Review: Lactic acid: considerations in favour of its acceptance as a meat decontamininant

Efficacy of antimicrobial interventions in reducing Salmonella enterica, Shiga toxin-producing Escherichia coli, Campylobacter, and Escherichia coli biotype I surrogates on non-chilled and chilled, skin-on and skinless pork

Effect of various antimicrobial interventions on pork carcass cuts - skin-on and skinless, non-chilled and chilled - was studied. Carcass pieces were inoculated with Salmonella enterica, Shiga toxin-producing Escherichia coli (STEC), Escherichia coli pathogen surrogates or Campylobacter spp. Inoculated pieces were assigned to one of the following antimicrobial treatments: 2.5% and 5.0% room temperature lactic acid, 2.5% and 5.0% warm (55 °C) lactic acid, 400 ppm (0.4 mg/mL) room temperature peroxyacetic acid (PAA) or warm (55 °C) water. Treated pieces were sampled before antimicrobial treatment of non-chilled pork tissue, then at 30 m and 24 h post-treatment. For chilled pork, samples were collected after 24 h chilling and 30 m post-treatment. Lactic acid and PAA treatments reduced (P < 0.05) pathogenic and surrogate bacteria; warm water did not produce similar results. Objective and sensory color evaluations on treated pork indicated minimal negative impacts on pork color. Various antimicrobial interventions were effective in reducing surrogates on pork without diminishing quality.

Probiotic Potential of Lactic Acid Starter Cultures Isolated from a Traditional Fermented Sorghum-Millet Beverage

The purpose of this study was to establish the probiotic potential of lactic acid bacteria (LAB) starter cultures, Lb. plantarum MNC 21, L. lactis MNC 24, and W. confusa MNC 20, isolated from a traditionally fermented sorghum-millet beverage from Uganda. The cultures were examined for tolerance to acid and bile salts, bile salt hydrolase (BSH) activity, antibiotic susceptibility, biogenic amine production, mucin degradation, hydrophobicity, auto-aggregation, adherence to the ileum, coaggregation, and antimicrobial properties against selected pathogenic species. Lb. rhamnosus yoba 2012, a known probiotic, was the reference. The isolates were tolerant to acid (pH = 3) and bile (1%). W. confusa MNC 20 and Lb. plantarum MNC 21 exhibited medium BSH activity (11-15 mm diameter of hydrolysis zone) while L. lactis and Lb. rhamnosus yoba 2012 exhibited low BSH activity (<10 mm diameter of hydrolysis zone). All isolates lacked mucolytic activity. Lb. plantarum MNC 21 and W. confusa MNC 20 produced agmatine. The candidate and reference microorganisms were resistant to 10 of 21 and 5 of 21 antibiotics, respectively. The isolates exhibited hydrophobic, auto-aggregation and coaggregation properties. These three properties were exhibited more (p < 0.05) by the reference than the potential probiotics. The ability of the potential probiotics to attach onto the goat ileum (7.3-8.0 log cfu/cm²) was comparable to that of Lb. rhamnosus yoba 2012 (7.6 log cfu/cm²). The four LAB inhibited E. coli, S. aureus, and S. enterica to the same extent (p < 0.05). The findings indicated potential probiotic activity of the starter cultures. However, further in vivo examination of these isolates is required to confirm their probiotic capabilities.

Effect of protease inhibitor specificity on dentin matrix properties

OBJECTIVE

To evaluate protease activity of dentin matrices subjected to treatment with non-specific (chlorhexidine - CHX), cysteine cathepsin specific (E-64), and cysteine cathepsin-K (CT-K) specific (Odanacatib - ODN) inhibitors.

METHODS

Pulverized dentin powder obtained from human dentin disks (0.5 mm thickness) completely demineralized with 10% H₃PO₄ were challenged in 1 mL lactic acid (LA) (0.1M, pH 5.5) or stored in deionized water for 30 min. Aliquots of dentin powder were then immersed in 1 mL of CHX (2%), E-64 (10 μM and 20 μM) or Odanacatib (0.2 nM and 1 μM) for 30min. Degradation of dentin collagen was determined by telopeptide assays measuring the sub-product release of C-terminal cross-linked telopeptides (ICTP) and C-terminal peptide (CTX) in incubation media, which correlates with matrix metalloproteinases (MMP) and CT-K activities respectively (n = 3). The ICTP and CTX data were normalized to concentration of total protein (ICTP_tp and CTX_tp) in the media, measured by bicinchoninic acid assay. Dentin matrix properties were also measured by gravimetric change (n = 8) and ultimate tensile strength (UTS) (n = 10). Data were analyzed by one-way ANOVA followed by Tukey's post-hoc test and independent t-test (α = 5%).

RESULTS

Telopeptide assays showed significantly lower CTX_tp values after treatment with E-64 and Odanacatib. E-64 and Odanacatib at all tested concentrations significantly reduced the release of ICTP_tp. Gravimetric analysis showed no significant difference between the tested inhibitors and control except for CHX after lactic acid challenge. UTS results showed significantly higher values for E-64 (20 μM) and Odanacatib (0.2 nM and 1 μM) groups in deionized water.

SIGNIFICANCE

Dentin therapies targeting enzymes such as CT-K by specific inhibitors may provide superior pharmacokinetics and optimum efficacy due to precise protein binding, consequently limiting collagen degradation directly or indirectly by enzyme related pathways.

Effect of lactic acid spray on microbial and quality parameters of buffalo meat

We evaluated the effect of lactic acid spray on micro-flora, instrumental color, shelf-life and sensory attributes of buffalo meat displayed under Modified Atmosphere Packaging. Buffalo calf carcasses (n = 12) were sliced into equal sagittal halves, n = 6 halves were randomly assigned to each of four treatments i.e. 2% LA, 4% LA, 6% LA and control. Afterwards, sirloin and tenderloin were vacuum packed and aged for 7 days. Later, steaks were packed in high-oxygen MAP. Microbial load, instrumental color, shelf-life and sensory attributes were evaluated at different days. Aerobic plate count of sprayed carcass and steaks was significantly lower than un-sprayed control. Similarly, though non-significant, redness and chroma value of sprayed carcass meat was found better than un-sprayed control. Lactic acid sprayed meat did not differ in terms of sensory attributes. It is concluded that spraying buffalo carcasses with 2-4% lactic acid after slaughter not only enhances microbial quality but it may also improve its instrumental color.

Surface pH of Fresh Beef as a Parameter To Validate Effectiveness of Lactic Acid Treatment against Escherichia coli O157:H7 and Salmonella

The U.S. beef industry must provide documentation to the U.S. Department of Agriculture, Food Safety and Inspection Service (USDA-FSIS) that the antimicrobial interventions implemented or any subsequent changes in the process are effective under the actual conditions that apply in its operation. The main objective of this study was to determine whether surface pH after application of diluted lactic acid solution on surfaces of fresh meat can be used as a control measure indicator for the reduction of E. coli O157:H7 and Salmonella. Samples (240 each) of lean and adipose beef tissues were inoculated with cocktail mixtures of Escherichia coli O157:H7 and Salmonella. Application parameters were varied such that lean and adipose tissues were spray treated with either 2 or 4.5% lactic acid solution at either 38 or 60°C for 1 to 10 s. Lean and adipose tissues were collected before and after spray treatments for enumeration of the pathogens. Based on the conditions of this study, there was no difference between spray treatments at 38 or 60°C, but 4.5% lactic acid solution reduced pathogens more effectively ( P ≤ 0.05) than did 2% lactic acid solution. Spray treatment with lactic acid solution for 1 to 10 s reduced surface pH values of lean tissues (3 to 3.8) and adipose tissues (2.75 to 3.65). At surface pH values of 3.0 and 2.75, lactic acid reduced E. coli O157:H7 on surfaces of lean and adipose tissues by approximately 1.60 and 1.54 log CFU/cm², respectively. At surface pH values of 3.8 and 3.65, lactic acid reduced E. coli O157:H7 on lean and adipose tissues by approximately 0.3 and 0.42 log CFU/cm², respectively. The surface pH values after lactic acid treatment and the reductions of both pathogens showed a strong linear relationship; this indicates that a surface pH of 3.1 would provide at least 1-log reduction of E. coli O157:H7 and Salmonella, regardless of lactic acid application parameters. Therefore, surface pH after spray treatment with lactic acid could be used to validate pathogen reduction.

Some aspects of vegetable pickling processes / Algunos aspectos de la elaboración de encurtidos vegetales

A topical review of pickled vegetables is presented that encompasses scientific considerations rele vant to processing with the ultimate goal of generating interest for this ancient preservation tech nique. The emphasis is placed on the potential application of pickling to a group of high quality vegetables, and directing research and development pertaining to pickling in a more educated way. A critical literature survey is presented on issues such as transport of solutes, in situ fermen tation, and textural changes throughout the pickling process.

Antibiotic susceptibility and heterogeneity in technological traits of lactobacilli isolated from Algerian goat's milk

The objective of this study was to identify and study the heterogeneity of technological traits of lactobacilli from goat's milk of Algeria and to evaluate in vitro their safety aspect. Using API50 CHL system and 16S rDNA sequencing, 51 % of strains were assigned as Lactobacillus plantarum, 34 % as L. pentosus, 7 % as L. rhamnosus and 8 % as L. fermentum. A large variability was noted for the acidifying capacity in skim milk after 6, 12 and 24 h of incubation. All strains expressed aminopeptidase activity against alanine-ρ-NA and leucine-ρ-NA at different levels. All strains were resistant to vancomycin and most of strains showed more susceptibility to β-lactam antibiotic. High susceptibility toward the inhibitors of protein synthesis was also observed. Minimum inhibitory concentrations data obtained revealed that isolates were susceptible to penicillin and chloramphenicol, and resistant to gentamicin and vancomycin. Minimum inhibitory concentrations distribution of other antibiotics showed variability. The analysis of graphical representation of principal component analysis of technological properties of L. plantarum and L. pentosus strains showed diversity among the isolates. Finally, eight L. plantarum (LAM1, LAM3, LAM21, LAM25, LAM35, LF15, LAM34, and LAM35), four L. pentosus (LAM38, LAM39, LF9 and LF16) and two L. rhamnosus (LF3 and LF10) strains, could be good candidates as adjunct culture in dairy product in Algeria.

Evaluation of Synergistic Interactions Between Cell-Free Supernatant of Lactobacillus Strains and Amikacin and Genetamicin Against Pseudomonas aeruginosa

BACKGROUND

The indiscriminate use of antibiotics in the treatment of infectious diseases can increase the development of antibiotic resistance. Therefore, there is a big demand for new sources of antimicrobial agents and alternative treatments for reduction of antibiotic dosage required to decrease the associated side effects.

OBJECTIVES

In this study, the synergistic action of aminoglycoside antibiotics and cell-free supernatant (CFS) of probiotic (Lactobacillus rahmnosus and L. casei) against Pseudomonas aeruginosa PTCC 1430 was evaluated.

MATERIALS AND METHODS

A growth medium for culturing of probiotic bacteria was separated by centrifugation. The antimicrobial effects of CFS of probiotic bacteria were evaluated using the agar well diffusion assay. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were evaluated using the micro dilution method. Finally, an interaction between CFS and amikacin or gentamicin against P. aeruginosa PTCC 1430 was examined through the checkerboard method and fractional inhibitory concentration (FIC). Furthermore, CFSs from Lactobacillus strains were analyzed by reversed phase HPLC (RP-HPLC) for antimicrobial compounds.

RESULTS

The results showed a significant effect of CFS on the growth of P. aeruginosa. The MIC and MBC of CFS from L. casei were 62.5 µL⁄mL while the MIC and MBC of CFS from L. rhamnosus were 62.5 μL⁄mL and 125 μL⁄mL, respectively. Using the FIC indices, synergistic interactions were observed in combination of CFS and antibiotics. Fractional Inhibitory Concentration indices of CFS from L. casei and aminoglycoside antibiotics were 0.124 and 0.312 while FIC indices of CFS from L. rhamnosus and aminoglycoside antibiotics were 0.124 and 0.56, respectively showing a synergism effect. The results of RP-HPLC showed that CFS of Lactobacillus strains contained acetic acid, lactic acid and hydrogen peroxide (H2O2).

CONCLUSIONS

Our findings indicate that probiotic bacterial strains of Lactobacillus have a significant inhibitory effect on the growth of P. aeruginosa PTCC 1430. The antimicrobial potency of this combination can be useful for designing and developing alternative therapeutic strategies against P. aeruginosa infections.

Validation comparing the effectiveness of a lactic acid dip with a lactic acid spray for reducing Escherichia coli O157:H7, Salmonella, and non-O157 Shiga toxigenic Escherichia coli on beef trim and ground beef

The objective of this research was to compare the effectiveness of two application methods (dip versus spray) of 4.4% lactic acid for reducing pathogens on inoculated beef trim and in ground beef. Beef trim inoculated with cocktail mixtures of E. coli O157:H7, non-O157 Shiga toxigenic E. coli (STEC), or Salmonella (10(5) to 10(6) CFU/g) at separate times was subjected to five treatments: lactic acid spray (LS), lactic acid dip (LD), water spray (WS), water dip (WD), and untreated control (CTL). Intervention effectiveness for pathogen reduction was measured at 1 and 20 h after treatment on beef trim. Trim was then ground and intervention effectiveness was measured 1 h, 24 h, 72 h, and 7 days after grinding. The LD treatment reduced all pathogens significantly (P < 0.05); E. coli O157:H7 was reduced by 0.91 to 1.41 log CFU/g on beef trim and ground beef, non-O157 STEC by 0.48 to 0.82 log CFU/g, and Salmonella by 0.51 to 0.81 log CFU/g. No other treatment significantly reduced any pathogen, although the WD treatment noticeably reduced (P > 0.05) both E. coli O157:H7 and non-O157 STEC populations compared with the CTL. The LS treatment reduced E. coli O157:H7 and Salmonella by up to 0.5 log CFU/g on beef trim, but these reduced counts did not significantly differ (P > 0.05) from the CTL counts. Overall, the LD treatment was most effective for reducing all pathogens and is the best of these options for improving the safety of beef trim and subsequently produced ground beef.

Inoculation of lactic acid bacteria on meat surfaces as a means of decontamination in semitropical conditions

Reduction of microbial populations on carcasses has been achieved and reported by some authors by spraying solutions of organic acids, mainly lactic acid, on the meat surface. However, in practice, lactic acid is very expensive. Production of lactic acid in situ by a controlled lactic fermentation seemed to be a feasible answer. The objective of the present study was to explore the viability of this concept at semitropical conditions, i.e. temperatures around 25°C. In a first experiment, seven starters were tested for their ability to produce lactic acid and reducing the growth rate of pseudomonads, taking these microorganisms as indicators of contamination by spoilage microorganisms. The lactic acid bacteria strains were isolated from native Mexican maize-based beverages, and inoculated on the meat surface. Addition of sucrose and wrapping the samples in PVC film in order to induce a microaerophilic environment encouraged the over-growth of L. bulgaricus and P. pentosaceous over pseudomonads. A second experiment was designed to test a mixture of these two strains and a commercial starter with respect to lactic acid production, overgrowth of lactic acid bacteria over pseudomonads, decolouration and oxidation of the meat samples. It was concluded that a commercial starter (L. plantarum + M. kristinae-varians) resulted in a reduction of pseudomonas growth rate, without notably affecting meat colour and degree of oxidation.

A glutamic acid-producing lactic acid bacteria isolated from Malaysian fermented foods

l-glutamaic acid is the principal excitatory neurotransmitter in the brain and an important intermediate in metabolism. In the present study, lactic acid bacteria (218) were isolated from six different fermented foods as potent sources of glutamic acid producers. The presumptive bacteria were tested for their ability to synthesize glutamic acid. Out of the 35 strains showing this capability, strain MNZ was determined as the highest glutamic-acid producer. Identification tests including 16S rRNA gene sequencing and sugar assimilation ability identified the strain MNZ as Lactobacillus plantarum. The characteristics of this microorganism related to its glutamic acid-producing ability, growth rate, glucose consumption and pH profile were studied. Results revealed that glutamic acid was formed inside the cell and excreted into the extracellular medium. Glutamic acid production was found to be growth-associated and glucose significantly enhanced glutamic acid production (1.032 mmol/L) compared to other carbon sources. A concentration of 0.7% ammonium nitrate as a nitrogen source effectively enhanced glutamic acid production. To the best of our knowledge this is the first report of glutamic acid production by lactic acid bacteria. The results of this study can be further applied for developing functional foods enriched in glutamic acid and subsequently γ-amino butyric acid (GABA) as a bioactive compound.

Characterisation and biochemical properties of predominant lactic acid bacteria from fermenting cassava for selection as starter cultures

A total of 375 lactic acid bacteria were isolated from fermenting cassava in South Africa, Benin, Kenya and Germany, and were characterised by phenotypic and genotypic tests. These could be divided into five main groups comprising strains of facultatively heterofermentative rods, obligately heterofermentative rods, heterofermentative cocci, homofermentative cocci and obligately homofermentative rods, in decreasing order of predominance. Most of the facultatively heterofermentative rods were identified by phenotypic tests as presumptive Lactobacillus plantarum-group strains, which also comprised the most predominant bacteria (54.4% of strains) isolated in the study. The next predominant group of lactic acid bacteria (14.1% of total isolates) consisted of obligately heterofermentative rods belonging either to the genus Lactobacillus or Weissella, followed by the heterofermentative cocci (13.9% of isolates) belonging to the genera Weissella or Leuconostoc. Homofermentative cocci were also isolated (13.3% of isolates). Biochemical properties such as production of alpha-amylase, beta-glucosidase, tannase, antimicrobials (presumptive bacteriocin and H(2)O(2)-production), acidification and fermentation of the indigestible sugars raffinose and stachyose, were evaluated in vitro for selection of potential starter strains. A total of 32 strains with one or more desirable biochemical properties were pre-selected and identified using rep-PCR fingerprinting in combination with 16S rRNA sequencing of representative rep-PCR cluster isolates. Of these strains, 18 were identified as L. plantarum, four as Lactobacillus pentosus, two each as Leuconostoc fallax, Weissella paramesenteroides and Lactobacillus fermentum, one each as Leuconostoc mesenteroides subsp. mesenteroides and Weissella cibaria, while two remained unidentified but could be assigned to the L. plantarum-group. These strains were further investigated for clonal relationships, using RAPD-PCR with three primers, and of the 32 a total of 16 strains were finally selected for the development as starter cultures for Gari production.

Efficacy of lactic acid against Listeria monocytogenes attached to poultry skin during refrigerated storage

AIMS

The aim of this study was to evaluate the effect of lactic acid washing on the growth of Listeria monocytogenes on poultry legs stored at 4 degrees C for 7 days.

METHODS AND RESULTS

Fresh inoculated chicken legs were dipped into either a 0.11, 0.22 mol l(-1) or 0.55 mol l(-1) lactic acid solution for 5 min or distilled water (control). Surface pH values, sensorial characteristics and L. monocytogenes, mesophiles and pychrotrophs counts were evaluated after treatment (day 0) and after 1, 3, 5 and 7 days of storage at 4 degrees C. Legs washed with 0.55 mol l(-1) lactic acid for 5 min showed a significant (P < 0.05) inhibitory effect on L. monocytogenes compared with control legs, being about 1.74 log units lower in the first ones than in control legs after 7 days of storage. Sensory quality was not adversely affected by lactic acid, with the exception of colour.

CONCLUSIONS

Treatments with 0.55 mol l(-1) lactic acid reduced bacterial growth and preserved reasonable sensorial quality after storage at 4 degrees C for 7 days. However, it was observed a reduction in the colour score within 1 day post-treatment with 0.55 mol l(-1) lactic.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates that, while lactic acid did reduce populations of L. monocytogenes on poultry, it did not completely inactivate the pathogen. The application of lactic acid may be used as an additional hurdle contributing to extend the shelf-life of raw poultry.

Application of electrochemical optical waveguide lightmode spectroscopy for studying the effect of different stress factors on lactic acid bacteria

Electrochemical optical waveguide lightmode spectroscopy (EC-OWLS) has been developed to combine evanescent-field optical sensing with electrochemical control of surface adsorption processes. For bioanalytical sensing, a layer of indium tin oxide (ITO) served as both a high-refractive index waveguide and a conductive electrode. In addition, an electrochemical flow-through fluid cuvette was applied, which incorporated working, reference, and counter electrodes, and was compatible with the constraints of optical sensing. The subject of our study was to monitor how the different stress factors (lactic acid, acetic acid and hydrogen peroxide) influence the survival of lactic acid bacteria. The advantage of EC-OWLS technique is that we could carry out kinetic studies on the behaviour of bacteria under stress conditions, and after exposure of lactobacilli to acid and oxidative stress we get faster results about the status of bacteria compared to the traditional quantitative methods. After optimization of the polarization potential used, calibration curve was determined and the sensor response of different rate of living and damaged cells was studied. The bacterial cells were adsorbed in native form on the surface of the sensor by ensuring polarizing potential (1V) and were exposed to different concentration of acetic acid and hydrogen peroxide solution to 1h, respectively and the behaviour of bacteria was monitored. Results were compared to traditional micro-assay method.

Inhibitory effect of organic acid salts on spoilage flora in culture medium and cured cooked meat products under commercial manufacturing conditions

Lactobacillus curvatus, isolated from a spoiled vacuum-packaged 'pariza' type meat product, was used to inoculate modified MRS broth containing sodium lactate, sodium acetate and potassium sorbate in different concentrations, alone or in inter se combinations. Two commercial preparations (MIX 1 and MIX 2) were also used containing combinations of the above antimicrobials. Results from the preservatives addition to the culture medium showed highest antimicrobial activity in the case of the sodium lactate (2%, 3% or 4%), sodium acetate (0.5%) and potassium sorbate (0.15%) combination. Results from the preservatives addition to two types of thermally processed meats showed that sodium lactate and the combination of sodium lactate, sodium acetate and potassium sorbate were the most effective; extending the products shelf life an additional 10 days. Finally, MIX 1 and MIX 2 suppressed the lactic acid bacteria (LAB) growth in the culture medium but not in the final product.

Escherichia coli O157 prevalence and enumeration of aerobic bacteria, Enterobacteriaceae, and Escherichia coli O157 at various steps in commercial beef processing plants

The effectiveness of current antimicrobial interventions used in reducing the prevalence or load of Escherichia coli O157 and indicator organisms on cattle hides and carcasses at two commercial beef processing plants was evaluated. Sponge sampling of beef cattle was performed at five locations from the initial entry of the animals to the slaughter floor to the exit of carcasses from the "hotbox" cooler. For each sample, E. coli O157 prevalence was determined and total aerobic bacteria, Enterobacteriaceae, and E. coli O157 were enumerated. E. coli O157 was found on 76% of animal hides coming into the plants, but no carcasses leaving the cooler were identified as contaminated with E. coli O157. A positive relationship was seen between the incidence of E. coli O157 in hide samples and that in preevisceration samples. Aerobic plate counts and Enterobacteriaceae counts averaged 7.8 and 6.2 log CFU/100 cm2, respectively, on hides, and 1.4 and 0.4 log CFU/100 cm2, respectively, on chilled carcasses. Aerobic plate counts and Enterobacteriaceae counts on preevisceration carcasses were significantly related to the respective levels on the corresponding hides; the carcasses of animals whose hides carried higher numbers of bacteria were more likely to carry higher numbers of bacteria. Implementation of the sampling protocol described here would allow processors to evaluate the efficacy of on-line antimicrobial interventions and allow industrywide benchmarking of hygienic practices.

Antagonistic action of cells of Lactobacillus delbrueckii subsp. lactis against pathogenic and spoilage microorganisms in fresh meat systems

Cells of Lactobacillus delbrueckii subsp. lactis RM2-5 were added to various meat model systems that had been inoculated with Escherichia coli O157:H7 or Salmonella Typhimurium to determine whether these lactobacilli were antagonistic to the pathogens during storage at 5 degrees C. Experiments in which L. delbrueckii subsp. lactis RM2-5 was directly applied to the surfaces of beefsteaks resulted in significant (P < 0.05) reductions in the growth of psychrotrophs and coliforms plus a slight decrease in the numbers of E. coli O157:H7 over time relative to those for control samples to which no lactobacilli had been added. Experiments involving the direct application of L. delbrueckii subsp. lactis RM2-5 to the surfaces of freshly slaughtered beef and pork carcass samples inoculated with either E. coli O157:H7 or Salmonella Typhimurium showed significant (P < 0.05) declines in numbers of the pathogens as well as a reduction in the growth of psychrotrophs during storage at 5 degrees C for 6 days. The results of the experiments suggest that lactobacillus cultures have potential for use in an intervention technology for the control of foodborne pathogens, especially on the surfaces of beef and pork carcasses. The results of this study also suggest that an extension of the shelf life of meat can result from the decreased growth of psychrotrophic spoilage organisms.

Combined effects of lactic acid and nisin solution in reducing levels of microbiological contamination in red meat carcasses

Changes in bacterial counts on beef carcasses at specific points during slaughter and fabrication were determined, and the effectiveness of nisin, lactic acid, and a combination of the lactic acid and nisin in reducing levels of microbiological contamination was assessed. Swab samples were obtained from the surfaces of randomly selected beef carcasses. Carcasses were swabbed from the neck, brisket, and renal site after skinning, splitting, and washing. Treatments involving lactic acid (1.5%), nisin (500 IU/ml), or a mixture of nisin and lactic acid were applied after the neck area was washed. A control group was not sprayed. Results indicated that the highest prevalence of aerobic plate counts (APCs), total coliforms, and Escherichia coli was found in the neck site after splitting, and the lowest level of microbial contamination was found after skinning. Washing with water did not significantly reduce the bacterial load. The largest reduction in APCs, total coliforms, and E. coli occurred on carcasses treated with a mixture of nisin and lactic acid. A mixture of nisin and lactic acid can be applied to beef carcasses through spray washing and can reduce bacterial populations by 2 log units.

Influence of poultry carcass skin sample site on the effectiveness of trisodium phosphate against Listeria monocytogenes

The aim of this study was to determine the influence of skin sample site on the efficacy of trisodium phosphate (TSP) solutions in reducing Listeria monocytogenes populations on chicken carcasses during refrigerated storage. Chicken skin samples from the legs, the breasts, and the dorsal area inoculated with L. monocytogenes (10(8) CFU/ml) were dipped for 15 min in sterile tap water (control) or in 8, 10, or 12% TSP. L. monocytogenes counts and surface pH values were determined after 0, 1, 3, and 5 days of storage at 2 degrees C. For all sampling times and TSP concentrations, the reductions in L. monocytogenes numbers in breast skin were significantly larger (P < 0.05) than those in leg skin or dorsal skin. No significant differences were found in pH values as an effect of skin site. Our results suggest that skin sampling site is an important factor that needs to be considered when decontamination protocols are developed for poultry carcasses with the TSP treatment.

Inactivation of Escherichia coli O157:H7, Salmonella enteritidis, and Listeria monocytogenes on apples, oranges, and tomatoes by lactic acid with hydrogen peroxide

The objective of this study was to develop a practical and effective method for inactivating or substantially reducing Escherichia coli O157:H7, Salmonella Enteritidis, and Listeria monocytogenes on apples, oranges, and tomatoes. Apples, oranges, and tomatoes were spot-inoculated with five-strain mixtures of E. coli O157:H7, Salmonella Enteritidis, and L. monocytogenes near the stem end and were submerged in sterile deionized water containing 1.5% lactic acid plus 1.5% hydrogen peroxide for 15 min at 40 degrees C. Inoculated samples treated with sterile deionized water at the same temperature and for the same duration served as controls. The bacterial pathogens on fruits subjected to the chemical treatment were reduced by >5.0 log10 CFU per fruit, whereas washing in deionized water decreased the pathogens by only 1.5 to 2.0 log10 CFU per fruit. Furthermore, substantial populations of the pathogens survived in the control wash water, whereas no E. coli O157:H7, Salmonella Enteritidis, or L. monocytogenes cells were detected in the chemical treatment solution. The sensory and qualitative characteristics of apples treated with the chemical wash solution were not adversely affected by the treatment. It was found that the treatment developed in this study could effectively be used to kill E. coli O157:H7, Salmonella Enteritidis, and L. monocytogenes on apples, oranges, and tomatoes at the processing or packaging level.

Survival of Listeria monocytogenes Scott A on vacuum-packaged raw beef treated with polylactic acid, lactic acid, and nisin

Low-molecular-weight polylactic acid (LMW-PLA) and lactic acid (LA) were used to inhibit growth of Listeria monocytogenes Scott A on vacuum-packaged beef. Nisin was also used simultaneously as an additional hurdle to the growth of this pathogen. Inoculated beef cubes were immersed in a solution of 2% LMW-PLA, 2% LA, 400 IU/ml of nisin, or combinations of each acid and nisin for 5 min and drip-dried for 15 min. The cubes were then vacuum-packaged and stored at 4 degrees C for up to 42 days. Surface pH values of beef cubes treated with 2% LMW-PLA, the combination of 400 IU/ml of nisin and 2% LMW-PLA (2% NPLA), or 400 IU/ml of nisin alone were significantly reduced from 5.59 to 5.18, 5.01, and 5.19, respectively, whereas those decontaminated with 2% LA or 400 IU/ml of nisin and 2% LA (2% NLA) were significantly decreased from 5.59 to 4.92 and 4.83, respectively, at day 0 (P < or = 0.05). The 2% LMW-PLA, 2% LA, 2% NPLA, 2% NLA, and 400 IU/ml of nisin showed immediate bactericidal effects on L. monocytogenes Scott A (1.22-, 1.56-, 1.57-, 1.94-, and 1.64-log10 reduction, respectively) compared with the initial number of 5.33 log10 CFU/cm2 of the untreated control at day 0 (P < or = 0.05). These treatments, combined with vacuum-packaging and refrigeration temperature, succeeded to inhibit growth of L. monocytogenes during storage up to 42 days. At the end of 42 days, the numbers of L. monocytogenes Scott A remaining viable on these samples were 1.21, 0.36, 2.21, 0.84, and 0.89 log10 CFU/cm2, respectively.

Integrating microbial decontamination with organic acids in HACCP programmes for muscle foods: prospects and controversies

A considerable literature reports the antibacterial efficacy of dilute solutions of organic acids (lactic, acetic). With carcasses an overall reduction in surface contaminants of 1.5 log cycles can be expected. Carcass decontamination may not improve the safety of the resultant meat, but laboratory trials confirm that acid decontamination of subprimal and retail cuts is more efficacious. An advantage over many other intervention strategies is that residual antimicrobial activity is demonstrable over extended periods of storage. These studies have also shown that some meatborne pathogens are particularly sensitive to organic acids (i.e., Yersinia enterocolitica) while others are resistant (i.e., E. coli O157:H7). Dilute solutions of organic acids (1 to 3%) are generally without effect on the desirable sensory properties of meat when used as a carcass decontaminant. However, dependent on treatment conditions, lactic and acetic acid can produce adverse sensory changes when applied directly to meat cuts, with irreversible changes in appearance being a frequent occurrence. It is speculated that organic acid decontamination will be implemented in American abattoirs in an effort to meet specified performance standards for pathogen reduction as part of an overall HACCP program. In contrast, the EU advocates that strictly controlled processing hygiene is sufficient to ensure the safety of the product. Additional research is necessary to establish a set of treatment conditions that may permit a practicable reduction in bacterial contamination throughout the processing chain with a measurable effect on safety and storage life, without imposing any change in sensory properties. It will also be necessary to develop standard, objective measures to assess HACCP and the efficacy of decontamination procedures. Without such commercial studies controversy on the practicality of acid decontamination will persist.

Identification and quantification of risk factors regarding Salmonella spp. on pork carcasses

The main elements of a descriptive epidemiological model for Salmonella spp. in Dutch pig slaughterlines, and the subsequent quantification of risk factors regarding the contamination of carcasses, are described. There is a strong correlation between the number of live animals that carry Salmonella spp. in their faeces and the number of contaminated carcasses at the end of the slaughterline. Live animals that carry Salmonella spp. are 3-4 times more likely to end up as a positive carcass than Salmonella-free animals. Currently, about 70% of all carcass contamination results from the animals themselves being carriers, and 30% because other animals were carriers (i.e. cross contamination). Furthermore, it is estimated that in general between 5-30% of the carcasses produced may contain Salmonella spp. With respect to carcass contamination with Enterobacteriaceae and Salmonella spp., inadequately cleaned polishing machines (odds ratio, OR, 6) and 'inapt procedures during evisceration' (OR 11), i.e. faulty evisceration and hygiene practices, are the most important risk factors. An estimated 5-15% of all carcass contamination with Salmonella spp. occurs during polishing after singeing. The remainder is the result of current evisceration practices (55-90%) and, to a lesser extent, further processing (5-35%), i.e dressing, splitting and meat inspection. Less likely Salmonella spp. already present on the skin of the live animals survive scalding and singeing. However, because pigs are the only important source for the Salmonella contamination of the line and the carcasses produced, it can also be concluded that if Salmonella-free pigs were produced, consumers could be provided with virtually Salmonella-free pork. As long as Salmonella-positive animals enter abattoirs, there will always be transmission of Salmonella spp. to consumers, even if the process is carried out according to stringent codes of good manufacturing practices (GMP). EU regulations should, therefore, allow for the decontamination of caracasses with a safe substance, e.g. lactic acid, on the condition that the slaughterhouse strictly adhers to GMP principles.

The effects of potassium sorbate and lactic acid on the shelf-life of vacuum-packed chicken meats

In this research, the effects of 5% potassium sorbate (PS) and 3% lactic acid (LA) applications on total mesophylic aerobic bacteria, total psychrotrophic aerobic bacteria, lactic acid bacteria, staphylococci and coliform bacteria, pH values, thiobarbituric acid (TBA) numbers, and sensorial properties of vacuum-packed chicken leg and breast meats were investigated during storage at 4 +/- 1 C. In addition, residual sorbate was examined. A decrease in bacterial counts of chicken leg and breast meats was observed in the periods following the treatments of PS and LA; however, towards the end of the storage period, the effectiveness of PS was greater than that of LA. Although no effect was observed on pH values of samples treated with PS, LA caused a decrease in pH values in chicken meats. Both PS and LA treatments resulted in high TBA numbers. Although the shelf-life periods of samples treated with PS and LA were about 30 d, vacuum-packed controls and unsealed controls (both of which were untreated) lost their edibility on the 18th and the 6th d, respectively. Sensory analysis panel members could not distinguish between PS samples and control samples. However, samples containing LA had lower scores than others. Both PS and LA treatments were considered to be acceptable. Quantities of sorbic acid found in the samples treated with PS were below the Acceptable Daily Intake established by the Food and Agriculture Organization/World Health Organization.

Lactic acid inhibition of the growth of spoilage bacteria and cold tolerant pathogens on pork

The antibacterial effects of a 3% solution of lactic acid at 55 degrees C were assessed, by examining aerobic bacterial growth on artificially-inoculated pork fat and lean tissue. Discs of fat or lean tissues, each of 10 cm2 surface area, were aseptically excised from pork Longissimus dorsi muscle and inoculated with the cold tolerant pathogens Listeria monocytogenes 4b Scott A no. 3, Yersinia enterocolitica 0:4,32 or Aeromonas hydrophila ATCC 7966, or with the wild type spoilage bacteria Pseudomonas fragi or Brochothrix thermosphacta. After inoculation, each meat disc was immersed in water or lactic acid for 15 s and aerobic bacterial growth followed during 15 days of storage at 4 degrees C. P. fragi and B. thermosphacta grew on both fat and lean, but the pathogens grew on fat tissue only and A. hydrophila did not survive on lean. Lactic acid reduced all test bacteria on fat to below detectable levels within 4 days of treatment and no bacteria could be recovered from acid-treated fat surfaces for the remainder of the 15-day storage interval. Bacteria attached to lean were generally more resistant to lactic acid. In some instances the acid was bacteriostatic (P. fragi, L. monocytogenes) while in others the population declined at a greatly reduced rate as compared with a similar population on fat (B. thermosphacta, Y. enterocolitica). A. hydrophila was equally sensitive to lactic acid on lean and fat. Depending upon the tested strain, tissue type and storage time, maximum reductions in the number of bacteria recovered from acid treated pork ranged from 1 to 8 log cycles. The high bactericidal efficacy of lactic acid applied to pork fat was attributable to a low tissue pH, which varied from 3.49 to 4.41 during the 15 days of aerobic storage.

Inhibition, survival and growth of Listeria monocytogenes on poultry as influenced by buffered lactic acid treatment and modified atmosphere packaging

The effect of the treatment with various concentrations (2%, 5% and 10% w/v) of lactic acid/sodium lactate buffer (pH 3.0), modified atmosphere (MAP) packaging (90% CO2 and 10% O2) and 10% (w/v) lactic acid/sodium lactate buffer (pH 3.0) combined with MAP on Listeria monocytogenes Z7 serotype 1 and on the shelf life of chicken legs stored at 6 degrees C was investigated. The initial contamination level of L. monocytogenes on the chicken legs surface was 8.3 x 10(2) cfu/cm2 of skin. After 2 days of storage at 6 degrees C the number of L. monocytogenes on legs treated with 2%, 5%, 10% lactic acid/sodium lactate buffer (pH 3.0) and 10% lactic acid/sodium lactate buffer (pH 3.0) combined with MAP was significantly lower than the initial number of L. monocytogenes. Later, growth of L. monocytogenes was observed. After 13 days of storage at 6 degrees C the number of L. monocytogenes on legs treated with 10% lactic acid/sodium lactate buffer (pH 3.0) combined with MAP was still similar to the initial number. Legs treated with 2%, 5%, 10% lactic acid/sodium lactate buffer (pH 3.0), MAP and 10% lactic acid/sodium lactate buffer (pH 3.0) combined with MAP, have a shelf life at 6 degrees C of respectively 8, 9, 10, 13 and 17 days. This means a prolongation of 2, 3, 4, 7 and 11 days, respectively for storage at 6 degrees C. The antimicrobial effect of lactic acid buffer systems (pH 3.0) increased with increasing concentrations of lactic acid in the buffered system. The best results were obtained by the combined use of 10% acid/sodium lactate buffer (pH 3.0) and MAP.

Antagonistic activities of lactic acid bacteria in food and feed fermentations

Many factors contribute to a successful natural fermentation of carbohydrate-rich food and feed products. Metabolic activities of lactic acid bacteria (LAB) play a leading role. Their ability to rapidly produce copious amounts of acidic end products with a concomitant pH reduction is the major factor in these fermentations. Although their specific effects are difficult to quantitate, other LAB metabolic products such as hydrogen peroxide and diacetyl can also contribute to the overall antibiosis and preservative potential of these products. The contribution of bacteriocins is also difficult to evaluate. It is suggested that they may play a role in selecting the microflora which initiates the fermentation. Bacteriocins are believed to be important in the ability of LAB to compete in non-fermentative ecosystems such as the gastrointestinal tract. During the past few decades interest has arisen in the use of the varied antagonistic activities of LAB to extend the shelf-life of protein-rich products such as meats and fish. Recent findings indicate that the newly discovered Lactobacillus reuteri reuterin system may be used for this purpose.