Abstract
Smoked vacuum-packed trout fillets have won importance in the market over the last few years, especially because of the increasing production in aqua cultures. According to the fish regulations (Fischhygiene-Verordnung 1994) fish processing facturies have to establish the principles of the HACCP-system for this potentially hazardous product. Similar control-plans were laid down also for the food trade in the ordinance about food hygiene (Lebensmittelhygiene-Verordnung 1997). Here, the most important control point is the maintenance of the cold chain according to the declared temperature in order to control the multiplying of spoiling bacteria and pathogenous microorganisms.
The aim of the thesis was to estimate the hazard of insufficient cold storage. First, this study determines the hygienic state of smoked vacuum-packed trout fillets that were taken from fish processing plants, wholesale trade and retail markets. Then, the storage temperatures in chilled cabinets of food handling establishments were controlled by long-term measurements. Afterwards, challenge tests were carried out in order to assess the influence of different temperature conditions on the product quality and shelf life. The hazard caused by growth of L. monocytogenes and toxin production of Cl. botlinum was discussed.
The results are summarized as follows: 1.) The median for the total aerobic bacterial count of 28 samples taken in fish processing plants was log 3,10 cfu/g. The market anlysis of 44 samples bought in wholesale trade and 76 samples bought in retail shops showed a median of log 6,38 cfu/g (wholesale) and log 6,80 cfu/g (retail) for the total count. The predominant spoilage bacteria belonged to the group of lactic acid bacteria and Pseudomonas spp., followed by coliform bacteria and yeasts. 2.) L. monocytogenes was isolated in 43 (31 %) smoked trouts from wholesale trade and retail markets. 42 % of the L. monocytogenes-positive samples showed levels between log 2 and log 4 L. monocytogenes/g, in 12 % of the samples levels of more than log 4 L. monocytogenes/g were detected. 3.) The long-term measurements of the storage temperature proved insufficient cooling in 9 of 12 chilled cabinets. On the one hand the storage temperature remained constant over the whole period of time but exceeded the declared temperature partly extreme. In other hand the smoked trout fillets were stored at extremely varying temperatures. The labeled storage temperature was mainly exceeded during the defrosting period. Furthermore, the long-term determination showed that neither spot checks of the storage temperature by single measurement nor integrated displays provide meaningful results, because the defrosting can not be recorded. 4.) A high total bacterial load (> log 6 cfu/g) was reached at 3,5 °C after 3 weeks storing of commercially produced smoked vacuum-packed trout fillets. A comparable result was attained within 8 days when the samples were stored at 11 °C. In samples stored at 6 °C, interrupted by one-hour storage at 11 °C, the limit of log 5 cfu/g was exceeded between the fifth and eighth day of storage. The minimum shelf life at a constant temperature of 4 °C should be fixed upon 14 days. 5.) Within the usual labeled shelf life of more than 3 weeks L. monocytogenes and Cl. botulinum will grow to high levels or produce toxin in smoked vacuum-packed trout fillets, if temperature abuse occurs (f.e., storage temperature of 10 °C). Therefore, for this potentially hazardous product a maximum storage temperature of 4 °C has to be settled. This indicates also a contribution to consumer protection. Furthermore, it is concluded from the results of this study that the trade has to be more responsible for the control point "storage temperature".
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