Raw milk flora affects composition and quality of Bergkäse. 1. Microbiology and fermentation compounds

Abstract

-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.

Article

“…bulgaricus [42,45,83]. Lactobacilli starters are normally present at levels of 10 9 bacteria/g, contribute to the lactic fermentation, and are involved at the beginning of ripening [70]. For example, in Emmental cheeses, lactobacilli ferment galactose excreted by Streptococcus thermophilus, achieve acidification processes, and contribute to primary proteolysis [31,35,59,74].…”

“…They originate from the raw milk, and this source was probably more important than the factory environment [17,58]. Differences have been observed between raw milk cheeses and pasteurised or microfiltered milk cheeses [58,70,164]. EliskasesLechner et al [70] found that Bergkäse (Austrian regional cheese) cheeses made from pasteurised milk contained less than one-thousandth the number of facultatively heterofermentative lactobacilli (FHL) present in raw milk cheeses.…”

Split defect and secondary fermentation in Swiss-type cheeses – A review

“…Also, raw milk may contain wild PAB and NSLAB strains that may promote secondary fermentation [45]. As previously discussed, there is a greater degradation of α s1 -casein in cheese manufactured from raw milk attributed to the raw milk microflora, their associated enzymes [21,23] and also possibly to cathepsin D [41].…”

“…Cooking temperatures during Emmental manufacture exceed 50°C resulting in little residual coagulant activity [37,90], while cooking temperatures of~36-40°C used in Maasdam/Leerdammer and Jarlsberg manufacture result in higher residual coagulant activities with greater hydrolysis of α s1 -casein or its breakdown products [75]. There is a greater degradation of α s1 -casein in cheese manufactured from raw milk which is attributed to the microflora of the raw milk and their associated enzymes [21,23] and also possibly to the indigenous milk enzyme, cathepsin D [41]. Studies have also suggested a putative role for cathepsin D and for thermophilic lactobacilli [7,33] in the hydrolysis of α s1 -casein during ripening of Swiss-type cheeses.…”

“…Swiss cheese is prone to split defect whether it is made from pasteurised or raw milk; however, no detailed work to compare both treatments in relation to this defect has been published. Higher numbers of lactobacilli (FHL), enterococci and coliforms are found in Bergkäse cheese made from raw milk compared with cheeses made from pasteurised milk [23]. Pasteurisation reduces the growth of microorganisms in general during ripening of Emmental [7].…”