Scientists examine growth curves for lactobacilli (LAB) in smoked ham

The research is part of a Masters paper by Needa Shaheen and Linda Sauer, from the University of Borås, Sweden, entitled ‘Validation of predictive models to predict the growth of lactic acid bacteria in cured ham’.

SP Food Bioscience

The work has been carried out at SP Food Bioscience, (formerly SIK – The Swedish Institute for Food and Biotechnology) with Elizabeth Fuek-Lagerstedt as examiner and Klara Båth and Marie Blomqvist, SP Food and Bioscience as supervisors.

The study lies within the VINNOVA-supported project DynhaMat, which is an acronym for ‘Dynamic shelf life expiration date for minimised food wastage’.

“DynhaMat aims to develop an intelligent logistic and packaging system, that can communicate and predict quality of cold stored foods in real time, based on novel sensors that measure parameters affecting food quality combined with predictive models,​” said Shaheen.

The objective of the Masters project was to determine growth curves for lactobacillae (LAB) in smoked ham I the temperature range +4°C to +12°C, the results of which were used for validating three available predictive models.

Lmonocytogenes in the ham

Also, inoculation tests with Lmonocytogenes in the ham were carried out to determine if growth rate was influenced by the LAB present.

The results showed, as expected, that growth and rate of spoilage of the smoke ham increased with temperature.

The determined initial concentration of the growth curves varied somewhat, which may be caused by a possible lag phase, which had not been considered, added Shaheen.

The three predictive models used (by Kreyenschmidt, Mataragas and Devlieghere) were validated by calculating accuracy and bias factor, showing they were suitable for predicting growth of LAB.

Devlieghere model slightly over-predicted growth

However, their application indicated the first two models under-predicted microbial growth, while the Devlieghere model slightly over-predicted growth, presenting an extra safety factor.

Experiments, where Lmonocytogenes was inoculated into the product, were carried out to assess if its growth was influenced by the presence of LAB.

Growth was found to be slowed, indicating such an influence, confirmed by calculations using FSSP prediction software.