Samples of strawberries were divided into two portions, they were wrapped and one portion was irradiated at 200 krad. A total of 30 samples of Dutch strawberries (10 greenhouse-and 20 outdoor-grown) were treated. The composition of the microflora before and after irradiation was investigated.
It was evident that the flora of the non-irradiated samples was composed mainly of gram-negative rod-shaped bacteria belonging, with only a few exceptions, either to the Enterobacteriaceae-family or to the genusPseudomonas. Also, moulds and yeasts were frequently encountered in varying quantities. Other groups were only incidentally demonstrable.
Moulds and yeasts did not appear to make good indicator organisms. Though their total numbers after irradiation almost always appeared to have undergone a certain reduction, the number seldom became too low to count. Special groups or species of molds and yeasts, showing such sensitivity that they were always absent after irradiation also were not demonstrable.
Gram-negative rod-shaped bacteria on the other hand were always found to be absent after irradiation when solid media were used, even when starting from samples with numbers in the order of magnitude 105–106/gm.
When outdoor-grown strawberries were used this always led to a clear difference from the corresponding untreated samples. Greenhouse strawberries, however, sometimes contain, even if they have not been treated, only a very small number of microorganisms; the possibility should therefore be taken into account that none of the media show any growth without irradiation having taken place.
Consequently, if gram-negative rod-shaped bacteria are present on strawberries (when using solid media) they most probably have not been irradiated. Of course, this does not apply if post-contamination has been possible.
If there is no growth of the above mentioned bacteria on any of the media used, considerable possibility exists that irradiation has taken place.
This is a preview of subscription content, log in to check access.
Buy single article
Instant access to the full article PDF.
Price includes VAT for USA
Subscribe to journal
Immediate online access to all issues from 2019. Subscription will auto renew annually.
This is the net price. Taxes to be calculated in checkout.
Colloquium on the identification of irradiated foodstuffs, Luxembourg, October 27, 1970. J. Smeets, ed. Commission of the European Communities (Eur 4695 d-f-e)
Food irradiation, Proceedings of the Symposium, organized jointly by IAEA and FAO, held in Karlsruhe, June 6–10, 1966, IAEA, STI/PuB/127, Vienna, 1966
Miller, T.D., Schrott,M.N. (1972). Phytopathology 62, 1175–1182
Mossel, D.A.A., Tamminga. S.K. (1973). Methoden voor het microbiologisch onderzoek van levensmiddelen, Zeist
Natarajan, A.T., Kim, Ch., Löfroth, G. (1969) Int. J. Appl. Rad. Isot. 20, 614–615
Radiation preservation of food, Proceedings of the Symposium organized jointly by IAEA and FAO, held in Bombay, November 13–17, 1972, IAEA, STI/PuB/317, Vienna, 1972
About this article
Cite this article
Tamminga, S.K., Beumer, R.R., van Kooij, J.G. et al. Microbiological possibilities to demonstrate that strawberries have been irradiated. European J. Appl Microbiol. 1, 79–93 (1975). https://doi.org/10.1007/BF01880622
- Special Group
- Solid Medium
- Untreated Sample
- Indicator Organism