Anthoula A. Argyri

Rapid monitoring of the spoilage of minced beef stored under conventionally and active packaging conditions using Fourier transform infrared spectroscopy in tandem with chemometrics.

Fourier transform infrared (FTIR) spectroscopy was exploited to measure biochemical changes within fresh minced beef in an attempt to rapidly monitor beef spoilage. Minced beef packaged either aerobically, under modified atmosphere and using an active packaging were held from freshness to spoilage at 0, 5, 10, and 15°C. Frequent FTIR measurements were collected directly from the sample surface using attenuated total reflectance, in parallel the total viable counts of bacteria, the sensory quality and the pH were also determined. Principal components analysis allowed illuminating the wavenumbers potentially correlated with the spoilage process. Qualitative interpretation of spectral data was carried out using discriminant factorial analysis and used to corroborate sensory data and to accurately determine samples freshness and packaging. Partial least-squares regressions permitted estimates of bacterial loads and pH values from the spectral data with a fit of R(2)=0.80 for total viable counts and fit of R(2)=0.92 for the pH. Obtained results demonstrated that a FTIR spectrum may be considered as a metabolic fingerprint and that the method in tandem with chemometrics represents a powerful, rapid, economical and non-invasive method for monitoring minced beef freshness regardless the storage conditions (e.g. packaging and temperature).

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.

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).

Performance of two potential probiotic Lactobacillus strains from the olive microbiota as starters in the fermentation of heat shocked green olives

The performance of two potential probiotic Lactobacillus strains from olive microbiota, namely L. pentosus B281 and L. plantarum B282 was assessed as starter cultures in Spanish-style fermentation of heat shocked green olives cv. Halkidiki. Two different initial salt levels were studied, 10% (w/v) and 8% (w/v) NaCl, and the brines were inoculated with (a) L. pentosus B281, (b) L. plantarum B282, and (c) a mixture of both strains. A spontaneous fermentation was also taken into account as control treatment. Prior to brining, olives were heat shocked at 80 °C for 10 min to reduce the level of the indigenous microbiota on olive drupes and facilitate the dominance of the inoculated cultures. Microbiological, physicochemical and sensory analyses were conducted throughout fermentation. The composition of LAB population and the evolution of added inocula were assessed by Pulsed Field Gel Electrophoresis (PFGE). The final population of LAB was maintained above 6 log cycles in olive flesh. Both L. pentosus B281 and L. plantarum B282 were able to dominate over indigenous LAB, albeit strain B281 exhibited higher recovery percentages (100 or 94.7% for B281 and 58.8% or 55.0% for B282 in 10% or 8% NaCl, respectively). L. pentosus B281 also dominated over L. plantarum B282, when the two strains were co-inoculated in olive fermentations. The sensory assessment showed higher preference for inoculated fermentations of L. pentosus and L. plantarum separately in 8% NaCl, followed by the L. plantarum in 10% NaCl. The present study showed that probiotic strains L. pentosus B281 and L. plantarum B282, may offer a great potential for use as functional starter cultures in olive fermentation and deliver a promising probiotic food to the consumer.

Potential of a simple HPLC-based approach for the identification of the spoilage status of minced beef stored at various temperatures and packaging systems

The shelf life of minced beef stored (i) aerobically, (ii) under modified atmosphere packaging (MAP), and (iii) under MAP with oregano essential oil (MAP/OEO) at 0, 5, 10, and 15°C was investigated. The microbial association of meat and the temporal biochemical changes were monitored. Microbiological analyses, including total viable counts (TVC), Pseudomonas spp., Brochothrix thermosphacta, lactic acid bacteria, Enterobacteriaceae, and yeasts/moulds, were undertaken, in parallel with sensory assessment, pH measurement and HPLC analysis of the organic acid profiles. Spectral data collected by HPLC were subjected to statistical analysis, including principal component analysis (PCA) and factorial discriminant analysis (FDA). This revealed qualitative discrimination of the samples based on their spoilage status. Partial least squares regression (PLS-R) was used to evaluate quantitative predictions of TVC, Pseudomonas spp., Br. thermosphacta, lactic acid bacteria, Enterobacteriaceae, and yeasts/moulds. Overall, the HPLC analysis of organic acids, was found to be a potential method to evaluate the spoilage and microbial status of a meat sample regardless of the storage conditions. This could be a very useful tool for monitoring the quality of meat batches during transportation and storage in the meat food chain.

Fate of Escherichia coli O157:H7, Salmonella Enteritidis and Listeria monocytogenes during storage of fermented green table olives in brine.

The survival of Escherichia coli O157:H7, Salmonella Enteritidis and Listeria monocytogenes during the storage of fermented green table olives cv. Halkidiki in brine was studied in parallel with the evolution of lactic acid bacteria (LAB), yeasts and pH. The olives were previously fermented with a starter culture (a potential probiotic strain of Lactobacillus pentosus B281--starter process) or with the indigenous microbiota (control). After the end of fermentation, olives were placed in brine, inoculated with a cocktail of 5 strains of E. coli O157:H7, 5 strains of L. monocytogenes and 4 strains of S. Enteritidis, with a final concentration in the brine of ca. 7.0 log CFU/ml, and subsequently packaged in polyethylene pouches and stored at 20 °C. The population of E. coli O157:H7 reduced gradually and was detected in the brine until the 27th day of storage in both cases (i.e., starter and control process), and on olive fruits until the 19th and 16th days of storage in the starter and control process, respectively. S. Enteritidis population showed also a decrease and it was detected until the 21st day of storage in both brine and olive fruits in both cases. The population of L. monocytogenes declined during storage and it was detected until the 31st day of storage in both brine and olive fruits in both cases, showing a longer survival period in comparison to the other two studied pathogens. The presence of the potential probiotic starter did not affect the pathogen survival. The results demonstrated that even though the growth of the pathogenic strains was not supported, they may survive for a long period in a stressful environment of a fermented product with low pH value (4.2) and high salt concentration (6.0%). These results are a valuable contribution to risk assessment studies related to ready to eat foods in general.

Nonthermal Pasteurization of Fermented Green Table Olives by means of High Hydrostatic Pressure Processing

Green fermented olives cv. Halkidiki were subjected to different treatments of high hydrostatic pressure (HHP) processing (400, 450, and 500 MPa for 15 or 30 min). Total viable counts, lactic acid bacteria and yeasts/moulds, and the physicochemical characteristics of the product (pH, colour, and firmness) were monitored right after the treatment and after 7 days of storage at 20°C to allow for recovery of injured cells. The treatments at 400 MPa for 15 and 30 min, 450 MPa for 15 and 30 min, and 500 MPa for 15 min were found insufficient as a recovery of the microbiota was observed. The treatment at 500 MPa for 30 min was effective in reducing the olive microbiota below the detection limit of the enumeration method after the treatment and after 1 week of storage and was chosen as being more appropriate for storing olives for an extended time period (5 months). After 5 months of storage at 20°C, no microbiota was detected in treated samples, while significant changes for both HHP treated and untreated olives were observed for colour parameters only (minor degradation). In conclusion, HHP treatment may introduce a reliable nonthermal pasteurization method to extend the microbiological shelf-life of fermented table olives.

Effect of High Hydrostatic Pressure Processing on Microbiological Shelf-Life and Quality of Fruits Pretreated with Ascorbic Acid or SnCl2

In the current study, the processing conditions required for the inactivation of Paenibacillus polymyxa and relevant spoilage microorganisms by high hydrostatic pressure (HHP) treatment on apricot, peach, and pear pieces in sucrose (22°Brix) solution were assessed. Accordingly, the shelf-life was determined by evaluating both the microbiological quality and the sensory characteristics (taste, odor, color, and texture) during refrigerated storage after HHP treatment. The microbiological shelf-life of apricots, peaches, and pears was prolonged in the HHP-treated products in comparison with the untreated ones. In all HHP-treated packages for apricots, peaches, and pears, all populations were below the detection limit of the method (1 log CFU/g) and no growth of microorganisms was observed until the end of storage. Overall, no differences of the L*, a*, or b* value among the untreated and the HHP-treated fruit products were observed up to the time at which the unpressurized product was characterized as spoiled. HHP treatment had no remarkable effect on the firmness of the apricots, peaches, and pears. With regard to the sensory assessment, the panelists marked better scores to HHP-treated products compared to their respective controls, according to taste and total evaluation during storage of fruit products.

Advances in vacuum and modified atmosphere packaging of poultry products.

: Temperature, humidity, light, oxygen and water activity (aw) can affect the behaviour of microorganisms that can result the type and the rate of spoilage in poultry meat. The potential use of traditional preservation techniques such as vacuum packaging (VP) and modified atmosphere packaging (MAP) can be combined with decontaminants, additives (natural or chemical), natural biopreservatives and/or can be integrated to emerging technologies such as active and intelligent packaging, irradiation and high pressure. In addition, the potential use of alternative methods such as metabolomics that correlate microbial growth and chemical changes occurring during meat storage can reveal chemical indicator(s) that may be useful tools for quantifying poultry quality or freshness.

Probiotics from the Olive Microbiota

Table olives are considered the most economically important fermented vegetable in the western world, with an increasing rate of production and consumption in recent years. In the last decade, a considerable research effort has been undertaken to transform table olives, a traditional fermented food, into a promising functional food that apart from its already increased nutritional value, serves as a vehicle for probiotic bacteria. Series of experiments have been performed to evaluate the imposition and survival of lactic acid bacteria (LAB) (of human, dairy, or olive origin) applied as adjunct, starter, or fortification cultures in table olives. The evaluation of the probiotic potential of microorganisms (LAB or yeasts) isolated from olives has received remarkable interest recently, because these isolates may be used as starter or adjunct cultures in table olive fermentations. Wild-type strains, isolated from the olive environment, are more likely to survive through the fermentation process, because natural selection has endowed them with ecological advantages. The imposition and survival of the probiotic strains to the final product is of great importance, in order to deliver and exert the beneficial effects in the human intestine.