Influence of harvesting and drying techniques on microflora and mycotoxin contamination of figs

Effect of pretreatments on mycotoxin profiles and levels in dried figs

The aim of this explorative study was to investigate how effective drying preservation methods are in reducing mycotoxin content in figs. Dried autochthonous varieties of white and dark figs (Petrovača Bijela and Šaraguja, respectively) were analysed for mycotoxins using an LC-MS/MS "dilute and shoot" method capable of determining 295 fungal and bacterial secondary metabolites. Before drying in a cabinet dryer the figs were preserved with 0.5 % citric acid solution or 0.5 % ascorbic acid solution or 0.3 % L-cysteine solution or 0.2 % chestnut extract solution or 0.15 % Echinacea extract solution by immersion. We found nine metabolites: aflatoxin B1 (AFB1), ochratoxin A, ochratoxin alpha, kojic acid, emodin, altenuene, alternariol methyl ether, brevianamide F, and tryptophol. The most efficient preserver was L-cysteine (15 % reduction), while ascorbic acid favoured mycotoxin production (158 % increase). However, all pretreatment solutions reduced AFB1, which is a major fig contaminant.

Impact of food processing and detoxification treatments on mycotoxin contamination

Mycotoxins are fungal metabolites commonly occurring in food, which pose a health risk to the consumer. Maximum levels for major mycotoxins allowed in food have been established worldwide. Good agricultural practices, plant disease management, and adequate storage conditions limit mycotoxin levels in the food chain yet do not eliminate mycotoxins completely. Food processing can further reduce mycotoxin levels by physical removal and decontamination by chemical or enzymatic transformation of mycotoxins into less toxic products. Physical removal of mycotoxins is very efficient: manual sorting of grains, nuts, and fruits by farmers as well as automatic sorting by the industry significantly lowers the mean mycotoxin content. Further processing such as milling, steeping, and extrusion can also reduce mycotoxin content. Mycotoxins can be detoxified chemically by reacting with food components and technical aids; these reactions are facilitated by high temperature and alkaline or acidic conditions. Detoxification of mycotoxins can also be achieved enzymatically. Some enzymes able to transform mycotoxins naturally occur in food commodities or are produced during fermentation but more efficient detoxification can be achieved by deliberate introduction of purified enzymes. We recommend integrating evaluation of processing technologies for their impact on mycotoxins into risk management. Processing steps proven to mitigate mycotoxin contamination should be used whenever necessary. Development of detoxification technologies for high-risk commodities should be a priority for research. While physical techniques currently offer the most efficient post-harvest reduction of mycotoxin content in food, biotechnology possesses the largest potential for future developments.

Alkali-based pre-treatment may prevent ochratoxin A in grapes

In traditional raisin production process in Turkey, one of the major raisin producers in the world, grapes undergo an alkali treatment prior to drying. This procedure involves dipping grapes in a potassium carbonate solution for 10-15 seconds to remove the wax layer on the surface to accelerate the drying process. In this study, we aimed to investigate the effect of alkali treatment on ochratoxin A (OTA), an important risk factor for grapes and grape-derived products. First, the stability of the OTA was examined under variable pH (4-12), ion type (Na+, K+), ionic strength (0.1-10%) and temperature (4-60 °C). Then, Aspergillus ochraceus contaminated grapes were treated with an alkaline solution and a subsequent OTA analysis was performed through a high performance liquid chromatography-fluorescence detection. OTA started to decompose at pH values exceeding 10.0. The degradation followed a first order kinetics. Although both sodium carbonate and potassium carbonate solutions were at the same alkali pH and they both triggered the OTA degradation at increasing concentrations, potassium carbonate was more effective even at low concentrations. Elevated temperatures were also found to effect degradation. The degradation rate constant at 40 °C was approximately 5 times greater than the one at 25 °C. Furthermore, OTA levels dropped up to 50% in contaminated grapes after the alkali treatment. Our results confirmed that the amide bond of OTA rapidly hydrolysed to a non-toxic ochratoxin-alpha and phenylalanine under strong alkaline conditions. The results suggest that the alkaline pre-treatment unintentionally offers a great advantage to reduce OTA levels in raisins and it could be a viable approach for other dried fruits through the application of good manufacturing practice.

Increased aflatoxin contamination of dried figs in a drought year

Dried figs (4917 samples) destined for export from Turkey to the European Union were collected between September and December during the very dry crop year of 2007 and tested for aflatoxins B(1), B(2), G(1) and G(2) by immunoaffinity column clean-up and reverse-phase high-performance liquid chromatography (RP-HPLC). While 32% of the samples contained detectable levels of total aflatoxins, 9.8% of them exceeded the European Union limits. Aflatoxin levels were in the range of 0.2-259.46 microg kg(-1) and 2.04-259.46 microg kg(-1) for all samples and samples that exceeded the limits, respectively. A substantial increase in the incidence of aflatoxins was observed in 2007 compared with previous years, most likely due to the drought stress, high temperatures and low relative humidity encountered during the period from January to September of that year. In 2007, the mean temperature was 1-2 degrees C higher, there was 300 mm less total rain, and the mean relative humidity was 10-15% lower than in 2002-06. The average concentration of individual aflatoxins present in the samples was quantified to determine whether the drought conditions promoted certain types of aflatoxins. Among the contaminated samples, aflatoxin B(1) occurred in 97% of the contaminated samples, followed by G(1) in 47%, B(2) in 24%, and G(2) in 6% of samples. Concentrations of individual aflatoxins exhibited great variability among the samples but were not significantly different from those reported in previous studies, which were conducted under conditions without drought and high temperatures.

Mycotoxins in botanicals and dried fruits: a review

Botanicals are used in many countries for medicinal and general health-promoting purposes. Numerous natural occurrences of mycotoxins in botanicals and dried fruits have been reported. Aflatoxins or ochratoxin A (OTA) have been found in botanicals such as ginseng, ginger, liquorice, turmeric, and kava-kava in the USA, Spain, Argentina, India, and some other countries, while fumonisins have been found in medicinal wild plants in South Africa and in herbal tea and medicinal plants in Turkey. Zearalenone was identified in ginseng root. Dried fruits can be contaminated with aflatoxins, OTA, kojic acid, and, occasionally, with patulin or zearalenone. One main area of concern is aflatoxins in dried figs; bright greenish yellow fluorescence under ultraviolet light is associated with aflatoxin contamination. OTA in dried vine fruits (raisins, sultanas, and currants) is another concern. There are also reports of aflatoxins in raisins and OTA in dried figs, apricots, dried plums (prunes), dates, and quince. Maximum permitted levels in the European Union include 4 microg kg(-1) for total aflatoxins in dried fruit intended for direct consumption and 10 microg kg(-1) for OTA in dried vine fruit. This review discusses the occurrence of mycotoxins in botanicals and dried fruits and analytical issues such as sampling, sample preparation, and methods for analysis. Fungal contamination of these products, the influence of sorting, storage, and processing, and prevention are also considered.

Identification of fumonisin B2, HT-2 toxin, patulin, and zearalenone in dried figs by liquid chromatography-time-of-flight mass spectrometry and liquid chromatography-mass spectrometry

Dried figs from Turkey that were visibly moldy (or fluorescent under UV light) and thus rejected as unsuitable for human food were screened for the presence of fungal metabolites. Crude solvent extracts from individual figs were directly analyzed by liquid chromatography combined with time-of-flight mass spectrometry to generate accurate mass data for all detectable components. A comparison of these data with a metabolite database indicated the presence of fumonisins B2 and B4, patulin, HT-2 toxin, and zearalenone among various other metabolites. Portions of the same figs were reextracted and then analyzed by conventional liquid chromatography-mass spectrometry. On the basis of coincident retention times and by matching selected ion monitoring for coincident ions with that of authentic standards, the identification of fumonisin B2, HT-2 toxin, patulin, and zearalenone was confirmed.

Incidence of toxigenic fungi and ochratoxin A in dried fruits sold in Brazil

A total of 117 dried fruit samples (black sultanas, white sultanas, dates, dried plums, dried figs and apricots) from different origins were analysed both for toxigenic fungi and for the presence of ochratoxin A. Amongst the fungi found, Aspergillus niger was predominant, with 406 isolates, of which 15% were ochratoxin A producers. They were followed by A. ochraceus, with 15 isolates and 87% ochratoxigenics, and A. carbonarius, with only five isolates of which 60% were ochratoxin A producers. The average infection rates for A. niger in black sultanas, plums, figs, dates and white sultanas were 22.0, 8.0, 4.0, 1.5 and 0.5%, respectively. The apricot samples were not contaminated by any fungi or ochratoxin A. Black sultana and dried figs contained the highest contamination with ochratoxin A, with 33 and 26.3% of the samples containing more than 5 microg kg(-1) respectively, while all the white sultanas, dates and plums had no sample that exceeded this limit.

Ochratoxin A-producing species in grapes and sun-dried grapes and their relation to ecophysiological factors

AIMS

To explain the dominance of OTA-producing fungal species in sun-dried grapes for special wine production through an ecophysiological approach.

METHODS AND RESULTS

Grapes at different ripening stages, sun-dried grapes and raisins were analysed for fungal presence, and isolates identified. Aspergillus section Nigri incidence in grapes increased with grape maturation. In the ecophysiological study five isolates (Alternaria alternata, Cladosporium herbarum, Penicillium decumbens, Aspergillus carbonarius, A. niger aggregate and A. section Nigri uniseriate) were inoculated in SNM medium at four a(w) (0.82-0.97) and incubated at 20, 30 and 40 degrees C for 18 d. Isolates were also inoculated in pairs to evaluate fungal interactions recording their growth rates and indexes of dominance. Aspergillus section Nigri grew in a wider range of temperature and a(w), had higher growth rates than the others under most of the conditions tested and showed behaviour usually dominant.

CONCLUSIONS

The presence of A. section Nigri is predominant in grapes during harvesting and sun-drying period likely because of a better adaptation to hot and humid environment.

SIGNIFICANCE AND IMPACT OF THE STUDY

The duration of the drying period should be reduced as much as possible without compromising the quality of the final product, or drying the grapes in controlled chambers with dry hot air flow.

Survey for co-occurrence of ochratoxin A and aflatoxin B1 in dried figs in Turkey by using a single laboratory-validated alkaline extraction method for ochratoxin A

A survey was carried out to determine the co-occurrence of ochratoxin A and aflatoxin B1 in dried figs from Turkey. Samples from two seasons of crops (2003 and 2004) intended for export to the European Union and the 2004 crop obtained from the domestic Turkish market were analyzed. Affinity column cleanup methods were employed for determining separately ochratoxin A and aflatoxin B1, but for ochratoxin A an alkaline extraction procedure was employed (in contrast to the conventionally employed acidic extraction), which gave consistently higher toxin recovery. In-house validation of the ochratoxin A method gave a limit of detection of 0.15 ng/g and a limit of quantification of 0.5 ng/g with a repeatability of 5.8% in the range 5 to 10 ng/g (with a mean recovery of 94% for spiked samples). Positive results for ochratoxin A were confirmed by liquid chromatography-mass spectrometry. For the 2003 export figs (58 samples), 7 samples contained only aflatoxin B1, 2 samples contained only ochratoxin A, and 2 samples contained both toxins (with maximum concentrations of 35.1 ng/g for aflatoxin B1 and 13.0 ng/g for ochratoxin A). Similarly for the 2004 export figs (41 samples), 16 samples contained only aflatoxin B1, 4 samples contained only ochratoxin A, and 2 samples contained both toxins (with maximum concentrations of 20.6 ng/g for aflatoxin B1 and 26.3 ng/g for ochratoxin A). Of 20 retail samples of dried figs from Turkey, only one sample contained ochratoxin A (2.0 ng/g) and none were contaminated with aflatoxin B1. This survey revealed a 14 to 15% incidence of occurrence of ochratoxin A for 2 years, which is higher than previously reported.

Mycotoxins in fruits, fruit juices, and dried fruits

This review gives an overview of the presence of mycotoxins in fruits. Although several mycotoxins occur in nature, very few (aflatoxins, ochratoxin A, patulin, Alternaria toxins) are regularly found in fruits. It has been shown that the presence of fungi on fruits is not necessarily associated with mycotoxin contamination. The formation of mycotoxins depends more on endogenous and environmental factors than fungal growth does. Mycotoxins may remain in fruits even when the fungal mycelium has been removed. Depending on the fruit and the mycotoxin, the diffusion of mycotoxins into the sound tissues of fruits may occur. The influence of the selection and storage of fruits and the influence of different processing steps involved in the production of fruit juices and dried fruits on possible mycotoxin contamination is described. It is shown that the careful selection, washing, and sorting of fruits is the most important factor in the reduction of mycotoxin contamination during the production of fruit juices. The processing of fruits does not result in the complete removal of mycotoxins.