Efstathios Z. Panagou

Microbiological and biochemical profile of cv. Conservolea naturally black olives during controlled fermentation with selected strains of lactic acid bacteria

The effect of controlled fermentation processes on the microbial association and biochemical profile of cv. Conservolea naturally black olives processed by the traditional anaerobic method was studied. The different treatments included (a) inoculation with a commercial starter culture of Lactobacillus pentosus, (b) inoculation with a strain of Lactobacillus plantarum isolated from a fermented cassava product and (c) uninoculated spontaneous process. Microbial growth, pH, titratable acidity, organic acids and volatile compounds were monitored throughout the fermentation. The initial microbiota consisted of Gram-negative bacteria, lactic acid bacteria and yeasts. Inhibition of Gram-negative bacteria was evident in all processes. Both starter cultures were effective in establishing an accelerated fermentation process and reduced the survival period of Gram-negative bacteria by 5 days compared with the spontaneous process, minimizing thus the likelihood of spoilage. Higher acidification of the brines was observed in inoculated processes without any significant difference between the two selected starter cultures (113.5 and 117.6mM for L. plantarum and L. pentosus, respectively). L. pentosus was also determined as the major species present during the whole process of spontaneous olive fermentation. It is characteristic that lactic acid fermentation was also initiated rapidly in the spontaneous process, as the conditions of fermentation, mainly the low salt level (6%, w/v) favored the dominance of lactic acid bacteria over yeasts. Lactic, acetic and propionic were the organic acids detected by HPLC in considerable amounts, whereas citric and malic acids were also present at low levels and degraded completely during the processes. Ethanol, methanol, acetaldehyde, ethyl acetate were the major volatile compounds identified by GC. Their concentrations varied among the different treatments, reflecting varying degrees of microbial activity in the brines. The results obtained from this study could help the Greek table olive industry to improve the existing processing schemes in order to increase product consistency and quality expanding the international market for naturally black olives.

Microbial colonization of naturally black olives during fermentation and associated biochemical activities in the cover brine.

Aims: To establish the site of microbial growth on naturally black fermented table olives, and to monitor the population dynamics of yeasts and selected micro‐organisms together with the changes in organic acid profile and pH in the cover brine during fermentation.

Use of titanium dioxide (TiO2) photocatalysts as alternative means for Listeria monocytogenes biofilm disinfection in food processing.

The aim of this work was to study the photocatalytic activity of titanium dioxide (TiO(2)) against Listeria monocytogenes bacterial biofilm. Different TiO(2) nanostructured thin films were deposited on surfaces such as stainless steel and glass using the doctor-blade technique. All the surfaces were placed in test tubes containing Brain Heart (BH) broth and inoculated with L. monocytogenes. Test tubes were then incubated for 10 days at 16°C in order to allow biofilm development. After biofilm formation, the surfaces were illuminated by ultraviolet A light (UVA; wavelength of 315-400 nm). The quantification of biofilms was performed using the bead vortexing method, followed by agar plating and/or by conductance measurements (via the metabolic activity of biofilm cells). The presence of the TiO(2) nanoparticles resulted in a fastest log-reduction of bacterial biofilm compared to the control test. The biofilm of L. monocytogenes for the glass nanoparticle 1 (glass surface modified by 16% w/v TiO(2)) was found to have decreased by 3 log CFU/cm(2) after 90 min irradiation by UVA. The use of TiO(2) nanostructured photocatalysts as alternative means of disinfecting contaminated surfaces presents an intriguing case, which by further development may provide potent disinfecting solutions. Surface modification using nanostructured titania and UV irradiation is an innovative combination to enhance food safety and economizing time and money.

Yeast heterogeneity during spontaneous fermentation of black Conservolea olives in different brine solutions

Aims:  To assess the yeast community structure and dynamics during Greek‐style processing of natural black Conservolea olives in different brine solutions.

Modelling the combined effect of temperature, pH and aw on the growth rate of Monascus ruber, a heat-resistant fungus isolated from green table olives

Aims: Growth modes predicting the effect of pH (3·5–5·0), NaCl (2–10%), i.e. aw (0·937–0·970) and temperature (20–40°C) on the colony growth rate of Monascus ruber, a fungus isolated from thermally‐processed olives of the Conservolea variety, were developed on a solid culture medium.

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.

Temperature-assisted high hydrostatic pressure inactivation of Staphylococcus aureus in a ham model system: evaluation in selective and nonselective medium

Aims:  The purpose of this study was to investigate the inactivation kinetics of Staphylococcus aureus in a ham model system by high hydrostatic pressure at ambient (25°C) and selected temperatures (45, 55°C). Selective [Baird Parker (BP) agar] and nonselective [brain heart infusion (BHI) agar] growth media were used for enumeration in order to count viable and sublethally injured cells.

A comparison of artificial neural networks and partial least squares modelling for the rapid detection of the microbial spoilage of beef fillets based on Fourier transform infrared spectral fingerprints.

A series of partial least squares (PLS) models were employed to correlate spectral data from FTIR analysis with beef fillet spoilage during aerobic storage at different temperatures (0, 5, 10, 15, and 20 °C) using the dataset presented by Argyri et al. (2010). The performance of the PLS models was compared with a three-layer feed-forward artificial neural network (ANN) developed using the same dataset. FTIR spectra were collected from the surface of meat samples in parallel with microbiological analyses to enumerate total viable counts. Sensory evaluation was based on a three-point hedonic scale classifying meat samples as fresh, semi-fresh, and spoiled. The purpose of the modelling approach employed in this work was to classify beef samples in the respective quality class as well as to predict their total viable counts directly from FTIR spectra. The results obtained demonstrated that both approaches showed good performance in discriminating meat samples in one of the three predefined sensory classes. The PLS classification models showed performances ranging from 72.0 to 98.2% using the training dataset, and from 63.1 to 94.7% using independent testing dataset. The ANN classification model performed equally well in discriminating meat samples, with correct classification rates from 98.2 to 100% and 63.1 to 73.7% in the train and test sessions, respectively. PLS and ANN approaches were also applied to create models for the prediction of microbial counts. The performance of these was based on graphical plots and statistical indices (bias factor, accuracy factor, root mean square error). Furthermore, results demonstrated reasonably good correlation of total viable counts on meat surface with FTIR spectral data with PLS models presenting better performance indices compared to ANN.

Effect of temperature and water activity on growth and ochratoxin A production boundaries of two Aspergillus carbonarius isolates on a simulated grape juice medium

Aims:  To develop and validate a logistic regression model to predict the growth and ochratoxin A (OTA) production boundaries of two Aspergillus carbonarius isolates on a synthetic grape juice medium as a function of temperature and water activity (aw).

The dynamics of the HS/SPME-GC/MS as a tool to assess the spoilage of minced beef stored under different packaging and temperature conditions

The aim of the current study was to assess meat spoilage through the evolution of volatile compounds using chemometrics. Microbiological and sensory assessment, pH measurement and headspace solid phase microextraction gas chromatography/mass spectroscopy (headspace SPME-GC/MS) analysis were carried out in minced beef stored aerobically and under modified atmosphere packaging (MAP) at 0, 5, 10, and 15 °C. It was shown that the HS/SPME-GC/MS analysis provided useful information about a great number of volatile metabolic compounds detected during meat storage. Many of the identified and semi-quantified compounds were correlated with the sensory scores through the use of chemometrics, depicting possible spoilage indicators such as 2-pentanone, 2-nonanone, 2-methyl-1-butanol, 3-methyl-1-butanol, ethyl hexanoate, ethyl propanoate, ethyl lactate, ethyl acetate, ethanol, 2-heptanone, 3-octanone, diacetyl, and acetoin. Finally, the applied GC/MS global models were able to estimate the microbial counts of the different microorganisms and the sensory scores of a meat sample regardless of storage conditions (i.e. packaging and temperature).