Proteolytic activity of Geotrichum candidum isolated from Natural Bloomy Rind Artisanal Minas Cheese

Geotrichum candidum is a fungus that is commonly associated with dairy products and plays an important role in the ripening of Natural Bloomy Rind Artisanal Minas Cheese (NBRAMC), where it is naturally predominant. G. candidum is linked to proteolysis and is responsible for the production of many compounds that are essential for flavor and aroma. Thus, this study aimed to evaluate the proteolytic capacity of G. candidum strains exhibiting distinct phenotypic characteristics and isolated from NBRAMC and the environment. Five strains were isolated from Artisanal Minas Cheese, and one was obtained from the wild environment. Qualitative evaluation of protease activity in the different G. candidum strains was performed using skim milk agar tubes. A volume of 6 µL of spore suspension at a concentration of 10⁵ spores/mL was inoculated into the agar, followed by incubation at 25 °C for 22 days. Proteolytic activity was assessed by measuring the length of the transparent region beneath the colony, resulting from the hydrolysis of milk proteins. Penicillium roqueforti and a non-identified bacterium isolated from milk were used as positive controls. Analysis of variance and Tukey’s test (p < 0.05) were performed using Sisvar software. Protease activity was found to vary among the G. candidum strains. Five out of six strains produced clear zones of different length, although all were smaller than those observed for the positive controls, P. roqueforti and the bacterium, at 48.7 mm and 52.7 mm, respectively. Notably, the G. candidum strain isolated from the environment was among those with the highest proteolytic activity, with lengths ranging from 17.7 mm to 23.3 mm. These findings highlight the intraspecific variability of G. candidum. This variability may explain the diversity of sensory profiles observed in NBRAMC, a cheese whose production relies on the natural, uninoculated development of G. candidum, which is not controlled during the process.