Inhibition of Non-proteolytic Clostridium botulinum with Lactic Acid Bacteria in Extended Shelf-Life Cook-Chill Soups

The possibility of protecting cook-chill foods with microbial cultures against the risk of botulism was demonstrated. Three commercial soups were incubated with Clostridium botulinum 17B (10³ spores/g) and protective cultures (PCs) during 10-15 days at 10°C. The PCs populations were enumerated on M17, MRS and maltose tryptic soy agar, C. botulinum—on sorbitol tryptic soy agar, botulinal toxin was detected by the immunoassay, bacteriocins—by well diffusion assay. C. botulinum did not grow in two soups with low pH (5.2-5.5) and was unaffected by the PCs. In seafood chowder (pH 6.2) C. botulinum populations reached 10⁸ cfu/g. The co-incubation with the PCs, nisin-producing Lactococcus lactis (10⁷ cfu/g) or pediocin-producing Pediococcus pentosaceus (3×10⁸ cfu/g) singularly and as a mixture, prevented toxigenesis as well as reduced the product pH to 4.8-5.0 and C. botulinum populations to undetectable levels. Color, mouth-feel, texture, flavor and the overall acceptability of seafood chowder was not affected by the presence of the PCs.     

Growth and toxigenesis of C. botulinum type E in fishes packaged under modified atmospheres

Modified atmosphere packaging of fresh fish is used to market high quality products in some European countries. The potential risk of C. botulinum growth in these extended shelf-life foods is still a concern; especially since toxigenesis may precede organoleptic spoilage. This paper will present toxigenic data from rockfish, salmon and sole muscle tissues which were inoculated with a pool of non-proteolytic C. botulinum type E at seven levels (10⁻² −10⁴ spores/sample), and stored under vacuum and 100% CO₂, at incubation temperatures between 30 and 4°C, for up to 60 days. Factorial experimental design allowed predictive formulae to be developed able to describe the lag time prior to C. botulinum toxigenesis and the probability of one spore to initiate toxigenesis based upon the storage conditions. Accurate characterization of the microbial ecology of C. botulinum in modified atmosphere-packaged fish, will support safe exploitation of these packaging systems in the market place, and identify critical control points for potential product or process abuses.     

PCR assay for differentiating between Group I (proteolytic) and Group II (nonproteolytic) strains of Clostridium botulinum

Groups I (proteolytic) and II (nonproteolytic) C. botulinum are genetically and physiologically distinct groups of organisms, with both groups being involved with human botulism. Due to differences in spore heat resistance and growth characteristics, the two groups possess different types of human health risks through foods, drink, and the environment. The epidemiology of human botulism due to Groups I and II C. botulinum is poorly understood, largely due to insufficient characterization of disease isolates, and warrants thorough outbreak investigation with a particular attention to discrimination between the different physiological groups of C. botulinum. In this study, a PCR assay was developed to discriminate between Group I and Group II C. botulinum. The assay is based on the fldB associated with phenylalanine metabolism in proteolytic clostridia, and employs an internal amplification control targeted to conservative regions of 16S rrn in Groups I and II C. botulinum. The assay correctly identified all 36 Group I and 24 Group II C. botulinum strains, possessing a 100% exclusivity and inclusivity. The assay provides a substantial improvement in discriminating between the Groups I and II C. botulinum, which traditionally is based on a time-consuming and error-prone culture method. Differentiation between the physiological groups of C. botulinum is an essential step in investigation of human botulism outbreaks, and should be considered as a diagnostic corner-stone in order to improve our epidemiological understanding of human botulism.     

Clostridium perfringens and its toxins in minced meat from Kars, Turkey

The aim of this study was to determine the prevalence of Clostridium perfringens and its toxins in minced meat. A total of 96 minced meat samples were collected from local markets (16) and small butcher's shops (80) in Kars (Turkey). Samples were analysed for the presence of C. perfringens and its toxins using a commercially available ELISA kit. A total of 31 (32%) Clostridium spp. strains were isolated and 17 (55%) of these isolates were identified as C. perfringens. Four (25%) of the samples from local markets and 27 (34%) from small butcher's shops were contaminated with Clostridium spp. Furthermore, C. perfringens was isolated from two (12%) and 15 (19%) samples from local markets and small butcher's shops, respectively. Mean counts of Clostridium spp. were 2.2 ± 0.83 × 10² CFU g^-1 for local markets and 4.35 ± 8.53 × 10² CFU g^-1 for small butcher's shops; mean counts for C. porringers were 2.75 ± 0.21 × 10² and 6.82 ± 10.96 × 10² CFU g^-1 from markets and butcher's shops, respectively. The number of samples contaminated with both Clostridium spp. and C. perfringens was higher in small butcher's shops than in local markets. Moreover, higher numbers of Clostridium spp. and C. perfringens were isolated in samples from small butcher's shops than from local markets. A total of 13 (13%) samples were also positive for toxins produced by the organism, as detected by ELISA. Eleven samples from small butcher's shops and two samples from local markets were positive for the C. perfringens toxins tested. Moreover, two (12%), one (1%), four (4%) and two (2%) samples were contaminated with C. perfringens types A, B, C and D, respectively. In conclusion, some meat samples collected from local markets and small butcher's shops contained C. perfringens and its toxins and, therefore, present a potential risk of food poisoning.     

Studies to determine the critical control points in pork slaughter hazard analysis and critical control point systems

Aerobic mesophilic counts (AMC), coliform (CC) and coliform resuscitation counts (CRCs) were obtained by swabbing 50 cm² areas at three sites (ham, belly and neck) on pig carcasses, after each of seven stages of the slaughter/dressing process (bleeding, scalding, dehairing, singeing, polishing, evisceration and chilling). In most cases, there were no statistical differences (P>0.05) among the counts derived by these three methods. Reductions in counts at individual sites were observed after scalding (3.5 log₁₀ cfu cm⁻²), and singeing (2.5 log₁₀ cfu cm⁻²). Increases in counts at individual sites were observed after dehairing (2.0 log₁₀ cfu cm⁻²) and polishing (1.5 log₁₀ cfu cm⁻²). The incidence of Salmonella on pig carcasses was also obtained by swabbing the outside surfaces of 100 half carcasses. Information on the incidence of Salmonella in scald tank water (108 samples) was also investigated. Carcass swabs and scald tank water were examined for the presence of Salmonella using standard enrichment methods. Salmonella were detected on 31% of carcasses immediately after bleeding, 7% of carcasses immediately after dehairing and evisceration, and 1% of carcasses immediately after scalding. Serovars included Salmonella Typhimurium, Salmonella Hadar, Salmonella Infantis and Salmonella Derby. No Salmonella were recovered from samples of scald tank water. The impact of pig slaughter/dressing processes on carcass microbiology and their potential use as critical control points (CCPs) during pork production are discussed.     

Antioxidant activity of Caryocar brasiliense (pequi) and characterization of components by electrospray ionization mass spectrometry

The Caryocar brasiliense known commonly as pequi is a tropical fruit of Brazilian Cerrado and is considered an important option of income and food for the populations living in this biome. Our previous study indicated that C. brasiliense had high total phenol content (209 g as gallic acid equivalent kg⁻¹) and excellent scavenging activity against 2,2-diphenyl-1-picrylhydrazyl radical (IC₅₀ of 9.44 μg ml⁻¹). In this study, we evaluated the highly efficient antioxidant activity of C. brasiliense using the biological relevant method of chemically induced lipid peroxidation. The half inhibition concentration did not exceed 0.8 μg ml⁻¹. In addition, polar components of pequi ethanolic extract were investigated by direct infusion electrospray ionization mass spectrometry (ESI-MS). The technique revealed the presence of important bioactive components widely reported as potent antioxidants such as gallic acid, quinic acid, quercetin, and quercetin 3-O-arabinose possibly explaining its higher antioxidant activity. This is the first report on the composition by ESI-MS of pequi extract demonstrating excellent antioxidant activity.     

Effect of modified atmospheres on microbiological, color and sensory properties of refrigerated pork

Pork loin samples were stored (4 °C) in nylon polyethylene plastic bags using different modified atmospheres packaging (MAP): vacuum, 100% CO₂ 99% CO₂ + 1% CO, 100% O₂ or 100% CO followed by vacuum. Throughout the storage period Pseudomonas growth was limited in loins packaged in all MAPs evaluated, except for 100% O₂. Psychrotrophs reached 10⁷ CFU g⁻¹ after 20 days of storage except for the loin samples in 100% O₂ MAP that present count above 10⁸ CFU g⁻¹. The 1% CO/99% CO₂ atmosphere was best for preserving the desirable pork loin color and the L* and a* values remained similar to the fresh meat values using this MAP. Pork loins in 99% CO₂/1% CO MAP obtained the highest consumer acceptance scores after 24 h of storage. These samples and those treated with CO and then vacuum packaged received the greatest acceptance scores even after 20 days of storage.     

A comparison of the toxicity of pirimiphos-methyl and malathion to Typhaea stercorea (L.) when applied to stored maize

The toxicity of freshly applied and aged residues of pirimiphos-methyl and malathion were assessed against adult Typhaea stercorea (L.). Maize was treated with each pesticide at doses of 2, 4, 6, and 8 mg kg⁻¹ and stored at a constant 25 °C and 70% r.h. for 12 weeks. All fresh deposits of pirimiphos-methyl produced 100% mortality as did malathion at 4, 6 and 8 mg kg⁻¹. After four weeks storage pirimiphos-methyl still gave 100% mortality at 6 and 8 mg kg⁻¹ but this dropped to 96% at 4 mg kg⁻¹ and 60% at 2 mg kg⁻¹, while mortality for malathion was less than 31% even at 8 mg kg⁻¹. After 12 weeks storage only pirimiphos-methyl gave effective control with 78% mortality at the highest dose of 8 mg kg⁻¹, while control by malathion had completely broken down. The effect of exposure time on T. stercorea for both pesticides at a single dose of 4 mg kg⁻¹ was also assessed. Beetles were left in contact with treated maize for 2, 4, 6, 8 and 10 d. Fresh and four-week-old pirimiphos-methyl residues produced over 98% mortality at all exposure periods but on 12-week-old residues mortality had dropped and was only 61% following 10 d exposure. Only freshly applied malathion gave 100% mortality and even the maximum exposure of 10 d only produced 51% mortality of T. stercorea at four weeks and 39% at 12 weeks.     

A practical trial of pyrethrins-in-oil surface sprays for the protection of bagged grain against infestation by Cadra cautella (Wlk.) (Lepidoptera, Phycitidae) in Kenya

Two formulations of synergized pyrethrins in technical white oil were tested as monthly protective sprays on stacks of fumigated bagged wheat, primarily against Cadra cautella (Wlk.) but also against Sitophilus oryzae (L) and Tribolium castaneum (Hbst.), under warm-temperate storage conditions in up-country Kenya. The formulations were: 0·4% pyrethrins with 2·0% piperonyl butoxide, applied at 50 ml/m², and 0·4% pyrethrins with 0·4% piperonyl butoxide at 20 ml/m².

Results were assessed by recording infestation in samples taken from each stack after 18 weeks storage and five spray applications.

Both treatments gave reasonably good protection against C. cautella but were not satisfactory against S. oryzae or T. castaneum. There was no evidence of any taint in bread made from the treated grain, but the higher application rate caused excessive staining of the bags.

It is concluded that satisfactory control of reinfestation by C. cautella can be expected in practice using 0·4% pyrethrins in oil with only a minimal quantity of added piperonyl butoxide, and that 20 ml/m² is a suitable rate for application to bagged produce.     

Effect of pretreatment and temperature on air-drying of Dioscorea alata and Dioscorea rotundata slices

Effects of pretreatment and drying conditions on yam varieties, namely Dioscorea alata and Dioscorea rotundata, in a fabricated laboratory scale hot air drier at temperature range of 50–80 °C and constant air velocity of 1.5 m²/s were investigated. Mass transfer during air-drying of yam slices was described using Fick’s diffusion model. Drying took place entirely in the falling rate period. Temperature dependency of moisture on diffusivity was illustrated by the Arrhenius relationship. Over the range of temperature, moisture diffusivities varied from 9.92 × 10⁻⁸ to 1.02 × 10⁻⁷ and 0.829 × 10⁻⁶ to 1.298 × 10⁻⁵ m²/s for D. alata and D. rotundata, respectively. Activation energy for drying of D. alata and D. rotundata varied from 25.25 to 46.46 and 41.75 to 72.47 kJ/mol, respectively.     

Effects of supercritical carbon dioxide extraction conditions on yields and antioxidant activity of Chlorella pyrenoidosa extracts

Yields and antioxidant activity of Chlorella pyrenoidosa extracts obtained by supercritical carbon dioxide extraction through an orthogonal experiment (L₁₆(4⁵)) were investigated to get the best extraction conditions. The results showed that extraction pressure, temperature and modifier were the main three variables that influenced the yields of extracts. The highest yield was obtained at 32 °C, 40 MPa, 20 L h⁻¹ with dosage of modifier 1 mL ethanol g⁻¹ sample for 3 h. Moreover, increasing pressure and concentrations of modifier led to the increase of extraction yields and antioxidant activity. DPPH radical scavenging method showed that almost all the extracts had significantly higher antiradical activities varying from 29.67 ± 0.29% to 54.16 ± 4.49% comparing to -tocopherol, Trolox, and BHT as references except extracts at 32 °C, 35 MPa and 15 L h⁻¹ without modifier for 1.5 h. These results indicate that supercritical extraction is a promising alternative process for recovering compounds of high antioxidant activity from C. pyrenoidosa.     

The influence of RN genotype, including the new V199I allele, on the eating quality of pork loin

The eating quality of M. longissimus dorsi (LD) from RN⁻ homozygotes, RN⁻ heterozygotes and RN⁻ non-carriers was investigated in a Swedish Hampshire×Finnish Landrace pig population. The recently identified new allele (V199I, here denoted rn*) at the RN locus was also detected among the pigs selected and included in the sensory evaluation. The number of animals varied from 10 to 15 in the five genotype groups; RN⁻/RN⁻, RN⁻/rn+, RN⁻/rn*, rn+/rn+ and rn+/rn* (in total 59 pigs). In addition, one pig was determined to be rn*/rn* but was excluded from the analysis. The three genotypes in which the RN⁻ allele was represented (RN⁻/RN⁻, RN⁻/rn+ and RN⁻/rn*) had higher glycogen and lower protein contents as well as lower ultimate pH (measured 48 h post-mortem) in LD than the non-carriers (rn+/rn+ and rn+rn*). Of the sensory parameters evaluated (tenderness, chewing time, chewing residual, juiciness, meat flavour and acidity), the five RN genotypes only affected acidity significantly; the RN⁻ allele contributing to a more acid taste in LD. The influence of the rn* allele resembled that of rn+ on the sensory parameters. When the material was divided into three groups (homozygous, heterozygous and non-carriers of the RN⁻ allele) the juiciness was found to be significantly influenced by RN genotype, and LD from animals that were homozygous and heterozygous with respect to the RN⁻ allele exhibited a higher juiciness than LD from non-carriers. The RN⁻ allele also tended to contribute to greater tenderness, which was significantly higher in LD from heterozygous carriers than from non-carriers of the RN⁻ allele. A more rapid decline in pH (measured as pH at 45 min and 3 h post-mortem) contributed to a greater tenderness in LD (according to a trained panel and Warner-Bratzler shear force). In addition to the RN genotype, the decline in pH was influenced by carcass weight, which varied between 71 and 97 kg, and by stunning procedure, which changed during the course of the study from individual to group stunning with CO₂. The individual stunning procedure contributed to a lower pH in the initial post-mortem phase (pH₄₅), whereas a higher carcass weight and the RN⁻ allele lowered the pH in the mid-post-mortem region (pH_3h and pH_24h), significantly (P0.05). The pH continued to decline after 24 h post-mortem and the ultimate pH was not reached until 48 h post-mortem. The cooking loss, juiciness and acidity were related to the specific characteristics of the RN⁻ carriers, such as higher glycogen content, lower protein content and lower ultimate pH (pH_48h).     

Thermal inactivation of lectins (PHA) isolated from Phaseolus vulgaris

The influence of the thermal process on the loss of ability to bind a carbohydrate target was studied on lectins (PHA) purified from Phaseolus vulgaris seeds. Thermal inactivation of aqueous solutions of pure PHA occurred according to a biphasic first-order mechanism, the thermodynamic parameters, at pH 7·3, being as follows: ΔH*₁ = ΔH*₂ = 86·2 kcal mole⁻¹, ΔS*₁ = − 54·04 cal deg⁻¹ and ΔS*₂ = − 56·71 cal deg⁻¹. The first-order rate constants appeared to be dependent on pH (minimal around 7) and divalent cations. All different subunits constituting the whole PHA were inactivated at the same rate. The biphasic nature of this process is independent of the presence of 10 m Ca⁺⁺ or Mg⁺⁺ and appeared to indicate a discrete aggregation of PHA molecules.     

Effect of a commercial freeze/tempering process on the viability of Cryptosporidium parvum oocysts on lean and fat beef trimmings

Lean and fat beef trimmings (25 cm⁻²) were inoculated with approximately 250,000 Cryptosporidium parvum oocysts, placed in commercial packages (28 kg boxes) and subjected to normal commercial processes i.e. blast frozen (to −20 °C within 60 h), stored (−20 °C, 21 days), tempered (48 h at −3 °C), and held at 0 °C for 10 h. Inoculated areas were then excised, pulsified (30 s in 50 ml PBST), and centrifuged (2500×g, 15 min). The resultant pellet was resuspended in 10 ml water and subjected to immunomagnetic separation and viability dye assay. Following the commercial freeze/tempering process the viability of the oocysts had decreased from 90.6% viable in the working stock suspension to 7.17% and 9.46% viable on lean and fat trimmings, respectively. The results of this study indicate that if C. parvum oocysts were present on beef trimmings their viability would be substantially reduced as a result of the freeze/tempering process.     

Laboratory evaluation of the entomopathogenic fungus, Metarhizium anisopliae for the control of the groundnut bruchid, Caryedon serratus on groundnut

The pathogenicity of five isolates of Metarhizium anisopliae to adult Caryedon serratus was evaluated in the laboratory. All the isolates tested were virulent to the beetle but pathogenicity varied among the isolates. One isolate, CPD 4 was consistently superior to all other isolates in terms of mortality of the beetle, protection of groundnut pods from damage, reduction in progeny production and repellency to the beetle. At 10 days post-treatment, adult mortality treated with 0.1, 0.5 and 1.0 g of dry conidia equivalent to 3.6×10⁸, 1.8×10⁹ and 3.6×10⁹ conidia of isolate CPD 4 per 50 g of groundnut pods was 100% which did not differ significantly from pirimiphos-methyl-treated pods at 10 ppm. At the lowest dosage of 0.1 g of conidia per 50 g of pods, damage in pods protected with isolate CPD 4 was 5% which did not differ significantly from the 2% damage in pods protected by pirimiphos-methyl at 10 ppm but significantly differed from damage in untreated pods which was 26%. Isolate CPD 4 caused complete reduction in progeny emergence at all dosages tested. It also exhibited some degree of repellency to the beetle with percentage repellency values of between 40–79% at concentrations of 0.1–1.0 g of conidia per 50 g of groundnut pods. These combined virulence and repellency characteristics of this isolate may increase its protectant potential against C. serratus.     

Selective enumeration and survival of bifidobacteria in fresh cheese

Five species of bifidobacteria (15 strains), two strains of Lactococcus lactis ssp. lactis, two strains of L. lactis ssp. cremoris, and one strain of L. lactis ssp. lactis var diacetylactis were included in a study to develop a selective medium for enumeration of bifidobacteria from fresh cheese. Viable counts of bifidobacteria or lactococci on modified Columbia agar base (CAB with 0.05% cysteine-HCl) plus raffinose (0.5%) containing various selective agents were compared with non-selective media. The mCAB plus raffinose with lithium chloride (2 g L⁻¹) and sodium propionate (3 g L⁻¹) with pH adjusted to 5.1 was used successfully as a selective medium for the enumeration of bifidobacteria from fresh cheese. Using this medium, it was determined that bifidobacteria could survive up to 15 days at a level higher than 10⁶ cfu g⁻¹ in a fresh cheese stored at 4 or 12°C. The decrease in the viable counts of bifidobacteria was faster during storage at 4°C than at 12°C.     

Inactivation of Enterobacter sakazakii by pulsed electric field in buffered peptone water and infant formula milk

The effect of high-intensity pulsed electric field (PEF) treatment on the survival of Enterobacter sakazakii suspended in buffered peptone water (BPW) and powdered infant formula milk (IFM) was evaluated. Reference medium and IFM samples were treated with PEF. Electric field intensity and treatment time were varied from 10 to 40 kV cm⁻¹ and from 60 to 3895 μs, respectively. Samples of buffered peptone water (3 g L⁻¹) and IFM were inoculated with E. sakazakii (CECT 858) (10⁹ cfu mL⁻¹) and then treated with PEF. The inactivation data were adjusted to the Weibull frequency distribution function and Bigelow model, and constants were calculated for both substrates. A maximum 2.7 log (cfu mL⁻¹) reduction was achieved in BPW after exposure of E. sakazakii to PEF for 360 μs (2.5 μs pulse width) at 40 kV cm⁻¹. In IFM, exposure of E. sakazakii to PEF, with the same conditions, led to a 1.2 log (cfu mL⁻¹) reduction. The greater the field strength and treatment time, the greater the inactivation achieved in both substrates. Even though further research will be necessary, according to the results, there are good prospects for the use of PEF in hospitals to achieve safe reconstituted infant formula before storage at refrigerated temperatures.     

Bacteriological quality assurance (BQA) of mechanically deboned meat (MDM)

Adequacy of bacteriological quality assurance during the commercial production of mechanically deboned meat (MDM) was assessed. Lax standards of hygiene during production were observed, resulting in high numbers of Staphylococcus aureus, viz. 10⁴ to 10⁵ cfu g⁻¹, and severe contamination with Enterobacteriaceae: 10⁵ to 10⁶ cfu g⁻¹. These data indicate that measures of hygiene observed during boning of carcasses and during collection, storage and transport of bones or poultry parts should be markedly tightened, while conditions of refrigerated storage of raw materials and MDM should be improved. Use of bones of poor sensory quality (discoloration, abnormal smell) generally resulted in MDM of inferior bacteriological quality.

Phage typing, biotyping and assessment of enterotoxin production was carried out with 136 St. aureus cultures, isolates from mechanically deboned pork produced at one plant. Fifty-five per cent of the isolates was not typable, 28% was typable with human phages, 8% with bovine phages. The majority of the strains could not be explicitly assigned to any Meyer and/or Hájek and Mar álek types. Applying the simplified system of Devriese to eighteen strains isolated in our investigation, ten were found to belong to the poultry ecovar, one to the bovine ecovar, while seven strains were non-host specific. None of the isolates produced enterotoxins A–E.

Microbiological inspection of end products is recommended as part of an integrated quality assurance system. The following reference values for the final product (maximal colony counts to be expected under GMP conditions expressed as 95th percentile) were calculated: Pig MDM: log₁₀ mesophilic colony count 6·8 and log₁₀ cfu mesophilic Enterobacteriaceae g⁻¹ 4·8; Poultry MDM: log₁₀ mesophilic colony count 6·6 and log₁₀ cfu mesophilic Enterobacteriaceae g⁻¹ 4·7.     

Antilisterial activity of lactic acid bacteria inoculated on cooked ham

This study was conducted to evaluate the ability of Lactobacillus sakei 1, a bacteriocin-producing (bac⁺) lactic acid bacterium (LAB), isolated from Brazilian fresh pork sausage to inhibit two Listeria monocytogenes strains (serotypes 4b and 1/2a) on cooked, sliced vacuum-packaged ham. L. sakei ATCC 15521 was used as a non-bacteriocin producer (bac⁻). L. monocytogenes (ca. 2 log CFU/mL) and LAB (ca. 6 log CFU/ml) were inoculated on the sterilized ham, vacuum-sealed and incubated at 8 °C for 10 days. A treatment with the bacteriocin Chrisin (UI/ml) was included. Both L. monocytogenes strains were significantly inhibited in the presence of either bac⁺ and bac⁻ LAB in comparison to the control (L. monocytogenes alone). Using a bacteriocinogenic strain of LAB did not offer an additional barrier to listerial growth in the studied meat system. The application of Chrisin did not affect at all the growth of L. monocytogenes.     

Behaviour of Listeria monocytogenes in raw sausages (merguez) in presence of a bacteriocin-producing lactococcal strain as a protective culture

The effectiveness of a bacteriocin produced by Lactococcus lactis subsp. lactis M in reducing population level and growth of Listeria monocytogenes ATCC 7644 in fermented merguez sausage was examined. Two different formulas (with or without added nitrites) were assayed and predetermined numbers of Listeria (ca 10⁶ cfu g⁻¹) were added to sausage mixture. The effect of in situ production of the bacteriocin by Lactococcus lactis M on Listeria monocytogenes ATCC 7644 during fermentation and storage of merguez sausages at room (ca 22 °C) or at refrigeration (ca 7 °C) temperature was tested. Results indicated that counts of Listeria monocytogenes were decreased during fermentation of merguez samples fermented with either the bacteriocin-producing Lactococcus lactis M (Bac⁺) or a nonbacteriocin-producing Lactococcus lactis J (Bac⁻). However, reduction in Listeria cfu's was greater in samples fermented with the Bac⁺ than in those fermented with the Bac⁻ starter. In merguez sausage made without nitrites addition, the Bac⁺ starter induced further decrease in Listeria counts by 1.5 log cycles compared with that induced by the Bac⁻ starter. While in merguez samples with added nitrites (0.4%), the effect of the bacteriocin produced in situ was less important than in those made without nitrites addition.