Marcela P. Castro

Lactic acid bacteria isolated from artisanal dry sausages: characterization of antibacterial compounds and study of the factors affecting bacteriocin production.

Lactic acid bacteria (LAB) were isolated from artisanal dry sausages sampled from north-eastern region of Chaco, Argentina. Among 141 isolates, 27 showed antimicrobial activity against Listeria innocua, Staphyloccus aureus or Brochothrix spp. One isolate, identified as Lb. curvatus/sakei, produced bacteriocin like substances (BLIS). These BLIS were heat stable, effective after refrigerated storage and freeze/thaw cycles and even active against pathogens when produced under refrigeration at 3% NaCl concentration. The influence of several factors on production of BLIS was assessed in MRS broth added with: EDTA, ascorbic acid, KCl, potassium sorbate, sodium citrate, 3 and 6% NaCl, Tween 20 or Brij 35. These additives showed different effects towards the effectiveness of the bacteriocin produced by Lb. sakei/curvatus against L. innocua and S. aureus. Conditions that provided high cell density favored high bacteriocin production. BLIS production by this LAB strain was greatly influenced by NaCl concentration and the presence of surfactants.

Sakacin Q produced by Lactobacillus curvatus ACU-1: Functionality characterization and antilisterial activity on cooked meat surface

This work was conducted to evaluate the antilisterial activity of sakacin Q produced by Lactobacillus curvatus ACU-1 on the surface of cooked pork meat. A genetic re-characterization of the producer strain and a study of the structural genes involved in bacteriocin production were carried out as complementary data. Studies indicated that the bacteriocin was not attached to the producer cells favoring pre-purifications steps. Bacteriocin effectiveness was not compromised by adsorption to meat and fat tissues. Several ways of dispensing the bacteriocin onto the meat surface, namely cell culture, cell free supernatant (CFS), a mixture of both and freeze-dried reconstituted CFS, were investigated. The use of the latter was the most effective one to control Listeria growth within studied systems. L. curvatus ACU-1 and its bacteriocin presented promising technological characteristics that made them suitable for meat biopreservation.

Use of Natural Preservatives in Seafood

Seafood products are known to be especially susceptible to both microbiological and biochemical spoilage pathways. Accordingly, efficient and hygienic preservation processes should be applied immediately after capture/slaughter to preserve product freshness and quality. The development of effective processing treatments to extend the shelf life of fresh fish products is a must.

Autochthonous starter culture selection to keep traditions in the manufacture of dry sausages alive

Lactic acid bacteria (LAB) and non-pathogenic staphylococci from naturally fermented sausages manufactured in northeastern Argentina were isolated and selected on the basis of physiological, technological, and safety properties. Eighty-seven isolates recovered from four small-scale facilities were studied to evaluate growth and acidification kinetics, nitrate-reductase, proteolytic, lipolytic, decarboxylase, and antagonistic activities, as well as growth ability at different temperatures, pH, and NaCl concentrations. Based on these characteristics as well as antibiotic resistance for CNC isolates, a selection and identification by sequencing the 16S rRNA gene was carried out. As a result, LAB isolates were identified as Lactobacillus sakei (seven isolates) and Lactobacillus farciminis (one isolate), while CNC revealed isolates as being Staphylococcus xylosus (two isolates), Staphylococcus vitulinus (one isolate), and Staphylococcus hominis (one isolate). Properties exhibited by selected isolates would make them eligible as starter cultures to enhance both sensorial and safety qualities of artisanal fermented sausages while keeping manufacturing traditions.

In vitro antimicrobial activity of 20 selected climber species from the Bignoniaceae family.

Hydroalcoholic and aqueous extracts of some climber species from the Bignoniaceae family that grow in the north of Argentina were evaluated for in vitro antibacterial activity against Gram-positive and Gram-negative strains. By means of bioautography and disc diffusion methods, it could be determined that all infusions were not active, whereas the hydroalcoholic extracts of seven species were able to inhibit bacterial growth. The minimum inhibitory concentration and minimum bactericidal concentration observed were between 62.5 and 1000 μg gallic acid equivalent (GAE)/mL and between 125 and 1000 μg GAE/mL, respectively. The tested extracts were more active against Gram-positive microorganisms. Time-kill experiments indicated that all extracts have bacteriostatic activity. Phytochemical screening showed the presence of terpenoids, phenols and flavonoids. The amount of phenolic compounds and flavonoids was higher in tinctures when compared with infusions. These results suggest the presence of antibacterial substances in the hydroalcoholic extracts, which could be used for the treatment of infections.

Interactions Between Additives: Its Effect on Sorbate Stability and Z. bailii Minimum Inhibitory Concentration in Model Aqueous Systems Resembling Salad Dressings

The effect on sorbate stability of several additives (EDTA, ascorbic and acetic acids) frequently present in the formulation of salad dressings, and the minimal inhibitory concentration (MIC) of sorbate concerning Z. bailii growth in the presence of that additives were studied in aqueous model systems of pH 3.5. The addition of EDTA, ascorbic acid and the use of acetic acid protected sorbic acid from destruction. In particular, the presence of 0.075 g/kg of EDTA was essential for minimizing sorbates destruction and keeping, after 90 days of storage at 33°C, its residual concentration above 0.400 g/kg. This value is the MIC for inhibiting the growth of Z. bailii when systems were packed in PET flasks and citric and acetic acids were used as acidulants. Packaging material, acidifying agent and EDTA level showed a strong influence on the effect of EDTA on sorbates stability. As an example, in the case of systems acidified only with citric acid and containing 0.075 g/kg or 0.500 g/kg of EDTA, it was necessary the use of glass flasks and the lowest concentration of EDTA to get a residual preservative concentration above the MIC after 90 days of storage at 33°C. Se estudió el efecto de varios aditivos (EDTA y ácidos ascórbico y acético) presentes frecuentemente en la formulación de aderezos para ensaladas en la estabilidad del ácido sórbico en sistemas modelo acuosos. También se determinó la mínima concentración inhibitoria de este conservante respecto al crecimiento de Z. bailii en presencia de dichos aditivos y a un pH de 3,5. La adición de EDTA, ácido ascórbico y el uso de ácido acético tuvieron un efecto protector en la destrucción del ácido sórbico. En particular, la presencia de 0.075 g/kg de EDTA resultó esencial para minimizar la destrucción del sorbato y mantener su concentración por encima de 0,400 g/kg, después de 90 días de almacenamiento a 33°C, ya que esa era la concentración mínima para inhibir el crecimiento de Z. bailii en sistemas envasados en frascos de PET y que contenían ácidos cítrico y acético como acidificantes. El material del envase y la concentración de EDTA ejercieron una fuerte influencia sobre la estabilidad de los sorbatos. Por ejemplo, en el caso de los sistemas acidificados sólo con ácido cítrico y con un 0,075 g/kg or 0,500 g/kg de EDTA, fue necesario el uso de frascos de vidrio y de la menor concentración del complejante para tener una concentración residual de ácido sórbico que fuese superior a la MIC después de 90 días a 33°C.

Evaluation of an autochthonous starter culture on the production of a traditional dry fermented sausage from Chaco (Argentina) at a small-scale facility.

The performance of a mixed starter culture, SAS-1, comprised of the autochthonous strains Lactobacillus sakei ACU-2 and Staphylococcus vitulinus ACU-10, was evaluated into the production process of a traditional dry sausage. Microbiological, physicochemical and sensory analyses were carried out to accomplish this goal. Results showed an improvement in performance through the introduction of SAS-1; adding mixed starter culture rapidly decreased pH, inhibited the growth of contaminant microorganisms and enhanced the beneficial ones, diminished TBARS, and highlighted color and aroma attributes. However, most influential organoleptic descriptors among consumer acceptance were not affected by the addition of the starter. This starter culture would represent a valuable tool to improve the homogeneity of artisanal manufacture of this traditional food.

Indigenous Starter Cultures to Improve Quality of Artisanal Dry Fermented Sausages from Chaco (Argentina)

Lactic acid bacteria (LAB) and coagulase negative cocci (CNC) were isolated from artisanal dry sausages sampled from the northeastern region of Chaco, Argentina. In order to evaluate their performance in situ and considering technological features of the isolated strains, two mixed selected autochthonous starter cultures (SAS) were designed: (i) SAS-1 (Lactobacillus sakei 487 + Staphylococcus vitulinus C2) and (ii) SAS-2 (L. sakei 442 + S. xylosus C8). Cultures were introduced into dry sausage manufacturing process at a local small-scale facility. Microbiological and physicochemical parameters were monitored throughout fermentation and ripening periods, while sensory attributes of the final products were evaluated by a trained panel. Lactic acid bacteria revealed their ability to colonize and adapt properly to the meat matrix, inhibiting the growth of spontaneous microflora and enhancing safety and hygienic profile of the products. Both SAS showed a beneficial effect on lipid oxidation and texture of the final products. Staphylococcus vitulinus C2, from SAS-1, promoted a better redness of the final product. Sensory profile revealed that SAS addition preserved typical sensory attributes. Introduction of these cultures could provide an additional tool to standardize manufacturing processes aiming to enhance safety and quality while keeping typical sensory attributes of regional dry fermented sausages.