Iron fortification modifies the microbial community structure and metabolome of a model surface-ripened cheese

Iron is a vital micronutrient for nearly all microorganisms, serving as a co-factor in critical metabolic pathways. However, cheese is an iron-restricted environment. Furthermore, it has been demonstrated that iron represents a growth-limiting factor for many microorganisms involved in cheese ripening and that this element is central to many microbial interactions occurring in this ecosystem. This study explores the impact of iron fortification on the growth and activity of a reduced microbial community composed of nine strains representative of the microbial community of surface-ripened cheeses. Three different iron compounds (ferrous sulfate, ferric chloride, ferric citrate) were used at three different concentrations, i.e., 18, 36, and 72 μM, to fortify cheese curd after inoculation with the consortium. This treatment significantly enhanced the growth of certain cheese-ripening bacteria in curd, resulting in substantial changes in the volatilome and metabolome profiles. These observations were dose-dependent, with more pronounced effects detected with higher iron concentrations. No statistically significant difference was observed in the microbial composition based on the iron compounds used for fortification, but this factor had an impact on the volatilome and amino acids profile. These findings highlight the importance of iron availability for the behavior of cheese microbial communities. They also open novel perspectives on cheesemakers' use of iron fortification to control microbial growth and improve cheese quality.