Competitiveness of three biocontrol candidates against ochratoxigenic Penicillium nordicum under dry-cured meat environmental and nutritional conditions.

The environmental conditions during the ripening of dry-cured meats and their nutritional composition promote the colonisation of their surface by Penicillium spp., including P. nordicum producer of ochratoxin A (OTA). The objective of this work was to study the competitiveness of three potential biocontrol candidates (Debaryomyces hansenii FHSCC 253H, Enterococcus faecium SE920 and Penicillium chrysogenum CECT, 20922) against the ochratoxigenic P. nordicum FHSCC4 under environmental and nutritional conditions simulating the ripening of dry-cured meat products. For this, the nutritional utilisation pattern, niche overlap index (NOI), interactions by dual-culture assays and OTA production were determined. The number of carbon sources (CSs) metabolised depended on the microorganism and the interacting water activity (aw) x temperature conditions. The number of CSs utilised by both filamentous fungi was quite similar and higher than those utilised by D. hansenii and E. faecium. The yeast isolate metabolised a number of CSs much larger than the bacterium. The NOI values showed that, in general, P. nordicum nutritionally dominated E. faecium and D. hansenii regardless of the environmental conditions evaluated. The relationship between the toxigenic and non-toxigenic fungal isolates depended on the aw x temperature combinations, although in none of the conditions a dominance of P. nordicum was observed. According to the interaction assays, both D. hansenii and P. chrysogenum decreased the growth of P. nordicum. The effect of D. hansenii could be attributed to the production of some extra-cellular compounds, while the action of P. chrysogenum is likely related to nutritional competition. In addition, both P. chrysogenum and D. hansenii reduced the OTA levels produced by P. nordicum. The effect of the yeast was more pronounced decreasing the concentration of OTA at quantities lower than the limit established by the Italian legislation. Therefore, P. chrysogenum and D. hansenii can be suggested as biocontrol candidates in the manufacture of dry-cured meat products.

Exogenous trehalose enhanced the biocontrol efficacy of Hanseniaspora uvarum against grape berry rots caused by Aspergillus tubingensis and Penicillium commune.

BACKGROUND: Primarily, chemical pesticides are commonly used to control preharvest and postharvest diseases of fruits and vegetables. However, there is strong public concern regarding the human and environmental health problems that might emanate from the residues of these chemical pesticides. As a result, biocontrol is often preferred due to its safety for humans and animals. The microbial antagonists employed often encounter variable climatic conditions, which affect their efficacy. In this study, the biocontrol efficacy of Hanseniaspora uvarum enhanced with trehalose against Aspergillus tubingensis and Penicillium commune in grapes was investigated. RESULTS: H. uvarum Y3 pretreated with 2.0% w/v trehalose in nutrient yeast dextrose broth (NYDB) before used significantly inhibited the incidence of decay and lesion diameter without affecting the sensory qualities of the grapes stored at either 4 °C or 20 °C. There was also a significant (P < 0.05) increase in the population dynamics of H. uvarum that was pretreated with 2% trehalose compared to that of H. uvarum alone. The in vitro assay on spore germination revealed an inhibition of A. tubingensis and P. commune by 85.6% and 87.0% respectively. Scanning electron microscopy results showed that both untreated H. uvarum and H. uvarum pre-treated with the 2% w/v trehalose before use inhibited fungal mycelium and development of grape rot. CONCLUSION: The biocontrol efficacy of H. uvarum was enhanced against grape rot caused by A. tubingensis and P. commune. The findings indicate the potential applicability of trehalose in the enhancement of H. uvarum. © 2018 Society of Chemical Industry.

Combined effect of antagonistic yeast and modified atmosphere to control Penicillium expansum infection in sweet cherries cv. Ambrunés.

Fruit decay caused by pathogenic moulds is a major concern in the postharvest quality and shelf life of fruit. Blue mould decay is caused by Penicillium expansum (P. expansum) and is one of the most important postharvest diseases in cherries (Prunus avium L.). Synthetic fungicides are the main medium used to control pathogenic moulds. However, alternative approaches are available for developing safer technologies to control postharvest disease. An integrated approach that combines biological control, using antagonistic yeasts and modified atmosphere packaging (MAP) with cold storage is a promising alternative to synthetic fungicide treatment. In this work, two microperforated films (M10 and M50) and two antagonistic yeast strains (Hanseniaspora opuntiae L479 and Metschnikowia pulcherrima L672) were evaluated for their effectiveness to control the development of P. expansum in wounded cherries stored at 1°C. Results showed that the microperforated films had fungistatic effects, particularly M50, due to the level of CO2 achieved (mean CO2 of 11.2kPa at 35days), and the decrease in disease severity. Antagonistic yeasts, particularly Metschnikowia pulcherrima L672, delayed the development of P. expansum and decreased disease incidence and severity. The combination of MAP and antagonistic yeasts was the most effective approach to control P. expansum, during cold storage.

Inhibition of ochratoxigenic moulds by Debaryomyces hansenii strains for biopreservation of dry-cured meat products.

The ability of the osmotolerant yeast Debaryomyces hansenii to inhibit Penicillium nordicum, the most common ochratoxigenic mould encountered in dry-cured meat products, was evaluated. The antagonistic effect of ten D. hansenii strains isolated from dry-cured ham was screened in vitro using malt extract media and meat extract peptone media with the water activity (a(w)) adjusted to 0.97 and 0.90. A significant inhibition of the two tested P. nordicum strains by D. hansenii cells and cell-free supernatants was observed. At 0.97 a(w), increasing D. hansenii inoculum concentrations significantly improved the inhibition of mould growth on solid medium, whereas at 0.90 a(w) this was not always the case. As observed by bright field microscopy, most D. hansenii strains were able to delay P. nordicum spore germination when co-cultured in malt extract broth. D. hansenii FHSCC 253H showed the highest overall in vitro inhibition of ochratoxigenic mould growth, and was therefore chosen for co-cultivation assays in dry-cured ham slices incubated at 0.94 and 0.84 a(w) simulating ham ripening. Regardless of the experimental conditions tested, lower levels of the inoculated P. nordicum strain were detected in co-cultivation batches compared with batches without D. hansenii. The highest level of mould growth inhibition was observed in batches at 0.94 a(w). Ochratoxin A (OTA) production in ham samples was detected by HPLC-MS. Co-culturing of P. nordicum with D. hansenii FHSCC 253H resulted in lower OTA levels compared with control samples without D. hansenii. The decrease of the mycotoxin presence due to D. hansenii FHSCC 253H was more efficient at 0.94 a(w) (OTA was below the detection limit). In conclusion, D. hansenii is potentially suitable as a biopreservative agent for preventing ochratoxigenic mould growth and OTA accumulation in dry-cured meat products. The inoculation of D. hansenii should be made at the beginning of processing (at the end of post salting) when the a(w) of the product is still high (near 0.94). This action in addition to application of appropriate hygienic actions and control of temperature and relative humidity throughout ripening is required to reduce health risks due to OTA exposure.