Zuzana Barboráková

Tomatoes represent a suitable substrate for the growth of microscopic filamentous fungi and yeasts, including potentially toxigenic species. The aim of this study was to compare the mycocenosis of tomatoes from retail chains in Slovakia and Hungary, with an emphasis on species diversity and the ability of selected isolates to produce mycotoxins. A total of 30 tomato samples (Slovakia, n = 21; Hungary, n = 9) were analysed. Fungal genera were identified based on macro- and micromorphological characteristics, while identification at the species, section, or group level was performed using standard taxonomic keys. Selected isolates of the genera Penicillium, Aspergillus, Alternaria, and Fusarium were tested for their ability to produce selected mycotoxins in vitro using thin-layer chromatography (TLC). Yeasts were identified using MALDI-TOF MS. In total, nine genera of filamentous fungi were identified. The dominant genus was Penicillium (73.3%), followed by Alternaria (30.0%). The most frequently isolated taxa were Penicillium olsonii (56.7%) and the Alternaria arborescens species group (36.6%), both detected in Slovak and Hungarian samples. Several isolates of Penicillium, Aspergillus, Alternaria, and Fusarium demonstrated the ability to produce at least one mycotoxin, including aflatoxins B1 and G1, patulin, citrinin, roquefortine C, penitrem A, cyclopiazonic acid, griseofulvin, alternariol, alternariol monomethylether, T-2 toxin, HT-2 toxin, and zearalenone. The results revealed differences in fungal species diversity and toxigenic profiles between Slovak and Hungarian tomatoes and highlight the potential food safety risks associated with the presence of mycotoxigenic fungi in fresh tomatoes.

The aim of this study was to investigate differences in the dynamics of ochratoxin A (OTA) production by various Aspergillus isolates under different cultivation conditions. Nine strains representing A. westerdijkiae, A. ochraceus, A. sulphureus, A. carbonarius, and A. albertensis were tested on malt extract agar (MEA), Czapek yeast extract agar (CYA), potato dextrose agar (PDA), and yeast extract sucrose agar (YES). Cultivations were performed at 18 °C, 22 °C, 25 °C, and 30 °C, and OTA production was monitored on the 6th, 10th, 14th, 21st, and 30th days using HPLC analysis. OTA yields strongly depended on the producing strain, with significant variability even among isolates of the same species. The most productive strain was A. ochraceus from cereals with a maximum concentration of 848 µg g⁻¹ OTA, followed by two isolates of A. westerdijkiae from grapes of Slovak origin (591 and 479 µg g⁻¹), and A. sulphureus from soil (546 µg g⁻¹). In contrast, A. carbonarius strains showed the weakest OTA production. Across media, YES supported the highest toxin levels, whereas the most favourable cultivation temperatures were 18 °C and 25 °C. Each strain reached its production maximum at different time points, highlighting the strain-specific nature of OTA biosynthesis.

This study investigated the contamination of 22 selected green coffee bean samples grown in South and Central America by microscopic filamentous fungi and their potential for mycotoxin (ochratoxin A, aflatoxins) production. A total of 2860 isolates belonging to 11 genera, including Aspergillus, Penicillium, Fusarium, Syncephalastrum, and Rhizopus, were identified. The genus Aspergillus was present in all samples (frequency of occurrence – Fr 100.00%, relative density – RD 88.49%) and exhibited the highest frequency, with sections Nigri (Fr 95.45%, RD 49.86%), Aspergillus (Fr 90.90%, RD 8.36%), and Flavi (Fr 77.27%, RD 27.94%). Toxigenic screening by thin layer chromatography (TLC) revealed that 27.8% of Aspergillus and 71.4% of Penicillium tested isolates were capable of producing mycotoxins, including ochratoxin A and aflatoxins. While aflatoxins were not detected in the green coffee beans by HPLC-FLD, ochratoxin A was found in 68.2% of them at low concentrations (from 0.375 to 1.487 ng/kg). These findings emphasize the importance of monitoring fungal contamination and mycotoxin levels in green coffee beans to ensure food safety and quality in the coffee industry.

Black soldier fly larvae (BSFL), Hermetia illucens, have shown remarkable potential for food waste bioconversion, contributing to sustainability and waste management efforts. This study evaluated the effects of different food waste compositions (three types of diets: egg pasta in milk, rice with peas, and couscous mixture with egg, spinach, and carrot peels) and their microbial quality (fresh vs. spoiled) on BSFL bioconversion efficiency, microbiology, and nutritional value. Microbiological analyzes of the larvae were performed using the plate dilution method and MALDI-TOF mass spectrometer. All test variants spotted successful bioconversion. However, bioconversion efficiency (BE) and waste reduction rate (WR) were highest for couscous-based diets, with fresh couscous yielding a highest BE of 27.41% and WR of 81.34%. Nutritionally, larvae reared on mixture of couscous, egg, spinach, and carrot peels displayed the highest protein content (up to 35.5%). Microbial analysis indicated increased microbial counts, particularly Enterobacteriaceae and spore-forming bacteria, in larvae fed spoiled diets. Potentially pathogenic microorganisms such as Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, and Morganella morganii were detected, underscoring the need for microbial safety measures in BSFL-based applications. This study highlights the critical role of feed composition and quality in determining the efficiency and safety of BSFL bioconversion, providing valuable insights for optimizing their use in sustainable food waste management and as a resource in feed or food production.

This study assessed the bioconversion efficiency of Hermetia illucens larvae (BSFL) fed on food waste stored under different conditions, focusing on the nutritional and microbial quality of the resulting larval biomass. Food waste was prepared as a fresh diet (FD) or naturally contaminated and stored at 20–22 °C (OS-T, opened storage-tempered) or under refrigeration, at 5–8 °C (CS-C, closed storage-cooled). Refrigerated, closed storage (CS-C) led to the highest rates of waste reduction (91.0%) and bioconversion efficiency (30.2%), with larvae exhibiting the highest protein content (36.83%) compared to the FD (35.5%) and OS-T (34.71%) groups. Microbiome analysis revealed that the CS-C condition promoted beneficial yeasts like Pichia and Diutia, which correlated positively with improved protein content and microbial safety. In contrast, OS-T storage supported spoilage fungi (Mucor, Rhizopus) and elevated total aerobic counts (7.28 log CFU/g), indicating higher microbial risks. The observed trends in waste reduction and protein content most probably relate to differences in microbial profiles, as controlled cooling affected microbial dynamics, preserving substrate quality and supporting larval growth. These findings emphasize the importance of refrigerated, closed storage to optimize bioconversion, improve larval nutritional value, and minimize microbiological hazards.

Black soldier fly larvae (BSFL) are considered a sustainable protein source and an effective means of recycling organic waste. They are rich in nutrients, including proteins and lipids, making them suitable for animal feed and potentially for human consumption. In addition to their nutritional benefits, BSFL also have environmental benefits, i.e., reducing waste and greenhouse gas emissions. However, concerns about their safety persist, particularly regarding contamination by pathogenic microorganisms, toxins, and heavy metals. The aim of our study was to investigate the effect of different feedstuffs on heavy metal accumulation and on the microcenosis (Enterobacteriaceae, aerobic bacterial endospores, microscopic filamentous fungi) of BSFL. BSFL were fed four feed treatments (I: egg pasta cooked in whole milk; II: cooked rice with peas; III: poultry feed; and IV: cooked couscous, boiled eggs, and raw carrot peels). The results of our study showed that feed variants significantly affect the microbial safety of BSFL. Using MALDI-TOF, we identified 13 species of family Enterobacteriaceae in BSFL, including facultative pathogenic species Enterobacter cloacae, Klebsiella aerogenes, Klebsiella pneumoniae, Morganella morganii, and Proteus mirabilis. Our research confirmed that BSFL fed different feed variants under experimental laboratory conditions contained heavy metals, including cadmium, copper, manganese, molybdenum, nickel, lead, and zinc. Cadmium concentrations in BSFL ranged from 0.12 to 0.18 mg.kg-1, with the highest values measured in BSFL in variant IV.

Recent reports of P. olsonii causing postharvest rot of cherry tomatoes emphasize the need for effective strategies to prolong fruit shelf life. This study is the first to explore the use of essential oils (EOs), recognized for their antimicrobial properties, as a potential method to prevent postharvest losses from P. olsonii. Antifungal activity was tested for ten EOs at a concentration of 625 μL/L using the vapor diffusion method. Thyme, wild thyme, savory, oregano, and marjoram completely inhibited fungal growth over 14 days. Thyme EO, at a minimum inhibitory concentration (MIC) of 250 μL/L, fully inhibited all strains, while oregano, wild thyme, and savory were effective at 500 μL/L. Marjoram EO showed weaker activity. The lowest IC90 values, ranging from 35.72 to 162.72 μL/L, were estimated for thyme and oregano. In cherry tomatoes, oregano EO completely halted P. olsonii growth at 250 μL/L; thyme was effective for seven days; wild thyme and savory for two days. Thyme EO prevented P. olsonii spore germination at 500 μL/L for seven days, though germination occurred at half that concentration. The IC90 values varied between 256.2 and 138.7 μL/L depending on the strain. The vapor phase of EOs at 125 μL/L influenced the sensory characteristics of cherry tomatoes; however, for thyme and oregano, this effect was not negative due to their culinary association with tomato flavor. The selected EOs could be used to control and prevent postharvest fruit losses, but further research is needed to optimize their application.

In this study, contamination by microscopic fungi (focused on Penicillium and Aspergillus species) of 75 fruit samples (strawberries, blackberries, blueberries, raspberries, grapes) and 29 tomato samples, which were obtained from Slovak stores was investigated. Totally 93.3% of fruit samples were contaminated with micromycetes (70.6% Botrytis spp., 52.0% Cladosporium spp., 42.7% Penicillium spp., 13.3% Rhizopus spp., 8.0% Alternaria spp., 6.7% Mucor spp., 5.3% Aspergillus spp., 4.0% Fusarium spp., and 1.3% Epicoccum spp.) and 6.7% of samples were contaminated with yeasts. The presence of 15 species of the genus Penicillium in fruits, namely P. atramentosum, P. aurantiogriseum, P. brevicompactum, P. bialowiezense, P. citrinum, P. crustosum, P. digitatum, P. expansum, P. fellutanum, P. glabrum, P. hordei, P. italicum, P. kiamense, P. olsonii, and P. purpurescens was found. With the highest frequency, P. brevicompactum (12.0%) and P. expansum (10.7%) were isolated from fruits. Four isolates of the genus Aspergillus were isolated from fruit samples (A. section Clavati, A. section Flavi, and two isolates of A. section Nigri). Thin layer chromatography (TLC) was used for testing of mycotoxin production by selected fungal isolates. Overall, 93.3% of tested Penicillium isolates and one tested Aspergillus of section Clavati proved the ability to produce at least one of the tested mycotoxins. As for tomato samples, 93.1% were contaminated with microscopic filamentous fungi (79.3% Penicillium spp., 24.1% Botrytis spp. and Alternaria spp., 10.3% Cladosporium spp., Mucor spp. and Rhizopus spp., 6.9% Aspergillus spp. and 3.4% Fusarium spp.) and 6.9% samples were contaminated with yeasts. In 65.5% of tomato samples, the occurrence of 8 species of the genus Penicillium (P. brevicompactum, P. crustosum, P. expansum, P. griseofulvum, P. italicum, P. olsonii, P. sublectaticum, P. thomii), and two species of the genus Aspergillus (from section Circumdati and Flavi) was recorded. P. olsonii (58.6%) and P. griseofulvum (10.3%) were isolated with the highest frequency. All 7 tested Penicillium isolates (100.0%) and 1 isolate of the genus Aspergillus (section Flavi), which were obtained from tomatoes, had the ability to produce at least one of the tested mycotoxins. Aspergillus section Flavi isolate (from tomatoes of Slovak origin) produced 5.5 µg.mL-1 of aflatoxin B1, 4.2 µg.mL-1 of aflatoxin B2, 154.4 µg.mL-1 of aflatoxin G1, and 5.6 µg.mL-1 of aflatoxin G2 on 14th day of cultivation on liquid YES medium at 25±1 °C in darkness, and detected by high pressure liquid chromatography (HPLC).

Essential oils (EOs) from aromatic plants seem to have the potential to control several fungal pathogens and food contaminants. Botrytis cinerea is the main strawberry fruit contaminant causing high losses during storage. Here, thirteen EOs applied in the vapor phase were evaluated for their potential to inhibit the growth of three different strains of B. cinerea isolated from strawberry fruits. Eight EOs (lemongrass, litsea, lavender, peppermint, mint, petitgrain, sage, and thyme) were able to completely inhibit the growth of B. cinerea for 7 days when applied at a concentration of 625 μL·L⁻¹. Four EOs with the lowest minimal inhibition concentrations (thyme, peppermint, lemongrass, and litsea) have been tested on strawberry fruits intentionally inoculated by B. cinerea. All four EOs showed high inhibition at a concentration of 250 or 500 μL·L⁻¹, but only peppermint EO was able to completely inhibit B. cinerea lesion development at a concentration of 125 μL·L⁻¹. The sensory evaluation of strawberries treated by EOs at a concentration 125 μL·L⁻¹ resulted in a statistically significant decrease in taste, aftertaste, aroma, and overall quality. Lemongrass and litsea EOs scored better than thyme and peppermint ones, thus forming two viable methods for B. cinerea suppression and the extension of packed strawberries’ shelf life.