Exploring Biocontrol of Unwanted Fungi by Autochthonous Debaryomyces hansenii Strains Isolated from Dry Meat Products

Abstract

The exploration of alternatives to the use of chemical preservatives in food is a topic that has attracted great attention. The implementation of regulations associated with the reduction of these elements directly affects the production of cured meat products, with the premise of looking for more “natural” alternatives. From a previously identified collection of 24 strains of Debaryomyces hansenii, isolated from dry meat products of the “Valle de los Pedroches” (Córdoba), a screening was carried out to determine which strains had inhibitory potential against a battery of fungi belonging to the genera Aspergillus, Penicillium, and Candida. After a series of general trials, four strains showing the greatest potential were selected by a streak inhibition assay performed at several concentrations of NaCl. The inhibitory activity of the selected D. hansenii strains was later evaluated by measuring their fungal antagonistic diffusible and volatile compound production following radial inhibition and mouth-to-mouth approaches, respectively. Growth aspects, sporulation, and morphology changes were also considered during these assays. The results support ideas already raised in previous studies, such as the presence of D. hanseniii could imply a reduction of pathogenic fungi in food. Autochthonous yeast strains inhibited not only the mycelial growth, but also sporulation, which strengthens the biocontrol activity of this yeast. Our results show that, under certain conditions, all tested D. hansenii strains were able to alter the growth/development of fungi, being especially evident in the cases of Penicillium expansum and Aspergillus niger. Finally, our research can facilitate the future comparison of results in this area, since we contributed to standardize the methodology described to date, we quantified the number of yeast cells and spores used during the experiments, we homogenized growth conditions for both, yeasts, and molds, and applied an image analyzer software to quantify the growth of the studied microorganisms in solid media.

Perspectives on the Probiotic Potential of Indigenous Moulds and Yeasts in Dry-Fermented Sausages

“…A positive effect on the organoleptic characteristics of dry-fermented sausages has been associated with some of their native yeasts [ 22 , 23 , 25 , 34 ]. For this reason, several studies have been focused on the intended inoculation of D. hansenii , promoting colour development through oxygen absorption and proteolytic activity ( Table 1 ), which in turn results in the production of positive volatile compounds [ 23 , 35 , 36 , 37 , 38 , 39 , 40 ]. These volatile compounds are also the result of lipid oxidation and carbohydrate fermentation [ 35 ], producing compounds, such as 3-methylbutanol, 3-methylbutanal, and 2-propanone, which give dry-fermented sausages their highly appreciated characteristic aroma.…”

“…Another important property of D. hansenii as a dominant species in dry-fermented sausages, is its antimicrobial capacity [ 24 , 36 ]. Currently, the use of protective cultures in the meat industry is mostly limited to the antifungal capacity of bacteria, such as LAB [ 43 ].…”

“…However, yeasts isolated from meat products are also being evaluated for their potential as inhibitors of toxigenic microorganisms with a possible application in the meat industry [ 44 , 45 , 46 , 47 , 48 ]. One of the main hazards to be addressed using D. hansenii as a protective culture is that posed by toxigenic moulds because this yeast has been shown to have an impact on the metabolism of Penicillium verrucosum [ 48 , 49 ], Penicillium nordicum [ 44 , 45 , 46 , 50 ], Penicillium expansum [ 36 ], Aspergillus niger [ 36 ], Aspergillus parasiticus [ 51 , 52 ], Fusarium graminearium and Penicillium crustosum [ 24 ], Penicillium griseofulvum [ 53 ], and Aspergillus westerdijkiae [ 54 ] ( Table 2 ). Additionally, D. hansenii has displayed activity against some pathogenic yeasts, such as Candida albicans [ 36 ].…”

“…One of the main hazards to be addressed using D. hansenii as a protective culture is that posed by toxigenic moulds because this yeast has been shown to have an impact on the metabolism of Penicillium verrucosum [ 48 , 49 ], Penicillium nordicum [ 44 , 45 , 46 , 50 ], Penicillium expansum [ 36 ], Aspergillus niger [ 36 ], Aspergillus parasiticus [ 51 , 52 ], Fusarium graminearium and Penicillium crustosum [ 24 ], Penicillium griseofulvum [ 53 ], and Aspergillus westerdijkiae [ 54 ] ( Table 2 ). Additionally, D. hansenii has displayed activity against some pathogenic yeasts, such as Candida albicans [ 36 ]. Different mechanisms of its antagonistic action have been established for D. hansenii ( Table 2 ).…”