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  • Changes in the microbial composition of raw milk induced by thermization treatments applied prior to traditional Greek hard cheese processing
    Samelis, John ...
    The microbiological quality, safety, and composition of mixturs of ewe's and goat's milk (90:10) used for cheesmaking were evaluated before and after thermization at 60 and 67 oC for 30 s. Such mild ... thermal tretaments are commonly applied to reduce natural contaminants of raw milk before processing for traditional hard Greek cheeses. Raw milk samples had an average total bacterial count of 7.3 log CFU/ml; most of these bacteria were lactic acid bacteria (LAB) and pseudomonads. The LAB flora of raw milk was dominanted by enterococci (40.8%), followed by lactococci (20.4%), leuconostocs (18.4%), and mesophilic lactobacilli (10.2%). Enterococcus faecalis (30.1%) and Enetrococcus faecium (13.7%) were the most common LAB isolates, followed by Enterococcus durans, Lactotoccus lactic subsp. lactis, Lactobacillus plantarum, and Leuconostoc lactis. Thermization at 60oC for 30 s was effective for reducing raw milk contamination by eneterobacteria (5.1 log CFU/ml), coagulase-positive staphylococci (3.3 log CFU/ml), and Listeria (present in 25-ml samples) to safe levels, but it also reduced mesophilic lactococci, leuconostocs, lactobacilli, and selected enterococci (72.0%) in thermized milk. Themization at 67% for 30 s had a major inactivation effect on all bacterial groups. Two nisin-producing L. lactis subsp. lactis strains (M78 and M104) were isolated from raw milk, but neither nisin-producing nor other bacteriocin-producing LAB strains were isolated from thermized milk. Thus, thermization treatments control harmful bacteria but also may have a negative impact on milk quality by reducing desirable LAB and the biodiversity of raw milk bacteria overall, inactivating potentially protective LAB strains and enhancing the ability of potentially pathogenic enterococci to grow in fresh cheese curds.
    Vir: Journal of food protection. - ISSN 0362-028X (Vol. 72, no. 4, 2009, str. 783-790)
    Vrsta gradiva - članek, sestavni del
    Leto - 2009
    Jezik - angleški
    COBISS.SI-ID - 2449800

vir: Journal of food protection. - ISSN 0362-028X (Vol. 72, no. 4, 2009, str. 783-790)
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