Susana Sanz

Relation between spoilage and microbiological quality in minimally processed artichoke packaged with different films

The atmosphere surrounding minimally processed vegetables is extremely important to extend their shelf-life, and one of the most influential factors on its composition is the permeability of the film used in the packaging. This study determined the impact of the preservation technologies on sensory quality (weight losses, color, texture and sensory acceptability) and on the growth of indicator micro-organisms (mesophiles, psychrotrophs, anaerobic micro-organisms, sporeformers, faecal coliforms, Salmonella and Escherichia coli) in minimally processed artichoke packaged with five different films (two PVC and three P-Plus). The atmospheres obtained, together with the different permeability to water vapor of the films under study, determined the evolution of the visual and microbiological quality of the artichoke. For most of the batches, no correspondence was found between microbial growth and changes in appearance. Those batches where the equilibrium atmosphere was clearly anaerobic showed microbial counts below the legally established microbiological limits but also showed a rapid loss of sensory quality. On the other hand, some batches with an acceptable sensory evaluation had microbial counts higher than those allowed by the legislation. This last situation is particularly dangerous from a health point of view since it allows the growth of micro-organisms (even pathogens) although the product may seem to be acceptable for consumption. This lack of correspondence constitutes an important point to be attended to on the microbiological safety of these foods, since the preservation technologies applied allow the prolonging of their sensory characteristics but, at the same time, may favor the growth of micro-organisms.

The effect of a commercial starter culture addition on the ripening of an artisanal goat's cheese (Cameros cheese)

The evolution of physicochemical parameters, and the most important microbial groups, were determined for the following three batches of ‘Cameros’ goats milk cheese during ripening: Batch R elaborated with raw milk, Batch RS elaborated with raw milk and with the addition of a starter culture, and Batch PS elaborated with pasteurized milk and with the addition of the same culture. No differences in total solids (TS) or in the content of NaCl, fat and total nitrogen (expressed as percentages of TS) were found during the ripening. The pH, fat acidity and non‐protein nitrogen (NPN, expressed as a percentage of TN) showed significant differences between the batches. The inoculated batches showed the fastest drop in pH at the beginning of the ripening period, but the cheeses of Batch R showed a higher degree of lipolysis and proteolysis. The addition of a starter influenced the microbiological quality of the cheeses. Differences in the counts of Enterobacteriaceae and faecal coliforms were found between Batches R and RS after 15 days. Staphylococcus aureus increased in number during the early period of ripening and attained a population above 6 log cfu g−1 in Batch R in the period from 5 to 10 days. However, enterotoxins were not detected in this Batch. Batch R showed lower values of lactic acid bacteria at the beginning of the ripening period, but no significant differences were found between batches in the period from 5 to 15 days of ripening. At the beginning of the ripening, Lactococcus was the main lactic acid bacteria, with L. lactis lactis being predominant. After 15 days, the lactic acid bacteria counts decreased in the three batches, especially in the cheeses of Batch PS (only 2·2 log cfu g−1 was found at 60 days), as lactococci (the only lactic acid bacteria present in Batch PS) are incapable of growing under the conditions found in cheeses at the end of their ripening period. At this time, Lactobacillus was the predominant genus in Batches R and RS, with L. plantarum predominant. No lactococci were found from day 30 in Batch R and from day 40 in Batch RS. The cheeses of Batch RS received the most favourable scores from the tasting panel for all attributes judged: cut appearance, colour, aroma, taste, texture and general acceptance.

Behaviour of Listeria monocytogenes in packaged fresh mushrooms (Agaricus bisporus)

Aims: The aim of this study was to evaluate the potential of Listeria monocytogenes to grow in mushrooms packaged in two different types of PVC films when stored at 4°C and 10°C.

A proposed methodology to determine the sensory quality of a fresh goat's cheese (Cameros cheese) : application to cheeses packaged under modified atmospheres

Abstract A sensory profile was proposed, together with a methodology which permited the quality control of a fresh goats cheese (Cameros cheese) from the sensory standpoint. Samples of Cameros cheese from four different cheesemakers were evaluated by a jury of 10 members. All panelists attended five tasting sessions to define an agreed lexicon of sensory characteristics of Cameros cheese. In order to quantify each one of the sensory attributes, a scorecard was elaborated. The intensity of the attributes selected was quantified on a scale from 1 to 7 according to the indications given in the sensory description. For each attribute the optimum score was established by the panelists to obtain the numerical score of samples. Using the proposed system, the sensory quality of Cameros cheeses packaged under modified atmospheres was evaluated. Five different modified atmosphere conditions were studied (carbon dioxide/nitrogen mixtures and vacuum) and compared to control cheeses packaged in air. The product stored at 3–4°C was evaluated periodically. After 14 days of storage, the sensory characteristics of the control cheeses were unacceptable in all the parameters studied. However, the overall score for cheeses stored in 40 and 50% CO 2 did not change substantially, retaining a reasonable acceptability until the end of the storage period. The 100% CO 2 atmosphere had a very negative effect on the sensory quality specially in taste. Cheeses packaged under vacuum showed a fast deterioration of surface appearance and texture. The proposed methodology allowed the quantification of the sensory differences between the packaging conditions investigated. With regard to Cameros cheese, packaging in 50%CO 2 /50%N 2 and 40%CO 2 /60%N 2 were the most effective for retaining good sensory characteristics specially in taste and odour. However, texture and appearance were negatively affected by these conditions.

The occurrence of fungi, yeasts and bacteria in the air of a Spanish winery during vintage

This research studies the presence of microorganisms of enological interest (yeasts, bacteria and molds) and their evolution in the air of a wine cellar. The samples were taken throughout the winemaking campaign (September-December) in a winery of the D.O.Ca. Rioja, Spain. They were collected using an airIDEAL atmosphere sampler from Biomerieux. For the isolation, specific selective media were used for each group of microorganisms. The results obtained indicate that the presence in the winery air of the various different microorganisms studied is directly related to the winemaking processes that are taking place in the winery. Thus, the number of molds present decreases once grapes have ceased to be brought into the winery. The maximum number of yeasts in the air is found when all the vats in the cellar are fermenting, while the lactic bacteria are not detected until the first malolactic fermentation begins. The species of yeasts and molds identified are also related to the winemaking processes. The coincidence of strains of Saccharomyces cerevisiae among those present in the vats during alcoholic fermentation and those isolated from the air, confirms the role of the latter as a transmitter of microorganisms.

Effectiveness of chlorine washing disinfection and effects on the appearance of artichoke and borage.

Aim: Optimal conditions for chlorine application to obtain a reasonable decrease in the microbial counts without damaging the appearance of artichoke and borage have been established.

Effect of packaging conditions on the growth of micro-organisms and the quality characteristics of fresh mushrooms (Agaricus bisporus) stored at inadequate temperatures.

Mushrooms were packed in two polymeric films (perforated and non‐perforated PVC) and stored at 17 °C and 25 °C. The carbon dioxide and oxygen content inside the packages, aerobic mesophiles, Pseudomonas spp., faecal coliforms, Escherichia coli, anaerobic spores and major sensory factors (colour, texture, development stage and presence of moulds) were determined. The non‐perforated packages had the highest contents of CO2 (6–7%), the lowest contents of O2 (0·013–0·17%) and the most desirable quality parameters (texture, development stage and absence of moulds). Pseudomonas spp. counts were around 1 logarithmic unit lower in mushrooms packaged in non‐perforated film as the O2 concentrations were lower than in perforated film. The mushrooms themselves were inoculated with an enterotoxin A‐producing strain of Staphylococcus aureus, packaged in overwrapped trays and stored at 17 and 25 °C. Staphylococcus aureus did not grow in the samples stored at 17 °C. Only slight growth was observed in mushrooms packaged with non‐perforated film after 1 day at 25 °C. No enterotoxin was detected in any package. Faecal coliform counts were <2 log cfu g−1. Escherichia coli was not isolated in any of the samples. At 25 °C, counts of anaerobic spores of around 2 log cfu g−1 were detected in those mushrooms packaged in non‐perforated film.

Strain typing of acetic acid bacteria responsible for vinegar production by the submerged elaboration method.

Strain typing of 103 acetic acid bacteria isolates from vinegars elaborated by the submerged method from ciders, wines and spirit ethanol, was carried on in this study. Two different molecular methods were utilised: pulsed field gel electrophoresis (PFGE) of total DNA digests with a number of restriction enzymes, and enterobacterial repetitive intergenic consensus (ERIC) - PCR analysis. The comparative study of both methods showed that restriction fragment PFGE of SpeI digests of total DNA was a suitable method for strain typing and for determining which strains were present in vinegar fermentations. Results showed that strains of the species Gluconacetobacter europaeus were the most frequent leader strains of fermentations by the submerged method in the studied vinegars, and among them strain R1 was the predominant one. Results showed as well that mixed populations (at least two different strains) occurred in vinegars from cider and wine, whereas unique strains were found in spirit vinegars, which offered the most stressing conditions for bacterial growth.

Presence of lactic bacteria in the air of a winery during the vinification period

In this paper we have studied the presence and evolution in the winery air of the lactic bacteria responsible for malolactic fermentation. Sampling took place during the winemaking process (between September 2007 and July 2008) in a winery from the Rioja appellation in Spain. The results obtained indicated that the presence of these microorganisms in the atmosphere was detected when grapes were entering the winery, while malolactic fermentation was taking place, and when liquid containing bacteria was manipulated. The species and clones of the lactic bacteria identified were also related to those present in the vinification tanks at any given stage of the process.

Fermentation Problem in Spanish North-Coast Honey

Twenty-one samples from the Cantabrian coast were analyzed to establish their microbiological quality and fermentation tendency. In a food with a very low free-water content like honey, microbiological growth is only possible when there is an increase in water activity. Since most of the samples studied were not extensively granulated, the risk of fermentation is mostly due to high water content. Among our samples, only two had a water content below 17.1% (no risk of fermentation), whereas the high water activity of the rest of the samples indicates the possibility of microbial growth. In fact, four of the samples analyzed showed a moisture content over the Spanish maximum legal limit, which means a high risk of fermentation. The absence of Enterobacteriaceae, coliforms, and Escherichia coli in our samples indicates an appropriate cleanliness during extractions and handling of honey. No Salmonella or Shigella were found. The relationship between water activity and mold and yeast counts found for the honeys analyzed allowed us to divide our samples in two groups: honeys with a high or a low risk of fermentation. Changes observed during storage of the samples confirmed this classification.