Use of nisin for inhibition of Alicyclobacillus acidoterrestris in acidic drinks

The inhibitory effects of nisin on the growth of the thermoacidophilic spoilage bacteriumAlicyclobacillus acidoterrestris were investigated for the purpose of preventing flat-sour-type spoilage in acidic drinks. Minimum inhibitory concentration values of nisin against the spores were from less than 0·78 to 12·5 IU ml⁻¹and from 25 to 100 IU ml⁻¹on mYPGA plates at pH 3·4 and 4·2, respectively. The levels of nisin inhibition against the vegetative cells were, however, higher than those of the spores. In determining the effects of nisin on the thermal resistance of A. acidoterrestris spores, the addition of nisin contributed to the reduction of the thermal resistance of A. acidoterrestris spores in acidic drinks. Furthermore, the outgrowth of A. acidoterrestris spores was inhibited by the addition of 25–50 IU ml⁻¹nisin in both orange and fruit-mixed drinks, but was not inhibited by the higher level (600 IU ml⁻¹) addition in a clear-apple drink. From these findings, we conclude that it would be useful to add nisin for preventing the spoilage caused by A. acidoterrestris in all but clear-apple acidic drinks.     

An inhibitory synergistic effect of a nisin–monolaurin combination on Bacillus sp. vegetative cells in milk

The inhibitory activities of nisin and monolaurin, used alone or in combination, were investigated against four Bacillus species vegetative cells in milk at 37°C for 5 days. In the absence of inhibitors, the four strains grew and sporulated at the end of the exponential growth step and throughout the stationary phase. Nisin (100 IU ml⁻¹) induced an immediate reduction in the population level but transient because regrowth appeared and was strain-dependent; cell concentrations reached the control culture level, e.g. 6–7 log₍₁₀₎as well as the spore load (4–5 log₍₁₀₎). On the other hand, monolaurin (250 μ g ml⁻¹) had a durable bacteriostatic effect followed by a regrowth level constantly lower than that of the control culture; sporulation was low (between 13 and 7×10³spl ml⁻¹) and did not occur in the case of B. coagulans. The use of these inhibitors in combination, induced a synergistic bactericidal effect leading to a total inhibition (0 cfu ml⁻¹) until day 5, except in the case of B. cereus where a concentration of 500 cfu ml⁻¹was constant till the end of the experiment; consequently, sporulation was absent.     

Incorporation of bacteriocin in plastic retains activity and inhibits surface growth of bacteria on meat

The bacteriocin, nisin, was incorporated into a polyethylene based plastic film and retained activity against the indicator bacteria Lactobacillus helveticus and Brochothrix thermosphacta . Beef carcass surface tissue sections (BCT) topically inoculated with the psychrotrophic spoilage bacterium B. thermosphacta were vacuum-packaged both with and without wrapping with the nisin impregnated plastic and held at 4° C. An initial reduction of 2 log₁₀cycles of B. thermosphacta was observed with nisin-impregnated wrapped BCT within the first 2 days of storage. After 20 days of refrigerated storage, B. thermosphacta populations from nisin impregnated plastic wrapped samples were significantly less than (P<0·05) control vacuum-packaged samples; log₁₀5·8 vs 7·2 cfu cm⁻²respectively. Temperature abuse was simulated by shifting inoculated packs from 4° C (after 2 days) to 12° C. Again, by 20 days, the B. thermosphacta populations of treated samples wrapped with nisin impregnated plastic were significantly less than (P<0·05) control vacuum-packaged samples; log₁₀3·6 vs 6·3 cfu cm⁻²respectively. This work highlights the potential for incorporating antimicrobial peptides with a wider and different range of inhibitory activity directly into plastics of different properties for use in controlling food spoilage as well as preservation to enhance product microbial safety.     

The potential application of plant essential oils as natural food preservatives in soft cheese

Investigations were carried out to assess the efficiency of four plant essential oils; bay, clove, cinnamon and thyme as natural food preservatives. The effect of the plant essential oils at concentrations of 0·1, 0·5 and 1% was studied in low-fat and full-fat soft cheese against Listeria monocytogenes and Salmonella enteritidis at 4° and 10°C respectively, over a 14-day period. The composition of the cheese was shown to be an important factor in determining the effectiveness of the plant essential oils. In the low-fat cheese, all four oils at 1% reduced L. monocytogenes to ≤1·0 log₁₀cfu ml⁻¹. In contrast, in the full-fat cheese, oil of clove was the only oil to achieve this reduction. Oil of thyme proved ineffective against S. enteritidis in the full-fat cheese, yet was equally as effective as the other three oils in the low-fat cheese, reducing S. enteritidis to ≤1·0 log₁₀cfu ml⁻¹from day 4 onwards. It is concluded that selected plant essential oils can act as potent inhibitors of L. monocytogenes and S. enteritidis in a food product.     

Biodegradable Poly(butylene adipate-co-terephthalate) Films Incorporated with Nisin: Characterization and Effectiveness against Listeria innocua

ABSTRACT: Biodegradable poly(butylene adipate-co-terephthalate) (PBAT) films incorporated with nisin were prepared with concentrations of 0, 1000, 3000, and 5000 international units per cm² (IU/cm²). All the films with nisin inhibited Listeria innocua, and generated inhibition zones with diameters ranging from 14 to 17 mm. The water vapor permeability and oxygen permeability after the addition of nisin ranged from 3.05 to 3.61 × 10¹¹ g m m⁻² s⁻¹ Pa⁻¹ and from 4.80 × 10⁷ to 11.26 × 10⁷ mL·m·m⁻²·d⁻¹·Pa⁻¹, respectively. The elongation at break (ɛ_b) was not altered by the incorporation of nisin (P > 0.05). Significant effect was found for the elastic modulus (E) and the tensile strength (σ_s) (P < 0.05). The glass transition and melting temperatures with the presence of nisin ranged from −36.3 to −36.6 °C and from 122.5 to 124.2 °C, respectively. The thermal transition parameters such as the crystallization and melting enthalpies and crystallization temperature were influenced significantly (P < 0.05) by incorporation of nisin into films. The X-ray diffraction patterns exhibited decreasing levels of intensity (counts) as the concentration of nisin increased in a range of 2θ from 8° to 35°. Formation of holes and pores was observed from the environmental scanning electron microscopy images in the films containing nisin, suggesting interaction between PBAT and nisin.     

Reductions ofListeria innocuaandBrochothrix thermosphactaon beef following nisin spray treatments and vacuum packaging

Sections of UV sterilized lean and adipose tissues from the surfaces of post-rigor (24 h post-mortem) beef carcasses were inoculated withBrochothrix thermosphactaorListeria innocuato obtain approximately 4.50 log₈cfu cm⁻²and subjected to spray treatments with sterile water or nisin (5000 AU ml⁻¹). Untreated and spray treated samples were vacuum-packaged, and incubated at 4°C for up to 4 weeks. Bacterial populations from untreated vacuum-packaged tissues and spray treated, vacuum-packaged tissues were enumerated on non-selective and selective media at 0, 7, 14, 21 or 28 days. Nisin spray treatments of lean and adipose vacuum-packaged tissues reduced the numbers ofL. innocuaup to 2.83 log₈cfu cm⁻². Additionally, nisin sprays and vacuum packaging effectively suppressedL. innocuaduring the 4-week incubation such that the remaining bacteria did not grow to the same level as untreated or water-treated, vacuum-packaged tissues. Nisin spray treatments and vacuum packaging of lean and adipose tissues reducedB. thermosphactato undetectable levels. Data from this study demonstrate that nisin spray treatments followed by vacuum packaging under refrigerated conditions could increase the shelf life by suppressing or inhibiting the growth of undesirable bacteria present on fresh beef.     

Destruction of Salmonella enteritidis inoculated in liquid whole egg by high hydrostatic pressure: comparative study in selective and non-selective media

The destruction of Salmonella enteritidis inoculated in liquid whole egg at approximately 10⁷−10⁸cfu ml^−lwas studied under combinations of pressure (350 and 450 MPa), temperature (50, 20, 2 and −15°C) and time (5, 10, 15 min and cycles of 5+5 and 5+5+5 min). One non-selective medium (tryptone soy agar) and two selective media (brilliant green agar and salmonella-shigella) were used to evaluate viability of S. enteritidis after pressurization. The inactivation rate increased with pressure and exposure time, being minimal at 350 MPa and −15°C for 5 min (over 1 log₁₀of reduction) and reaching total inactivation (8 log₁₀of reduction) in several treatments at 50°C. Treatments in cycles showed greater effectiveness than continuous treatments of the same total time. The effect of pressure was enhanced by elevated temperatures. The higher counts were obtained in the non-selective medium, indicating the presence of injured cells after pressure treatment. D -values obtained for two temperatures (2 and 20°C) and different times (0–60 min) under controlled pressure (400 MPa) showed that microbial inactivation followed a first-order kinetics with a decimal reduction time evaluated in tryptone soy agar medium of 9·5 min at 2°C and 8·8 min at 20°C.     

Nisin–EDTA treatments and modified atmosphere packaging to increase fresh chicken meat shelf-life

The effect of nisin and EDTA treatments on the shelf-life of fresh chicken meat stored under modified atmosphere packaging at 4 °C was evaluated. Chicken meat was subjected to the following antimicrobial treatment combinations: Nisin–EDTA treatments (added post-production to the chicken samples) included: N1 (no nisin–EDTA added; control sample), N2 (500 IU/g; no EDTA added), N3 (1500 IU/g; no EDTA added), N4 (500 IU/g-10 mM EDTA), N5 (1500 IU/g-10 EDTA), N6 (500 IU/g-50 mM EDTA), N7 (1500 IU/g-50 EDTA), N8 (10 mM EDTA; no nisin added), and N9 (50 mM EDTA; no nisin added). N3, N4, N5, N6 and N7 affected populations of mesophilic bacteria, Pseudomonas sp., Brochothrix thermosphacta, lactic acid bacteria, and Enterobacteriaceae. The antimicrobial combination treatments N5, N6 and N7 had a significant effect on the formation of volatile amines, trimethylamine nitrogen (TMA-N) and total volatile basic nitrogen (TVB-N) in chicken meat. The use of MAP in combination with nisin–EDTA antimicrobial treatments resulted in an organoleptic extension of refrigerated, fresh chicken meat by approximately 1–2 days (N2), 3–4 days (N3 and N4), 7–8 days (N5), 9–10 (N7) and by 13–14 days (N6). Chicken was better preserved under treatments N6 and N7, maintaining acceptable odour attributes even up to 24 and 20 days of storage, respectively.     

Survival of Campylobacter coli in porcine liver

Enteropathogenic Campylobacter jejuni, Campylobacter coli and Campylobacter lari are currently the most common causes of acute infectious diarrhoeal illness in the UK and in most developed countries. Many domestic animals, including pigs, act as natural reservoirs of these organisms and infection may occur through the ingestion of contaminated foodstuffs. Therefore, the safety of porcine liver produced in Northern Ireland was assessed in relation toCampylobacter spp. Storage trials showed that Campylobacter spp. were not able to proliferate in liver at 37°C, but could persist at 4°C and 15°C. Survival was better, however, during storage at 4°C than at 15°C.Campylobacter were rapidly killed in raw liver homogenates and distilled water at 37°C, but not at 4°C. An initial inoculum of 8 log₁₀cfu g⁻¹C. coli was undetectable in liver homogenates after 24h storage at 37°C. Campylobacter coli were sensitive to freezing on liver slices at −18°C and were reduced by 5 log₁₀cycles after 7 days storage. Cells survived better on chilled liver slices and in autoclaved liver homogenates than in raw liver homogenates at all temperatures, which indicates the presence of a heat-labile antagonistic agent in raw liver homogenates. Growth and survival of C. coli was not affected by Lactobacillus plantarum, as C. coli was able to reach 8·5 log₁₀cfu ml⁻¹in 7 days and maintain its viability in the presence of 8·0 log₁₀cfu ml⁻¹L. plantarum. Thus, storage of C. coli on porcine liver at 4°C selected for the survival of this pathogen compared to similar storage at 37°C.Such information may be useful in identifying conditions and treatments that could be integrated in HACCP strategies, or be used to design processes that prevent proliferation and/or destroy Campylobacter spp. that may be present in liver.     

Synergistic Processing of Skim Milk with High Pressure Nitrous Oxide,Heat, Nisin,and Lysozyme to Inactivate Vegetative and Spore-Forming Bacteria

Individual and combined effects of high pressure nitrous oxide (HPN₂O), heat, and antimicrobials on the inactivation of Escherichia coli, Listeria innocua, and Bacillus atrophaeus endospores in milk were all evaluated after 20-min treatments. Stand-alone milk treatments with HPN₂O (15.2 MPa), heat (45 and 65 °C), or nisin (50 and 150 IU mL^?1) resulted in log₁₀ reductions ranging only from 0.1 to 2.1 for E. coli and L. innocua. Combining HPN₂O (15.2 MPa) with heat (65 °C) inactivated 6.0 and 5.1 log₁₀ in the vegetative bacteria, respectively. Similarly, reductions of 5.9 and ≥ 6.0 log₁₀ of respective E. coli and L. innocua cells in milk were achieved through a combination of HPN₂O (15.2 MPa), heat (65 °C), and nisin (150 IU mL^?1). A 2.5 log₁₀ cycle inactivation of spores was obtained by HPN₂O, nisin (at both 50 and 150 IU mL^?1), and lysozyme (50 μg mL^?1) at 85 °C. Combining these processing techniques resulted in significantly greater microbial inactivation (p < 0.05) than the sum of individual reductions from each treatment alone, indicating synergistic effects. HPN₂O irrespective of processing temperatures did not cause any occurrence of sub-lethally injured cells or disruption in colloidal stability of milk at 65 and 85 °C (p ≥ 0.05). Color and pH changes in milk following the most demanding treatment conditions were minimal.     

Sensitivity of multidrug-resistant Salmonella typhimurium DT104 to organic acids and thermal inactivation in liquid egg products

A mixture of four Salmonella typhimurium DT104 strains and a mixture of four S. typhimurium non-DT104 strains were examined for their ability to grow in tryptic soy broth (TSB) acidified with acetic, lactic, citric, or malic acids at pH 5·4, 4·4, and 3·7. Significantly (P<0·05) higher numbers of S. typhimurium DT104 cells were detected at pH 4·4 and 4·0 in TSB acidified with acetic acid and at pH 4·4 and 3·7 in TSB acidified with lactic acid compared to non-DT104 cells. Acid-shocked and non-shocked (control) cells were plated on TSA (pH 7·3) acidified with lactic acid at pH 5·4, 4·4, and 4·0 and on TSA (pH 7·0±0·2) containing 0·5, 2·5, and 5% sodium chloride. Populations of acid-shockedS. typhimurium DT104 and non DT104 cells recovered on acidified or salt-supplemented TSA were significantly (P<0·05) lower than those of non-shocked cells. A significantly lower number of acid-shocked non-DT104 cells recovered on TSA at pH 5·4, compared to acid-shocked DT104 cells, suggests that DT104 cells may be more resistant to acid shock and subsequent exposure to acid pH. D values and z values of acid-shocked or non-shocked cells of DT104 and non-DT104 strains in liquid whole egg (WE), egg yolk (EY), egg white (EW), whole egg+10% salt (WES), and egg yolk+10% salt (EYS) were determined. Differences in thermal sensitivity of the two types of cells were few. Rates of thermal inactivation of S. typhimurium DT104 cells indicate that the USDA pasteurization process would eliminate >8 log₁₀cfu ml⁻¹of EW heated at 57°C and >11 log₁₀cfu ml⁻¹of WE, EY, WES, or EYS heated at 61°C. D values of acid-shocked DT104 and non-DT104 cells heated in liquid egg products were significantly (P<0·05) lower than those of respective non-shocked cells.     

The effect of a competitive microflora,pH and temperature on the growth kinetics of Escherichia coli O157:H7

Growth curves were generated for Escherichia coli O157:H7 in brain–heart infusion broth incubated at 37 or 15°C in the presence of individual and combinations of competing microflora. Broths were inoculated withE. coli O157:H7 (log₁₀3·00 cfu ml⁻¹) and competitors (log₁₀4·00 cfu ml⁻¹) and the initial pH of the broth was either neutral (7·0) or adjusted to 5·8 and then sequentially reduced to 4·8 over 10 h to simulate fermentation conditions. Growth curves were also generated for the competitors in these cultures, including Pseudomonas fragi, Hafnia alvei, Pediococcus acidilactici (pepperoni starter culture) and Brochothrix thermosphacta . Gompertz equations were fitted to the data and growth kinetics including lag phase duration, exponential growth rates and maximum population densities (MPD) calculated. In pure culture, the growth parameters for E. coli O157:H7 in neutral pH broths were significantly different from those recorded in simulated fermentation broths (P<0·05). The presence of competitors in the broth also had a significant effect on the growth kinetics of the pathogen. H. alvei significantly inhibited the growth (lag phase, growth rate and MPD) of E. coli O157:H7 at 37°C, neutral pH and outgrew the pathogen under these conditions. In neutral pH cultures, two other competitors, B. thermosphacta and P. acidilactici also inhibited the lag phase of the pathogen but had no effect on the other growth parameters. In simulated fermentation broths, the growth rate of E. coli O157:H7 was consistently slower and the MPD lower in the presence of a competitive microflora than when grown individually. At 15°C, only one competitor, P. fragi significantly inhibited the lag phase of the pathogen. The implications of these findings for food safety are discussed.     

Inactivation ofEscherichia coliO157:H7 by combinations of GRAS chemicals and temperature

Reported outbreaks of foodborne illness involvingEscherichia coliO157:H7 have increased in the United States during the last decade, with a variety of food products being implicated as vehicles of infection. Studies were carried out to determine the efficacy of combinations of various GRAS chemicals and moderate temperatures to killE. coliO157:H7. A five-strain mixture ofE. coliO157:H7 of approximately 10⁸cfu ml⁻¹was inoculated into 0·1% peptone solutions containing 1·0 or 1·5% lactic acid plus 0·1% hydrogen peroxide, 0·1% sodium benzoate or 0·005% glycerol monolaurate. The solutions were incubated at 8°C for 0, 15 and 30 min; at 22°C for 0, 10 and 20 min; or at 40°C for 0, 10 and 15 min; populations ofE. coliO157:H7 were determined at each sampling time. At 40°C, the pathogen was inactivated to undetectable levels within 10 min of incubation in the presence of 1·0 or 1·5% lactic acid plus hydrogen peroxide, and within 15 min of incubation in the presence of 1·5% lactic acid plus sodium benzoate or glycerol monolaurate. At 22°C, complete inactivation ofE. coliO157:H7 was observed after 20 min of exposure to 1·5% lactic acid plus 0·1% hydrogen peroxide, whereas a reduction of 5 log₁₀cfu ml⁻¹was observed with a treatment of 1·5% lactic acid plus glycerol monolaurate. None of the treatments resulted in total inactivation of the pathogen at 8°C. The aforementioned treatments could potentially be used to inactivate or reduceE. coliO157:H7 populations on raw produce.     

Hardaliye: fermented grape juice as a traditional Turkish beverage

Twenty-six aged hardaliye samples, collected from different spots of the Kirklareli province of Turkey and hardaliye produced in laboratory conditions using the traditional method were investigated in this study. The pH ranged from 3·21 to 3·97. Red colour (Hunter Lab a_Lvalue) of samples ranged from 1·33 to 9·66. The total bacterial count ranged from 3·5×10²to 8×10⁵cfu ml⁻¹. The lactic acid bacteria counts of the samples were found to be between 1·0×10²and 4·0×10⁴cfu ml⁻¹. Yeasts and moulds, which were found in 21 samples out of 26, ranged from 1·0×10²to 8·1×10⁴cfu ml⁻¹. Coliforms and Escherichia coli were found in none of the samples. The changes of some microbiological and chemical properties of hardaliye during fermentation were investigated. The pH of hardaliye dropped from 3·86 to 3·39. The ethanol content of the end product was determined as 595·50 mg dl⁻¹. During the fermentation process, the total bacteria count, lactic acid bacteria count and yeast count changed from 2·1×10⁵, 6·0×10⁴and 1·2×10⁵cfu ml⁻¹to 1·3×10², 1·2×10³and 1·1×10³cfu ml⁻¹, respectively.Lactobacilli isolated from hardaliye samples were characterized by API 50 CH and other phenotypic criteria. A succession of Lactobacillus species, dominated by L. paracasei subsp. paracasei and L. casei subsp. pseudoplantarum were found during the fermentation process.     

Purification and characterisation of two pectinmethylesterase from persimmon (Diospyros kaki)

Two pectinmethylesterase isoforms, PME I and PME II, have been separated and purified from persimmon using chromatography techniques. Both isoforms presented differences in molecular weight (PME I: 51 kDa, PME II: 30 kDa), isoelectric point (PME I: 8·4, PME II: 6·9) and K_m values (PME I: 54 μg ml⁻¹, PME II: 31 μg ml⁻¹). They differed in their optimum pH and thermal stability, PME I being the more thermostable isoform. Both isoforms exhibited similar behaviour with respect to Ca²⁺ and Na⁺ concentrations and were strongly inhibited by CaCl₂ concentrations of over 80 mM and by NaCl concentrations of over 500 mM . Both isoforms were activated by low concentrations of polygalacturonic acid and were competitively inhibited by D -galacturonic acid and high concentrations of polygalacturonic acid. ©1997 SCI     

Activity of trisodium phosphate compared with sodium hydroxide wash solutions against Listeria monocytogenes attached to chicken skin during refrigerated storage

The potential of using trisodium phosphate (TSP) and sodium hydroxide (NaOH) to reduce Listeria monocytogenes populations in chicken skin was studied. Raw chicken legs inoculated with L. monocytogenes were dipped in water (control), in 8% (pH=12·59), 10% (pH=12·68) and 12% (pH=12·75) (w/v) TSP solutions, or in NaOH solutions of equal pH values to those of TSP: 0·175%, 0·200% and 0·220% (w/v). Surface pH values and L. monocytogenes counts of chicken skin were determined immediately after treatment (day 0) and after 1, 3 and 5 days of storage at 2°C. Compared with water dipping, TSP and NaOH treatments significantly (P<0·05) reduce Listeria populations at days 0, 1, 3 and 5 of refrigerated storage. Bacterial reductions varied between 1·12 and 3·34 log₁₀ cycles for TSP-treated samples and between 1·80 and 3·28 log₁₀ cycles for NaOH treated samples. The observed reductions in all treated samples were significantly (P<0·05) greater following storage. The concentration of the TSP solution was a significant factor in reducing the populations of L. monocytogenes. However, bacterial reductions were similar in samples treated with different concentrations of NaOH. The TSP or NaOH treatments resulted in relatively high residual surface pH values (8–9) initially and throughout storage. The pH values were significantly higher in the samples treated with TSP than in those treated with NaOH.     

Antimicrobial effects of butylated hydroxyanisole alone or in combination with potassium sorbate on quality changes in palm oil co-inoculated with Aspergillus flavus and Bacillus spp

Palm oil was sterilised and subjected to different concentrations (0.2 to 1.0 g litre⁻¹) of butylated hydroxyanisole (BHA) alone or in combination with potassium sorbate (KS) and co- inoculated with Aspergillus flavus and Bacillus species, the most prevalent organisms isolated from the palm oil. A dramatic increase of c3.43, 3.16 or 1.83 log₁₀ cfu ml⁻¹ microbial populations occurred in control samples or those treated with 0.2 or 1.0 g litre⁻¹ of BHA alone respectively. On the contrary, populations lower by approximately 1.0–1.3 log₁₀ cfu ml⁻¹ occurred in samples subjected to the combination treatment. Bi-phasic minima-extended-lag-phases were observed in the samples treated with BHA + KS. Mycelial growth was markedly inhibited in samples preserved with BHA + KS, being more apparent at concentrations of between 0.4 and 0.8 g litre⁻¹ of BHA in combination with potassium sorbate. Similarly, significantly (P = 0.05) lower free fatty acid content was observed in samples subjected to the combination treatment particularly at concentrations ranging from 0.6 litre⁻¹. Changes in pH were minimal suggesting less microbial activity, but significantly lower values occurred in samples treated with BHA alone after 14 days of ambient (30(±3) °C) storage. Better sensory qualities (less ‘separation’ i.e enhanced stability and aroma) were exhibited by samples preserved with the combination of BHA with KS. These various induced changes demonstrate the importance of concentration, residence time and synergism in relation to the effectiveness of antimicrobial agents. The benefits of the application of combination treatments have been shown and could be exploited by palm oil processors and importers. However, samples treated with the low concentrations are more likely to present potential hazards to consumers. © 1999 Society of Chemical Industry     

A Combination of Chemical and Ultrasonication Treatments to Reduce Campylobacter jejuni on Raw Poultry

Cost-effective and acceptable decontamination technologies that can be readily applied to the broiler-processing industry have been proposed as a strategy to reduce pathogenic organisms on carcasses and improve food safety. The objective of this study was to determine the potential of combining chemical and ultrasonication processes to reduce Campylobacter, total viable counts (TVCs) and total Enterobacteriaceae counts (TECs) on broiler carcasses. Drumsticks were inoculated with Campylobacter jejuni and immersed in 12 % (w/v) trisodium phosphate (TSP), 2 % (w/v) citric acid (CA) or 5 % (w/v) capric acid sodium salt (CP) solutions for 1 min, while ultrasonication was performed at 40, 60 or 80 kHz. In addition, chemicals were administered in sequential combination (TSP?+?CA, TSP?+?CP or CA?+?CP) while ultrasonication was performed at the frequencies mentioned. The sequential treatment of TSP and CP with ultrasonication at 80 kHz achieved the greatest reductions for C. jejuni (4.5–4.6 log₁₀ colony forming units (CFU)/cm²) and TVC (1.9 log₁₀ CFU/cm²). Enterobacteriaceae were susceptible to the sequential application of CA and CP and ultrasonication at 80 kHz (2 log₁₀ CFU/cm²). This study demonstrated that combining chemical decontaminants with ultrasonication can significantly (p?相似文献   

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.     

The effects on vegetative cells and spores of three bacteriocins from lactic acid bacteria

The sensitivities of vegetative cells of strains ofListeria, Clostridium, Staphylococcus, Lactococcus, Lactobacillus, MicrococcusandPediococcus, and of spores ofClostridiumandBacillusto three broad spectrum bacteriocins (nisin A, nisin Z and pediocin) from lactic acid bacteria were determined by a critical dilution micro-assay. The minimal inhibitory concentrations (MIC) of partially purified bacteriocins, prepared by a pH-dependent adsorption/desorption process, were determined and expressed in arbitrary units ml⁻¹and in μ g ml⁻¹of pure bacteriocin. The MICs of bacteriocins varied considerably between species and even between strains of the same species, as clearly shown for nine strains ofListeria monocytogenes. When bacteriocin activity was expressed in μ g ml⁻¹, pediocin was more effective againstListeria monocytogenesthan nisin A or nisin Z. The latter bacteriocins, in concentrations between 23 and 69 μ g ml⁻¹, prevented outgrowth ofClostridiumandBacillusspores for at least 10 days. Although pediocin at 17 μ g ml⁻¹prevented outgrowth ofB. stearothermophilusandC. butyricumspores for up to 7 days, it apparently activated the germination ofB. subtilisspores.