Publicaciones científicas 1987

Fate of Listeria monocytogenes during manufacture and ripening of semi-hard cheese

Letters In Applied Microbiology 4:125-127.

     Semi-hard cheeses were experimentally elaborated with pasteurized milk from sheep, goat and cow (15: 35: 50) and inoculated to contain 1.9 times 105Listeria monocytogenes/ml in cheeses 1 and 2 and 4 times 103L. monocytogenes/ml in cheeses 3 and 4. Counts of L. monocytogenes were determined by direct surface plating of samples on listeria selective agar medium. The results show the substantial survival of L. monocytogenes present in milk during manufacture and ripening of this type of cheese.… Leer más

Dominguez L., Fernandez-Garayzabal JF., Vazquez-Boland JA., Blanco JL. y Suarez G.

Survival of Listeria monocytogenes in raw milk treated in a pilot plant size pasteurizer

The Journal Of Applied Bacteriology 63(6):533-7.

     The survival of Listeria monocytogenes in raw milk treated in a pilot plant size pasteurizer was investigated. Raw milk was inoculated with different initial concentrations of L. monocytogenes and heated at temperatures ranging from 69 degrees to 73 degrees C. Listerias were not isolated from any of the milk samples immediately after thermal treatment. They were isolated, however, from 46.6% of heated samples (none from samples heated at 73 degrees C) after variable periods at refrigeration temperature. The results suggest that a low number of listerias survive some thermal treatments, but a cold enrichment is necessary to repair the thermally injured cells and detect these organisms in milk. The importance of the isolation technique in the… Leer más

Fernandez-Garayzabal JF., Dominguez L., Vazquez-Boland JA., Rodriguez-Ferri E., Briones V., Blanco JL. y Suarez G.

Effect of ultraviolet light irradiation on viability and aflatoxin production by Aspergillus parasiticus

Canadian Journal Of Microbiology 33(10):927-9.

     The effect of ultraviolet light irradiation (254 nm) on both the viability and the aflatoxin-producing ability of the fungus Aspergillus parasiticus NRRL 2999, a good aflatoxin-producing strain, was studied. This strain showed noticeable resistance and irradiation for more than 10 min was necessary to reduce survival to under 10%, while the white mutants were more susceptible (5 min of irradiation reduced survival to under 1%). Induction of mutants with complete loss of aflatoxigenicity was rare and only 3 of the 1463 survivors tested were aflatoxinless… Leer más

Moreno MA., Ramos MC., Gonzalez A. y Suarez G.

Growth of Staphylococcus aureus and enterotoxin production in homemade mayonnaise prepared with different pH values

Journal Of Food Protection 50:872-875.

     The ability of Staphylococcus aureus to grow and produce enterotoxins in homemade mayonnaise prepared at different pH values was studied. Ten enterotoxigenic strains, producing one or two enterotoxin types (A, B, C, or D) were inoculated into mayonnaise samples with pH adjusted to values ranging between 4.0 and 5.8, and incubated at 37°C for 7 d. Counts were made on days 1, 3, 5, and 7 and extracts were prepared on day 7 to detect enterotoxin by ELISA. An important difference was seen between those samples prepared with pH below or equal to 4.9 and those over or equal to 5.0; in the range of pH between 4.0 and 4.9 the average of staphylococcal population was 100 CFU/g; at pH 5.0 it was 1.6 × 105, and at pH 5.15 and above it was at least 8 ×… Leer más

Gomez-Lucia E., Goyache J., Blanco JL., Fernandez-Garayzabal JF., Orden JA. y Suarez G.

Viability of Listeria monocytogenes in milk treated with hydrogen peroxide

Journal Of Food Protection 50(8):636-639.

     The susceptibility of Listeria monocytogenes to hydrogen peroxide in sterilized and raw milk was studied. In raw milk, L. monocytogenes was less susceptible to H2O2 than milk microflora. The ratio of L. monocytogenes to total milk micro-organisms (natural microflora plus added L. monocytogenes) increased when raw milk was stored at refrigeration temperature (4°C), due to a selective enrichment of Listeria present in milk. In sterilized milk, a concentration of 0.0495% H2O2 and 9 h were required to produce complete destruction of L. monocytogenes when this microorganism was in pure culture, although a reduction in listeria counts was observed at 1.5 h. When sterilized milk was simultaneously contaminated with L. monocytogenes, Staphylococcus… Leer más

Dominguez L., Fernandez-Garayzabal JF., Rodriguez-Ferri E., Vazquez-Boland JA., Gomez-Lucia E., Ambrosio C. y Suarez G.

Determination of aflatoxin M1 in milk and milk products contaminated at low levels

Journal - Association Of Official Analytical Chemists 70(3):470-2.

     A new method is described for the determination of aflatoxin M1 in milk and dairy products by thin layer chromatography. The main characteristic is the extraction system using an alkaline solution. Lipids are removed by centrifuging at low temperatures, and the aflatoxins are then extracted with CHCl3. The method has 2 options: Technique II (detection limit 0.02 ppb) requires cleanup on a chromatographic column; this is not necessary in Technique I (detection limit 0.1 ppb). The recovery rate in both techniques is over 92.8% in milk and yoghurt. This method may also be used for other aflatoxins. Because of the advantages of the method, Technique II is recommended for aflatoxin M1 control in milk, where a low detection limit is necessary. Te… Leer más

Dominguez L., Blanco JL., Gomez-Lucia E., Rodriguez EF. y Suarez G.

Staphylococcus aureus growth and survival during curding of Manchego type cheese produced with normal and subnormal starter activity

Zeitschrift Für Lebensmittel-Untersuchung Und -Forschung 184(4):304-7.

     Manchego type cheese was manufactured from milk from cows, goats and ewes artificially contaminated with 2 X 10(4) S. aureus cells ml. Lactic starter culture was added to the milk at the rate of 1.0 or 0.1% (v/v). the industrial process of Manchego type cheese manufacture was imitated. Cheeses were analyzed for both staphylococcal and non-staphylococcal total aerobic counts, as well as for the pH and enterotoxin production. Growth differences in staphylococcal counts in cheeses prepared with both starter concentrations were seen only after the brine treatment, the counts were 10 times greater with the 0.1% starter. Nevertheless, with the 1% starter culture the staphylococcal counts did not decrease from the moment of inoculation remaining h… Leer más

Gomez-Lucia E., Goyache J., Blanco JL., Vadillo S., Fernandez-Garayzabal JF. y Suarez G.

Occurrence of Listeria monocytogenes in raw-milk

The Veterinary Record 120(11):258-9.

Fernandez-Garayzabal JF., Dominguez L., Vazquez-Boland JA., Gomez-Lucia E., Rodriguez-Ferri E. y Suarez G.

A rapid extraction method for detecting aflatoxin producing isolates

Mycotoxin Research 3(1):33-5.

     A rapid extraction method for screening aflatoxin producing potential ofAspergillus flavus group isolates is described. The method is performed using a moist wheat medium with ca. five infected grains extracted with 2 mL of chloroform, and using thin layer chromatography. This method was proved with 95A. flavus isolates from animal feeds… Leer más

Moreno MA., del Carmen P. y Suarez G.