Microbiological changes throughout the manufacturing and ripening of a Spanish goat's raw milk cheese (Armada variety)

Abstract

-The microbial groups of technological interest (aerobic mesophilic flora, presumptive lactococci, presumptive lactobacilli, presumptive leuconostocs, presumptive enterococci, presump-tive Micrococcaceae and mou Ids and yeasts) were enumerated throughout the ripening process in 4 batches of Armada goat's milk cheese (2 ripened in summer and 2 ripened in autumn). High counts of ail microbial groups were observed in milk (loglO cfu/g: aerobic mesophilic flora 6.72-7.55, presump-tive lactococci 6.53-7.40, presumptive lactobacilli 4.84-5.05, presumptive leuconostocs 5.47-5.68, pre-sumptive enterococci 2.9~.29, presumptive Micrococcaceae 4.47-4.66, mou Ids and yeasts 4.59-4.66); the highest counts being generally reached in ail the microbial groups in 1-week-old cheese. Beyond this, they progressively dropped until the end of ripening. In the first 8 weeks of ripening, no significant differences were observed in the counts related to the season when the cheeses were ripened. Only in 16-week-old cheeses were the counts in ripened cheeses during the summer lower than those determined in autumn ripened cheeses. The lactic acid bacteria were the most abundant flora during manufacturing and ripening of this cheese. Lactococci (Lactococcus lactis subsp lactis and Lacto-coccus lactis subsp cremoris) dominated in milk (50% of the isolates carried out in M17 agar), curd (70% of the isolates carried out in M17 agar) and 1-week-old cheese (70% of the isolates carried out in M17 agar) and lactobacilli (mainly Lactobacillus casei subsp casei and Lactobacillus plantarum) were the most abundant group during the last stages of ripening (92.5, 95 and 77.5% of the isolates carried out in Rogosa agar in 4-, 8-and 16-week-old cheese, respectively). M17 agar showed a moderate selec-tivity for the isolation of lactococci (45.71 % of the isolates carried out in M17 agar were classified as lac-tococci). The selectivity of MSE agar for the isolation of leuconostoc was very low (only 16.42% of the isolates carried out in MSE agar were c1assified as leuconostocs). On the other hand, Rogosa agar and KAA agar showed a very high selectivity for the isolation of lactobacilli and enterococci, respectively * Correspondence and reprints. 552 ME Tornadijo et al (86.42% of the isolates carried out in Rogosa agar were classified as lactobacilli and 91.85% of the iso-lates carried out in KAA agar were classified as enterococci). Values of sorne physicochemical param-eters (pH, a, and moisture and NaCI contents) as weil as the correlation coefficients between the values of these parameters and the microbial group counts throughout ripening were also determined. Armada cheese 1 goat cheese 1 microbiological change Ilactic acid bacteria Résumé -Modifications de la flore bactérienne pendant la fabrication et l'affinage du fromage de chèvre Armada, une variété espagnole fabriquée à partir de lait cru. La présente étude a