Ochratoxin A-producing fungi from grapes intended for liqueur wine production

Effects of Aspergillus niger Infection on the Quality of Jujube and Ochratoxin A Cumulative Effect

The jujube is one of the most popular fruits in China because of its delicious taste and high nutritional value. It has a long history of usage as an important food or traditional medicine. However, the jujube is easily infected by fungi, which causes economic losses and threatens human health. When the jujube was infected by Aspergillus niger (H1), the changes in nutritional qualities were determined, such as the content of total acid, vitamin C, reducing sugar, etc. In addition, the ability of A. niger (H1) to produce ochratoxin A (OTA) in different inoculation times and culture media was evaluated, and the content of OTA in jujubes was also analyzed. After jujubes were infected by A. niger (H1), the total acid, and vitamin C contents increased, while the total phenol content decreased, and the reducing sugar content increased after an initial decrease. Although A. niger (H1) infection caused the jujubes to rot and affected its quality, OTA had not been detected. This research provides a theoretical foundation for maximizing edible safety and evaluating the losses caused by fungal disease in jujubes.

Environmental Conditions Affecting Ochratoxin A during Solar Drying of Grapes: The Case of Tunnel and Open Air-Drying

Drying optimization, to mitigate fungal growth and Ochratoxin A (OTA) contamination is a key topic for raisin and currant production. Specific indicators of environmental conditions and drying properties were analyzed using two seedless grape varieties (Crimson—red and Thompson—white), artificially inoculated with Aspergillus carbonarius under open air and tunnel drying. The air temperature (T), relative humidity, grape surface temperature (T_s) and water activity throughout the drying experiment, the grapes’ moisture content and the fungal colonization and OTA contamination during the drying process and their interactions were recorded and critically analyzed. Drying properties such as the water diffusivity (D_eff) and peel resistance to water transfer were estimated. The grapes T_s was 5–7 °C higher in tunnel vs. open air–drying; the infected grapes had higher maximum T_s vs. the control (around 4–6 °C). OTA contamination was higher in tunnel vs. open air–dried grapes, but fungal colonies showed the opposite trend. The D_eff was higher in tunnel than in the open air–drying by 54%; the infected grapes had more than 70% higher D_eff than the control, differences explained by factors affecting the water transport. This study highlighted CFU and OTA indicators that affect the water availability between red and white grapes during open air and tunnel drying, estimated by the D_eff and peel resistance. This raises new issues for future research.

Antifungal activity of Saccharomyces cerevisiae and assessment of ochratoxigenic load on currants by means of Real Time PCR

Currants are prone to contamination by ochratoxin during cultivation, processing and storage conditions. Saccharomyces cerevisiae is considered to be among the main species of grape yeast flora able to control antagonistic fungi. In this study, the potential of S. cerevisiae Y₃₃ was investigated to inhibit the growth of several fungal species indigenous to the microbiota of grapes. Moreover, the efficacy of this yeast species was investigated to inhibit OTA by toxin producing fungi both in vitro and in situ. For this purpose thirty-five different fungal species, belonging to the genera Aspergillus, Penicillium, Cladosporium, Fusarium and Alternaria interacted in vitro with S. cerevisiae on Malt Extract agar plates, stored at 25 °C for 14 days. Results showed that the highest OTA producer A. carbonarius F₇₁ was inhibited more than 99% from day 7, in contrast to A. niger strains that presented enhanced OTA production at day 14 due to interaction with S. cerevisiae Y₃₃. Additionally, the antifungal potential of the selected yeast was also studied in situ on currants subjected to different treatments and stored at 25 °C for 28 days. Microbiological analysis was undertaken for the enumeration of the bacterial and fungal flora, together with OTA determination at 7 and 21 days. To quantify A. carbonarius on all treated currant samples, molecular analysis with Real Time PCR was employed. A standard curve was prepared with A. carbonarius DNA. The efficiency of the curve was estimated to 10.416, the slope to -3.312 and the range of haploid genome that could be estimated was from 1.05 to 105∙10⁵. The amount of A. carbonarius DNA in all treated currants samples, where the fungus was positively detected, ranged from as low as 0.08 to 562 ng DNA/g currants. The antifungal activity of S. cerevisiae Y₃₃ was observed in all studied cases, causing inhibition of fungal growth and OTA production.

Pest Management and Ochratoxin A Contamination in Grapes: A Review

Ochratoxin A (OTA) is the most toxic member of ochratoxins, a group of toxic secondary metabolites produced by fungi. The most relevant species involved in OTA production in grapes is Aspergillus carbonarius. Berry infection by A. carbonarius is enhanced by damage to the skin caused by abiotic and biotic factors. Insect pests play a major role in European vineyards, and Lepidopteran species such as the European grapevine moth Lobesia botrana are undoubtedly crucial. New scenarios are also emerging due to the introduction and spread of allochthonous pests as well as climate change. Such pests may be involved in the dissemination of OTA producing fungi even if confirmation is still lacking and further studies are needed. An OTA predicting model is available, but it should be integrated with models aimed at forecasting L. botrana phenology and demography in order to improve model reliability.

Effect of potassium sorbate (E-202) and the antifungal PgAFP protein on Aspergillus carbonarius growth and ochratoxin A production in raisin simulating media

BACKGROUND

Ochratoxin A (OTA) is a mycotoxin produced by several species of Aspergillus and Penicillium fungi. The presence of OTA in raisins is mainly related to black Aspergillus spp. contamination. This toxin poses risks to human and animal health due to its high toxicity and carcinogenicity. New strategies to avoid the risk associated with OTA are therefore necessary.

RESULTS

A comparison was made between the effects of the antifungal protein PgAFP and potassium sorbate (E-202) on the growth of Aspergillus carbonarius, biosynthetic- and stress-related gene expression and its OTA production at two water activity (a_w ) levels, 0.95 and 0.93 a_w . The results showed that PgAFP successfully controlled OTA production, whereas E-202, despite being able to reduce Aspergillus carbonarius growth, caused a significant increase in OTA production by the fungus.

CONCLUSION

PgAFP protein, a biological compound with an antifungal activity, is safer to use than E-202 and may be proposed as a food preservative and a useful strategy to control ochratoxigenic A. carbonarius in raisins. © 2018 Society of Chemical Industry.

Differentiation and identification of grape-associated black aspergilli using Fourier transform infrared (FT-IR) spectroscopic analysis of mycelia

The purpose of this study was to evaluate the potential of FT-IR spectroscopy as a high-throughput method for rapid differentiation among the ochratoxigenic species of Aspergillus carbonarius and the non-ochratoxigenic or low toxigenic species of Aspergillus niger aggregate, namely A. tubingensis and A. niger isolated previously from grapes of Greek vineyards. A total of 182 isolates of A. carbonarius, A. tubingensis, and A. niger were analyzed using FT-IR spectroscopy. The first derivative of specific spectral regions (3002-2801cm^-1, 1773-1550cm^-1, and 1286-952cm^-1) were chosen and evaluated with respect to absorbance values. The average spectra of 130 fungal isolates were used for model calibration based on Discriminant analysis and the remaining 52 spectra were used for external model validation. This methodology was able to differentiate correctly 98.8% in total accuracy in both model calibration and validation. The per class accuracy for A. carbonarius was 95.3% and 100% for model calibration and validation, respectively, whereas for A. niger aggregate the per class accuracy amounted to 100% in both cases. The obtained results indicated that FT-IR could become a promising, fast, reliable and low-cost tool for the discrimination and differentiation of closely related fungal species.

Diversity of black Aspergilli isolated from raisins in Argentina: Polyphasic approach to species identification and development of SCAR markers for Aspergillus ibericus

Aspergillus section Nigri is a heterogeneous fungal group including some ochratoxin A producer species that usually contaminate raisins. The section contains the Series Carbonaria which includes the toxigenic species Aspergillus carbonarius and nontoxigenic Aspergillus ibericus that are phenotypically undistinguishable. The aim of this study was to examine the diversity of black aspergilli isolated from raisins and to develop a specific genetic marker to distinguish A. ibericus from A. carbonarius. The species most frequently found in raisins in this study were Aspergillus tubingensis (35.4%) and A. carbonarius (32.3%), followed by Aspergillus luchuensis (10.7%), Aspergillus japonicus (7.7%), Aspergillus niger (6.2%), Aspergillus welwitschiae (4.6%) and A. ibericus (3.1%). Based on inter-simple sequence repeat (ISSR) fingerprinting profiles of major Aspergillus section Nigri members, a sequence-characterized amplified region (SCAR) marker was identified. Primers were designed based on the conserved regions of the SCAR marker and were utilized in a PCR for simultaneous identification of A. carbonarius and A. ibericus. The detection level of the SCAR-PCR was found to be 0.01 ng of purified DNA. The present SCAR-PCR is rapid and less cumbersome than conventional identification techniques and could be a supplementary strategy and a reliable tool for high-throughput sample analysis.

Factors affecting distribution and abundance of Aspergillus section Nigri in vineyard soils from grapevine growing regions of Argentina

BACKGROUND

Aspergillus species belonging to section Nigri are the main fungi responsible for ochratoxin (OTA) contamination in grapes and wine. These species live as saprophytes in the superficial layer of the vineyard soil. We evaluated the biodiversity of potentially ochratoxigenic strains of Aspergillus section Nigri isolated from vineyard soils from different grapevine growing regions of Argentina. The isolates were characterized by classical and molecular methods. A multiple correspondence analysis was performed to identify the overall correlation of the Aspergillus group distribution with environmental conditions, geographical characteristics and vineyard practices.

RESULTS

Aspergillus niger aggregate was the prevalent group (71%) and A. carbonarius made up only 2%. Species discrimination by species-specific primers showed that in A. niger aggregate 89% were A. tubingensis; 97% of the uniseriate were A. japonicus/A. aculeatus. Isolates belonging to these groups were unable to produce OTA. Our results clearly demonstrate a strong association between presence of A. carbonarius, high average temperatures and drip irrigation. Precipitation levels appear as a secondary factor, and altitude, vineyard age, predominant species, grape variety or total fungal count showed no association with A. carbonarius.

CONCLUSION

We demonstrated a low prevalence of ochratoxigenic species in vineyard soil from the grape-growing regions of Argentina.

Non-Botrytis grape-rotting fungi responsible for earthy and moldy off-flavors and mycotoxins

The grape microflora is complex and includes filamentous fungi, yeasts and bacteria with different physiological characteristics and effects on wine production. Most studies have focused on the wine microbiota, but a few studies have reported the ecology of grape microorganisms. Some of these organisms - such as non-Botrytis bunch rotting fungi, which greatly influence the safety or sensory quality of wine, due to the production of mycotoxins and off-flavors, respectively - are considered to be spoilage agents. We review here the diversity of filamentous fungi on grapes and the factors influencing their development, such as grape ripening stage, environmental factors (climate, rain and cultivation practices), grape variety and grape health status. We also discuss the pathways by which mycotoxins and off-flavors are produced, the control of the population, the metabolites responsible for wine spoilage and the methods for detecting and characterizing the microorganisms involved.

Effect of yearly conditions and management practices on ochratoxin A production in Sultana Seedless vineyards

Sun drying of seedless grapes (Vitis vinifera cv. Sultanina) is widely practised in the western Aegean Region providing Turkey with a significant share in the world trade of sultanas. Research was initiated in 1998 to determine the incidence of ochratoxin A (OTA), to identify the major factors resulting in contamination and to develop techniques to reduce or prevent contamination. This paper assesses OTA formation in five experimental vineyards located in Manisa province of Turkey between 1998 and 2003. The cultural practices recorded were tillage (type and timing), fertilisation, plant protection, irrigation, trellising, pruning, GA(3) application, harvest maturity and date, and drying practices (type of drying yard, dipping into alkaline solution, length of drying period). In the experimental vineyards, no OTA was found at veraison. OTA levels in grapes harvested at fresh maturity ranged between <LOD and 8 ng g(-1), whereas in dried sultanas they were between <LOD and 35 ng g(-1). The frequency of OTA-positive samples increased in dried grapes compared with fresh. The number and timing of tillage, number of damaged berries, and removal of damaged/infected berries prior to sun drying were identified as the major good practices that may contribute to the reduction of OTA in sultanas.

Occurrence of ochratoxin A in Korean red paprika and factors to be considered in prevention strategy

A large amount-260,000 tons-of red paprika is consumed annually in Korea, where the people prefer hot and pungent to sweet foods. Concern has recently grown among consumers over contamination of paprika powder by mycotoxins; contamination can occur at any stage from pre-harvest to drying, storage, grinding, and eventually transport to the retail market. This study had dual aims: to investigate the current level of contamination of hot peppers by ochratoxin A and to identify the critical control points in the food chain. We measured the ochratoxin A (OTA) content of 200 samples from various sources including supermarkets, an online shopping mall, small stakeholder mills, Hazard Analysis and Critical Control Points (HACCP)-implemented factories, and an import company. Mycotoxin was determined using immunoaffinity column cleanup/HPLC quantification as well as strong anion exchange cleanup/stable isotope dilution assay. Monitoring revealed that approximately 30% of red paprika samples were OTA-positive, indicating a need to establish a maximum level for regulation. We selected two model factories that had adopted HACCP in different ways, and compared data in order to develop guidelines for alleviation of mitigation of the mycotoxin contamination.

Ochratoxin A producing species in the genus Penicillium

Ochratoxin A (OTA) producing fungi are members of the genera Aspergillus and Penicillium. Nowadays, there are about 20 species accepted as OTA producers, which are distributed in three phylogenetically related but distinct groups of aspergilli of the subgenus Circumdati and only in two species of the subgenus Penicillium. At the moment, P. verrucosum and P. nordicum are the only OTA producing species accepted in the genus Penicillium. However, during the last century, OTA producers in this genus were classified as P. viridicatum for many years. At present, only some OTA producing species are known to be a potential source of OTA contamination of cereals and certain common foods and beverages such as bread, beer, coffee, dried fruits, grape juice and wine among others. Penicillium verrucosum is the major producer of OTA in cereals such as wheat and barley in temperate and cold climates. Penicillium verrucosum and P. nordicum can be recovered from some dry-cured meat products and some cheeses.

Aspergillus carbonarius growth and ochratoxin A production on irradiated dried grapes under different water activity and temperature conditions

Grapes have different destinations. The most important in the national and international market is wine production, but another is dehydration to produce raisins. Dried vine fruits are at greater risk of ochratoxin A (OTA) contamination than wine grapes because the ratio of Aspergillus carbonarius to Aspergillus niger aggregate increases during drying. The growth of these species, and consequently OTA production, can be influenced by different environmental factors, the two most important being water activity (aW) and temperature. The objective of the present work was to evaluate the lag phase, growth rate and OTA production by two A. carbonarius isolates on irradiated dried grapes at different aW (0.910, 0.928, 0.955, 0.973 and 0.995), temperatures (15, 25 and 30 °C) and incubation times (7, 14 and 21 days). Growth was observed at all aW and temperature ranges assayed. No significant differences between the growth rates reached at 25 °C and 30 °C by both isolates were observed. At the assayed conditions, OTA production occurred over the whole range of temperatures (15-30 °C), with the maximum at 25 and 30 °C depending on the aW. In general, OTA concentration increased as aW increased with no statistically significant differences at the tested incubation times. This work provides information that can be used by companies for the purpose of preventing A. carbonarius and OTA contamination during storage on this and other substrates (e.g. dried prunes, figs and apricots) destined for human consumption.

Early discrimination of fungal species responsible of ochratoxin A contamination of wine and other grape products using an electronic nose

An electronic nose (e-nose) system using an array of metal oxide sensors (Fox 3000, Alpha MOS) was used to detect and discriminate two ochratoxigenic fungal species, Aspergillus carbonarius (Bain.) Thom and A. niger Van Tieghem, that are responsible for the contamination of wine and other wine grape products, using their volatile production patterns. Two well-known ochratoxigenic strains were used in this study: A. carbonarius A941 and A. niger A75. These strains were grown on three culture media, Czapek Dox modified (CDm) agar, yeast extract sucrose (YES) agar and white grape juice (WGJ) agar, and the volatile organic compounds produced in the headspace by these species were evaluated over periods of 48-120 h. The e-nose system was able to differentiate between the two species within 48 h of growth on YES and WGJ agar using principal component analysis (PCA), which accounted for 99.9% and 97.2% of the data respectively, in principal components 1 and 2, based on the qualitative volatile profiles. This differentiation was confirmed by cluster analysis of data. However, it was not possible to separate these species on CDm agar. Our results show that the two closely related ochratoxigenic species responsible for the contamination of wine and other wine grape products can be discriminated by the use of qualitative volatile fingerprints. This approach could have potential for rapid identification of A. carbonarius and A. niger on wine grape samples, thereby significantly reducing the time of detection of these ochratoxin A producing species.

Review of secondary metabolites and mycotoxins from the Aspergillus niger group

Filamentous fungi in the Aspergillus section Nigri (the black aspergilli) represent some of the most widespread food and feed contaminants known but they are also some of the most important workhorses used by the biotechnological industry. The Nigri section consists of six commonly found species (excluding A. aculeatus and its close relatives) from which currently 145 different secondary metabolites have been isolated and/or detected. From a human and animal safety point of view, the mycotoxins ochratoxin A (from A. carbonarius and less frequently A. niger) and fumonisin B(2) (from A. niger) are currently the most problematic compounds. Especially in foods and feeds such as coffee, nuts, dried fruits, and grape-based products where fumonisin-producing fusaria are not a problem, fumonisins pose a risk. Moreover, compounds such as malformins, naptho-gamma-pyrones, and bicoumarins (kotanins) call for monitoring in food, feed, and biotechnology products as well as for a better toxicological evaluation, since they are often produced in large amounts by the black aspergilli. For chemical differentiation/identification of the less toxic species the diketopiperazine asperazine can be used as a positive marker since it is consistently produced by A. tubingensis (177 of 177 strains tested) and A. acidus (47 of 47 strains tested) but never by A. niger (140 strains tested). Naptho-gamma-pyrones are the compounds produced in the highest quantities and are produced by all six common species in the group (A. niger 134 of 140; A. tubingensis 169 of 177; A. acidus 44 of 47; A. carbonarius 40 of 40, A. brasiliensis 18 of 18; and A. ibericus three of three).

Low occurrence of patulin- and citrinin-producing species isolated from grapes

AIMS

To assess the ability of fungi isolated from grapes to produce patulin and citrinin.

METHODS AND RESULTS

A total of 446 Aspergillus isolates belonging to 20 species and 101 Penicillium isolates were inoculated in Czapek yeast extract agar and yeast extract sucrose agar and incubated for 7 days at 25 degrees C. Extracts were analysed for patulin and citrinin by thin-layer chromatography. None of the isolates of Aspergillus spp. produced either patulin or citrinin. Patulin was produced by three isolates of Penicillium expansum and two of Penicillium griseofulvum. Citrinin was produced by five isolates of P. expansum, two of Penicillium citrinum and one of Penicillium verrucosum.

CONCLUSIONS

Our results show that the Aspergillus and Penicillium species commonly isolated from grapes are not a source of the mycotoxins, patulin and citrinin.

SIGNIFICANCE AND IMPACT OF THE STUDY

The possibility of co-occurrence of patulin and citrinin with ochratoxin A in grapes and grape products remain low, owing to the low frequency of isolation of potentially producing species.

Microbiological quality and organochlorine pesticide residue in commercially available ready-to-eat raisins

Microbiological quality and organochlorine pesticide residual contamination in raisins in a restricted area of Lucknow city, India was assessed in 20 samples. Total bacterial count was found in both open and packed raisin samples within the acceptable range (10(5)-<10(6)). The presence of food pathogens like Salmonella spp. and Enterobacteriaceae was detected more in open samples whereas Staphylococcus spp. and Pseudomonas spp. were absent. Lactobacilli spp. was found in all open samples and two packed samples. Presence of OCP residue was also found below the MRL although low levels of alpha-HCH and gamma-HCH were detected in samples. The study shows presence of spoilage and pathogenic microorganisms as well as OCP residue within permissible limits which was more in open samples than in packed ones.

Complex etiology, prophylaxis and hygiene control in mycotoxic nephropathies in farm animals and humans

Various etiological factors contributing to the development of mycotoxic nephropathy in farm animals and humans are reviewed. The possible synergistic effect between ochratoxin A (OTA) and other mycotoxins, as penicillic acid (PA) and fumonisin B(1) (FB(1)), contributing to this nephropathy is also considered and discussed. The most convenient ways of prophylaxis and various preventive measures against OTA contamination of feeds or foods are reviewed. A reference is made concerning the most successful methods of veterinary hygiene control in the slaughterhouses in order to prevent the entering of OTA in commercial channels with a view to human health. The economic efficacy of these prophylactic procedures is also considered. An evaluation of human exposure to OTA is made.

Effect of germicidal UVC light on fungi isolated from grapes and raisins

AIMS

To examine how UVC affects the different genera of fungi commonly isolated from grapes, with the aim of understanding changes in mycobiota during grape ripening and possible applications for preventing grape decay during storage.

METHODS AND RESULTS

Spores of Aspergillus carbonarius, Aspergillus niger, Cladosporium herbarum, Penicillium janthinellum and Alternaria alternata (between 100-250 spores/plate agar) were UVC irradiated for 0 (control), 10, 20, 30, 60, 300 and 600 s. Plates were incubated at 25 degrees C and colonies were counted daily up to 7 days. Alternaria alternata and Aspergillus carbonarius were the most resistant fungi. Conidial germination in these species was reduced by approx. 25% after 10 s of exposure, compared with greater than 70% reduction for the remaining species tested. Penicillium janthinellum spores were the most susceptible at this wavelength. UVC exposures of 300 s prevented growth of all isolates studied, except for Alternaria alternata.

CONCLUSIONS

UVC irradiation plays a major role in selecting for particular fungi that dominate the mycobiota of drying grapes.

SIGNIFICANCE AND IMPACT OF THE STUDY

The UVC irradiation of harvested grapes could prevent germination of contaminant fungi during storage or further dehydration.

Fungi and mycotoxins in vineyards and grape products

Many fungi may occur on grapes during growth in the vineyard, but the main concern from the viewpoint of mycotoxin contamination is the black Aspergilli, Aspergillus carbonarius and A. niger. These fungi are capable of producing ochratoxin A (OA) which may contaminate grapes and grape products such as wine, grape juice and dried vine fruit. Understanding the ecology and physiology of the black Aspergilli can provide tools for management of OA at all stages of grape production and processing. In the vineyard, careful management of cultivation, irrigation and pruning can assist in minimising the levels of black Aspergilli in the soil, which in turn, can minimise contamination of grapes by these fungi. Minimising damage to grapes on the vine by the use of open vine canopies, grape varieties with resistance to rain damage and by the management of insect pests and fungal diseases (e.g., mildew, Botrytis bunch rot) can reduce the incidence of Aspergillus rot in mature berries. The risk of OA in table grapes can be minimised by careful visual inspection to avoid damaged and discoloured berries. In wine, harvesting grapes with minimal damage, rapid processing and good sanitation practices in the winery assist in minimising OA. During vinification, pressing of grapes, and clarification steps which remove grape solids, grape proteins and spent yeast can also remove a significant proportion of OA. For dried vine fruit production, avoiding berry damage, rapid drying, and final cleaning and sorting to remove dark berries can reduce overall OA levels in finished products.

Occurrence of pathogenic fungal species in Tunisian vineyards

Mycotoxins are secondary metabolites produced by filamentous fungi detected in food, such are grapes. OTA was evaluated in ten handle musts from different Tunisian vineyard. This mycotoxin was found at levels 1.1 mug/L to 4.3 mug/L. A survey was conducted to assess the contamination of the Tunisian vineyard with pathogenic fungal species, in particular those responsible of the OTA production. The results were evaluated for the first time in parcels cultivated in the North, in the Centre and in the South of the country. Italia Muscate and Superior Seedless varieties were concerned at three developmental stages of the berry, setting, veraison and maturity. Carigon variety was used as positive control for musts contaminating by OTA. The main fungal species isolated were Aspergillus spp. (33.32%), Botrytis cinerea (23.32%), Alternaria spp. (12.80%), Cladosporium spp. (10.59%) and Penicillium spp. (8.3%). The isolates of the Aspergillus genus were identified as Aspergillus niger aggregate (77%), Aspergillus carbonarius (15%) and Aspergillus flavus (8%). Their presence was characterized by a significant decrease in the Centre during the veraison and a slight increase in the North and the South during the maturity stage. Furthermore, when comparing Superior Seedless and Italia Muscate cultivated in the same area, the aspergilli were particularly less abundant at the setting stage in the case of Superior Seedless. There is no correlation between the OTA amount in musts and the contamination by Aspergillus species in different vineyards and for grape varieties studied.