Controle de Aspergillus ochraceus por Geotrichum candidum e leveduras autóctones: impacto na qualidade e segurança do queijo minas artesanal

Abstract

Queijo Minas Artesanal (QMA) has international prominence for cheese production, recognized by the Mondial du Fromage et des Produits Laitiers competition. This cheese is produced in a traditional way and maturation takes place on wooden shelves, exploiting the mycobiota that naturally occurs in the environment. The autochthonous fungi that colonize are mostly beneficial and provide important sensory characteristics, as well as bioprotective potential. However, undesirable ochraxigenic species such as Aspergillus ochraceus may develop. However, growth does not imply that ochratoxin A (OTA) is present in the product, since its biosynthesis is multifactorial. In this sense, the present study aimed to evaluate the influence of water activity (aw) and temperature on the growth and potential risk of OTA production (ORI) by A. ochraceus URMICRO 11727 and 11728 in a cheese-based medium, as well as to evaluate the efficiency of autochthonous fungi in controlling the growth of A. ochraceus URMICRO 11727 and ORI risk. The Central Composite Rotational Design (DCCR) was used with aw varying from 0.90 to 0.99 and temperatures from 15 to 35 °C. The ideal growth for A. ochraceus strains was between 0.94 and 0.99 aw and temperature between 23 and 32 °C. The conditions under which the strains showed the highest ORI risk were aw above 0.93 and temperature between 18 and 30 °C. Furthermore, it was observed that the condition 18°C and 0.98 aw requires greater attention, as it corresponds to the aw of the cheese in the initial process of QMA maturation. From these results, we selected three conditions (0.95 aw / 25 °C, 0.98 aw / 18 °C and 0.99 aw / 25 °C) in which the A. ochraceus strain URMICRO 11727 presented the highest risk ORI, in order to evaluate the antagonistic effect of autochthonous fungi. The results showed that all six native species tested exerted an antagonistic effect on co-cultivation. The highest inhibition rates were found using Geotrichum candidum as the antagonist species, with 88.37% and 100% reduction under conditions 0.98 aw /18 °C and 0.99 aw / 25 °C, respectively. The ORI risk was also significantly reduced, with emphasis on Yarrowia lipolytica, which completely inhibited ORI in all conditions evaluated. The effect of volatile organic compounds (VOCs) and soluble substances produced by antagonistic species was evaluated. We observed a reduction in the growth and sporulation of A. ochraceus due to the production of VOCs, with emphasis on G. candidum, which exerted a fungicidal effect under conditions 0.98 aw / 18 °C and 0.99 aw / 25 °C. The growth inhibition of A. ochraceus was probably based on synergistic effects of factors such as competition for nutrients and space and production of VOCs. The main VOCs with antifungal properties already reported were 2-methyl-1-butanol, 3-methyl-1-butanol and 2-phenylethanol, as detected by Headspace-Solid Phase Microextraction analysis coupled to Gas Chromatography with a Mass Spectrometry detector (HS-SPME-GC-MS). It is concluded that the presence of autochthonous species in the QMA confers protection, without altering the typicality of the product.