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Food Science and Technology

Print version ISSN 0101-2061On-line version ISSN 1678-457X


ZACARCHENCO, Patrícia Blumer; LEITAO, Mauro Faber de Freitas; DESTRO, Maria Tereza  and  ANDRIGHETO, Cristiano. Occurrence of Bacillus sporothermodurans and the influence of the thermal processing procedure on its presence in brazilian UHT milk. Ciênc. Tecnol. Aliment. [online]. 2000, vol.20, n.3, pp.363-368. ISSN 1678-457X.

Bacillus sporothermodurans (BSP) has been isolated worldwide, but mainly in European contries as an usual contaminant of milk by the UHT system. Even being non pathogenic, generally its presence results in product rejection based on international microbiological standards limiting the counts to a maximum of 100 cfu/ml. In this research work, the occurrence of BSP was evaluated in UHT milk samples produced in different regions of Brazil (Central, South and Southeast) and processed by the indirect thermal treatment system (plate or tube exchangers) or by the direct system (steam infusion or steam injection). A total of 100 commercial samples were analysed both quantitatively by spread plate technique using Brain Heart Infusion Esculin Agar (BHI-E agar) and qualitatively after thermal shock treatment (115°C/7min), followed by incubation and plating in that medium. The results showed a total of 45% of the examined samples with counts above 100 cfu/ml, varying from 2 .104 and 9,5 .105 cfu/ml. However, 71.4% of the samples processed by indirect system were above limits, while none of the samples heat treated by the direct system, that allows a more drastic temperature condition, were rejected. A similar picture was observed in the qualitative evaluation, with contamination levels of 71,7 and 22,2% for the indirect and direct system, respectively. A total of 300 cultures were isolated from contaminated samples, showing cultural, morphological and biochemical patterns similar to BSP, except a late glucose fermentation capacity showed by most of the isolated strains. When 24 representative strains were submitted to PCR-RAPD evaluation and compared to the reference BSP strain (DSMZ 10599), they were confirmed as Bacillus sporothermodurans based on their DNA pattern.

Keywords : PCR-RAPD; UHT milk; Bacillus sporothermodurans; heating system.

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