Ana M. Diez

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.

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.

Characterization by culture-dependent and culture-independent methods of the bacterial population of suckling-lamb packaged in different atmospheres.

This study offers insight into the dynamics of bacterial populations in fresh cuts of suckling lamb under four different atmospheric conditions: air (A), and three Modified Atmosphere Packaging (MAP) environments, 15%O2/30%CO2/55%N2 (C, commercial), 70%O2/30%CO2 (O), and 15%O2/85%CO2 (H) for 18 days. Microbial analyses by both conventional methods and PCR-DGGE were performed. Controversial and surprising results emerged from comparing both methods in relation to the genus Pseudomonas. Thus, conventional methods detected the presence of high numbers of Pseudomonas colonies, although PCR-DGGE only detected this genus in air-packaged samples. PCR-DGGE detected higher microbial diversity in the control samples (A) than in the modified atmospheres (C, O, H), having atmosphere H the fewest number of species. Brochothrix thermosphacta, LAB (Carnobacterium divergens and Lactobacillus sakei), and Escherichia spp. were detected in all the atmospheres throughout storage. Moreover, previously undescribed bacteria from lamb meat such as Enterobacter hormaechei, Staphylococcus equorum and Jeotgalicoccus spp. were also isolated in this study by DGGE. Additionally, qPCR analysis was used to detect and characterize strains of Escherichia coli. Virulence genes (stx1, stx2 and eae) were detected throughout storage in 97% of the samples. A high CO2 atmosphere was the most effective packaging combination doubling storage time in comparison with commercial atmosphere.

Effect of edible chitosan/clove oil films and high‐pressure processing on the microbiological shelf life of trout fillets

BACKGROUND The inhibitory effect of chitosan films with clove oil (0-50 g kg(-1) ) was evaluated on a range of ten representative food spoilage and pathogenic bacteria. RESULTS The most sensitive bacteria to the films was Shewanella putrefaciens and the most resistant was Aeromonas hydrophila (inhibition was apparent only at 50 g kg(-1) clove essential oil (CEO)). Films with 20 g kg(-1) CEO inhibited nine of ten of the bacteria tested. Chitosan films with 20 g kg(-1) CEO were combined with high-pressure (HPP) processing as treatments for trout fillets, and changes in physicochemical parameters and microbial load were evaluated at 4 °C over 22 days of storage. The films reduced weight loss and water activity compared to fresh and treated samples (HPP and cooking). Results showed that microbial load (total aerobic mesophilic, lactic acid bacteria and total coliform) of the trout fillets covered with chitosan films was lower than that for HPP-treated samples, and similar to cooked samples, except for coliform counts. CONCLUSION The use of 20 g kg(-1) CEO-chitosan films showed a further improvement in the shelf-life of trout fillets when compared to that obtained with HPP and cooking treatment.

The influence of different preservation methods on spoilage bacteria populations inoculated in morcilla de Burgos during anaerobic cold storage

Blood sausage is a widely consumed traditional product that would benefit from an extended shelf life. The two main spoilage bacteria in vacuum-packaged morcilla de Burgos are Weissella viridescens and Leuconostoc mesenteroides. This study examines the way in which three preservation treatments--organic acid salts (OAS), high-pressure processing (HPP) and pasteurization--influence these bacterial populations and their spoilage behaviour. HPP and pasteurization treatments were found to inhibit growth of the inoculated species and delay sensory spoilage of the product. In both treatments, L. mesenteroides was observed to have a longer recovery time; even so, once its growth started, it grew faster than W. viridescens. This longer recovery time might be due to metabolic modification following treatment, which would affect the production of metabolites such as acetic acid and some aldehydes. W. viridescens was the first strain to recover from the two treatments. It preserved its spoilage behaviour and even increased the production of certain compounds such as acetoin or ethanol. The extended product shelf life following HPP and pasteurization treatments might be due to a combination of various factors such as the fall in both microbial populations, as well as the delay in spoilage caused by damage to L. mesenteroides cells, as this strain is the fastest-acting, most intensive spoilage microorganism. It was observed that the addition of organic salts neither diminished nor delayed the growth of the two inoculated species. Nevertheless, the results also indicate that this treatment inhibits the metabolic activity of L. mesenteroides, resulting once again in an extended product shelf life.

Control of Escherichia coli and Listeria monocytogenes in suckling-lamb meat evaluated using microbial challenge tests

Escherichia coli and Listeria monocytogenes microbial challenge tests were performed on fresh suckling-lamb meat. Hind leg slices were chilly stored under two modified atmosphere packaging (MAP) environments (A: 15%O2/60%CO2/25%N2, B: 15%O2/30%CO2/55%N2) and vacuum packaging (V). Only E. coli was reduced between 0.72-1.25 log cfu/g from day 1 to day 4 by the combined use of MAP/V, chilling storage and the growth of native lactic acid bacteria. However, L. monocytogenes was not inhibited by the application of V or MAP. Even do, in inoculated samples, this pathogen increased between 1.2-2.7 log cfu/g throughout the study. Consequently, a second experiment that combined the effects of MAP/V and a protective culture (Leuconostoc pseudomesenteroides PCK 18) against L. monocytogenes was designed. Two different levels of protective cultures were assayed (4 and 6 log cfu/g). Lc. pseudomesenteroides PCK 18 was able to control the growth of L. monocytogenes when the differences between them are higher than 2 log cfu/g. Moreover, when high level of protective culture was used a significant reduction of L. monocytogenes counts were noticed in samples packaged in 60% of CO2 along the storage period, although sensory properties were also affected.

Effect of raspberry pomace extracts isolated by high pressure extraction on the quality and shelf‐life of beef burgers

Summary Raspberry pomace extracts isolated with supercritical carbon dioxide (SCE) and pressurised ethanol/water (ETE) were tested in beef burgers. Only ETE additives effectively inhibited lipid oxidation and the growth of microorganisms, as it was observed by measuring the changes of thiobarbituric acid reactive substances, bacterial counts and the content of O2 and CO2 during storage in the modified atmosphere package. ETE additives also demonstrated some meat colour preservation effects, which were assessed by the intensity of hamburger colour and metmyoglobin concentration. However, ETE additives did not alter burgers taste at the applied concentrations (up to 1%). It may be concluded that the most effective extracts possessing strong antioxidant and antimicrobial activity may be isolated from raspberry pomace by the pressurised liquid extraction with a hydroethanolic solvent; such extracts may be considered as promising additives in meat products for improving their stability and enriching with beneficial to health phytochemicals.