Characterization and purification of a new bacteriocin with a broad inhibitory spectrum produced by Lactobacillus plantarum lp 31 strain isolated from dry-fermented sausage.

AIMS: Characterization and purification of a new bacteriocin produced by Lactobacillus plantarum LP 31 strain, isolated from Argentinian dry-fermented sausage. METHODS AND RESULTS: Lactobacillus plantarum LP 31 strain produces an antimicrobial compound that inhibits the growth of food-borne pathogenic bacteria. It was inactivated by proteolytic enzymes, was stable to heat and catalase and exhibited maximum activity in the pH range from 5.0 to 6.0. Consequently, it was characterized as a bacteriocin. It was purified by RP (reverse-phase) solid-phase extraction, gel filtration chromatography and RP-HPLC. Plantaricin produced by Lact. plantarum LP 31 is a peptide with a molecular weight of 1558.85 Da as determined by Maldi-Tof mass spectrometry and contains 14 amino acid residues. It was shown to have a bactericidal effect against Pseudomonas sp., Staphylococcus aureus, Bacillus cereus and Listeria monocytogenes. CONCLUSIONS: The bacteriocin produced by Lact. plantarum LP 31 may be considered as a new plantaricin according to its low molecular weight and particular amino acid composition. SIGNIFICANCE AND IMPACT OF THE STUDY: In view of the interesting inhibitory spectrum of this bacteriocin and because of its good technological properties (resistance to heat and activity at acidic pH), this bacteriocin has potential applications as a biopreservative to prevent the growth of food-borne pathogens and food spoilage bacteria in certain food products.

Antibacterial activity of enterococci strains against Vibrio cholerae.

Thirty-seven strains of enterococci isolated from milk and milk products from Santa Fe (Argentina) region were tested for antagonistic activity against Vibrio cholerae 01 and non-01. Seven of 17 strains of Enterococcus faecalis, five of 10 strains of Enterococcus faecium and four of 10 strains of Enterococcus durans produced inhibition zones against the indicator species. The activity of the antibacterial compounds was completely destroyed by treatment with trypsin and pronase E in most cases (only the supernatant fluids of a few strains remained weakly active after the treatment), but was resistant to heat treatment at 100 degrees C during 10 and 30 min. When the 10-fold concentrated supernatant fluids were added to a fresh culture of sensitive cells it produced a rapid inactivation. According to these preliminary tests, different strains of enterococci produced compounds with slightly different antivibrio properties, and these compounds were heat-resistant and had a predominantly proteinaceous nature.

Bacterias del género Bacillus en canales y hamburguesas de pollo / Bacteria of genus Bacillus in chicken carcasses and hamburguers

Se estudió la incidencia de bacterias aerobias mesófilas y de bacterias aerobias esporuladas en canales y hamburguesas de pollo, identificando las especies de bacterias esporuladas aisladas. Se procesaron 47 canales evisceradas procedentes de una planta procesadora de la provincia de Entre Ríos, y 50 muestras de hamburguesas provenientes de dos establecimientos elaboradores y expendedores de la ciudad de Santa Fe. Todas las canales resultaron contaminadas con bacterias aerobias mesófilas en un rango comprendido entre 6 . 1.000 y 1,2 . 1.000.000 UFC/ml de líquido de lavado, y el 94 por ciento de ellas también con bacterias esporuladas, en niveles inferiores a 100 UFC/ml. Las hamburguesas de ambos establecimientos elaboradores mostraron contaminación, en el 100 por ciento de los casos, con bacterias aerobias mesófilas, en el orden de 1 . 100.000 - 3,3 . 1.000.000 UFC/g para el establecimiento A, y de 2,2 . 100.000 - 1,7 . 10.000.000 UFC/g para el establecimiento B; la incidencia de bacterias esporuladas estuvo comprendida entre 4,3 . 100 y 1,2 . 10.000 UFC/g para el establecimiento A, y entre 6,2 . 100 y 3,8 . 10.000 UFC/g para el B. De las canales se aislaron y purificaron 214 cepas del género Bacillus, y 595 de las hamburguesas. Las especies de mayor incidencia fueron: B. subtilis y B. megaterium, para canales; B. licheniformis, B. subtilis y B. pumilis para hamburguesas del establecimiento A; y B. subtilis y B. pumilis para las del establecimiento B. En todos los tipos de muestras se detectó también, aunque en bajos niveles, la presencia de B. cereus. La importante contaminación con bacterias esporuladas de las hamburguesas provendría fundamentalmente de sus ingredientes no cárnicos y de la falta de higiene de los establecimientos, siendo potencialmente peligrosa por tratarse de agentes causantes de enfermedades transmitidas por alimentos

Bacterias del género Bacillus en canales y hamburguesas de pollo / Bacteria of genus Bacillus in chicken carcasses and hamburguers

Se estudió la incidencia de bacterias aerobias mesófilas y de bacterias aerobias esporuladas en canales y hamburguesas de pollo, identificando las especies de bacterias esporuladas aisladas. Se procesaron 47 canales evisceradas procedentes de una planta procesadora de la provincia de Entre Ríos, y 50 muestras de hamburguesas provenientes de dos establecimientos elaboradores y expendedores de la ciudad de Santa Fe. Todas las canales resultaron contaminadas con bacterias aerobias mesófilas en un rango comprendido entre 6 . 1.000 y 1,2 . 1.000.000 UFC/ml de líquido de lavado, y el 94 por ciento de ellas también con bacterias esporuladas, en niveles inferiores a 100 UFC/ml. Las hamburguesas de ambos establecimientos elaboradores mostraron contaminación, en el 100 por ciento de los casos, con bacterias aerobias mesófilas, en el orden de 1 . 100.000 - 3,3 . 1.000.000 UFC/g para el establecimiento A, y de 2,2 . 100.000 - 1,7 . 10.000.000 UFC/g para el establecimiento B; la incidencia de bacterias esporuladas estuvo comprendida entre 4,3 . 100 y 1,2 . 10.000 UFC/g para el establecimiento A, y entre 6,2 . 100 y 3,8 . 10.000 UFC/g para el B. De las canales se aislaron y purificaron 214 cepas del género Bacillus, y 595 de las hamburguesas. Las especies de mayor incidencia fueron: B. subtilis y B. megaterium, para canales; B. licheniformis, B. subtilis y B. pumilis para hamburguesas del establecimiento A; y B. subtilis y B. pumilis para las del establecimiento B. En todos los tipos de muestras se detectó también, aunque en bajos niveles, la presencia de B. cereus. La importante contaminación con bacterias esporuladas de las hamburguesas provendría fundamentalmente de sus ingredientes no cárnicos y de la falta de higiene de los establecimientos, siendo potencialmente peligrosa por tratarse de agentes causantes de enfermedades transmitidas por alimentos (AU)

[Bacteria of the genus Bacillus in chicken carcasses and hamburgers]. / Bacterias del género Bacillus en canales y hamburguesas de pollo.

The incidence of mesophilic aerobic sporulate bacteria in chicken carcasses and hamburgers was studied and the species of isolated sporulate bacteria were identified. Forty seven eviscerated carcasses from a processing plant of Entre Ríos province (Argentina) were analyzed together with fifty samples of hamburgers from two supermarkets of Santa Fe city. All carcasses resulted in contamination with aerobic mesophilic bacteria in the range from 6 x 10(3) to 1.2 x 10(6) CFU/ml liquid washed, and 94% them with sporulate bacteria, the threshold being under 100 CFU/ml (Figure 1). Hamburgers from both places resulted with aerobic mesophilic bacteria in 100% of the cases, in the range of 1 x 10(5)-3.3 x 10(6) CFU/g for supermarket A and 2.2 x 10(5) to 1.7 x 10(7) CFU/g for supermarket B; the incidence of sporulate bacteria was between 4.3 x 10(2) and 1.2 x 10(4) CFU/g for A, while the range for B was 6.2 x 10(2) and 3.8 x 10(4) CFU/g (Figure 2). Two hundred and fourteen Bacillus Genus strains were isolated and purified from the carcasses and five hundred and ninety five from hamburgers. B. subtilis and B. megaterium were most involved in carcasses; while B. licheniformis, B. subtilis and B. pumilus were in hamburgers from supermarket A and B. subtilis and B. pumilus were found in supermarket B (Table 1). The presence of B. cereus was also found, although in low levels, in all the samples (Table 1). Pollution levels with aerobic mesophilic bacteria are high in both kinds of samples.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacterias del género Bacillus en canales y hamburguesas de pollo. / [Bacteria of the genus Bacillus in chicken carcasses and hamburgers]

The incidence of mesophilic aerobic sporulate bacteria in chicken carcasses and hamburgers was studied and the species of isolated sporulate bacteria were identified. Forty seven eviscerated carcasses from a processing plant of Entre Ríos province (Argentina) were analyzed together with fifty samples of hamburgers from two supermarkets of Santa Fe city. All carcasses resulted in contamination with aerobic mesophilic bacteria in the range from 6 x 10(3) to 1.2 x 10(6) CFU/ml liquid washed, and 94

them with sporulate bacteria, the threshold being under 100 CFU/ml (Figure 1). Hamburgers from both places resulted with aerobic mesophilic bacteria in 100

of the cases, in the range of 1 x 10(5)-3.3 x 10(6) CFU/g for supermarket A and 2.2 x 10(5) to 1.7 x 10(7) CFU/g for supermarket B; the incidence of sporulate bacteria was between 4.3 x 10(2) and 1.2 x 10(4) CFU/g for A, while the range for B was 6.2 x 10(2) and 3.8 x 10(4) CFU/g (Figure 2). Two hundred and fourteen Bacillus Genus strains were isolated and purified from the carcasses and five hundred and ninety five from hamburgers. B. subtilis and B. megaterium were most involved in carcasses; while B. licheniformis, B. subtilis and B. pumilus were in hamburgers from supermarket A and B. subtilis and B. pumilus were found in supermarket B (Table 1). The presence of B. cereus was also found, although in low levels, in all the samples (Table 1). Pollution levels with aerobic mesophilic bacteria are high in both kinds of samples.(ABSTRACT TRUNCATED AT 250 WORDS)

[Production of non-volatile amines by strains of enterococci]. / Producción de aminas no volátiles por cepas de enterococos.

During the last few years there has been great interest concerning the problems related with the presence of pressor amines in different kinds of cheese, specially since the "cheese syndrome" was made evident. Since the capacity of the bacterial groups involved in cheese manufacture to produce these amines has not yet been clarified, it was decided to study the production capacity of tyramine, tryptamine and histamine of enterococci strains probably used in the starter cultures. Forty-one enterococci strains were analysed cultivating them in milk and in milk with the addition of the corresponding aminoacids. It was determined that only low percentages of Streptococcus faecalis subsp. liquefaciens and Streptococcus durans strains (34% and 11% respectively) produced traces of tyramine and tryptamine in milk. But when cultivated in the presence of the corresponding aminoacids, a large percentage of strains of all the species produced tyramine in high concentrations and different percentages of them produced tryptamine in concentrations no higher than 200 ppm. All strains analysed proved to be unable to produce histamine. It can be concluded that there exists a strong probability for enterococci to produce tyramine and tryptamine in different concentrations specially when developed in the presence of the corresponding aminoacids.

Producción de aminas no volátiles por cepas de enterococos. / [Production of non-volatile amines by strains of enterococci]

During the last few years there has been great interest concerning the problems related with the presence of pressor amines in different kinds of cheese, specially since the [quot ]cheese syndrome[quot ] was made evident. Since the capacity of the bacterial groups involved in cheese manufacture to produce these amines has not yet been clarified, it was decided to study the production capacity of tyramine, tryptamine and histamine of enterococci strains probably used in the starter cultures. Forty-one enterococci strains were analysed cultivating them in milk and in milk with the addition of the corresponding aminoacids. It was determined that only low percentages of Streptococcus faecalis subsp. liquefaciens and Streptococcus durans strains (34

and 11

respectively) produced traces of tyramine and tryptamine in milk. But when cultivated in the presence of the corresponding aminoacids, a large percentage of strains of all the species produced tyramine in high concentrations and different percentages of them produced tryptamine in concentrations no higher than 200 ppm. All strains analysed proved to be unable to produce histamine. It can be concluded that there exists a strong probability for enterococci to produce tyramine and tryptamine in different concentrations specially when developed in the presence of the corresponding aminoacids.

Incidencia de Bacillus cereus en alimentos deshidratados en polvo / Incidence of Bacillus cereus on dehydrated powdered foods

Se estudió la incidencia de Bacillus cereus (y su relación con el número de bacterias aerobias totales) en alimentos deshidratados en polvo, puestos a la venta en supermercados de la ciudad de Santa Fe. Se examinaron 250 muestras pertenecientes a 5 clases diferentes de alimentos: postres, mousses, sopas, polentas precocidas y purés de papas. Se analizó la actividad toxicogénica de las cepas confirmadas como Bacillus cereus, mediante el test de letalidad en ratón. Se comprobó que, para cada tipo de alimento, la relación entre el número de muestras positivas y el número de muestras analizadas, resultó siempre igual o superior al 6%. Además, ninguno de los alimentos analizados superó el límite máximo de aceptabilidad (10**5 UFC de B. cereus/g), propuesto por el I.C.M.S.F. Se constató en todos los casos, que no existe correlación lineal simple entre los recuentos de B. cereus y de bacterias aerobias totales. Por otra parte, se verificó que el porcentaje de cepas letales para el ratón supera en cada alimento el 42,8%. Se concluye que, si bien no se detectaron niveles de contamianción riesgosos, sería conveniente continuar el estudio referido a la evaluación de la capacidad toxicogénica de las cepas, para conocer su real implicancia epidemiológica

Incidencia de Bacillus cereus en alimentos deshidratados en polvo / Incidence of Bacillus cereus on dehydrated powdered foods

Se estudió la incidencia de Bacillus cereus (y su relación con el número de bacterias aerobias totales) en alimentos deshidratados en polvo, puestos a la venta en supermercados de la ciudad de Santa Fe. Se examinaron 250 muestras pertenecientes a 5 clases diferentes de alimentos: postres, mousses, sopas, polentas precocidas y purés de papas. Se analizó la actividad toxicogénica de las cepas confirmadas como Bacillus cereus, mediante el test de letalidad en ratón. Se comprobó que, para cada tipo de alimento, la relación entre el número de muestras positivas y el número de muestras analizadas, resultó siempre igual o superior al 6%. Además, ninguno de los alimentos analizados superó el límite máximo de aceptabilidad (10**5 UFC de B. cereus/g), propuesto por el I.C.M.S.F. Se constató en todos los casos, que no existe correlación lineal simple entre los recuentos de B. cereus y de bacterias aerobias totales. Por otra parte, se verificó que el porcentaje de cepas letales para el ratón supera en cada alimento el 42,8%. Se concluye que, si bien no se detectaron niveles de contamianción riesgosos, sería conveniente continuar el estudio referido a la evaluación de la capacidad toxicogénica de las cepas, para conocer su real implicancia epidemiológica (AU)

[Incidence of Bacillus cereus in powdered dehydrated food]. / Incidencia de Bacillus cereus en alimentos deshidratados en polvo.

Bacillus cereus incidence on dehydrated powdered foods on sale in supermarkets of Santa Fe city was studied. Two hundred and fifty samples of five different foods: desserts, soups, mousses, pre-cooked "polenta" and mashed potatoes, were examined. Toxinogenic activity of strains confirmed as B. cereus by means of the test of lethality in rats, was analyzed. The ratio between contaminated samples and total analyzed samples was always greater than 6% (Table 1). Besides, none of the analyzed foods exceeded acceptability maximum limit (10(5) UFC/g), established by I.C.M.S.F. (Table 2). It was checked in all cases that no simple lineal correlation existed between B. cereus and total aerobic bacteria enumerations. On the other hand, the percentage of strains with lethal effects was in all cases greater than 42.8% (Table 3).

Incidencia de Bacillus cereus en alimentos deshidratados en polvo. / [Incidence of Bacillus cereus in powdered dehydrated food]

Bacillus cereus incidence on dehydrated powdered foods on sale in supermarkets of Santa Fe city was studied. Two hundred and fifty samples of five different foods: desserts, soups, mousses, pre-cooked [quot ]polenta[quot ] and mashed potatoes, were examined. Toxinogenic activity of strains confirmed as B. cereus by means of the test of lethality in rats, was analyzed. The ratio between contaminated samples and total analyzed samples was always greater than 6

(Table 1). Besides, none of the analyzed foods exceeded acceptability maximum limit (10(5) UFC/g), established by I.C.M.S.F. (Table 2). It was checked in all cases that no simple lineal correlation existed between B. cereus and total aerobic bacteria enumerations. On the other hand, the percentage of strains with lethal effects was in all cases greater than 42.8

(Table 3).

[Methods of preserving strains of enterococci and evaluation of the technological properties as a function of storage time]. / Métodos de conservación de cepas de enterococos y evaluación de las propiedades tecnológicas en función del tiempo de almacenamiento.

The preservation possibilities of eight enterococci strains were studied following different techniques. The strains were selected considering their technological properties, specially their diacetyl and acetaldehyde producing capacities which favour their use in the cheese industry. The conservation methods tried out were: modified Sordelli, adsorption on anhydrous silica gel, periodical transfers and preservation in distilled water, salt solution and phosphate buffer solutions. The conservation capacity was evaluated during six months; the bacteria were reactivated monthly and viability, acid power and diacetyl and acetaldehyde production capacity were tested. The microorganisms preserved either by periodical transfers, or in distilled water, salt solution and phosphate buffer solutions, lost their viability and suffered deep changes into their technological properties before thirty days. On the other hand, those bacteria preserved following the modified Sordelli's method and by adsorption on anhydrous silica gel kept ther viability (Table 1), acid power (Table 2) and flavor compounds production capacity (Tables 3 and 4) until six months later. These results show that modified Sordelli's method and the anhydrous silica gel are equally efficient to preserve the enterococci properties being simplicity and lower cost of the latter an additional advantage.

[Trials of cheese-making using concentrated bacterial starters]. / Ensayos de elaboración de quesos con fermentos bacterianos concentrados.

Studies about cheese preparation with frozen and concentrated bacterial starters have been carried out. The Pategras cheeses were obtained from raw milk. The starters were prepared with a selected strain of Streptococcus lactis, concentrated until reaching a value of 3.10(9) colony forming units/ml and resuspended in milk previously supplemented with 8% of yeast extract. These concentrates were frozen at -40 degrees C and kept at -20 degrees C for 60 days. Three kinds of starters were tested: one thawed by placing the flask in a 40 degrees C water bath, another added to the cheese vat without previous thawing and a control sample prepared in steamed reconstituted milk. In order to evaluate the convenience of each technique several chemical and microbiological analysis were performed during the preparation (Table 1 and 2) and the ripening of the cheese (Table 3). The results have showed that the direct use of thawed frozen concentrates in the cheese vat allows the obtaining of high quality cheese. On the other hand, the technique based on thawing through a water bath did not lead to good results.

Ensayos de elaboración de quesos con fermentos bacterianos concentrados / Assays of cheese preparation with concentrated bacterial starters

En el presente trabajo se llevaron a cabo estudios de elaboración de quesos con fermentos bacterianos concentrados y congelados. Los citados quesos, de pasta semicocida, se obtuvieron a partir de leche pasteurizada. Los fermentos se preparaon con una cepa seleccionada de Streptococcus lactis, concentrada hasta alcanzar un valor de 3.10**9 U.F.C./ml y resuspendida en lecha adicionada con el 8% de extracto de levadura. Dichos concentrados se congelaron a -40- y se almacenaron a -20-C durante 60 días. Se ensayaron tres varianes de fermento: uno descongelado en baño María a -40-C, otro agregado a la tina quesera sin previo descongelamiento y un testigo preparado en leche reconstituída estéril. Con el objeto de evaluar la conveniencia del empleo de dichas variantes, se realizaron análisis químicos y microbiológicos durante el proceso de elaboración y maduración de los quesos. Los resultados obtenidos han demostrado que el empleo de concentrados congelados descongelados directamente en la tina, permite obtener quesos de muy buena calidad. No sucedió lo mismo con los descongelados en baño María, lo que torna desaconsejable esta tecnología

Metodos de conservacion de cepas de enterococos y evaluacion de las propiedades tecnologicas en funcion del tiempo de almacenamiento / Enterococci strains conservation methods and technological properties evaluation in relation to the storage time

Se estudiaron las posibilidades de conservar ocho cepas de enterococos por metodos de Sordelli modificado, adsorcion en silica gel anhidra, repiques periodicos y conservacion en aguda destilada, solucion salina y soluciones reguladoras de fosfatos.La capacidad de conservacion de evaluo hasta los seis meses, reactivando las bacterias cada mes y realizando pruebas de viabilidad, poder acidificante y capacidad de produccion de diacetilo y acetaldehido.Se comprobo una disminucion de la viabilidad de los microorganismos conservados por repiques periodicos y en agua destilada, solucion salina y soluciones reguladoras de fosfatos, a la vez que se observaron profundos cambios en sus propiedades tecnologicas antes de los treinta dias. En cambios las bacterias conservadas segun el metodo de Sordelli modificado y por adsorcion en silica gel anhidra mantuvieron su viabilidad, poder acidificante y capacidad de produccion de componentes de aroma al cabo de seis meses. Se aconseja adoptar uno de los ultimos metodos citados siendo preferible la adsorcion en silica gel anhidra por su mayor simplicidad y menor costo

Métodos de conservación de cepas de enterococos y evaluación de las propiedades tecnológicas en función del tiempo de almacenamiento. / [Methods of preserving strains of enterococci and evaluation of the technological properties as a function of storage time]

The preservation possibilities of eight enterococci strains were studied following different techniques. The strains were selected considering their technological properties, specially their diacetyl and acetaldehyde producing capacities which favour their use in the cheese industry. The conservation methods tried out were: modified Sordelli, adsorption on anhydrous silica gel, periodical transfers and preservation in distilled water, salt solution and phosphate buffer solutions. The conservation capacity was evaluated during six months; the bacteria were reactivated monthly and viability, acid power and diacetyl and acetaldehyde production capacity were tested. The microorganisms preserved either by periodical transfers, or in distilled water, salt solution and phosphate buffer solutions, lost their viability and suffered deep changes into their technological properties before thirty days. On the other hand, those bacteria preserved following the modified Sordellis method and by adsorption on anhydrous silica gel kept ther viability (Table 1), acid power (Table 2) and flavor compounds production capacity (Tables 3 and 4) until six months later. These results show that modified Sordellis method and the anhydrous silica gel are equally efficient to preserve the enterococci properties being simplicity and lower cost of the latter an additional advantage.

Ensayos de elaboración de quesos con fermentos bacterianos concentrados. / [Trials of cheese-making using concentrated bacterial starters]

Studies about cheese preparation with frozen and concentrated bacterial starters have been carried out. The Pategras cheeses were obtained from raw milk. The starters were prepared with a selected strain of Streptococcus lactis, concentrated until reaching a value of 3.10(9) colony forming units/ml and resuspended in milk previously supplemented with 8

of yeast extract. These concentrates were frozen at -40 degrees C and kept at -20 degrees C for 60 days. Three kinds of starters were tested: one thawed by placing the flask in a 40 degrees C water bath, another added to the cheese vat without previous thawing and a control sample prepared in steamed reconstituted milk. In order to evaluate the convenience of each technique several chemical and microbiological analysis were performed during the preparation (Table 1 and 2) and the ripening of the cheese (Table 3). The results have showed that the direct use of thawed frozen concentrates in the cheese vat allows the obtaining of high quality cheese. On the other hand, the technique based on thawing through a water bath did not lead to good results.

Metodos de conservacion de cepas de enterococos y evaluacion de las propiedades tecnologicas en funcion del tiempo de almacenamiento / Enterococci strains conservation methods and technological properties evaluation in relation to the storage time

Se estudiaron las posibilidades de conservar ocho cepas de enterococos por metodos de Sordelli modificado, adsorcion en silica gel anhidra, repiques periodicos y conservacion en aguda destilada, solucion salina y soluciones reguladoras de fosfatos.La capacidad de conservacion de evaluo hasta los seis meses, reactivando las bacterias cada mes y realizando pruebas de viabilidad, poder acidificante y capacidad de produccion de diacetilo y acetaldehido.Se comprobo una disminucion de la viabilidad de los microorganismos conservados por repiques periodicos y en agua destilada, solucion salina y soluciones reguladoras de fosfatos, a la vez que se observaron profundos cambios en sus propiedades tecnologicas antes de los treinta dias. En cambios las bacterias conservadas segun el metodo de Sordelli modificado y por adsorcion en silica gel anhidra mantuvieron su viabilidad, poder acidificante y capacidad de produccion de componentes de aroma al cabo de seis meses. Se aconseja adoptar uno de los ultimos metodos citados siendo preferible la adsorcion en silica gel anhidra por su mayor simplicidad y menor costo

Ensayos de elaboración de quesos con fermentos bacterianos concentrados / Assays of cheese preparation with concentrated bacterial starters

En el presente trabajo se llevaron a cabo estudios de elaboración de quesos con fermentos bacterianos concentrados y congelados. Los citados quesos, de pasta semicocida, se obtuvieron a partir de leche pasteurizada. Los fermentos se preparaon con una cepa seleccionada de Streptococcus lactis, concentrada hasta alcanzar un valor de 3.10**9 U.F.C./ml y resuspendida en lecha adicionada con el 8% de extracto de levadura. Dichos concentrados se congelaron a -40- y se almacenaron a -20-C durante 60 días. Se ensayaron tres varianes de fermento: uno descongelado en baño María a -40-C, otro agregado a la tina quesera sin previo descongelamiento y un testigo preparado en leche reconstituída estéril. Con el objeto de evaluar la conveniencia del empleo de dichas variantes, se realizaron análisis químicos y microbiológicos durante el proceso de elaboración y maduración de los quesos. Los resultados obtenidos han demostrado que el empleo de concentrados congelados descongelados directamente en la tina, permite obtener quesos de muy buena calidad. No sucedió lo mismo con los descongelados en baño María, lo que torna desaconsejable esta tecnología (AU)