Summary -Randomly-selectedAustrian bacterial surface-ripened cheeses were examined for changes in the microbiological composition of the smear. The bacterial counts of the Tilsit cheeses from 14 cheese plants and of 3 types of soft cheeses selected varied fram 1()4 ta 109 cfu/cm2 smear 3 d after manufacture and fram 108 ta 109 cfu/cm2 smear after a ripening period of 3 weeks. The flora tolerated a NaCI content of at least 80 g/kg in the plate count agar. A total of 386 isolates of coryneform bacteria were identified. The bacterial flora proved ta be of mixed population. However, Brevibacterium linens accounted for a large share of the flora, comprising 30% of the total bacterial count, Besides Brevibacterium linens, the other main types found ta be present in the heterogeneous flora were creamcoloured and yellow-pigmented coryneforms, which were predominantly identified as Arthrobacter globiformis and Brevibacterium ammoniagenes. The coryneforms isolated fram the cheeses 3 d after manufacture were more prateoly1ic than those isolated at later stages of ripening.
Parallel productions of Austrian Bergkâse from raw or pasteurised milk were perfonned to monitor the effect of heat treatment on physical and sensory properties of the mature cheeses and, in sorne parameters, during ripening. Apart from sorne seasonal variations, analyses of variance showed that neither mechanical properties nor cheese body col our were influenced by the pasteurisation of the milk. However, sensory characterisation of smell and aroma as weil as of the basic taste categories of the mature Bergkâse samples showed that pasteurisation leads to reduced intensities of the typical Bergkâse flavour but increases bitterness scores significantly. In line with results from preceding papers, it may be concluded that it is essential to use raw milk for the production of Bergkâse with satisfactory product properties. © Inra/Elsevier, Paris.
-Experimental samples of Bergkâse, an Austrian regional hard cheese variety usually made from raw milk, were produced from raw or pasteurised milks in parallel to evaluate the influence of the indigenous microflora on microbiological composition and selected fermentation compounds. Facultatively heterofermentative lactobacilli (FHL) dominated the non-starter flora in cheeses made from raw milk. Viable numbers increased from 1Q4-10 6 cfu-g-' at the age of 1 week to reach their final levelof 10 8 cfu-g! within the first month of ripening. In contrast, cheeses made from pasteurised milk exhibited FHL counts which were at least three orders of magnitude lower or even undetectable. In the raw milk cheeses, the development of organic acids during maturation differed from that in the pasteurised ones, and was dependent on the number and the metabolic activity of the microorganisms. Differences in the citrate metabolism and in propionic acid fermentation, which occurred in raw milk cheeses only, cau be attributed to the occurrence ofFHL and propionic acid bacteria, respectively. © InralElsevier, Paris.Bergkâse / raw milk flora / pasteurisation / microbiology / organic acid Résumé -La flore du lait cru influe sur la composition et la qualité du fromage Bergkâse.
A large number of microorganisms, both starter microorganisms and non-starter lactic acid bacteria originating from the base milk, or from various contamination sources during cheese manufacture, is associated with cheese ripening and the formation of flavour, texture and aroma. Under controlled conditions, Emmental and Bergkäse, a Gruyère-type cheese variety, were produced from pasteurised milk with standard starters and defined strains of facultatively heterofermentative lactobacilli (FHL), and partly with addition of a defined mixture of enterococci. Lactobacillus casei subsp. casei and L. rhamnosus (two strains each) were selected with respect to their potential for the utilisation of citric acid and ribose as sole energy source. The FHL developed up to 10(8) cfu/g within the first weeks of ripening, and viable counts in mature cheeses were 10(7) cfu/g, independent of the cheese variety. Bergkäse made with addition of L. rhamnosus strains showed a more pronounced proteolysis, resulting in reduced firmness and elasticity values of the cheese body, and FHL strains able to utilise citric acid improved the appearance of the cheeses by increasing the number of small eyes to the desired level. In Emmental cheese, the citric acid (+) strains reduced the intensity of propionic acid formation as the FHL apparently competed with the propionibacteria, and enterococci disappeared completely during maturation. Although further work is needed the study shows that, depending on the cheese variety, particular properties of FHL adjunct starters significantly affect important quality attributes of the resulting cheeses.
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