Impact of carbon dioxide on the radial growth of fungi isolated from dairy environment

Abstract

In dairy industry, filamentous fungi are used as adjunct cultures in fermented products for their technological properties but they could also be responsible for food spoilage and mycotoxin production. The consumer demands about free-preservative products has increased in recent years and lead to develop alternative methods for food preservation. Modified Atmosphere Packaging (MAP) can inhibit fungal growth and therefore increase the food product shelf-life. This study aimed to evaluate radial growth as a function of CO₂ and more particularly carbonic acid for fourteen adjuncts and/or fungal spoiler isolated from dairy products or dairy environment by using predictive mycology tools. The impact of the different chemical species linked to CO₂ (notably carbonic acid) were study because it was reported previously that undissociated carbonic acid impacted bacterial growth and bicarbonates ions were involved in modifications of physiological process of fungal cells. A significant diversity in the responses of selected strains was observed. Mucor circinelloides had the fastest growth rates (μ > 11 mm. day^-1) while Bisifusarium domesticum, Cladosporium herbarum and Penicillium bialowiezense had the slowest growth rates (μ < 1 mm. day^-1). Independently of the medium pH, the majority of strains were sensitive to total carbonic acid. In this case, it was not possible to conclude if CO₂ active form was gaseous or aqueous so modeling were performed as a function of CO₂ percentage. Only Geotrichum candidum and M. circinelloides strains were sensitive to undissociated carbonic acid. Among the fourteen strains, P. bialowiezense was the less sensitive strain to CO₂, no growth was observed at 50% of CO₂ only for this strain. M. lanceolatus was the less sensitive strain to CO₂, the CO₂₅₀ which reduce the growth rates by 50% was estimated at 138% of CO₂. Low CO₂ percentage improved the growth of Penicillium expansum, Penicillium roqueforti and Paecilomyces niveus. Mathematical models (without and with optimum) were suggested to describe the impact of CO₂ percentage or undissociated carbonic acid concentration on fungal growth rate.

Keywords: Carbon dioxide; Carbonic acid; Modified atmosphere; Mycelial growth; Predictive mycology.