Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Identication of the yeasts and bacteria on the surface of Gubbeen cheese

Bacteria and yeasts from six batches of cheese collected over a five and a half year period were isolated after ripening for 4, 16, 23 and 37 d in the case of Batches 1, 2 and 3 and after 4, 10 and 16 d in the case of Batches 4, 5 and 6. The cheese was deliberately smeared with commercial cultures 2-3d after manufacture. FTIR spectroscopy was used to identify the yeast and PFGE, using sma or spe as restriction enzymes and rep-PCR in the case of the bacteria. A total of 1151 strains of bacteria were isolated and 1083 strains were identified. Eighteen species from 9 genera including Agrococcus, Arthrobacter, Brevibacterium, Corynebacteriun, Curtobacterium, Halomonas, Microbacterium, Psychrobacter and Staphylococcus were identified. Numerically, the most important organism was Staphylococcus saprophyticus (317 isolates), followed by Corynebacterium casei (257 isolates), Brevibacterium aurantiacum (190 isolates) and Corynebacterium variabile (134 isolates), each of which were isolated from every batch of cheese, and Microbacterium gubbeenense (55 isolates) which was isolated from cheese batches 1 to 4. The number of isolates of many of these species varied significantly between batches, e.g., B. aurantiacum dominated Batch 1 and only 1 isolate was found in Batch 2, 3 in Batch 4 and 2 in Batch 5; C. case dominated Batches 2 and 3 and very small numbers of isolates were found in Batch 1. This species also increased in number as ripening progressed in Batches 4 and 5. This data implies that each batch of cheese had a unique flora, which was not surprising given that this cheese is made at farmhouse level. Sporadic isolation of other species occurred, and one new species, Agrococcus sp. was isolated. Very few isolates (<10) from the commercial cultures used to smear the cheese were identified and these were only isolated at the initial stage of ripening, implying that the commercial cultures do not implant on the cheese.
A progression of Gram-positive bacteria occurred during ripening with staphylococci dominating day 4 of ripening and coryneforms increasing as ripening progressed
A total of 828 strains of yeast were isolated from the 6 batches of cheese and all were identified by FTIR spectroscopy. Debaryomyces hansenii was by far the most dominant yeast (75% of isolates), and was found in high numbers in all batches of cheese, except Batch 2; Candida catenulata (19% of isolates) was found in relatively high numbers in Batches 2 and 3 and much smaller numbers in Batches 1 and 4 while Clavispora lusitaniae(7.5% of isolates) was found in Batches 1 and 2 with 1 isolate in Batch 3. In contrast to the bacteria, no evidence of a progression of yeasts was found during ripening.

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Tim COGAN, (Co-ordinator)
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