Occurrence of Listeria monocytogenes in food in Chile.

Out of 2145 food samples analysed 77 were found contaminated with Listeria monocytogenes in Santiago, Chile. Samples were: 603 ice-cream (3.5% contaminated), 256 soft cheese (0.8%), 155 hard cheese (0%), 229 baby milk bottles (0%), 634 processed meat products (3.6%) and 268 crustaceous shellfish (11.6%). Three different isolation media were used: for 318 samples, Modified McBride Agar (MMA), Lithium chloride Phenylethanol Moxalactam agar, and Polymyxin Acriflavine Lithium chloride Ceftazidime Aesculin Mannitol agar; for 1827 samples MMA was replaced by Listeria Selective Agar Oxford Formulation. Isolates were classified as follow: serovar 1/2a (25 isolates), serovar 4b (20), serovar 1/2b (19), serovar 3b (7), serovar 1/2c (2), untypable (4). A high variety of phagovars was detected although 52% of strains was untypable.     

Occurrence and ribotypes of Listeria monocytogenes in Gorgonzola cheeses

In this study 1656 Gorgonzola cheeses, collected from October 2003 to April 2004 in the same industrial plant located in Lombardia (Italy), were analysed in order to evaluate their level of contamination with Listeria monocytogenes after packaging, as well as at the end of the shelf life. A subset of Gorgonzola isolates was submitted to automated EcoRI ribotyping to evaluate their DUP-IDs (DuPont identification library code) and their level of genetic diversity. The isolate ribotyping profiles were included in an on-line database named PathogenTracker database. The strain DUP-IDs and the similarities between Gorgonzola isolates and PathogenTracker human sporadic strains allowed to evaluate the potential virulence of Gorgonzola-associated strains. The L. monocytogenes detection rates observed in the cheese samples monitored after packaging and at the end of the shelf life were 2.1% and 4.8%, respectively. Seventy percent of the strains genotyped were classified in the same ribotype, labelled as 204 S5, indicating that L. monocytogenes population associated to Gorgonzola cheese shows a low level of genetic diversity. Ninety percent of the strains were classified in DUP-IDs belonging to the II pathogenicity lineage identified for L. monocytogenes. That lineage includes serotype 1/2a, 1/2c and 3c strains, associated to the 35% of the human sporadic isolates described in the literature as causing listeriosis. Moreover, 16.7% of Gorgonzola isolates showed a similarity >or=99% with PathogenTracker human sporadic strains. The results of this study showed that the incidence of L. monocytogenes in Gorgonzola cheeses commercialised by the plant tested was lower than that observed in other Italian blue-veined cheeses by other authors. However, it increased during cheese storage and it become double at the end of the cheese shelf life, ranging from 30 to 60 days after packaging.     

Reuse of ozonated alkaline solutions as fermentation brines in Spanish green table olives

ABSTRACT:  The water used to reduce the excess NaOH after the immersion of green olives in lye becomes a heavily polluted, alkaline wastewater (AW) once it has come into contact with the fruits. Its treatment with ozonated air for 72 h (TAW) destroyed all polyphenols in the solution. A comparison of the microbial, physicochemical, and organoleptic characteristics of olives processed in the traditional way (W) and those reusing AW or TAW was made. The reuse of TAW or diluted TAW (TAW + W) as fermentation brines led to a shorter lag phase, higher maximum specific growth of lactobacillus, and higher lactic acid accumulation (in TAW) than the traditional process; differences among other physicochemical characteristics were not relevant, except that reused brines (AW) always had higher polyphenol contents. The organoleptic panel test did not detect significant differences among treatments in acidic taste, firmness, pit detachment, or olive color. Overall quality was fairly similar for olives from the traditional process and those from the reused TAW. Direct (or diluted) reuse of AW was also possible but produced a more bitter tasting olive.     

Triterpenic acids in table olives

An experimental investigation was carried out for the first time on the triterpenic acids in table olives. Maslinic acid was found in a higher concentration than oleanolic acid in the flesh of 17, unprocessed olive varieties, with the Picual and the Manzanilla varieties showing the highest and almost the lowest contents, respectively. The level of triterpenic acids in several types of commercial black and green olives ranged from 460 to 1470 mg/kg fruit, which represents a much higher value than reported for virgin olive oils. In fact, the NaOH treatment employed to debitter black and green olives reduced the concentrations of these substances in the flesh because of their solubilisation into alkaline solutions. Thus, natural black olives, which are not treated with NaOH, showed a higher concentration than 2000 mg/kg in the olive flesh. These results will contribute to the reevaluation of table olives from a nutritional and functional point of view because of the promising bioactivity properties attributed to olive triterpenic acids.     

Growth modelling of Listeria monocytogenes in packaged fresh green asparagus

Growth of Listeria monocytogenes in packaged fresh green asparagus was investigated at different temperatures. The present study monitored the growth of L. monocytogenes in packaged fresh green asparagus stored at 2, 4, 8, 12 and 20°C. Changes in carbon dioxide, oxygen concentrations and pH were determined. Growth data were fitted to the Baranyi equation. The influence of storage temperature was very apparent, at higher temperatures (8, 12 and 20°C) an increase of two logarithmic units of L. monocytogenes took place, criteria used for the determination of the sanitary risk. The recommended storage temperatures for the optimal and safe conservation of asparagus are the lower ones studied (2 and 4°C), because growth of L. monocytogenes is not allowed, although it can survive, so in cases of a high contamination of this micro-organism it could be a sanitary risk. Predictive modelling appears to be a useful tool in estimating growth rates ofL. monocytogenes in these products.     

Occurrence of Campylobacter and Listeria monocytogenes in a poultry processing plant

The occurrence of Campylobacter and Listeria monocytogenes was studied in 645 samples from surfaces, water, and poultry products (chicken carcasses, chicken parts, viscera, and spoils) in a poultry processing plant in southern Brazil. The automated mini-VIDAS system was used to detect the presence of Campylobacter and L. monocytogenes on the samples. The positive samples were confirmed by conventional methods. Campylobacter and L. monocytogenes were found in 16.6 and 35.6% of the analyzed samples, respectively. The sampling points with the highest Campylobacter incidence were intestine (63.3%, 19 of 30 samples), gallbladder (46.7%, 14 of 30), carcasses before evisceration (33.33%, 10 of 30), and carcasses after plucking (30%, 9 of 30). For L. monocytogenes, the majority of positive samples were from frozen breast (100%, 15 of 15 samples), frozen wing (93.3%, 14 of 15), fresh breast (83.3%, 25 of 30), fresh wing (80%, 24 of 30), skin of breast and leg (76.7%, 23 of 30), frozen leg (60%, 9 of 15), and fresh leg (50%, 15 of 30).     

Occurrence of Listeria monocytogenes in freshwater fish farms and fish-smoking plants

Three Swiss fish farms, farming rainbow trout (Oncorhynchus mykiss), and their affiliated smoking plants were analyzed for the presence of Listeria spp. 590 samples were collected from the farming environment (raceway water, sludge), faecal content and skin of the fish, fish during processing, and the processing environment.Listeria spp. were found at prevalences of 2·3% in plant A, 31·6% in plant B (mainly L. monocytogenes), and 13·8% in plant C (mainly L. innocua). This high contamination rate in plant B may be explained by the following facts: (i) farm B uses river water flowing through agricultural land; (ii) plant B rears fish in earth ponds instead of concrete ponds or raceways; (iii) fish from farm B had not been denied feed prior to slaughter; and (iv) total lack of regular mechanical and chemical cleaning in the fish farm B and processing plant B.In all three plants samples taken after smoking but before packaging did not contain Listeria spp., although in plant B and C the raw fish was contaminated. Hygienic defaults during packaging can lead to contaminated ready-to-eat products, detected in plant B (L. monocytogenes) and plant C (L. innocua) with one sample each. To minimize a possible health hazard to the consumer, it is of great importance to prevent postprocessing contamination of smoked fish.Finally, means of preventing Listeria contamination during farming, slaughtering, processing and storage are suggested.     

Changes in the volatile composition of Spanish-style green table olives induced by pasteurisation treatment

Thermal treatment of pasteurisation is the most widely used stabilisation method for packed green table olives. In the present work, the influence of pasteurisation on the composition of volatile compounds in packed Spanish-style green table olives was studied. To this aim, two thermal processes (P1 = 85 °C for 7 min; P2 = 85 °C for 15 min) were evaluated by comparing the contents of volatile compounds in pasteurised olives with those in unpasteurised olives. Volatiles were analysed, both in olive juice and cover brine, by means of headspace solid-phase microextraction (HS-SPME) followed by gas chromatography-mass spectrometry (GC-MS). Both pasteurisation treatments caused significant increases in diverse ethyl and methyl esters and in volatile compounds derived from several chemical reactions (lipid oxidation, Maillard reaction, degradation of carotenoids). Significant differences between samples subjected to P1 and P2 were only found for 1-octen-3-ol, pentanal and 6-methyl-5-hepten-2-one in olive juice.     

Determination of killer activity in yeasts isolated from the elaboration of seasoned green table olives

In this work 51 yeasts strains isolated from seasoned green table olives and belonging to the Candida, Debaryomyces, Kluyveromyces, Pichia, and Saccharomyces genera were characterized by their killer activity in different conditions. Killer activity of isolates was analyzed in a medium with different pH's (3.5 to 8.5) and NaCl concentrations (5, 8, and 10%). At every pH tested, all the genera studied had killer strains, although the smallest percentages of killer yeasts were found at the highest pH (8.5). The presence of 5 and 8% NaCl increased the detected killer percentage, but the highest salt concentration (10%) decreased it. The interaction between the reference killer yeasts and yeasts isolated from olives was analyzed. Most isolates were killer-sensitive to one or more killer reference strains. Only 2 of the 51 strains tested were considered killer-neutral. Cross-reaction trials between isolates and spoilage yeasts showed that, of the isolates, nine killer strains, belonging to Debaryomyces hansenii, Kluyveromyces marxianus, Pichia anomala, Pichia guilliermondii, and Saccharomyces cerevisiae, had the broadest spectra of action against yeasts that cause spoilage. These killer yeasts and the toxins that they produce are candidates for further investigation as suppressors of indigenous olive table yeast growth. The results confirmed the highly polymorphic expression of the killing activity, with each strain showing different killer activities. This method may thus be very useful for simple and rapid characterization of yeast strains of industrial interest.     

Mineral content and sensory characteristics of Gordal green table olives fermented in chloride salt mixtures

This work studies the effects of the initial brine concentrations of NaCl, KCl, and CaCl(2) on the mineral content and gustatory and kinaesthetic sensations of fermented green table olives, using a simplex centroid mixture design augmented with interior points. The sodium in the flesh was linearly related to the mixture concentrations while potassium and calcium were linked by quadratic and special cubic models respectively. Acidity, saltiness, hardness, fibrousness, and crunchiness were expressed as linear funtions of the NaCl, KCl, and CaCl(2) initial brine contents but bitterness required quadratic equations. The models can be used to produce table olives with specific mineral contents in the flesh and to predict their corresponding sensory characteristics. PRACTICAL APPLICATION: The study provides the industry with models to estimate the Na, K, and Ca mineral contents in the flesh of fermented Gordal green table olives as well as their sensory characteristics as a function of the NaCl, KCl, and CaCl(2) initial compositions in the brining solution. Therefore, the paper provides tools which are able to support the production of commercial presentations which not only satisfy consumer demand for low Na, but are also K and Ca fortified table olive presentations with specific sensory profiles.     

Content of biogenic amines in table olives

Content of biogenic amines in flesh and brines of table olives was determined by high-pressure liquid chromatography analysis of their benzoyl derivatives. No biogenic amines were found in the flesh of fresh fruits at any stage of ripeness. Contents of biogenic amines in Spanish-style green or stored olives increased throughout the brining period but were always higher in the former. Putrescine was the amine found in the highest concentration. Small quantities of cadaverine were found in the samples taken after 3 months of brining. This compound and histamine, tyramine, and tryptamine were also found in samples taken after 12 months. Gordal cultivar showed the highest contents, followed by Manzanilla and Hojiblanca. No relationship was found between contents of biogenic amines and lactic acid production or table olive spoilages, although zapatera olives had considerably higher amounts than those brines that had undergone a normal process. Concentrations in directly brined olives were markedly lower than contents in Spanish-style olives. With respect to partition between flesh and brine, there was equilibrium between both media in the case of Spanish-style olives, whereas the contents in directly brined olives were higher in flesh than brine.     

Fermentation profiles of Manzanilla-Aloreña cracked green table olives in different chloride salt mixtures

NaCl plays an important role in table olive processing affecting the flavour and microbiological stability of the final product. However, consumers demand foods low in sodium, which makes necessary to decrease levels of this mineral in fruits. In this work, the effects of diverse mixtures of NaCl, CaCl₂ and KCl on the fermentation profiles of cracked directly brined Manzanilla-Aloreña olives, were studied by means of response surface methodology based in a simplex lattice mixture design with constrains. All salt combinations led to lactic acid processes. The growth of Enterobacteriaceae populations was always limited and partially inhibited by the presence of CaCl₂. Only time to reach half maximum populations and decline rates of yeasts, which were higher as concentrations of NaCl or KCl increased, were affected, and correspondingly modelled, as a function of salt mixtures. However, lactic acid bacteria growth parameters could not be related to initial environmental conditions. They had a longer lag phase, slower growth and higher population levels than yeasts. Overall, the presence of CaCl₂ led to a slower Enterobacteriaceae and lactic acid bacteria growth than the traditional NaCl brine but to higher yeast activity. The presence of CaCl₂ in the fermentation brines also led to higher water activity, lower pH and combined acidity as well as a faster acidification while NaCl and KCl had fairly similar behaviours. Apparently, NaCl may be substituted in diverse proportions with KCl or CaCl₂ without substantially disturbing water activity or the usual fermentation profiles while producing olives with lower salt content.     

Identification and characterization of yeast isolated from the elaboration of seasoned green table olives

The purpose of this study was to investigate the yeast population during the processing of green table olives. In the fresh olives, yeast were found at concentrations of around 3.0 log cfu/g, with Cryptococcus spp. being predominant. In the brine, the yeast concentrations were greater than 4.9 log cfu/ml, with Pichia anomala, Kluyveromyces marxianus, and Saccharomyces cerevisiae being the predominant species. Unlike the yeast isolated from the fresh olives, the strains obtained from the olive brine mostly showed low pectolytic but high catalase activities. Some of these strains also exhibited other biochemical desirable properties for the fermentation of green table olives, including their lipolytic activities and their assimilation or production of organic acids in the brine. Seven strains in particular of P. anomala, K. marxianus, S. cerevisiae, and Candida maris showed the best properties for use in trials as starter culture in pilot fermenters.     

Occurrence of Listeria monocytogenes in fresh and processed foods in Navarra (Spain)

The presence of Listeria spp. was investigated in a total of 3685 food samples obtained from different industries and markets of Northern Spain in the last 4 years. The samples analyzed include fresh raw products (meat, milk and poultry) and treated products (cooked and cured meats, frozen vegetables and smoked salmon). Occurrence of Listeria spp. varied from 8.1% in soft cheese to 76.3% in raw poultry samples. The highest incidence of L. monocytogenes also occurred in raw poultry (36.1% positive samples). Despite this high incidence of contamination, these kinds of products carry a low risk of listeriosis transmission because of the heat treatment prior to consumption. On the other hand, the ready-to-eat products (RTE) tested in this study showed incidences that could pose serious health problems, taking into account that the storage conditions may allow for rapid growth of the pathogen. It was also found that up to 75.5% of the L. monocytogenes strains isolated in this study belonged to serogroup 1, mainly serotype 1/2a, while the clinical cases observed in Navarra in the same period of time belonged mainly to serotype 4b/4bx.     

Chlorophyll pigment composition in table olives (cv. Gordal) with green staining alteration.

Metallochlorophyllic complexes of copper are present in green table olives, showing the alteration known as green staining. They were formed stepwise in such a way that new metallochlorophyll derivatives were detected as the fruits became more altered. Cu-15-glyoxylic acid pheophytin a was the first compound formed, followed in order by Cu-pheophytin a, Cu-15-glyoxylic acid pheophytin b, Cu-15-formyl-pheophytin a, and Cu-pyropheophytin a. Pigment analysis in fruits classified according to the surface area affected by green staining showed a progressive increase in the concentration of all copper complexes with the course of the alteration. The metallochlorophyll derivatives of copper were present both in the part of the fruit affected by the alteration and in the remainder part, although the amount was significantly greater in the former. On the other hand, not all the copper present in the fruits was accessible for the formation of such compounds, since the concentration of copper complexes found in olives with the maximum degree of alteration observed did not exceed 20% of the total copper of the fruit.     

Volatile profile of Spanish-style green table olives prepared from different cultivars grown at different locations

The volatile profiles of Spanish-style green table olives elaborated with Manzanilla, Gordal and Hojiblanca cultivars grown at different locations in Spain were established by solid phase micro-extraction (SPME) and gas chromatography coupled to mass spectrometry (GC–MS). A total of 102 volatile compounds were identified, belonging to distinct chemical classes, and 20 of them are reported for the first time in table olives. The headspace profile was predominated by alcohols and phenols, followed by acids and esters, whereas the relative amounts of the remaining classes were quite lower (< 5% in general). The principal compounds characterizing the headspace for most samples were p-creosol, phenylethyl alcohol, acetic acid, ethanol, benzyl alcohol, ethyl acetate, and (Z)-3-hexen-1-ol. Significant differences in the proportions of volatile compounds between samples from the Gordal cultivar and those from Manzanilla and Hojiblanca cultivars were detected and statistically visualized by principal component analysis (PCA). Among all the identified compounds, only (E)-2-decenal showed significant differences between the three cultivars without being significantly affected by locations where the fruits were grown.     

Occurrence and Antimicrobial Susceptibility of Listeria monocytogenes Isolated from Brined White Cheese in Jordan

Listeria monocytogenes is a serious foodborne pathogen that has been isolated from different dairy food products. Several foodborne outbreaks of listeriosis have been associated with consumption of cheese. The aims of this study were to determine the occurrence of L. monocytogenes and Listeria spp. in brined white cheese (BWC) sold in Jordan, and to determine the susceptibility of isolated L. monocytogenes to antimicrobials. Three hundred and fifty samples of 5 different types of BWC (akkawi, boiled, halloumi, pasteurized, and shellal) were collected from a local market in Jordan. The ISO (11290-1) procedure was followed for isolation and identification of Listeria spp. from cheese samples and a polymerase chain reaction (PCR) technique was used for confirmation of L. monocytogenes isolates. The VITEK2 automated system was used for testing antimicrobial susceptibility of L. monocytogenes isolates. The overall prevalence of Listeria spp. in cheese sample was 27.1%. L. monocytogenes was isolated from 39 (11.1%) samples. Other isolated species were L. grayi (6.9%), L. innocua (2%), L. ivanovii (4%), L. seeligeri (2%), and L. welshimeri (0.3%). The pH values and salt concentrations of L. monocytogenes positive cheese samples ranged from 5.10 to 6.32 and 5.64 to 13.16, respectively. L. monocytogenes isolates were sensitive or intermediate susceptible to imipenem, gentamicin, linezolid, teicoplanin, vancomycin, fusidic acid, trimethoprim/sulfamethoxazole, benzylpenicillin, ciprofloxacin, erythromycin, tetracycline, and rifampicin, but resistant to fosfomycin, oxacillin, and clindamycin.