Fachbereich Veterinärmedizin



    Die Eignung der Impedanzmessung als Schnellmethode zur Erfasung mikrobieller Kontamination in Eiprodukten (2001)

    Schützle, Ulla
    Berlin, 2001 — 145 Seiten
    Institut für Lebensmittelsicherheit und -hygiene

    Königsweg 69
    14163 Berlin
    +49 30 838 62550

    Abstract / Zusammenfassung

    In order to check the microbiological contamination during the overall production from liquid whole egg to the pasteurised product "CVE" (concentrated whole egg) in a Berlin egg product factory, the bacterial content of the egg products (190 lots of raw material tested as well as 10 step by step controls, monitoring four stages during the production flow), the inside air (n = 30), the pasteurisation system (n = 2) and the condensation collected from the final containers (n = 10) were determined. A homogeneity test was used to record the distribution of microorganisms throughout 4 lots of untreated liquid egg. Labour intensive and timeconsuming culture methods do not ensure a permanent monitoring of the production process and bacterial counts of the raw material are not available before the final production run. Therefore, the suitability of the impedance technique was
    evaluated for quality assurance in egg products parallel to the common standards. Analogue impedance and culture methods were performed to detect coliforms qualitatively in 190 intermediate products using presence absence-test and quantitatively in 95 samples of "CVE" using MPN-procedure. Thus, results were directly comparable. For the enumeration of coliforms in the final product "CVE", moreover the detection times yielded in the lowest dilution"s of the impedimetric MPN assay were associated with conventional MPN values (linear regression analysis). Colony forming units (logio CFU/ml) of 138 fresh and 52 frozen lots of the supplied raw material confirmed by drop-plating-test were correlated to corresponding impedance detection times. The results led to following conclusions:More than 50% of the total bacterial counts of untreated liquid whole egg range above the acceptable limit of 106 CFU/ml. This, together with a constant prevalent amount of
    enterobacteriaceae, indicates a lack of hygienic management in the suppliers plant.Under existing law, three out of ten checked "CVE" batches - with an averagef ten sampled containers per batch - were not permitted for sale. Within the three unsuitable batches a total of 4 containers were found exceeding the upper legal limit "M" fixed at 102 enterobacteriaceae1 (1 or 2 contaminated containers/batch). The step by step controls verified the product to be safe directly after pasteurisation [74 "C x 10 min). However, subsequent recontamination is possible resulting from coliform containing egg material scorched to the evaporator. In the evaporating cycle, contaminated material was washed off continuously or by degrees in the pasteurised product. This led to a synchronous contamination of the evaporating material as well as the final product. To a less degree the coliform contamination in end product was due to the homogenous distributed microflora in raw material, the environment (inside air, condensation) and the handling.Impedance technique permits the egg processing industry permanent monitoring, better of personnel,material and time combined with a maximum of examination capacity proof rapid impedance production management and therefore safer egg products. Minimum need measurements superior to culture methods even with regard to economical aspects. Besides always fast results the following advantages of impedance analysis can be emphasised:1) Two most common but complicated and tedious standard methods, the drop-plating-technique for raw material as well as the NTN-procedure for pasteurised products, could be replaced by simple, rapid impedance screens with an increased sample capacity and either a close (drop-plating-test) respectively a loose correlation (MPN-method) of detection times and reference values,2) The impedimetric presence/absence-test as well as the impedimetric MPN-technique can be immediately used without calibration. There is excellent correlat
    ion to the corresponding reference methods. However, the MPN by impedance failed to reduce effort and increase sample capacity. Therefore, enumeration of coliforms on the basis of the criterion detection time is recommended despite of its lower correlation.3) Furthermore, rapid analysis of raw material (10 6 CFU/ml] within 4,5 hours) enables direct steering of production. Impedance technique particularly permits either to reject high contaminated raw material or to process the contaminated lot under high pasteurisationstandards, in order to achieve a saf e product. Especially in egg products, the perishable and often highly contaminated untreated egg substrate could have negative effects on the bacteriological quality of the final product, since preserving heat sensitive quality attributes sets a narrow temperature-time margin. Costs for reprocessing or even discarding of unsuitable batches can be avoided.4) Being able to evaluate the microbiological parameters of source, intermediate and final product with impedance technique at an uniform temperature of 3 7 "C in comparison with cultural results, allow
    s all different kinds of egg products to be analysed simultaneously invariable quantities. Thus, the demand for flexible utilisation of a measuring instrument is assured. The unit temperature for impedance technique is important since even large eggfactories hardly process more than one batch of raw material per day, however, always will have several intermediate or final products for testing.For manufacturers, whose quality assurance is not only restricted to controlling the finalproduct according to official guide lines, the high investment costs of impedance equipment will be amortised within a short time period.