Microbiological Quality of Toroi: A Māori food delicacy
Dixon, L. L. (2007). Microbiological Quality of Toroi: A Māori food delicacy (Thesis, Master of Philosophy (MPhil)). The University of Waikato, Hamilton, New Zealand. Retrieved from http://hdl.handle.net/10289/2229
Permanent Research Commons link: http://hdl.handle.net/10289/2229
A study was undertaken to determine the food safety of the fermented Māori delicacy, Toroi. Ten batches of Toroi were prepared by a commonly used traditional method that consisted of boiling the vegetable component, either watercress or puha, and combining it with chopped mussel flesh. The mixture was cooled and then stored in a refrigerator for up to eight months to allow natural fermentation to take place. All ingredients were sourced from retail outlets. The Toroi was examined at intervals over eight months for a range of pathogens (seven in all) that have been related to incidents of food poisoning in ready-to-eat foods in New Zealand. The survival of a faecal contamination indicator, the laboratory grown strain Escherichia coli NZRM 916, was mapped over eight months. Two strategies to prevent the growth of Listeria monocytogenes in Toroi were also investigated. Only one of the seven pathogens sought was recovered from any sample. This pathogen was Bacillus cereus, a spore-former known to be associated with vegetables. All batches contained B. cereus on the day of preparation but after two weeks refrigerated storage there was no further recovery from any sample. There was a very low incidence of natural E. coli in the Toroi, consistent with levels permitted in mussels sold in retail outlets. The laboratory grown strain, E. coli declined substantially over two months and was not recovered from any samples at eight months. A laboratory grown strain of Listeria monocytogenes, (L70) was added to Toroi and grew well with an increase in concentration of about seven-fold, over 19 days storage in a refrigerator. A bacteriocin producing lactic acid bacterium, Lactobacillus sake Lb706, was added in combined culture with L. monocytogenes to Toroi. It was found that at least 5 x108 L. sake cells were required as an inoculum to ensure elimination of L. monocytogenes from the Toroi. When a purified bacteriocin; nisin, was added, a concentration of 10 mg g-1 in the Toroi was required to eliminate L. monocytogenes. The inhibition study results suggest that unacceptably high inocula or purified bacteriocin would be required to prevent the growth of L. monocytogenes in Toroi. The results of this suggest that Toroi be prepared from mussels either purchased from a retail outlet or harvested from sites known to be free from contamination. Toroi should be safe to eat if prepared carefully, chilled promptly and thoroughly and allowed to ferment for at least two weeks. In addition, care should be taken to maintain Toroi at refrigerated temperatures until it is eaten.
The University of Waikato
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