Characterization of secondary starters occurring on traditional Apulian cheese: a chance to improve and control the aging process

Filamentous fungi contribute significantly to the organoleptic characteristics of mature cheese when used as secondary starters during the aging process, because their metabolic activities can positively influence aroma, texture, colour, and appearance. However, uncontrolled fungal colonisations may include species capable of producing mycotoxins, secondary metabolites that pose risks to human and animal health. To mitigate these hazards and enhance cheese quality, the deliberate addition of selected secondary starters can be an effective strategy in leading the aging process. In this study aiming to select appropriate strains, we evaluated the pro-technological activities of nineteen Penicillium spp. strains, isolated from the surface of Apulian cheese aged in cave and refrigerated cell. The fungal strains were DNA-based identified and further characterized in vitro, through polyphasic approach. Metabolic activities, such as proteolysis and lipolysis, responsible for flavour development, and the capacity to grow on a cheese-like synthetic substrate were evaluated. A subset of strains was further assessed for the volatile organic compounds (VOCs) emission, providing insights into related potential role in the sensory profile of aged cheese and in the identification of markers for traceability. Additionally, the interaction between Penicillium spp. strains and Aspergillus westerdijkiae, an unwanted ochratoxin A-producing species often associated with natural-aged cheese, was evaluated in vitro. Among the selected strains, Penicillium biforme ITEM 19069 emerged as good candidate as potential secondary starter, due to its compatibility with the cheese-like environment, its high proteolytic and lipolytic activities, as well as a characteristic VOCs emission, and ability to affect the growth of A. westerdijkiae.