Occurrence and fumonisin B2 producing potential of Aspergillus section Nigri in Brazil nuts

Occurrence of fumonisin-producing black aspergilli in Australian wine grapes: effects of temperature and water activity on fumonisin production by A. niger and A. welwitschiae

Black aspergilli are some of the most common mycotoxigenic fungi in vineyards worldwide. The aims of this research were to assess the occurrence of fumonisin-producing black aspergilli in Australian wine grapes and the effects of environmental factors on fumonisin production by A. niger and A. welwitschiae (syn. A. awamori). Thirty-eight Aspergillus isolates (black aspergilli) were collected from six wine grape varieties grown in Australian vineyards. LC-MS/MS analysis of culture extracts revealed that six isolates produced fumonisins FB₂ and FB₄. Molecular data revealed that all fumonisin-producing isolates were A. niger and A. welwitschiae. None of the reference isolates, A. carbonarius, A. tubingensis, A. japonicus, and A. foetidus, were positive for fumonisin production. The effects of temperature and water activity on the growth and production of fumonisins were studied using two A. niger and an isolate of A. welwitschiae on synthetic grape juice medium (SGJM) at 20 °C, 25 °C, 30 °C, and 35 °C, and 0.92 a_w, 0.95 a_w, and 0.98 a_w levels. All isolates produced FB₂ and FB₄ at 0.95 a_w and 0.98 a_w and 20 °C, 25 °C, and 30 °C. The highest growth rate observed was 14.89 mm/day for A. welwitschiae at 0.98 a_w and 35 °C, whereas the highest fumonisin production observed was 25.3 mg/kg at 0.98 a_w and 20 °C for A. welwitschiae. None of the isolates produced fumonisins at 35 °C at any water activity levels. To our knowledge, this is the first report on the occurrence of fumonisin-positive isolates of Aspergillus from Australian wine grapes and the impact of the environmental factors on fumonisin production by A. welwitschiae.

Diversity within Aspergillus niger Clade and Description of a New Species: Aspergillus vinaceus sp. nov

Diversity of species within Aspergillus niger clade, currently represented by A. niger sensu stricto and A. welwitshiae, was investigated combining three-locus gene sequences, Random Amplified Polymorphic DNA, secondary metabolites profile and morphology. Firstly, approximately 700 accessions belonging to this clade were investigated using calmodulin gene sequences. Based on these sequences, eight haplotypes were clearly identified as A. niger (n = 247) and 17 as A. welwitschiae (n = 403). However, calmodulin sequences did not provide definitive species identities for six haplotypes. To elucidate the taxonomic position of these haplotypes, two other loci, part of the beta-tubulin gene and part of the RNA polymerase II gene, were sequenced and used to perform an analysis of Genealogical Concordance Phylogenetic Species Recognition. This analysis enabled the recognition of two new phylogenetic species. One of the new phylogenetic species showed morphological and chemical distinguishable features in comparison to the known species A. welwitschiae and A. niger. This species is illustrated and described as Aspergillus vinaceus sp. nov. In contrast to A. niger and A. welwitschiae, A. vinaceus strains produced asperazine, but none of them were found to produce ochratoxin A and/or fumonisins. Sclerotium production on laboratory media, which does not occur in strains of A. niger and A. welwitschiae, and strictly sclerotium-associated secondary metabolites (14-Epi-hydroxy-10,23-dihydro-24,25-dehydroaflavinine; 10,23-Dihydro-24,25-dehydroaflavinine; 10,23-Dihydro-24,25-dehydro-21-oxo-aflavinine) were found in A. vinaceus. The strain type of A. vinaceus sp. nov. is ITAL 47,456 (T) (=IBT 35556).

New morphological criteria and molecular characterization of black aspergilli aggregate from corn, sorghum and wheat grains

Corn, sorghum and wheat grains are used as livestock feed in the world. Identification of black aspergilli associated with these grains is necessary to make sure of the safety of the grains because its occurrence is an indicator of mycotoxin production. Forty-five isolates were isolated from the samples collected from Upper Egypt's markets and identified morphologically based on colony color, conidia, stipe and vesicle size and molecularly by using β-tubulin and calmodulin genes. Isolates were divided into 30 strains of Aspergillus welwitschiae and 15 strains of A. niger. We have found new criteria in the morphological identification of A. welwitschiae as its colony color was black to brown with yellow edge, but in A. niger was black with white edge, also A. welwitschiae sometimes produced finely-to-distinctly roughened brownish conidia on malt extract agar (MEA) media. Thirteen isolates of A. welwitschiae and six of A. niger were recognized as potential producers for ochratoxin A.

Real-time PCR-based method for rapid detection of Aspergillus niger and Aspergillus welwitschiae isolated from coffee

Some species from Aspergillus section Nigri are morphologically very similar and altogether have been called A. niger aggregate. Although the species included in this group are morphologically very similar, they differ in their ability to produce mycotoxins and other metabolites and their taxonomical status has evolved continuously. Among them, A. niger and A. welwitschiae are ochratoxin A and fumonisin B₂ producers and their detection and/or identification is of crucial importance for food safety. The aim of this study was the development of a real-time PCR-based method for simultaneous discrimination of A. niger and A. welwitschiae from other species of the A. niger aggregate isolated from coffee beans. One primer pair and a hybridization probe specific for detection of A. niger and A. welwitschiae strains were designed based on the BenA gene sequences, and used in a Real-time PCR assay for the rapid discrimination between both these species from all others of the A. niger aggregate. The Real-time PCR assay was shown to be 100% efficient in discriminating the 73 isolates of A. niger/A. welwitschiae from the other A. niger aggregate species analyzed as a negative control. This result testifies to the use of this technique as a good tool in the rapid detection of these important toxigenic species.

Brazil nuts: Nutritional composition, health benefits and safety aspects

Brazil nuts are among the richest selenium food sources, and studies have considered this Amazonian nut as an alternative for selenium supplementation. Besides selenium, Brazil nuts present relevant content of other micronutrients such as magnesium, copper, and zinc. The nutritional composition of nuts, also characterized by adequate fatty acid profile and high content of protein and bioactive compounds, has many health benefits. In the present review, we examine the nutritional composition of Brazil nuts, comparing it with other nuts, and describe the relevance of possible contaminants and metal toxicants observed in this nut for human health. Furthermore, we report different trials available in the literature, which demonstrate positive outcomes such as modulation of the lipid serum profile, enhancement of the antioxidant system and improvement of anti-inflammatory response. These effects have been assessed under different conditions, such as cognitive impairment, dyslipidemia, cancer, and renal failure.