Selection of non-conventional yeasts that limit the growth of Penicillium roqueforti fungi posing a threat in bakery products - Izabela Podgórska-Kryszczuk
Baked goods are perishable foods and particularly vulnerable to toxigenic fungi, primarily of the Aspergillus and Penicillium genera. A strategy to control them is the addition of preservatives, but they have some disadvantages, i.e. they can change the aftertaste of products made from light flours, delay the fermentation of dough, and are not indifferent to the consumer. In addition, chemical preservatives are ineffective against some common fungal species in baked goods, such as Penicillium paneum and P. roqueforti. The threat to food health safety posed by the presence of pathogenic fungi and their toxic metabolites, as well as the increasing demands of consumers, the demand for natural products without the addition of chemical compounds, prompts the search for new methods of bread fixation and elimination of harmful microorganisms and their metabolites. Currently, there are high hopes for the development of new starter cultures with antimicrobial activity, which would largely eliminate preservatives added to baked goods. The primary objective of this research was to select and characterise yeast strains that synthesise antifungal compounds against the toxigenic fungus Penicillium roqueforti, which poses a serious threat, especially in the baking industry. The yeasts most effective in vitro (collection isolates and those isolated from cereal ears) were selected. The mechanisms of action of the most effective yeast strains - competition for nutrients and space, the ability to inhibit pathogen spore germination, the ability to produce lytic enzymes (β-1,3-glucanase, chitinase, protease, cellulase), the ability to produce siderophores, and the ability to produce volatile metabolites that inhibit pathogen mycelial growth - were also investigated. The stress resistance of the selected isolates was also determined - thermotolerance, resistance to freezing and thawing, tolerance to pH changes, to low/high osmotic stress, to ethanol content in the medium, and sensitivity to digestive enzymes. The safety of selected yeasts was also tested by determining their ability to produce biogenic amines, and whether they produce hydrogen sulfide. The effect of adding non-conventional yeast on bread quality (volume) and shelf life, until signs of microbial spoilage appeared, was also evaluated under laboratory conditions.
Keywords: biocontrol; microbiology; Non-conventional yeast; Penicillium roqueforti