Abstract
The microbiological quality, pH and serving size of typical meals served in 18 Thai restaurants in Vienna were studied. During the summer and winter season, one ready-to-eat food portion was sampled per restaurant and per food category (A: raw or insufficient heat treatment; B: heat treated main dish garnished/mixed with raw side-dishes; C: thorough heat treatment, served alone; total number = 108). In addition, ― where possible ― some typical side dishes were sampled (n = 25). The average weight of main dishes varied dependent on category from 360―510 g. The lowest pH was observed in group A (average 4.5), most probably because of the addition of acids via lime juice. Expectedly, group A had significantly higher total aerobic counts (6.1 ± 0.8 log cfu/g) than group B (4.5 ± 1.7 log cfu/g) and C (2.6 ± 0.9 log cfu/g). In side-dishes, average total aerobic counts were higher in raw vegetables (4.9 log cfu/g) than in rice (2.6 log cfu/g). With respect to hygiene indicator bacteria, there was a clear association between presumably insufficient heat treatment and/or the likelihood of cross-contamination (groups A B) on the one hand and the presence of E. coli and Enterobacteriaceae on the other. All 133 samples tested negative for Salmonella spp., Listeria monocytogenes and Campylobacter spp. (25 g aliquots). In groups A and B the warning limits for total aerobic count and Enterobacteriaceae established by the German Society for Microbiology and Hygiene were exceeded in 30-60 % of the samples. For food classification we used an empirical scheme taking into account heat treatment and the likelihood of cross-contamination, assuming that these two factors would be associated with the risk of presence of pathogenic bacteria in the ready-to-eat food portion. This empirical classification was well reflected in total aerobic counts. As regards pathogens, the usefulness of such a classification scheme could not be evaluated due to the low frequency of pathogens. This indicates that on this issue further studies should be conducted.
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