Using the gamma concept in modelling fungal growth: A case study on brioche-type products

Fungi are common spoilers of intermediate moisture foods such as bakery products. Brioche are bakery products prone to fungal spoilage due to their pH (5.8-6.2) and water activity (aw) (0.82-0.84). The aims of the present study were: (i) the identification of fungal species occurring in brioche products, (ii) the in vitro assessment of their growth potential, and (iii) the development of a validated growth model following the gamma concept. A total of 102 fungal strains were isolated, with Penicillium sp., Cladosporium sp., and Aspergillus sp. being the main genera, representing 90% of the isolates. Given the isolation frequency, any potential fungal prevalence throughout the bakery processs and/or the results of in vitro assessment of fungal growth potential under conditions mimicking brioche (pH, aw, temperature), Aspergillus flavus, Aspergillus fumigatus, and Penicillium sp. were selected for the development of the gamma model. According to in vitro validation, the model successfully predicted fungal growth, while on in situ experiments, the intrinsic parameters (aw and/or level of used preservative) of brioche in combination with packaging conditions (modified atmosphere) did not allow fungal growth.