Validation of Shelf-life Model designed for Cold Stored Foods - Characterization of spoilage flora and initial contamination

Examensarbete för masterexamen

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Type: Examensarbete för masterexamen
Master Thesis
Title: Validation of Shelf-life Model designed for Cold Stored Foods - Characterization of spoilage flora and initial contamination
Authors: Lysberg, Emelie
Abstract: Today large amounts of good quality cold stored foods are thrown away due to expiration of labeled static shelf life. In order to minimize waste and improve product safety there is a need to study the concept of a dynamic shelf life. One approach in this area is the three year Vinnova funded innovation project DYNAHMAT (in Swedish: Dynamiskt Hållbarhetsdatum för Minimerat Svinn), operated by Lund University together with the Swedish Institute for Food and Biotechnology (SIK) and Malmö University. The project goal is to develop intelligent logistics- and packaging systems that communicate and predict quality and product safety of cold stored food in real-time. Since shelf-life of such products most often is limited by microbial action models describing growth of the specific organism responsible for spoilage must be applied. For the models to predict time to spoilage an input variable representing the initial amount of the specific spoilage organism (SSO) is needed. The aim of this thesis work is to determine the initial concentration of the SSO responsible for spoilage of modified atmosphere packed (MAP) cod, previously identified as Photobacterium phosphoreum. With the starting concentration known, the purpose is furthermore to validate an existing shelf-life predictive model that is ought to be applied in the DYNAHMAT project. Moreover, the intention is to identify and characterize the general spoilage flora of MAP cod. Initial cultivation and storage studies revealed aerobically incubated Long and Hammer plates as the most appropriate method for determination of the initial amount of the SSO. Partial 16s rRNA gene sequencing identified glass-like colonies growing on these plates as members of the Photobacterium family, but was unfortunately not enough to distinguish P. phosphoreum from other closely related Photobacterium species. Based on the assumption that observed glass-like colonies are P. phosphoreum, performed long term storage study resulted in an initial concentration of 2.15 log (cfu/g) for fish fillets packed in an modified atmosphere immediately after filleting. Shelf-life model validation revealed that the model is able to accurately illustrate growth of P. phosphoreum and based on existing sensory rejection evaluation hence predict shelf-life of MA-packed cod. Future studies including multi-locus gene analysis need to be performed in order to reliably conclude that glass-like colonies aerobically cultivated on Long and Hammer plates exclusively belong to the specie P. phosphoreum. If the outcome of these studies reveals a mixed Photobacterium flora the respective species must be inoculated into fresh cod and spoilage development must be studied in order to confirm P. phosphoreum as the SSO of MA-packed cod and exclude other species contribution to fish spoilage. Last but not least, the performed long term storage study needs to be repeated in order to find a truly representative initial concentration of the SSO that hence can be used to accurately predict shelf-life of MA-packed cod in the DYNAHMAT project.
Keywords: Livsvetenskaper;Biologiska vetenskaper;Annan naturvetenskap;Livsmedelsteknik;Livsmedelsvetenskap;Life Science;Biological Sciences;Other Natural Sciences;Food Engineering;Food Science
Issue Date: 2014
Publisher: Chalmers tekniska högskola / Institutionen för kemi- och bioteknik
Chalmers University of Technology / Department of Chemical and Biological Engineering
Collection:Examensarbeten för masterexamen // Master Theses

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