Roberto Martín Sarmiento

Microbiological study of León raw cow-milk cheese, a Spanish craft variety

The levels of several microbial groups (aerobic mesophilic flora, aerobic psychrotrophic flora, lactic acid bacteria, Micrococcaceae, enterococci, Enterobacteriaceae, and molds and yeasts), and some biochemical parameters were investigated during the manufacture and ripening of four batches of León cow cheese produced from raw milk without the addition of starter cultures. The study of the microbial characteristics of this cheese constitutes the first step towards the establishment of a starter culture which would allow the making of a product both more uniform and safer from the point of view of health. The total microbial counts were high throughout the elaboration and ripening. Almost all the microbial groups reached their maximum counts in curd and afterwards dropped throughout the ripening process. The greatest drop was shown by Enterobacteriaceae, which had disappeared after 3 months of ripening. Lactic acid bacteria were the major microbial group, reaching counts similar to the total aerobic mesophilic flora at all sampling points. Lactococcus lactis subsp. lactis dominated in milk (62.5% of the isolates obtained in de Man-Rogosa-Sharpe (MRS) agar at this sampling point), curd (82.5% of the isolates obtained at this sampling point) and one-week-old cheese (85% of isolates obtained at this sampling point), while Lactobacillus casei subsp. casei was the most predominant species in eight-week-old cheese (55% of isolates obtained at this sampling point) and twelve-week-old cheese (47.5% of isolates obtained at this sampling point). According to our data, a starter suitable for the production of León cow cheese would be made up of these two species. Some species of Leuconostoc or enterococci could also be added to this starter with the aim of improving the organoleptic characteristics of the final product or to emphasize the characteristics of this variety.

Population Levels, Species, and Characteristics of Micrococcaceae during the Manufacturing and Ripening of Armada-Sobado Hard Goat's Milk Cheese

The changes in the counts and the species of Micrococcaceae were studied throughout the manufacturing and ripening of a Spanish hard goats milk cheese, the Armada-Sobado variety. In the milk, counts on mannitol salt agar (MSA) ranged from 2 × 104 to 5 × 104 CFU/g. These counts showed the maximum value in the curd (7 × 104 to 4 × 105 CFU/g), decreasing afterwards slowly but steadily throughout the ripening process to reach final counts on average 2 logarithmic units lower than those found in the curd. Of 280 isolates obtained from MSA during manufacturing and ripening, 66 (24%) were considered to be Micrococcaceae . Staphylococcus sciuri (22.5% of the isolates at this sampling point) and Staphylococcus saprophyticus (7.5%) were the only two species of staphylococci isolated from the milk. In the curd, S. sciuri increased its proportion (30%) whilst the percentage of S. saprophyticus remained constant. None of these species was isolated from the cheese. S. aureus was detected only in curd (7.5% of the isolates obtained at this sampling point). S. xylosus , S. capitis , S. epidermidis , and S. warneri were isolated from curd and cheese, or exclusively from cheese, but always in very low proportions. Micrococcus varians (10%) and M. roseus (5%) were the two species of micrococci isolated from the milk. M. varians increased its proportion in curd (17.5%) and could not be isolated in cheese. M. roseus appeared neither in curd nor in cheese. All the isolated staphylococcal strains were tested for production of A, B, C, and D enterotoxins. The three isolated strains of Staphylococcus aureus produced A and C enterotoxins, but neither B or D. Of 41 coagulase-negative strains only two of the Staphylococcus sciuri isolated from milk produced C enterotoxins.

Comparison of the classical methods and the API ATB 32C system in the identification of yeasts isolated from goat cheese

Abstract A comparison of the results obtained using the classical methods was carried out with those of the API ATB 32C system in identifying 34 yeast strains isolated from goat cheese of the Armada variety. The results of both identification systems coincided exactly in 13 strains (∼1/3 of the strains studied). In 5 strains (∼1/7) the identification carried out using the API ATB 32C system can be considered as satisfactory since it gave as a result the imperfect forms of the identified species using the classical methods. In 3 strains (∼1/10) the result obtained using the classical methods did not coincide with that offered by the API ATB 32C system. Finally 13 strains (∼1/3) could not be identified using the API 32C strips. The results obtained show once again the importance of the morphological and sexual tests in order to carry out a reliable identification of foodborne yeasts.