Olga S. Papadopoulou

Potential of multispectral imaging technology for rapid and non-destructive determination of the microbiological quality of beef filets during aerobic storage

The performance of a multispectral imaging system has been evaluated in monitoring aerobically packaged beef filet spoilage at different storage temperatures (0, 4, 8, 12, and 16°C). Spectral data in the visible and short wave near infrared area (405-970nm) were collected from the surface of meat samples and correlated with microbiological data (log counts), for total viable counts (TVCs), Pseudomonas spp., and Brochothrix thermosphacta. Qualitative analysis (PLS-DA) was employed for the discrimination of meat samples in three microbiological quality classes based on the values of total viable counts, namely Class 1 (TVC<5.5log10CFU/g), Class 2 (5.5log10CFU/g7.0log10CFU/g). Furthermore, PLS regression models were developed to provide quantitative estimations of microbial counts during meat storage. In both cases model validation was implemented with independent experiments at intermediate storage temperatures (2 and 10°C) using different batches of meat. Results demonstrated good performance in classifying meat samples with overall correct classification rate for the three quality classes ranging from 91.8% to 80.0% for model calibration and validation, respectively. For quantitative estimation, the calculated regression coefficients between observed and estimated counts ranged within 0.90-0.93 and 0.78-0.86 for model development and validation, respectively, depending on the microorganism. Moreover, the calculated average deviation between observations and estimations was 11.6%, 13.6%, and 16.7% for Pseudomonas spp., B. thermosphacta, and TVC, respectively. The results indicated that multispectral vision technology has significant potential as a rapid and non-destructive technique in assessing the microbiological quality of beef fillets.

Genotypic characterization of Brochothrix thermosphacta isolated during storage of minced pork under aerobic or modified atmosphere packaging conditions.

A total of 306 colonies were isolated from the selective medium for Brochothrix spp., during the spoilage of minced pork stored at 0, 5, 10 and 15 °C and packed aerobically and under modified atmosphere packaging conditions (MAP). Brochothrix biodiversity was assessed by Pulsed Field Gel Electrophoresis (PFGE), and representative strains were further analysed by Rep-PCR using primer (GTG)₅ and Sau-PCR with primers SAG₁ and SAG₂. Although, different results were obtained from the different methods, a significant diversity among isolates recovered from aerobic conditions was observed. On the contrary, isolates from MAP showed a lower degree of heterogeneity. The storage conditions affected the Brochothrix diversity, the strains isolated in the initial stage being different from the ones present at the final stage of storage at chill temperatures. A representative number of isolates, based on the results of the clustering by molecular methods, were subjected to 16S rRNA gene sequencing, revealing that all belonged to Brochothrix thermosphacta.

Transfer of foodborne pathogenic bacteria to non-inoculated beef fillets through meat mincing machine.

The aim of this study was to evaluate the transfer of pathogens population to non-inoculated beef fillets through meat mincing machine. In this regard, cocktails of mixed strain cultures of each Listeria monocytogenes, Salmonella enterica ser. Typhimurium and Escherichia coli O157:H7 were used for the inoculation of beef fillets. Three different initial inoculum sizes (3, 5, or 7 log CFU/g) were tested. The inoculated beef fillets passed through meat mincing machine and then, six non-inoculated beef fillets passed in sequence through the same mincing machine without sanitation. The population of each pathogen was measured. It was evident that, all non-inoculated beef fillets were contaminated through mincing with all pathogens, regardless the inoculum levels used. This observation can be used to cover knowledge gaps in risk assessments since indicates the potential of pathogen contamination and provides significant insights for the risk estimation related to cross-contamination, aiming thus to food safety enhancement.

Probiotic Potential of Lactic Acid Bacteria from Traditional Fermented Dairy and Meat Products: Assessment by In Vitro Tests and Molecular Characterization

The aim of the present study was to evaluate the probiotic potential of lactic acid bacteria (LAB) isolated from Greek traditional fermented products. A series of In vitro tests that included survival in simulated gastrointestinal conditions (resistance to low pH, bile salts resistance and bile salts hydrolysis) and safety assessment (resistance to antibiotics, haemolytic and antimicrobial activity) were performed to select potential probiotic candidates, while Lactobacillus rhamnosus GG and Lactobacillus casei Shirota were used as reference strains. Initially, a total of 255 isolates of LAB have been recovered and screened for their survival in simulated gastrointestinal tract conditions and 133 isolates that exhibited moderate or good behavior in these tests were subsequently differentiated and characterized at species level with molecular tools. Pulsed Field Gel Electrophoresis was applied for strain differentiation, while species differentiation was based on restriction analysis of the amplified 16S rRNA gene. Specific multiplex PCR assay targeting the recA genes was applied to resolve the species level of the isolates, belonged to Lb. plantarum group. From the 133 isolates, 47 different strains were recovered and were assigned to Lactobacillus sakei(14), Lactobacillus curvatus (4), Leuconostoc mesenteroides (4), Lactococcus lactis (4), Lactobacillus casei group (1), Lactobacillus brevis (1), Lb. plantarum (10), Lb. pentosus (7) and Lb. paraplantarum (2). The identified strains with good behavior to the gastrointestinal tract tests were selected and further evaluated for their safety aspect. In conclusion, 19 out of the 47 identified strains were assessed as well-behaved, under simulated gastrointestinal conditions and also considered as safe, possessing thus desirable In vitro probiotic properties similar or better to that of the reference strains. These strains may be considered as good candidates for further investigation at in vivo and in situ studies to assess their potential health benefits and their performance as novel probiotic starters or adjunct cultures.

Molecular Detection of Two Potential Probiotic Lactobacilli Strains and Evaluation of Their Performance as Starter Adjuncts in Yogurt Production

A molecular method for efficient and accurate detection and identification of two potential probiotic lactobacilli strains isolated from fermented olives, namely Lactobacillus pentosus B281 and Lb. plantarum B282, was developed in the present study. Random Amplified Polymorphic DNA (RAPD) analysis was performed, and strain specific primers were designed and applied in a multiplex polymerase chain reaction (PCR) assay. The specificity of the assay was tested and successfully confirmed in 27 and 22 lactobacilli strains for Lb. pentosus B281 and Lb. plantarum B282, respectively. Moreover, the two strains were used as starter cultures in yogurt production. Cell enumeration followed by multiplex PCR analysis demonstrated that the two strains were present in yogurt samples at levels ≥6 log CFU/g even after 35 days of storage at 4 °C. Microbiological analysis showed that lactobacilli and streptococci were present within usual levels, whereas enterobacteriaceae and yeast/mold counts were not detected as expected. Although the pH values of the novel products were slightly lower than the control ones, the yogurt containing the probiotic cultures scored similar values compared to the control in a series of sensory tests. Overall, these results demonstrated the possible use of the two strains as starter adjuncts in the production of yogurt with potential probiotic properties.

Greek functional Feta cheese: Enhancing quality and safety using a Lactobacillus plantarum strain with probiotic potential

The aim of the study was to investigate the performance of Lactobacillus plantarum T571 with probiotic potential as a co-starter culture in Feta cheese production and in its long-term storage. For this reason, Feta cheese was manufactured without (control) or with the probiotic T571 strain (probiotic) and then monitored during storage at 4 and 12 °C, respectively. The products were also inoculated with Listeria monocytogenes (3-strain cocktail). The results showed that lactic acid bacteria exceeded 6 log CFU/g during storage in all trials. The probiotic samples displayed higher acidity (≈1.5% lactic acid) and lower pH (≈4.2). Coliforms and L. monocytogenes, were inactivated in shorter time in probiotic samples, in comparison with the control ones. Pulsed field gel electrophoresis verified the presence of the probiotic strain in the cheese, until the end of storage at both temperatures, whilst the survival and distribution of the pathogenic strains depended on the trial. The sensory evaluation showed that the probiotic cheeses had desirable sensory characteristics similar to the control ones, with scores of ca. 8 on a 10 cm-scale. Finally, Fourier transform infrared spectroscopy was applied for the first time during Feta cheese storage with promising results for the rapid estimation of the microbiological counts and sensory status of cheese. Results showed that Lb. plantarum T571 highlighted desirable and robust technological properties and may be used in cheese making as an adjunct culture.