Isabel Jaime

Characterisation of Micrococcaceae isolated from different varieties of chorizo.

A total of 426 strains of Micrococcaceae bacteria isolated from chorizo (a traditional Spanish fermented sausage) were identified. The chorizos were sampled from three regions of Castilla and León in Spain: Burgos, Segovia and Salamanca. Two factories were chosen in each region and the samples were taken at three stages of ripening. Staphylococcus xylosus was the most predominant species isolated (95%). Twelve strain types of S. xylosus were established according to their fermentation patterns, and two of them, S. xylosus type 2 and S. xylosus type 5, made up the majority of the strains of S. xylosus isolated (27 and 52%). Production of acetoin, nitrate reductase, urease activity, proteolytic and lipolytic activity were determined for all isolates. The percentage of strains of S. xylosus producing acetoin depends on the manufacturing location. In general, the proteolytic and lipolytic activities of the S. xylosus isolated from chorizo from Castilla and León were low and moderate; 97% of the strains showed nitrate reductase and urease activity. According to our results and to previous investigations, it seems that S. xylosus type 5, showing nitrate reductase and urease activity, low-moderate proteolytic and lipolytic activities and not producing acetoin would be suitable as a starter culture. Of the strains isolated in this study, 38% comply with these requirements.

Effect of the packaging method and the storage time on lipid oxidation and colour stability on dry fermented sausage salchichón manufactured with raw material with a high level of mono and polyunsaturated fatty acids.

The effects of fatty acid composition, two packaging methods (vacuum and 20% CO(2)/80% N(2)) and storage under refrigeration for 210 days were evaluated on a dry fermented sausage (salchichón), manufactured with raw material enriched in monounsaturated or polyunsaturated fatty acids. Fatty acid composition was determined on sausage mixtures and on ripened sausages and lipid oxidation and colour stability was determined on ripened sausage at different times during storage. The modification of fatty acid composition of the sausages raised the nutritional quality, slightly affecting the colour properties. Dry fermented sausages enriched in polyunsaturated and monounsaturated fatty acids presented higher lipid oxidation values than the control ones. Both packaging methods (vacuum and 20% CO(2)/80% N(2)) during 210 days of chilled storage had minor effects on the colour and the lipid oxidation stability.

The effect of sugar concentration and starter culture on instrumental and sensory textural properties of chorizo-Spanish dry-cured sausage

In this study, instrumental and sensory textural properties of chorizo with different levels of glucose (0.1%, 0.5% and 1.0%) and with different starter cultures (Lactobacillus sakei K29, Pediococcus sp. P22 and Pediococcus sp. P208) were studied as well as the relationship between them. The ripening process was followed by physico-chemical and microbiological analysis. Starter culture and concentration of glucose had a highly significant effect on pH, moreover an interactive effect of both factors was found; and also of day of ripening and both starter culture and concentration of glucose. In general terms, changes of pH over time are influenced by the presence of sugar and starter culture even if all chorizos showed at first a rapid decrease, a stay or slow decrease, and a final rise. Texture profile analysis (TPA) proved that hardness and chewiness differ significantly among chorizos with or without starter cultures, except in the batch with 0.1% sugar. Furthermore, the highest values in both textural parameters were found in batches with 0.5% and 1% sugar. The texture differences between chorizos just described were also noticeable in the sensorial evaluation. Likewise, instrumental textural attributes showed significant correlations with sensorial analysis.

Study of the shelf life of a dry fermented sausage “salchichon” made from raw material enriched in monounsaturated and polyunsaturated fatty acids and stored under modified atmospheres

The microbiological, physico-chemical and sensory properties of salchichon with high unsaturated fat content, packed under vacuum and 20/80% CO(2)/N(2) modified atmosphere, were evaluated to determine its quality changes during storage under refrigeration. These sausages were manufactured with pork meat and pork backfat obtained from pigs fed with three different diets (control diet-CO, high oleic diet-HO and high linoleic diet-HL). In general, few significant differences were found in counts of different groups of microorganism between the three types of sausages and no difference between the packaging methods. A reduction in pH values was observed during storage and no great differences were determined by storage period on water activity (a(w)). Both parameters (pH and a(w)) presented similar results to those found in different Spanish sausages and other European dry fermented products. The sensory results denoted that sensory quality gradually decreased during storage under both packaging conditions (vacuum and 20/80% CO(2)/N(2)), so it is not advisable to store longer than 150days. On the other hand, fermented sausages with high content of unsaturated fatty acids had similar sensory properties to those of conventional sausages, and even a comparable sensory stability. In conclusion, the results showed healthier salchichons (HO and HL) similar to the traditional (CO) one could be manufactured and stored under refrigeration after slicing for a reasonable period, but the advantage of the gas mixture packaging (20/80% CO(2)/N(2)) versus vacuum packaging was not clear.

Spoilage of blood sausages morcilla de Burgos treated with high hydrostatic pressure

In this study, the microbial ecology of the blood sausage morcilla de Burgos, subjected to high hydrostatic pressure treatment (HPP), was studied by culture-dependent and -independent methods. Morcilla de Burgos is the most traditional and famous blood sausage in Spain. The producers are interested in extending its shelf-life in order to expand their market and to reduce losses attributed to spoilage. Sausage batter prior to stuffing and blood sausages HPP treated or not (control) were analyzed at 0, 9, 14, 21, 28 and 35 days of storage at 4 degrees C. Lactic acid bacteria, Pseudomonas spp. and aerobic mesophilic bacteria were investigated by traditional plating. PCR-denaturing gradient gel electrophoresis (DGGE) was used to analyze the DNA and the RNA extracted directly from the blood sausages, as well as bulk cells of LAB and Pseudomonas spp. The results showed that HPP improved the shelf life of morcilla de Burgos to 28 days in comparison with control samples. The populations responsible for spoilage, namely LAB, remained lower in HPP treated samples when compared with the control samples. Only at 35 days of storage they reached values of 10(8) cfu/g, leading to the spoilage of the product. Although, HPP affected the LAB population, they were able to recover the injury provoked by the treatment. Lastly, HPP seemed to affect differently LAB species detected. While Leuconostoc mesenteroides was completely inactivated by HPP, Weissella viridescens was able to recover and carry out the typical spoilage of the product. Pseudomonas spp. remained under detection level (<10(2) CFU/g) after the HPP treatment.

Physicochemical and sensory characterisation of Morcilla de Burgos, a traditional Spanish blood sausage

Morcilla de Burgos is a popular cooked blood sausage produced in the region around Burgos in the north of Spain. Physicochemical and sensory properties of this traditional product were investigated in order to support the claim for a Protected Geographical Indication. Products from 14 manufacturers were analysed for pH, water activity (a(w)), moisture, ether-extractable fat, starch, protein, total sugar, ash, iron and sodium contents as well as sensory parameters related to visual, olfactory, texture and flavour attributes. Principal component analysis confirmed the existence of three varieties of Morcilla de Burgos. Morcillas from group I were characterised by a notable blood smell and blood and pepper flavour, a high pH, and a(w) and a high protein content. Morcillas from group II were characterised by strong cumin smell and flavour and a high softness. Morcillas from group III had a high onion odour, high presence of onion and high contents of fat, total sugar and fibre.

Tracing Campylobacter jejuni strains along the poultry meat production chain from farm to retail by pulsed-field gel electrophoresis, and the antimicrobial resistance of isolates

In this study Campylobacter jejuni isolates were recovered from birds, carcasses and carcass portions from two broiler chicken flocks and from equipment used for carcass and meat processing along the production chain from farms to retail stores. Isolates were subjected to pulsed-field gel electrophoresis (PFGE) using SmaI and KpnI restriction enzymes and their antimicrobial susceptibilities were determined. C. jejuni was recovered from product and equipment used with both flocks at each point in the production chain. The prevalence of C. jejuni in poultry products at retail stores was 58.97% (flock 1) and 69.23% (flock 2). SmaI divided 122 C. jejuni strains from flock 1 and 106 from flock 2 into 17 and 13 PFGE types, respectively. PFGE types H and F were present at all steps along the chain, from farms to retail products. Similarly, for both flocks PFGE type D was detected in crates, slaughterhouse and retail stores. Moreover, the PFGE types were highly diverse at the processing and retail steps. Most PFGE types were resistant to ciprofloxacin (95.45%) and tetracycline (81.82%); and multidrug resistant PFGE types were found in the final products. Our study showed that there were several points of cross-contamination of product along the chain, and a high diversity of PFGE types with antimicrobial resistance to ciprofloxacin and tetracycline in the retail products.

Effectiveness of combined preservation methods to extend the shelf life of Morcilla de Burgos

Morcilla de Burgos is the most famous blood sausage in Spain. However, while producers are interested in extending its shelf life, the consumer is increasingly demanding more natural food. This situation has led to the current search for new and mild preservation technologies. Two batches of four different products: control without any treatment, control with organic acid salts (CnOAS; a 3% mixture of potassium/sodium l-lactate), control with high hydrostatic pressure processing (CnHPP; 600MPa-10min), and a combination of both treatments (OAS+HPP), were carried out to evaluate any synergistic effect that occurs when combining OAS and HPP, and the influence of different preservative treatments on the spoilage bacterial population and their evolution. HPP (with or without addition of OAS) can be considered the most suitable method for preserving morcilla de Burgos as it does not produce negative changes in sensory attributes. No clear selective effect of different treatments on the composition of the spoilage bacteria was seen and similar spoilage patterns were observed independently of the preservation treatment used.

Microbial, sensory and volatile changes during the anaerobic cold storage of morcilla de Burgos previously inoculated with Weissella viridescens and Leuconostoc mesenteroides.

Blood sausage, a widely consumed traditional product, would benefit from an increased commercial life. It is therefore pertinent to investigate the type, the evolution, and the behaviour of the Lactic Acid Bacteria responsible for their spoilage. This study aims to clarify the role played by Weissella viridescens and Leuconostoc mesenteroides, identified as their principal spoilage agents in vacuum-packaged morcilla de Burgos, through the study of microbiological, sensory, and volatile profile changes, following inoculation of the morcilla, both jointly and separately, with the two species. L. mesenteroides grew more rapidly and influenced the drop in pH, milky exudates and the sour smell, whereas W. viridescens influenced vacuum loss. With respect to volatile profiles, L. mesenteroides samples were richer in aldehydes (hexanal) and acids (acetic), on the contrary W. viridescens samples showed greater amounts of alcohols (ethanol) and ketones (acetoin and diacetyl). Both species inoculated together increased particular signs of morcilla spoilage.

Prevalence and quantification of Shiga-toxin producing Escherichia coli along the lamb food chain by quantitative PCR.

Shiga-toxin producing Escherichia coli (STEC), which is responsible for numerous food-borne disease outbreaks, is the most important human pathogen found in ruminants. In this study, conventional microbiology and quantitative PCR (qPCR) were used to detect and quantify STEC along the lamb food chain, from slaughterhouses to butcheries, in both meat and environmental samples. Microbial Assessment Scheme (MAS) was used to select Critical Sampling Locations (CSLs) in each establishment. The rpoB gene was used to enumerate total E. coli by qPCR, whereas the genes stx(1), stx(2) and eae were directly amplified for quantification of E. coli virulent populations. The results obtained show that E. coli carrying all three virulence genes were the most prevalent in slaughterhouses (69%), whereas E. coli with the eae gene alone were found more frequently in the processing plant (32%), and stx(1)- and stx(2)-positive E. coli were predominant in butcheries (9-10%). E. coli virulent populations were not common in butcheries. Samples determined to be positive for E. coli virulent populations after enrichment were quantified by qPCR and compared with conventional microbiology counts using validated methods. The results showed a higher number of positive CSLs for E. coli virulent populations, and higher counts were obtained when qPCR was used than when using conventional methods.