P. Hammer et al., CHARACTERIZATION OF A HEAT-RESISTANT MESOPHILIC BACILLUS SPECIES AFFECTING QUALITY OF UHT-MILK - A PRELIMINARY-REPORT, Kieler Milchwirtschaftliche Forschungsberichte, 47(4), 1995, pp. 297-305
Heat resistant mesophilic sporeformers (HRS) first occurred in Germany
after the new Milk Ordinance (EC-Directive 85/397, Milchverordnung 23
.6.1989) came into effect. According to these regulations a maximum co
lony count of 10 cfu/0.1 ml is required after 15 days incubation of th
e packages at 30 degrees C. HRS reach colony counts up to 10(5)/ml wit
hout changing milk composition or sensoric properties. The problem now
adays is evident in a number of dairies in several countries. A biolog
ical characterization of the HRS including morphological patterns as w
ell as growth conditions and biochemical properties is presented. The
taxonomy is not yet clear. Several working groups are involved using g
enetical or phenotypical methods to establish a new taxon group. Produ
cts involved are UHT-milk, UHT-cream, chocolate milk and milk powder.
Contamination occurs in all types of UHT-equipment of several supplier
s. For detection of the HRS only a conventional autoclaving method is
available, faster methods as gene probes or PCR are under development.
Regarding the time consuming and insensitive detection method the way
of contamination as well as the contamination sources are not clear.
Possibilities at the dairy and the farm level are discussed, however,
problems regarding reprocessing of contaminated UHT-milk or processing
of contaminated milk powder are under consideration too. The probably
extreme heat resistance of the HRS was investigated by several labora
tories. Results are differing, most probably because HRS-strains in na
turally contaminated milk seem to be much more resistant than laborato
ry cultured strains. With regard to the consumers safety investigation
s concerning the pathogenicity of the HRS started as early as the prob
lem was known. Pathogenicity tests in mice and embryonized chicken egg
s and cytotoxicity tests on different cell lines are presented. At thi
s moment there is no evidence for any pathogenic or toxic properties o
f the HRS.