The Hurdle Technology Metaphor Revisited

Abstract

In the original and variants of the hurdle technology metaphor, factors affecting a food preservation process’s efficacy are represented by horizontally spaced athletic hurdles that the targeted microbes have to overcome or expire. But while the utility of combined preservation methods and exploiting synergism is not in doubt, there are issues with the hurdles metaphor itself, namely assignment of the same icon to factors of different categories, the lack of clear relationship between the hurdles’ heights, shape, and the distances between them and the actual antimicrobial effect. According to Troller (1983), a more suitable metaphor is a wall constructed from the vertically stacked obstacles whose total height represents the magnitude of the challenge to the microbes’ survival or sustained growth. His idea can be refined by adding a distinction between active lethal or growth suppressing agents, such as heat, ultra high pressure and chemical antimicrobials, and auxiliary non-lethal factors which only affect the former’s efficacy, such as pH, a_W, and oxygen tension. In this revised metaphor, those of the first kind are the stacked obstacles forming the wall, and those of the second kind only affect their heights. Since microbial inactivation or growth suppression is manifested in a survival or growth curve, not a number, the role of kinetics, absent in the traditional metaphor, ought to be factored in too. This can be done, by defining the effective combined wall’s height in terms of the microbial population’s size reduction for inactivation, or its growth level for shelf life expiration.