Avaliação da contaminação por microorganismos esporulados e indicadores em requeijão cremoso / Microbiological evaluation of indicators and sporeforms in requeijão cream cheese

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The objective of this research was to carry out a microbiological survey of Brazilian cream cheese ?Requeijão? ( pH 5,8 ), production line and to evaluate its shelf life, in relation to contamination by sporeformers and pathogens such as L. monocytogenes, coagulase positive S. aureus and Coliforms ( 45°C) and to determinate the microorganism(s), surviving the thermal process. Fifty samples, from two different lots were analized, lot 1 was produced during winter and lot 2 during summer . The detection of L. monocytogenes was carried through with the "Mini Vidas LMOII" kit (BioMerieux). The essays for enumeration of S. aureus coagulase and DNAse positive, Coliforms (45ºC), C. perfringens and sporeformers were tested according to APHA methods ? ?American Public Health Association?. No contamination of L. monocytogenes and coagulase positive S. aureus, Coliforms at 45°C and C. perfringens was observed in any of the samples of final product. Therefore all samples analyzed were in agreement to Mercosul Technical Regulation 82, and RDC 12 ANVISA resolution. The most contaminated ingredient, with mesophilic and thermophilic anaerobic and aerobic sporeformers, was protein concentrate (4log10spores/10g), followed by Petit Swiss mass, in both lots. The spore load from these contaminated ingredients was not totally eliminated after the thermal process. There were isolated 207 sporeformers from lot 1 and 270 from lot 2. The less contaminated ingredients were sodium citrate and water. The mean contamination from lot 2 samples was higher and significatively different (p<0,1) than that of lot 1 in regard to the following groups of spore former : mesophilic aerobic, thermophilic aciduric flat sour producers and mesophilic and thermophilic anaerobic. Tle microbial load of protein concentrate from lot 2 showed highest seasonal effect. During cream cheese shelf life studies, five samples from lot 2 per week, were incubated at 4°C for up to 50 days. The result s from shelf life survey showed no contamination by L. monocytogenes, coagulase positive S. aureus, Coliforms at 45°C and C. perfringens. No alteration was observed on color, flavor and texture. Until the 22th day of incubation, the anaerobic sporoformers increased in number while the aerobic sporoformers were reducing its population suggesting germination, and consumtion of the package residual oxygen . After the 22th day, the sporulation of the aerobic sporoformers organisms increased by the adverse effect of temperature and potassium sorbate barriers, while the anaerobic sporoformers started late germination, nevertheless limited by the barriers indicated above. The thermal process applied to Requeijão cream cheese was not dimensioned to eliminate the unexpected high contamination of the sporoformers organisms. This can be justified by the low decimal reductions, of only 1,3 log cycles, on the inline product population of total thermophilic sporoformers, from lot 2 . So, the commercial process had to be re-dimensioned on the basis of the contamination in the in line product from lot 2.It was observed also an increased in the final product mesophilic aerobic sporoformer population from lot 2 suggesting line contamination in this section of the processing line . There were isolated, 325 cultures during the shelf life studies. The largest number of these isolates came from 1st and 22th storage days; therefore, all isolates from these dates were induced to "in vitro" sporulation in order to determinate the most resistant microorganism(s) from the cream cheese. Each one of 58 aerobic sporeformers isolates were submitted to successive thermal shocks from 95°C/5 to 130°C/3 .Only one isolate survived 130ºC/3´heat sh ock In the same manner, 46 strict and facultative anaerobic sporeformers received thermal shocks from 130°C/3 to 140ºC/1?. Thirty isolates survived the last heat shock The facultative anaerobic mesophilic sporeformers predominated among the survivors (18 isolates) most of them were able to coagulate and hidrolisate casein, to produce proteolisis and liberate gas. As it was not detected deterioration after shelf life monitoring at 4ºC it was concluded that the temperature and antibacterial hurdles were efficient to maintain the final product stable up to 50 days. However, considering the high sporeformers contamination, which can potentially deteriorate the final product, Requeijão cream cheese can not be submitted to abuse refrigeration temperatures, during its sale and distribution

ASSUNTO(S)

cream cheese patogenicos vida de prateleira pathogens shelf-life microbiological survey levantamento microbiologico requeijão cremoso

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