Oscar Alfredo Garro

Modeling lactic acid bacteria growth in vacuum-packaged cooked meat emulsions stored at three temperatures

Abstract The effect of three storage temperatures on the growth of lactic acid bacteria (LAB) in cooked meat emulsions packaged in low oxygen permeability film was investigated. Bacterial counts at 0°C, 8°C and 15°C were fitted to the Gompertz equation and the maximum specific growth rate ( μ ) was obtained as derived parameter, this value being maximal at 15°C (1.16 days −1 ). Arrhenius and root square models were used to describe the effect of different storage temperatures on maximum specific growth rate. The models were statistically validated and the mean square error (MSE), coefficient of determination ( R 2 ), bias factor and accuracy factor were used to evaluate and compare the performance of predictive models. The effect of temperature was better interpreted by root square model than by Arrhenius type model, showing the least deviations from the observed value, which would lead to “fail-safe” prediction of shelf-life. Since the final number of LAB did not show significant changes with storage temperature after 25 days, a temperature abuse during storage will not result in an increase of spoilage by LAB.

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.

Isolation of a yeast strain able to produce a polygalacturonase with maceration activity of cassava roots

The objective of the present study was the isolation of a yeast strain, from citrus fruit peels, able to produce a polygalacturonase by submerged fermentation with maceration activity of raw cassava roots. Among 160 yeast strains isolated from citrus peels, one strain exhibited the strongest pectinolytic activity. This yeast was identified as Wickerhamomyces anomalus by 5.8S-ITS RFLP analysis and confirmed by amplification of the nucleotide sequence. The yeast produced a polygalacturonase (PG) in Erlenmeyer shake flasks containing YNB, glucose, and citrus pectin. PG synthesis occurred during exponential growth phase, reaching 51 UE.mL-1 after 8 hours of fermentation. A growth yield (Yx/s) of 0.43 gram of cell dry weight per gram of glucose consumed was obtained, and a maximal specific growth rate (µm) of 0.346 h-1 was calculated. The microorganism was unable to assimilate sucrose, galacturonic acid, polygalacturonic acid, or citrus pectin, but it required glucose as carbon and energy source and polygalacturonic acid or citrus pectin as inducers of enzyme synthesis. The crude enzymatic extract of Wickerhamomyces anomalus showed macerating activity of raw cassava. This property is very important in the production of dehydrated mashed cassava, a product of regional interest in the province of Misiones, Argentina.

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.

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.

Selección de un Modelo Primario para Describir la Curva de Crecimiento de Bacterias Lácticas y Brochothrix thermosphacta sobre Emulsiones Cárnicas Cocidas

Resumen Se han comparado tres modelos primarios para describir la curva de crecimiento de bacterias lacticas y Brochothrix thermosphacta sobre emulsiones carnicas cocidas y para estimar los parametros cineticos de crecimiento: tiempo de latencia (λ), maxima velocidad especifica de crecimiento ( µ max ) y maxima densidad bacteriana ( y ma x ). Se usaron los modelos Logistico, Gompertz y Baranyi y se comparo la bondad de ajuste de los modelos, la incertidumbre y precision de las estimaciones. Los modelos de Gompertz y Baranyi produjeron los mejores ajustes en la mayoria de los casos presentados. No se detectaron diferencias apreciables entre los modelos en relacion a la incertidumbre y precision de las estimaciones de y ma x y µ max . Sin embargo, las estimaciones de λ dadas por el modelo de Baranyi fueron menos exactas y los resultados muestran que el modelo de Gompertz mostro un mejor comportamiento. Palabras claves: curva de crecimiento, bacterias lacticas, Brochothrix thermosphacta, modelado,

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.