RESUMO
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.
Assuntos
Histamina/biossíntese , Streptococcus/metabolismo , Triptaminas/biossíntese , Tiramina/biossíntese , Aminoácidos/metabolismo , Animais , Meios de Cultura , Leite/metabolismoRESUMO
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.
RESUMO
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.
Assuntos
Queijo , Manipulação de Alimentos , Microbiologia de Alimentos , Lactococcus lactis/fisiologia , Animais , Técnicas Bacteriológicas , Bovinos , Congelamento , LeiteRESUMO
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.