Elena González-Fandos

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.

Efficacy of lactic acid against Listeria monocytogenes attached to poultry skin during refrigerated storage

Aims:  The aim of this study was to evaluate the effect of lactic acid washing on the growth of Listeria monocytogenes on poultry legs stored at 4°C for 7 days.

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.

Efficacy of Acetic Acid against Listeria monocytogenes Attached to Poultry Skin during Refrigerated Storage

This work evaluates the effect of acetic acid dipping on the growth of L. monocytogenes on poultry legs stored at 4 °C for eight days. Fresh inoculated chicken legs were dipped into either a 1% or 2% acetic acid solution (v/v) or distilled water (control). Changes in mesophiles, psychrotrophs, Enterobacteriaceae counts and sensorial characteristics (odor, color, texture and overall appearance) were also evaluated. The shelf life of the samples washed with acetic acid was extended by at least two days over the control samples washed with distilled water. L. monocytogenes counts before decontamination were 5.57 log UFC/g, and after treatment with 2% acetic acid (Day 0), L. monocytogenes counts were 4.47 log UFC/g. Legs washed with 2% acetic acid showed a significant (p < 0.05) inhibitory effect on L. monocytogenes compared to control legs, with a decrease of about 1.31 log units after eight days of storage. Sensory quality was not adversely affected by acetic acid. This study demonstrates that while acetic acid did reduce populations of L. monocytogenes on meat, it did not completely inactivate the pathogen. The application of acetic acid may be used as an additional hurdle contributing to extend the shelf life of raw poultry and reducing populations of L. monocytogenes.

Effect of propionic acid on Campylobacter jejuni attached to chicken skin during refrigerated storage.

The ability of propionic acid to reduce Campylobacter jejuni on chicken legs was evaluated. Chicken legs were inoculated with Campylobacter jejuni. After dipping legs in either water (control), 1% or 2% propionic acid solution (vol/vol), they were stored at 4ºC for 8 days. Changes in C. jejuni, psychrotrophs and Pseudomonas counts were evaluated. Washing in 2% propionic acid significantly reduced C. jejuni counts compared to control legs, with a decrease of about 1.62 log units after treatment. Treatment of chicken legs with 1 or 2% propionic acid significantly reduced numbers of psychrotrophs 1.01 and 1.08 log units and Pseudomonas counts 0.75 and 0.96 log units, respectively, compared to control legs. The reduction in psychrotrophs and Pseudomonas increased throughout storage. The highest reductions obtained for psychrotrophs and Pseudomonas counts in treated legs were reached at the end of storage, day 8, being 3.3 and 2.93 log units, respectively, compared to control legs. Propionic acid treatment was effective in reducing psychrotrophs and Pseudomonas counts on chicken legs throughout storage. It is concluded that propionic acid is effective for reducing C. jejuni populations in chicken.