100A-7 |
Sensibility and specificity of methods for Alicyclobacillus detection and quantification: A collaborative study |
P. R. D. MASSAGUER, Dept. de Ciencia de Alimentos, Univ. Estadual de Campinas, Cidade Universitária Zeferino Vaz, Caixa postal 6121, Campinas - SP, 13081-970, Brazil In the past 5 years, many methods for detection, confirmation and quantification of Alicyclobacillus have appeared. Nowadays there is a need for standardization and adoption of reliable procedures. The IFU Microbiology Working Group has prepared an inventory of methods used by the industry for concentrated and single strength fruit juice for detection, confirmation and enumeration of Alicyclobacillus. Our objective was to carry out a collaborative study with Brazilian Citrus Juice Industries (ABESCitrus) to determine the efficiency of four methods, carefully selected from the IFU inventory. Methods compared were: (1) Eguchi et al. 1989, (2) NFPA, (3) Previdi (Parma-Italy) and (4) Baumgart and Menje 2000. Four laboratories tested all four methods. There were three different levels of inoculation: 0, 102 and 104 Alicyclobacillus spores/ml of concentrated orange juice. Eighty samples were tested for each level, twenty by laboratory. Levels of inoculation were unknown by the analysts. Statistical analysis was conducted by ANOVA and Newman-Keuls multiple range test. The specificity and sensibility rate were calculated as McClure, 1990. Method 1 has the highest sensibility rate and counting performance for 102 and 104 inoculation level, but its specificity was lowest (0,75), compared with the other methods (1,00). To improve the performance of this method, confirmatory test must be conducted. As a second option, method 2 performed very well; it has 100% specificity and a good sensibility rate for 102 (0.30) and 104 (0.55) spores/ml of concentrate. Performance of methods 3 and 4 was lower. As the guaiacol taint usually appears when high contamination is observed, proper method must have the best sensibility and counting performance, even lacking some specificity. Guaiacol production test must be chemical and not sensorial, due to subjective error. Biochemical API series is not always consistent for Alicyclobacillus, it represent a cost and analytical effort not reliable for confirmation.
Session 100A, Food Microbiology: General II
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