A Microsoft © Excel tool for testing ten different types of microbial survival models on user-specific experimental data

What is GInaFiT?

 

 

GInaFiT is a freeware add-in for Microsoft © Excel, aiming at bridging the gap between people developing predictive modelling approaches and end-users in the food industry or research groups not disposing of advanced non-linear regression analysis tools.

The tool is useful for testing ten different types of microbial survival models on user-specific experimental data relating the evolution of the microbial population with time. The ten model types are: (i) classical log-linear curves, (ii) curves displaying a so-called shoulder before a log-linear decrease is apparent, (iii) curves displaying a so-called tail after a log-linear decrease, (iv) survival curves displaying both shoulder and tailing behavior, (v) concave curves, (vi) convex curves, (vii) convex/concave curves followed by tailing, (viii) biphasic inactivation kinetics, (ix) biphasic inactivation kinetics preceded by a shoulder, and (x) curves with a double concave/convex shape. The models were originally published as Bigelow and Esty (1920), Cerf (1977), Geeraerd et al. (2000), Mafart et al. (2002), Albert and Mafart (2005), Geeraerd et al. (2005) and Coroller et al. (2006).

Next to the obtained parameter values, the following statistical measures are automatically reported: standard errors of the parameter values, the Sum of Squared Errors, the (Root) Mean Sum of Squared Errors, the R2 and the adjusted R2. In addition, t4D, the time needed for a 4 log reduction of the initial microbial population, as originally proposed by Buchanan et al. (1993), is also automatically reported (for data sets covering at least 4 decimal reductions).

The tool can be used in two ways. On one hand, for end-users having already a qualitative idea of the general shape of their survival curves, the choice for one of the model types is obvious. On the other hand, if the end-user does not have a clear idea yet, two or more of the different model types available can be tested and compared. The time for a 4 decimal reduction can be useful to summarize the information present in a data set, for example, if a common survivor curve shape can not be selected for a range of different conditions tested.

Additionally, the tool has some built-in features testing for mis-use, for example, when trying to identify a model with tailing on data not having a tail or when using a too limited number of data points (observations) in comparison with the number of parameters in the model type chosen (the number of parameters ranges from 2 to 5 for the ten model types available).

Further illustration on the use of GInaFiT can be found in Geeraerd et al. (2005).

References

 

 

  • Albert I. and P. Mafart 2005. A modified Weibull model for bacterial inactivation, International Journal of Food Microbiology, 100, 197-211.
  • Bigelow W.D. and J.R. Esty 1920. The thermal death point in relation to typical thermophylic organisms, Journal of Infectious Diseases, 27, 602-617.
  • Buchanan R.L., Golden M.H. and Whiting R.C. 1993. Differentiation of the effects of pH and lactic or acetic acid concentration on the kinetics of Listeria monocytogenes inactivation, Journal of Food Protection 56, 474-478, 484.
  • Cerf O. 1977. A review. Tailing of survival curves of bacterial spores, Journal of Applied Microbiology, 42, 1-19.
  • Coroller L., Leguerinel I., Mettler E., Savy N. and Mafart P. 2006. General model, based on two mixed Weibull distributions of bacterial resistance, for describing various shapes of inactivation curves, Applied and Environmental Microbiology, 72 (10), 6493-6502.
  • Geeraerd A.H., C.H. Herremans and J.F. Van Impe 2000. Structural model requirements to describe microbial inactivation during a mild heat treatment,International Journal of Food Microbiology, 59, 185-209.
  • Geeraerd A.H., V.P. Valdramidis and J.F. Van Impe 2005. GInaFiT, a freeware tool to assess non-log-linear microbial survivor curves, International Journal of Food Microbiology, 102, 95-105.
  • Mafart P., O. Couvert, S. Gaillard and I. Leguerinel 2002. On calculating sterility in thermal preservation methods: application of the Weibull frequency distribution model, International Journal of Food Microbiology, 72, 107-113.

History of GInaFiT

 

 

History of GInaFiT GInaFiT 1.2 was on-line available from October 2003 to July 2004, followed by GInaFiT 1.3 till April 2005, GInaFiT 1.4.1 from May to July 2005, GInaFiT 1.4.2 from August 2005 to May 2008, followed by GInaFiT 1.5 till March 2012. As they are part of version 1.6, these older versions are no longer distributed.