Rapid and cost-effective method for micro-organism enumeration based on miniaturization of the conventional plate-counting technique

International audienc

Continuous raw skim milk processing by pulsed electric field at non-lethal temperature: effect on microbial inactivation and functional properties

International audiencePulsed electric field (PEF) is an emerging non-thermal processing technology used to inactivate microorganisms in liquid foods such as milk. The objective of this research was to study the effectiveness of continuous PEF equipment (square wave pulses) on total microorganisms of raw skim milk and on Salmonella enteritidis inactivation under moderate temperatures (T < 50 °C). Processing parameters (electric field and pulse width) were chosen as follows: 45 kV*cm-1/500 ns and 55 kV*cm-1/250 ns, with increasing pulse frequencies from 40 to 120 Hz, that corresponds to an energy input varying from range 0-100 kJ*kg-1. In these conditions, the effectiveness of PEF processing on microbial inactivation was very limited: 1.4-log reduction of total microflora and S. enteritidis was the maximal inactivation ratio obtained. The effect of these PEF treatments on physicochemical and technological properties of the milk was also evaluated. These process conditions had an effect on proteinic components of milk such as casein micelles, since viscosity of PEF-treated milk decreased and coagulation properties were enhanced for high field levels (45-55 kV*cm-1) with 2.1 to 3.5 µs cumulated treatment time and square waves. This study demonstrated that, contrary to numerous previous studies, PEF treatments had an impact on some food constituents.Traitement de lait écrémé cru par champs électriques pulsés à température non létale : efficacité au plan de la destruction microbienne et effet sur les propriétés fonctionnelles. La tendance actuelle de l'industrie alimentaire est de proposer des alternatives aux traitements thermiques de pasteurisation. Ces traitements alternatifs doivent être efficaces sur le plan de la destruction bactérienne, mais moins sévères au plan physico-chimique, afin de garantir la qualité hygiénique des aliments tout en préservant leurs qualités nutritionnelles, sensorielles et fonctionnelles. Les traitements par champs électriques pulsés (CEP) sont souvent reconnus dans la littérature comme un des procédés innovants capables de répondre à ces nouvelles exigences. L'objectif de cette étude était donc ici d'évaluer l'efficacité de traitements en continu par CEP (impulsions électriques rectangulaires) réalisés à température non létale (T < 50 °C) sur la destruction de la flore endogène et des coliformes du lait ainsi que sur du lait préalablement inoculé avec Salmonella enteritidis. Les paramètres de traitements choisis (champs électriques et largeur des impulsions) étaient les suivants : 55 kV*cm-1/250 ns et 45 kV*cm-1/500 ns, avec des fréquences d'impulsion variant de 40 à 120 Hz, ce qui se traduit par un apport d'énergie compris entre 0 et 100 kJ*kg-1. Dans ces conditions, l'efficacité des traitements est très limitée puisque au maximum 1,4 log de réduction microbienne a pu être atteint sur la flore endogène et S. enteritidis. Parallèlement, l'effet des traitements par champs électriques pulsés sur les principales caractéristiques physico-chimiques et techno-fonctionnelles du lait a été évalué. Un effet sur les composants protéiques tels que les micelles de caséine a été constaté suite aux traitements CEP les plus intenses (45-55 kV*cm-1 pendant 2,1 à 3,5 µs) puisque la viscosité du lait était diminuée et ses aptitudes à la coagulation étaient améliorées. En conclusion, ces expériences ont permis de montrer que, contrairement à ce qui est classiquement reporté dans la littérature, les traitements par CEP ont un impact non nul sur des constituants tels que les micelles de caséine

Continuous raw skim milk processing by pulsed electric field at non-lethal temperature: effect on microbial inactivation and functional properties

International audiencePulsed electric field (PEF) is an emerging non-thermal processing technology used to inactivate microorganisms in liquid foods such as milk. The objective of this research was to study the effectiveness of continuous PEF equipment (square wave pulses) on total microorganisms of raw skim milk and on Salmonella enteritidis inactivation under moderate temperatures (T < 50 °C). Processing parameters (electric field and pulse width) were chosen as follows: 45 kV*cm-1/500 ns and 55 kV*cm-1/250 ns, with increasing pulse frequencies from 40 to 120 Hz, that corresponds to an energy input varying from range 0-100 kJ*kg-1. In these conditions, the effectiveness of PEF processing on microbial inactivation was very limited: 1.4-log reduction of total microflora and S. enteritidis was the maximal inactivation ratio obtained. The effect of these PEF treatments on physicochemical and technological properties of the milk was also evaluated. These process conditions had an effect on proteinic components of milk such as casein micelles, since viscosity of PEF-treated milk decreased and coagulation properties were enhanced for high field levels (45-55 kV*cm-1) with 2.1 to 3.5 µs cumulated treatment time and square waves. This study demonstrated that, contrary to numerous previous studies, PEF treatments had an impact on some food constituents.Traitement de lait écrémé cru par champs électriques pulsés à température non létale : efficacité au plan de la destruction microbienne et effet sur les propriétés fonctionnelles. La tendance actuelle de l'industrie alimentaire est de proposer des alternatives aux traitements thermiques de pasteurisation. Ces traitements alternatifs doivent être efficaces sur le plan de la destruction bactérienne, mais moins sévères au plan physico-chimique, afin de garantir la qualité hygiénique des aliments tout en préservant leurs qualités nutritionnelles, sensorielles et fonctionnelles. Les traitements par champs électriques pulsés (CEP) sont souvent reconnus dans la littérature comme un des procédés innovants capables de répondre à ces nouvelles exigences. L'objectif de cette étude était donc ici d'évaluer l'efficacité de traitements en continu par CEP (impulsions électriques rectangulaires) réalisés à température non létale (T < 50 °C) sur la destruction de la flore endogène et des coliformes du lait ainsi que sur du lait préalablement inoculé avec Salmonella enteritidis. Les paramètres de traitements choisis (champs électriques et largeur des impulsions) étaient les suivants : 55 kV*cm-1/250 ns et 45 kV*cm-1/500 ns, avec des fréquences d'impulsion variant de 40 à 120 Hz, ce qui se traduit par un apport d'énergie compris entre 0 et 100 kJ*kg-1. Dans ces conditions, l'efficacité des traitements est très limitée puisque au maximum 1,4 log de réduction microbienne a pu être atteint sur la flore endogène et S. enteritidis. Parallèlement, l'effet des traitements par champs électriques pulsés sur les principales caractéristiques physico-chimiques et techno-fonctionnelles du lait a été évalué. Un effet sur les composants protéiques tels que les micelles de caséine a été constaté suite aux traitements CEP les plus intenses (45-55 kV*cm-1 pendant 2,1 à 3,5 µs) puisque la viscosité du lait était diminuée et ses aptitudes à la coagulation étaient améliorées. En conclusion, ces expériences ont permis de montrer que, contrairement à ce qui est classiquement reporté dans la littérature, les traitements par CEP ont un impact non nul sur des constituants tels que les micelles de caséine

Use of pulsed-field gel electrophoresis to characterize the heterogeneity and clonality of Salmonella serotype Enteritidis, Typhimurium and Infantis isolates obtained from whole liquid eggs.

RA2007ACL09-RIVInternational audienceSalmonella is a well-documented pathogen known to occur in a wide range of foods, especially poultry products. The most frequently reported food-sources of human infection are eggs and egg products. In this study, in order to describe Salmonella contamination of egg products, 144 liquid egg samples were collected from 3 different egg-breaking plants during the 3 sampling periods. Salmonella detection was performed on raw samples stored at 2 degrees C for 2 days (D+2) and on pasteurised samples stored at 2 degrees C at D+2 and at shelf-life date. Salmonella was detected in 130 of the 144 raw egg samples collected and in 11 of the 288 pasteurised egg samples analysed. 740 Salmonella isolates were collected and serotyped: 14 serovars were demonstrated. A great diversity, particularly during summer, was noted. The dominant serovars were S. Enteritidis, S. Typhimurium and S. Infantis, mainly found in whole raw egg products. Typing of 325 isolates of S. Enteritidis, 54 isolates of S. Typhimurium and 58 isolates of S. Infantis was carried out by macrorestriction of the genomic DNA with XbaI and SpeI enzymes followed by pulsed field gel electrophoresis (PFGE). The Salmonella Enteritidis isolates could be grouped into 3 clusters. Cluster 1 was predominant at all 3 egg-breaking companies during the different sampling periods. This cluster seemed to be adapted to the egg-breaking plants. Cluster 2 was linked to plant 1 and cluster 3 to plant 3. Two main clusters of Salmonella Typhimurium were demonstrated. Cluster A was mainly found at plant 2 during autumn. Plant 3 was contaminated by all the Salmonella Typhimurium genotypes but in a more sporadic manner during the three seasons studied. Plant 1 seemed to be less contaminated by Salmonella Typhimurium than the others. Three clusters and 2 genotypes of Salmonella Infantis were shown. The main cluster, cluster alpha, consisted of 75% of the S. Infantis isolates and was mainly found during summer at plants 1 and 3. Plant 2 seemed to be less contaminated by S. Infantis. In this study, molecular typing demonstrated that, although certain clusters were common to all three companies, specific clusters, notably of S. Enteritidis were present at each plant

Occurrence of Bacteria of the Bacillus cereus Group in Conventional Henhouses and in Egg Breaking Factories

Bacteria belonging to the Bacillus cereus group are found in soil, air, dust, water and in many raw and processed foods. Several strains of this group are able to produce toxins in food or in the human intestine that can lead to emesis or diarrhoea, respectively. Their various enzymatic activities are also recognised as causing food spoilage, even at refrigerated temperatures when psychrotrophic strains are involved. Since liquid egg products usually receive mild heat treatments inefficient on spores and they are stored at low temperature, monitoring and control of bacteria belonging to the B. cereus group are of high importance for the sector of egg production. The aim of the present study was to get new insights on the consequences of breeding practices on the occurrence of this type of bacteria on eggshells and in liquid whole egg products. The study consisted in an inquiry about the breeding practices of about sixty farms in parallel with egg collection. Samples of liquid egg products were simultaneously collected in six egg breaking industries. The study was carried out during hot and cold seasons in order to identify a putative relationship between the season and the relative occurrence of mesophilic and psychrotrophic bacteria of the group. All the samples were enriched at 10°C during 5 days and 30°C during 24 h, to favor the growth of psychrotrophic and mesophilic bacteria, respectively. The presence of bacteria belonging to the B. cereus group was then investigated by real-time PCR. Molecular analyses were carried out for the discrimination between psychrotrophic and mesophilic strains in the positive enrichments. Statistical analyses were conducted in order to identify factors favoring contamination at the breeding level. These findings form the starting point for a detailed study on the control of this type of bacteria in the sector of egg production