar at pH 4.0; Method B, which involved pour plating using potato dextrose agar (PDA) at pH 3.7; or Method C, which made use of membrane filtration followed by incubation on K agar at pH 3.7. The performance of the three methods differed significantly, with the IFU Method No. 12 recovering the highest percentage of cells at 75.97%, followed by Method B at 66.79% and Method C at 3.43%. These findings strengthen the proposal of the IFU for the use of the IFU Method No. 12 as a standard international method for the detection of Alicyclobacillus. To investigate the effect on growth of different incubation temperatures A. acidoterrestris (three strains) and A. acidocaldarius (two strains) were incubated at either 45 °C or 25 °C. Growth at 25 °C was slower and maximum cell concentrations were lower (1 × 10⁵-10⁶ cfu/mL compared to 1 × 10⁷-10⁸ cfu/mL) than at 45 °C for A. acidoterrestris. A. acidocaldarius was unable to grow at 25 °C and cell concentrations decreased by 1-2 logs. Since a growth temperature of 25 °C could not inhibit growth of A. acidoterrestris, cooling to room temperature (20°-25 °C) is not an effective control measure for A. acidoterrestris inhibition.     

Growth inhibition and inactivation of Alicyclobacillus acidoterrestris endospores in apple juice by hyperbaric storage at ambient temperature

Control of endospores of Alicyclobacillus acidoterrestris in pasteurized apple juice using hyperbaric storage at 18 to 23 °C was compared to storage at atmospheric pressure and 18 to 23 °C, as well as refrigeration at ~4 °C for up to 30 days. The juice samples were inoculated with approximately 1 × 10⁵ CFU/mL spores. The juice spoiled quickly at atmospheric pressure and ambient temperature, while under refrigeration spore levels remained unchanged for 30 days. Hyperbaric storage of inoculated apple juice at 25, 50 and 100 MPa at 18 to 23 °C resulted in spore inactivation at more rapid rates as pressure magnitudes increased, reaching levels below the detection limit of 10 CFU/mL at 50 and 100 MPa. In highly acid foods such as apple juice, hyperbaric storage at pressures ≤100 MPa and ambient temperature was effective in inactivating spores of A. acidoterrestris for periods up to 30 days.These results indicate hyperbaric storage at ambient temperature as a clearly more efficient preservation procedure to control the development of A. acidoterrestris endospores, compared to ambient temperature and refrigerated storage, in highly acidic foods as apple juice.     

Effect of single and combined UV-C and ultra-high pressure homogenisation treatments on inactivation of Alicyclobacillus acidoterrestris spores in apple juice

Alicyclobacillus acidoterrestris is a spore-forming bacterium that can survive thermal pasteurization and acidic conditions. It produces changes in the odour and flavour of fruit juices leading to economical loses. A. acidoterrestris CECT 7094 spores were inoculated in clarified and cloudy apple juices (Golden delicious var.) in the range of 5–6 log₁₀ spores/mL and submitted to different short-wave ultraviolet light (UV-C) doses (7.2–28.7 J/mL) and ultra-high pressure homogenisation (UHPH) treatments (100–300 MPa), including their combination. A. acidoterrestris could be inactivated in clarified apple juice at a level of 4.8 log₁₀ CFU/mL by a 300 MPa-UHPH treatment when the inlet temperature was 80 °C. UV-C treatments showed to be more efficient achieving a lethality of 5.5 log₁₀ CFU/mL with a dose of 21.5 J/mL at 20 °C. In cloudy apple juice (2357 NTU) UV-C treatments were less efficient with a maximum lethality of 4.07 CFU/mL after a dose of 28.7 J/mL. A previous application of UHPH contributed with UV-C to obtain higher reductions of A. acidoterrestris spores at the doses of 14.3 and 21.5 J/mL compared with UV-C single treatments. On the other hand, this previous treatment also changed the properties of particles in the matrix which apparently reduced the effectiveness of UV-C at 28.7 J/mL.     

Control of food spoiling bacteria in cooked meat products with nisin,lacticin 3147, and a lacticin 3147-producing starter culture

Nisin, in the form of the commercial product Nisaplin, and lacticin 3147 in whey powdered form were added to minced pork-meat in amounts of 0.15% (w/w) and 1.5% (w/w), respectively. The meat was cooked and inoculated with a Staphylococcus aureus strain of meat origin and a Listeria innocua strain at a level of 10⁷ or 10⁵ CFU g^–1. The batches were stored vacuum-packaged for 21 days at 8 °C. Nisin and lacticin 3147 immediately reduced the L. innocua population at the time of inoculation. Nisin showed higher inhibitory activity than lacticin 3147. During the storage period, a slight L. innocua growth was observed in the batches inoculated with the larger inoculum, and a bacteriostatic effect was observed against Listeria in the batches inoculated with 10⁵ CFU g^–1. Nisin maintained a constant S. aureus population in the cooked batch inoculated with 10⁷ CFU g^–1, although the bacteriocin was capable of reducing the amount of S. aureus by 90% in the batch inoculated with 10⁵ CFU g^–1. On the other hand, lacticin 3147 did not show an inhibitory effect against S. aureus in the cooked meat. The starter culture Lactococcus lactis DPC 303-T4 (containing the conjugative plasmid encoding production of lacticin 3147) was inoculated in a portion of a Longissimus dorsi pork muscle with brine. L. lactis DPC 303-T4 performed a good fermentation, but lacticin 3147 production was not found after 7 days at 12 °C of storage.     

Biological control of Penicillium italicum of Citrus and Botrytis cinerea of Grape by Strain 34–9 of Kloeckera apiculata

The biological control capability of strain 34-9 of Kloeckera apiculata against Penicillium italium (Wehmer), postharvest rot of citrus fruits and Botrytis cinerea, postharvest rot of grape fruits was studied in vitro and in vivo. Strain 34-9 of K. apiculata at 3×10⁸ CFU (colony-forming unit)/ml of washed cells provided complete control of 3×10⁵ spores/ml of P. italium and B. cinerea during storage at 25 °C for 6 d. Antagonist population increased 40, 195 times in citrus fruit wound site and grape fruit wound site at 25 °C for 3 d, respectively, then the population stabilized for the remaining storage period. Cell-free culture filtrate, supernatant fluid and sterilized solution of strain 34-9 of K. apiculata had no antagonist against P. italium of citrus and B. cinerea of grape. These results showed that competition for nutrient, not antibiotic production, played a major role in the biological control capability of strain 34-9 of K. apiculata against P. italium of citrus and B. cinerea of grape.     

Biological control of postharvest green mold decay of oranges by Rhodotorula glutinis

The biocontrol activity of Rhodotorula glutinis on green mold decay of oranges caused by Penicillium digitatum was investigated in vitro and in vivo. Significant control was achieved with a washed cell suspension and an unwashed cell culture mixture of R. glutinis. Treatment of wounds with autoclaved cell cultures or cell-free culture filtrate did not prevent decay. The protection provided by the washed yeast cells was dose-dependent. The higher the concentration of R. glutinis, the better the effect of the biocontrol capacity. At concentrations of yeast of 1×10⁹ colony-forming units per milliliter or higher and pathogen spore suspensions of 5×10⁴ spores per milliliter, green mold was almost inhibited after 4-days incubation at 20 °C. The interval between the pathogen inoculation and the antagonist application significantly influenced the biocontrol ability. The biocontrol efficacy of R. glutinis applied before the pathogen was better than that of applied after the pathogen. Surprisingly, R. glutinis was also effective in controlling green mold at low temperature (4 °C). Rapid colonization of the yeast in wounds was observed during the first 3 days at 20 °C, and remained stable after 5-days incubation. On fruits stored at 4 °C, even after 21 days, the population of R. glutinis in wounded fruits was more than 1,600-fold of what it was just prior to storage. In the test on potato dextrose agar plates, agar disks of R. glutinis nutrient yeast dextrose agar cultures placed on PDA plates seeded with pathogens did not inhibit the growth of P. digitatum. Spore germination of pathogens in potato dextrose broth was greatly controlled in the presence of living cell suspensions.     

Effects of process parameters on growth and metabolism of<Emphasis Type="Italic"> Lactobacillus sanfranciscensis</Emphasis> and<Emphasis Type="Italic"> Candida humilis</Emphasis> during rye sourdough fermentation

The effects of temperature, pH, inoculum level, and NaCl on the growth and metabolism of Lactobacillus sanfranciscensis and Candida humilis in rye sourdough were determined. The temperature optima for growth of C. humilis and L. sanfranciscensis were 28 and 32 °C, respectively. Yeast growth was inhibited at 35 °C. The pH did not affect yeast growth in the range 3.5–5.5, whereas growth of L. sanfranciscensis was inhibited at pH 4.0. A NaCl concentration of 4% (flour base) inhibited growth of L. sanfranciscensis but not C. humilis. The effects of the process parameters on the formation of lactate, acetate, ethanol, and CO₂ by the organisms were generally in agreement with their effects on growth. However, decreased formation of acetate by L. sanfranciscensis was observed at 35 °C although lactate and ethanol formation were not affected. In conclusion, the study provides a rationale for the stable persistence of L. sanfranciscensis and C. humilis in traditional sourdoughs and will facilitate the optimisation of sourdough fermentations in traditional and new applications.     

Thermal resistance ofAlicyclobacillus acidoterrestrisspores in different buffers and pH

The influence of buffers and pH on the thermal resistance of a novel flat sour-type of spoilage bacterium,Alicyclobacillus acidoterrestris, was investigated. At a low concentration (20 mM), decimal reduction times (D-values) in citrate and phosphate buffers were 13.6 and 12.9 min, respectively, showing little variation. At a high concentration (100 mM), however, theD-value in citrate buffer, 14.4 min, was significantly higher than that in the phosphate buffer, 12.3 min.D-values in McIlvaine buffers did not vary widely within the pH range of 3.0 to 8.0. At 88, 90, 92 and 95°C in McIlvaine buffers,D-values were 24.1–29.1, 14.8–16.8, 5.7–7.1 and 2.2–2.8 min, respectively. The thermal resistance ofA. acidoterrestrisspores was affected very little by varying the pH of the heating menstruum. TheZ-values also did not vary widely as the pH varied among the different buffers, ranging from 6.4 to 7.1°C. It was evident thatA. acidoterrestrisspores showed a special relationship, unknown among other bacterial spores, between their thermal resistance and the pH of the heating menstruum. Therefore,A. acidoterrestrisshould be targeted when the quality of acidic food products is being tested.     

Combined high pressure and heat treatment effectively disintegrates spore membranes and inactivates Alicyclobacillus acidoterrestris spores in acidic fruit juice beverage

The commercial potential of high pressure and thermal processing (HPTP) was investigated against Alicyclobacillus acidoterrestris spores in commercial acidic apple juice beverage and in acidified and neutral potassium buffers. With starting spore counts prior to treatments being 6.5 and 7.2 log₁₀ respectively for strains AJA 66 (D_90°C 15.4 min) and ATCC 49025 (D_90°C 8.5 min), HPTP at 600 MPa at 80 °C for 3 min provided an optimal treatment with spore viability reduced below the detection limit for both strains. HPTP at 80 °C for 1 min and HPTP at 70 °C for 3 min achieved 4.1–4.5 log₁₀ CFU/mL reduction. HPTP at 70 °C for 1 min reduced the number of viable spores by 2.0–2.5-log₁₀ CFU/mL. Flow cytometry revealed the presence of membrane-compromised spores among culturable spores following HPTP and heat alone treatments at different temperatures. Electron microscopy clearly showed the efficiency of HPTP with crushed or hollow spores predominating after treatments. No correlation between HPTP susceptibility and genetic diversity was observed for two genotypes of A. acidoterrestris spores. The treatment combination provides a promising option for industrial utility since it requires lower heat and processing time.     

UV-C inactivation of Escherichia coli at different temperatures

The influence of treatment parameters (dose and temperature), treatment medium characteristics (absorption coefficient, pH and water activity) and microbiological factors (strain, growth phase and UV damage and repair capacity) on Escherichia coli UV-C resistance has been investigated. UV-C doses to inactivate at 25 °C 99.99% of the initial population (4D) of five strains of E. coli in McIlvaine buffer of pH 7.0 with tartrazine added (absorption coefficient of 10.77 cm⁻¹) were 16.60, 14.36, 14.36, 13.22, 11.18 J/mL for strains E. coli STCC 4201, STCC 471, STCC 27325, O157:H7 and ATCC 25922, respectively. The entrance in the stationary growth phase increased the 4D value of the most resistant strain, E. coli STCC 4201, from 13.09 to 17.23 J/mL. Survivors to UV treatments showed neither oxidative damages nor injuries in cell envelopes. On the contrary, the photoreactivation by the incubation of plates for 60 min below visible light (11.15 klx) increased the dose to 18.97 J/mL. The pH and the water activity of the treatment medium did not affect the UV tolerance of E. coli STCC 4201, but the lethal effect of the treatments decreased exponentially (Log₁₀4D = − 0.0628α + 0.624) by increasing the absorption coefficient (α). A treatment of 16.94 J/mL reached 6.35, 4.35, 2.64, 1.93, 1.63, 1.20, 1.02 and 0.74 Log₁₀ cycles of inactivation with absorption coefficients of 8.56, 10.77, 12.88, 14.80, 17.12, 18.51, 20.81 and 22.28 cm⁻¹. The temperature barely changed the UV resistance up to 50.0 °C. Above this threshold, inactivation rates due to the combined process synergistically increased with the temperature. The magnitude of the synergism decreased over 57.5 °C. An UV treatment of 16.94 J/mL in media with an absorption coefficient of 22.28 cm⁻¹ reached 1.23, 1.64, 2.36, 4.01 and 6.22 Log₁₀ cycles of inactivation of E. coli STCC 4201 at 50.0, 52.5, 55.5, 57.5 and 60.0 °C, respectively.

Industrial relevance

Results obtained in this investigation show that UV light applied at mild temperatures (57.5 to 60 °C) could be an alternative to heat treatments for 5-Log₁₀ reductions of E. coli in liquid foods. Since microbial resistance to UV-C light did not depend on the pH and water activity (a_w) of the treatment media, eventual advantages of UV light for pasteurization purposes will be higher in low a_w foods. E. coli STCC 4201 could be considered as a target when UV light processing of foods.     

Effect of microencapsulation and resistant starch on the probiotic survival and sensory properties of synbiotic ice cream

Two types of synbiotic ice cream containing 1% of resistant starch with free and encapsulated Lactobacillus casei (Lc-01) and Bifidobacterium lactis (Bb-12) were manufactured. The survival of L. casei and B. lactis were monitored during the product’s storage for 180 days at −20 °C. The viable cell number of L. casei and B. lactis in the free state in prepared ice cream mixture was 5.1 × 10⁹ and 4.1 × 10⁹ CFU/mL at day one and after 180 days storage at −20 °C, these numbers were decreased to 4.2 × 10⁶ and 1.1 × 10⁷ CFU/mL, respectively. When we encapsulated the mentioned probiotic bacteria in calcium alginate beads, the probiotic survival raised at rate of 30% during the same period of storage at same temperature. In general, the results indicated that encapsulation can significantly increase the survival rate of probiotic bacteria in ice cream over an extended shelf-life. The addition of encapsulated probiotics had no significant effect on the sensory properties of non-fermented ice cream in which we used the resistant starch as prebiotic compound.     

Expression of DnaJ Gene in Alicyclobacillus acidoterrestris under Stress Conditions by Quantitative Real-Time PCR

Abstract: This article describes the cloning, sequence analysis and expression of the DnaJ gene from Alicyclobacillus acidoterrestris. The genome walking technique was used to clone the full‐length sequence of DnaJ and quantitative real‐time PCR was used to analyze DnaJ expression under stress conditions. AadnaJ (GenBank accession nr: HQ893544) containing an open reading frame of 1137 bp encoding 378 amino acid residues was cloned from A. acidoterrestris DSM 3922^T. The nucleotide sequence of AadnaJ shows 77% homology with the DnaJ of A. acidocaldarius LAA1. The DnaJ expression level was upgraded rapidly under heat or acid stress. Its mRNA expression level reached a peak value at 25 min after the onset of heat stress (70 °C) and at 1 h after the onset of acid stress (pH = 1). Acid stress at pH 1 for 25 and 60 min led to the DnaJ expression levels 2.1 times and 35.7 times above that of the control, respectively. In response to cold stress at 0 °C, the DnaJ expression level decreased drastically to 0.04 times that of the control level after 1 h. The expression patterns of DnaJ in response to the stress conditions shown here explained the heat and acidity endurance of A. acidoterrestris. Practical Application: This study directly addresses the role of the DnaJ gene in temperature and acid endurance in A. acidoterrestris. This provides a basis for the development of genetic and molecular techniques that may minimize the adverse effects of A. acidoterrestris in fruit juice production. This study also sheds light on the design of heat‐ and acid‐tolerant recombinases and the understanding of the molecular mechanisms underlying heat and acid resistance in A. acidoterrestris.     

Germination and inactivation of Bacillus coagulans and Alicyclobacillus acidoterrestris spores by high hydrostatic pressure treatment in buffer and tomato sauce

Acidothermophilic bacteria like Alicyclobacillus acidoterrestris and Bacillus coagulans can cause spoilage of heat-processed acidic foods because they form spores with very high heat resistance and can grow at low pH. The objective of this work was to study the germination and inactivation of A. acidoterrestris and B. coagulans spores by high hydrostatic pressure (HP) treatment at temperatures up to 60 °C and both at low and neutral pH. In a first experiment, spores suspended in buffers at pH 4.0, 5.0 and 7.0 were processed for 10 min at different pressures (100-800 MPa) at 40 °C. None of these treatments caused any significant inactivation, except perhaps at 800 MPa in pH 4.0 buffer where close to 1 log inactivation of B. coagulans was observed. Spore germination up to about 2 log was observed for both bacteria but occurred mainly in a low pressure window (100-300 MPa) for A. acidoterrestris and only in a high pressure window (600-800 MPa) for B. coagulans. In addition, low pH suppressed germination in A. acidoterrestris, but stimulated it in B. coagulans. In a second series of experiments, spores were treated in tomato sauce of pH 4.2 and 5.0 at 100 - 800 MPa at 25, 40 and 60 °C for 10 min. At 40 °C, results for B. coagulans were similar as in buffer. For A. acidoterrestris, germination levels in tomato sauce were generally higher than in buffer, and showed little difference at low and high pressure. Remarkably, the pH dependence of A. acidoterrestris spore germination was reversed in tomato sauce, with more germination at the lowest pH. Furthermore, HP treatments in the pH 4.2 sauce caused between 1 and 1.5 log inactivation of A. acidoterrestris. Germination of spores in the high pressure window was strongly temperature dependent, whereas germination of A. acidoterrestris in the low pressure window showed little temperature dependence. When HP treatment was conducted at 60 °C, most of the germinated spores were also inactivated. For the pH 4.2 tomato sauce, this resulted in up to 3.5 and 2.0 log inactivation for A. acidoterrestris and B. coagulans respectively. We conclude that HP treatment can induce germination and inactivation of spores from thermoacidophilic bacteria in acidic foods, and may thus be useful to reduce spoilage of such foods caused by these bacteria.     

Biofilm Formation of O157 and Non‐O157 Shiga Toxin‐Producing Escherichia coli and Multidrug‐Resistant and Susceptible Salmonella Typhimurium and Newport and Their Inactivation by Sanitizers

This study compared biofilm formation by 7 serogroups of pathogenic Escherichia coli and 2 or 3 phenotypes of Salmonella (susceptible, multidrug‐resistant [MDR], and/or multidrug resistant with ampC gene [MDR‐AmpC]). One‐week mature biofilms were also exposed to water, quaternary ammonium compound‐based (QAC), and acid‐based (AB) sanitizers. Seven groups (strain mixture) of above‐mentioned pathogens were separately spot‐inoculated onto stainless steel coupons surfaces for target inoculation of 2 log CFU/cm², then stored statically, partially submerged in 10% nonsterilized meat homogenate at 4, 15, and 25 °C. Biofilm cells were enumerated on days 0, 1, 4, and 7 following submersion in 30 mL for 1 min in water, QAC, and AB. Counts on inoculation day ranged from 1.6 ± 0.4 to 2.4 ± 0.6 log CFU/cm² and changed to 1.2 ± 0.8 to 1.9 ± 0.8 on day 7 at 4 °C with no appreciable difference among the 7 pathogen groups. After treatment with QAC and AB on day 7, counts were reduced (P < 0.05) to less than 0.7 ± 0.6 and 1.2 ± 0.5, respectively, with similar trends among pathogens. Biofilm formation at higher temperatures was more enhanced; E. coli O157:H7, as an example, increased (P < 0.05) from 1.4 ± 0.6 and 2.0 ± 0.3 on day 0 to 4.8 ± 0.6 and 6.5 ± 0.2 on day 7 at 15 and 25 °C, respectively. As compared to 4 °C, after sanitation, more survivors were observed for 15 and 25 °C treatments with no appreciable differences among pathogens. Overall, we observed similar patterns of growth and susceptibility to QAC and AB sanitizers of the 7 tested pathogen groups with enhanced biofilm formation capability and higher numbers of treatment survivors at higher temperatures.     

Attachment and Biofilm Formation by Selected Strains of Salmonella enterica and Entrohemorrhagic Escherichia coli of Fresh Produce Origin

This study compared the abilities of selected Salmonella enterica and enterohemorrhagic Escherichia coli (EHEC) strains of fresh produce origin to form biofilms on polystyrene surface and to attach to alfalfa and bean sprouts. Each of the 7 S. enterica and 4 EHEC inocula (2 mL; 10⁷ CFU/mL) was placed in 6 different broths in 24‐well polystyrene tissue culture plates at 28 °C for 1 to 7 d. Developed biofilms were quantified using the crystal violet binding assay. In a separate experiment, alfalfa and mung bean sprouts (5 g) were exposed to 25 mL inocula (10⁷ CFU/mL) of S. enterica or EHEC at 22 °C for 2 h with shaking at 40 rpm. Contaminated sprouts were thoroughly rinsed and homogenized in 0.1% peptone water, and bacteria attached to sprouts were enumerated. Biofilm mass accumulated on polystyrene surface increased with incubation time (P < 0.05). Among the microbiological media used, LB no salt (NaCl) broth better supported biofilm development (P < 0.05). Two EHEC strains formed more biofilms than the Salmonella and other two EHEC strains (P < 0.05). However, more Salmonella cells (5.66 log CFU/g) attached to sprouts than EHEC cells (3.46 log CFU/g). Both Salmonella and EHEC attached in higher numbers to mung bean, than alfalfa, sprouts (P < 0.05).     

Evaluation of lactic acid and monolaurin to controlListeria monocytogeneson Stracchino cheese

The behaviour ofListeria monocytogeneswas evaluated during storage of Italian Stracchino cheese dipped in lactic acid (1.4%) or surface treated with (1)-monolauroyl-(rac)-glycerol (monolaurin, 200 μg cm⁻²). The cheese was surface inoculated with approximately 5×10²cfu cm⁻²ofL. monocytogenes, and stored under vacuum at 5°C for 12 days. The lactic acid treatment resulted in lower counts (P<0.05) ofL. monocytogenescompared with counts on untreated cheese washed with water. When lactic-treated cheese was stored at 5°C, levels ofL. monocytogenesdid not change appreciably. Treating cheese with monolaurin also significantly reduced the number ofL. monocytogenes. Furthermore, 12 day counts were less than the untreated control.     

Microbiological stability and diversity in raw pre-peeled potatoes packed in different atmospheres

Microbial growth on raw pre-peeled potatoes was analysed in relation to different process and storage parameters. Raw peeled potatoes with or without tumbling were packed in vacuum or modified atmosphere (MA) and stored at 4 °C and 15 °C for 7 and 5 days, respectively. Microbial growth was analysed throughout the storage period and growth was observed for mesophilic and psychrotrophic bacteria, lactic acid bacteria, Pseudomonas spp., and coliform bacteria. Growth at 4 °C was significantly lower compared to 15 °C. The number of bacteria was after seven days significantly higher on tumbled potatoes stored at 4 °C than on the untumbled potatoes. The bacterial counts generally exceeded 10⁶ CFU/g on tumbled potatoes after 7 days at 4 °C and 5 days at 15 °C, respectively. The CO₂ content increased during the storage period. A total of 243 isolates were grouped according to ITS-PCR profiles. Of these 47% had similar band profiles and thereby constituted the dominating flora at the end of shelf life. The dominating flora, identified on the basis of sequencing and microbial analysis of a subset of isolates, belonged to Enterobacteriaceae and consisted mainly of Enterobacter spp. and Kluyvera spp.     

Survivability and β‐galactosidase activity of bifidobacteria stored at low temperatures

Abstract

This work evaluated the ability of strains representing six species of Bifidobacterium with probiotic potential to survive and maintain β‐galactosidase activity through a two‐step, low‐temperature storage period. Cultures were also evaluated for their ability to ferment skim milk and retain viability during storage at 4°C. Bifidobacterium longum ATCC 15707, B. breve 15700, and B. bifidum 29521 maintained the greatest viabilities at > 1 x 10⁷ CFU/mL, and B. infantis 15702 maintained the highest β‐galactosidase activity at > 1 U/ml (with < 1 × 10⁵ CFU/mL) after ‐60 to 4°C storage. In fermented skim milk, B. breve 15700, B. bifidum 29521, and B. animalis 25527 tolerated a final product pH of 4.75 with > 1 × 10⁸ CFU/mL remaining after 14 days of storage at 4°C. Overall, it was found that highest levels of β‐galactosidase activities did not necessarily correlate to the highest plate‐count populations.