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Evaluation of Plant Origin Essential Oils as Herbal Biocides for the Protection of Caves Belonging to Natural and Cultural Heritage Sites. Microorganisms 2021; 9:microorganisms9091836. [PMID: 34576731 PMCID: PMC8470480 DOI: 10.3390/microorganisms9091836] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2021] [Revised: 08/02/2021] [Accepted: 08/12/2021] [Indexed: 11/20/2022] Open
Abstract
The present study concerns the serious issue of biodeterioration of the caves belonging to natural and cultural heritage sites due to the development of various microorganisms. Thus, a series of 18 essential oils (EOs) extracted from various Greek plants were evaluated in vitro (concentrations of 0.1, 0.2, 0.5, 1.0 and 5.0% v/v) against 35 bacterial and 31 fungi isolates (isolated from a Greek cave) and the antimicrobial activity was evident through the changes in optical density of microbial suspensions. In continuance, eight (8) representative bacterial and fungal isolates were further used to evaluate the minimum inhibitory concentration (MIC) and non-inhibitory concentration (NIC) values of the most effective EOs. According to the results, two EOs of Origanum vulgare were the most effective by inhibiting the growth of all the tested microorganisms at 0.1% (v/v), followed by that of Satureja thymbra which inhibited all bacterial isolates at 0.1% (v/v) and fungal isolates at 0.1, 0.2 and 0.5% (v/v) (depending on the isolate). The MIC ranged between 0.015–0.157 and 0.013–0.156 (v/v) for the bacterial and fungal isolates respectively, depending on the case. The current study demonstrated that conventional biocides may be replaced by herbal biocides with significant prospects for commercial exploitation.
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Tamminen A, Happonen P, Barth D, Holmström S, Wiebe MG. High throughput, small scale methods to characterise the growth of marine fungi. PLoS One 2020; 15:e0236822. [PMID: 32764772 PMCID: PMC7413501 DOI: 10.1371/journal.pone.0236822] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2020] [Accepted: 07/14/2020] [Indexed: 11/26/2022] Open
Abstract
Various marine fungi have been shown to produce interesting, bioactive compounds, but scaling up the production of these compounds can be challenging, particularly because little is generally known about how the producing organisms grow. Here we assessed the suitability of using 100-well BioScreen plates or 96-well plates incubated in a robot hotel to cultivate eight filamentous marine fungi, six sporulating and two non-sporulating, to obtain data on growth and substrate (glucose, xylose, galactose or glycerol) utilisation in a high throughput manner. All eight fungi grew in both cultivation systems, but growth was more variable and with more noise in the data in the Cytomat plate hotel than in the BioScreen. Specific growth rates between 0.01 (no added substrate) and 0.07 h-1 were measured for strains growing in the BioScreen and between 0.01 and 0.27 h-1 for strains in the plate hotel. Three strains, Dendryphiella salina LF304, Penicillium chrysogenum KF657 and Penicillium pinophilum LF458, consistently had higher specific growth rates on glucose and xylose in the plate hotel than in the BioScreen, but otherwise results were similar in the two systems. However, because of the noise in data from the plate hotel, the data obtained from it could only be used to distinguish between substrates which did or did not support growth, whereas data from BioScreen also provided information on substrate preference. Glucose was the preferred substrate for all strains, followed by xylose and galactose. Five strains also grew on glycerol. Therefore it was important to minimise the amount of glycerol introduced with the inoculum to avoid misinterpreting the results for growth on poor substrates. We concluded that both systems could provide physiological data with filamentous fungi, provided sufficient replicates are included in the measurements.
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Affiliation(s)
- Anu Tamminen
- VTT Technical Research Centre of Finland Ltd, Espoo, Finland
| | - Petrus Happonen
- VTT Technical Research Centre of Finland Ltd, Espoo, Finland
| | - Dorothee Barth
- VTT Technical Research Centre of Finland Ltd, Espoo, Finland
| | - Sami Holmström
- VTT Technical Research Centre of Finland Ltd, Espoo, Finland
| | - Marilyn G. Wiebe
- VTT Technical Research Centre of Finland Ltd, Espoo, Finland
- * E-mail:
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Castellá G, Bragulat MR, Cigliano RA, Cabañes FJ. Transcriptome analysis of non-ochratoxigenic Aspergillus carbonarius strains and interactions between some black aspergilli species. Int J Food Microbiol 2019; 317:108498. [PMID: 31918247 DOI: 10.1016/j.ijfoodmicro.2019.108498] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2019] [Revised: 12/18/2019] [Accepted: 12/23/2019] [Indexed: 01/07/2023]
Abstract
Aspergillus carbonarius consistently produces large amounts of ochratoxin A (OTA), a mycotoxin with nephrotoxic effects on animals and humans. In the present study, we analyzed the transcriptional changes associated to OTA production in three atypical non-ochratoxigenic strains of A. carbonarius. In addition, in vitro interactions between ochratoxigenic strains of A. carbonarius and A. niger and non-ochratoxigenic strains of A. carbonarius and A. tubingensis were studied in order to evaluate their potential for controlling OTA production. RNA-seq analysis revealed that there are 696 differentially expressed genes identified in the three non-OTA-producing strains, including 280 up-regulated and 333 down-regulated genes. A functional and gene ontology enrichment analysis revealed that the processes related to metabolic and oxidation processes, associated with functions such as oxidoreductase and hydrolase activity were down regulated. All the genes related with OTA biosynthesis in A. carbonarius were the most down-regulated genes in non-ochratoxigenic strains. We also showed that these strains possess a deleterious mutation in the AcOTApks gene required for OTA biosynthesis. Moreover, one of these strains gave the best control of OTA production resulting in an OTA reduction of 98-100% in co-inoculation with an ochratoxigenic strain of A. niger and an OTA reduction of 79-89% with an ochratoxigenic strain of A. carbonarius. Results of this study provided novel insights into the knowledge of the OTA biosynthetic pathway in these non-ochratoxigenic wild strains, and showed the biocontrol potential of these strains.
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Affiliation(s)
- Gemma Castellá
- Veterinary Mycology Group, Department of Animal Health and Anatomy, Universitat Autònoma de Barcelona, Bellaterra, Catalonia, Spain
| | - M Rosa Bragulat
- Veterinary Mycology Group, Department of Animal Health and Anatomy, Universitat Autònoma de Barcelona, Bellaterra, Catalonia, Spain
| | | | - F Javier Cabañes
- Veterinary Mycology Group, Department of Animal Health and Anatomy, Universitat Autònoma de Barcelona, Bellaterra, Catalonia, Spain.
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Bragulat MR, Abarca ML, Castellá G, Cabañes FJ. Intraspecific variability of growth and ochratoxin A production by Aspergillus carbonarius from different foods and geographical areas. Int J Food Microbiol 2019; 306:108273. [PMID: 31382055 DOI: 10.1016/j.ijfoodmicro.2019.108273] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2019] [Revised: 07/17/2019] [Accepted: 07/26/2019] [Indexed: 10/26/2022]
Abstract
Ochratoxin A (OTA) is a nephrotoxic mycotoxin naturally found in a wide range of food commodities throughout the world. Aspergillus carbonarius is the most important source of OTA in food commodities such as wine, grapes and dried vine fruits and is also responsible for the formation of OTA in coffee. The aim of this study was to determine the simultaneous effect of three culture media (Czapek Yeast Extract Broth (CYB); Synthetic Grape Juice Medium (SGM) and White grape juice (WGJ)) at three water activity (aw) levels (0.90; 0.95 and 0.98-0.99), and three incubation temperatures (15 °C, 25 °C and 35 °C) on the growth and OTA production by 16 strains of A. carbonarius. The strains were mainly isolated from grapes from areas with a Mediterranean climate. All the strains were confirmed for identity by sequencing of the calmodulin gene. The assay was performed in microtiter plates, determining the absorbance at 530 nm and the concentration of OTA after 1, 2, 4 and 10 days of incubation. No significant differences were observed in absorbance values between the strains. The highest absorbance values were recorded in CYB at 0.99 aw and at 0.95 aw after 10 days of incubation at 25 °C and 35 °C. None of the strains were able to grow at 0.90 aw and 15 °C in any culture media after 10 days of incubation. OTA concentration was statistically higher at 15 °C than at 25 °C or 35 °C. The highest significant OTA values were obtained at 0.98-0.99 aw and the best culture media for OTA production was CYB, followed by WGJ and SGM. While strains isolated from Mediterranean climate foods had a similar behavior despite being isolated from different geographical areas, OTA concentration produced by one Robusta coffee strain from Thailand was statistically higher at 25 °C than at 15 °C. This would suggest that the type of food matrices and consequently the adaptation of A. carbonarius strains to different climatic conditions would have a greater influence on the ecophysiology of the strains than only their geographical origin.
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Affiliation(s)
- M R Bragulat
- Veterinary Mycology Group, Department of Animal Health and Anatomy, Universitat Autònoma de Barcelona, Bellaterra, Spain
| | - M L Abarca
- Veterinary Mycology Group, Department of Animal Health and Anatomy, Universitat Autònoma de Barcelona, Bellaterra, Spain
| | - G Castellá
- Veterinary Mycology Group, Department of Animal Health and Anatomy, Universitat Autònoma de Barcelona, Bellaterra, Spain.
| | - F J Cabañes
- Veterinary Mycology Group, Department of Animal Health and Anatomy, Universitat Autònoma de Barcelona, Bellaterra, Spain
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Abarca ML, Bragulat MR, Castellá G, Cabañes FJ. Impact of some environmental factors on growth and ochratoxin A production by Aspergillus niger and Aspergillus welwitschiae. Int J Food Microbiol 2018; 291:10-16. [PMID: 30419474 DOI: 10.1016/j.ijfoodmicro.2018.11.001] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2018] [Revised: 10/08/2018] [Accepted: 11/02/2018] [Indexed: 11/17/2022]
Abstract
Ochratoxin A (OTA) is a nephrotoxic mycotoxin which may contaminate various foods and feed products worldwide. Aspergillus niger is one of the species responsible for OTA contamination in grapes and derived products. This species has recently been split into A. niger and Aspergillus welwitschiae. Both species can not be distinguished by phenotypic or extrolite profiles and to date there is no ecophysiological information of A. welwitschiae. The aim of this study was to determine the effects of water activity (aw) (0.90; 0.95 and 0.98-0.99), culture media (Yeast Extract Sucrose Broth (YESB); Synthetic Grape Juice Medium (SGM); White grape juice (WGJ)) and temperature (15 °C, 25 °C and 35 °C) on the growth and OTA production of four strains of A. niger and six strains of A. welwitschiae. The assay was performed in microtiter plates, determining the absorbance at 530 nm and the concentration of OTA at 1, 2, 4 and 10 days. No significant differences were observed in absorbance and OTA values between the two species under study. The highest absorbance values were recorded in YESB, followed by SGM and WGJ. Absorbance values increased with increasing aw and temperature. The highest OTA values were obtained at 0.98-0.99 aw and the best culture media for OTA production was YESB, followed by WGJ and SGM. The studied strains of A. niger produced the highest mean OTA level at 25 °C whereas A. welwitschiae strains produced the highest mean OTA concentration at 15 °C, although not differing significantly from concentration produced at 25 °C. To our knowledge, this is the first report on the impact of some environmental factors on growth and OTA production by A. welwitschiae.
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Affiliation(s)
- M L Abarca
- Veterinary Mycology Group, Department of Animal Health and Anatomy, Universitat Autònoma de Barcelona, Bellaterra, Spain
| | - M R Bragulat
- Veterinary Mycology Group, Department of Animal Health and Anatomy, Universitat Autònoma de Barcelona, Bellaterra, Spain
| | - G Castellá
- Veterinary Mycology Group, Department of Animal Health and Anatomy, Universitat Autònoma de Barcelona, Bellaterra, Spain.
| | - F J Cabañes
- Veterinary Mycology Group, Department of Animal Health and Anatomy, Universitat Autònoma de Barcelona, Bellaterra, Spain
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Natskoulis PI, Lappa IK, Panagou EZ. Evaluating the efficacy of turbimetric measurements as a rapid screening technique to assess fungal susceptibility to antimicrobial compounds as exemplified by the use of sodium metabisulfite. Food Res Int 2018; 106:1037-1041. [DOI: 10.1016/j.foodres.2018.01.058] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2017] [Revised: 11/22/2017] [Accepted: 01/22/2018] [Indexed: 10/17/2022]
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Bragulat MR, Eustaquio A, Cabañes FJ. Study on the presence of ochratoxin α in cultures of ochratoxigenic and non- ochratoxigenic strains of Aspergillus carbonarius. PLoS One 2017; 12:e0185986. [PMID: 29016677 PMCID: PMC5634603 DOI: 10.1371/journal.pone.0185986] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2017] [Accepted: 09/23/2017] [Indexed: 11/25/2022] Open
Abstract
Ochratoxin A (OTA) is a potent nephrotoxin and carcinogen which is found in a wide variety of common foods and beverages and it is produced by several species of Aspergillus and Penicillium. Ochratoxin α (OTα), a major metabolite of OTA, has also been reported to occur in cultures of OTA-producing species. However there is some controversial about the participation of OTα in the biosynthesis of OTA, mainly because its biosynthesis pathway has not yet been completely characterized. Aspergillus carbonarius is the main responsible source of ochratoxin A (OTA) in food commodities such as wine, grapes or dried vine fruits from main viticultural regions worldwide. However, little is known about the presence of OTα in isolates of A. carbonarius. In this study we evaluated the effects of temperature and incubation time on OTα production by both OTA and non-OTA-producing strains of A. carbonarius. OTA and OTα were detected on the basis of HPLC fluorometric response compared with that of their standards and confirmed by HPLC-MS in selected samples. The non-OTA-producing strains did produce neither OTA nor OTα at any of the conditions tested. The OTA-producing strains studied were able to produce both OTA and OTα in most of the conditions tested. In general, higher amounts of OTA than OTα were produced, but a positive correlation in the production of these two metabolites was detected. The lack of production of both OTA and OTα in the non-OTA-producing strains could be caused by the presence of silent genes or by mutations in functional or regulatory genes involved in OTA production.
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Affiliation(s)
- M. Rosa Bragulat
- Veterinary Mycology Group, Departament of Animal Health and Anatomy, Universitat Autònoma de Barcelona, Bellaterra, Spain
| | - Alba Eustaquio
- Chemical Analysis Service, Universitat Autònoma de Barcelona, Bellaterra, Spain
| | - F. Javier Cabañes
- Veterinary Mycology Group, Departament of Animal Health and Anatomy, Universitat Autònoma de Barcelona, Bellaterra, Spain
- * E-mail:
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Zhang X, Li Y, Wang H, Gu X, Zheng X, Wang Y, Diao J, Peng Y, Zhang H. Screening and Identification of Novel Ochratoxin A-Producing Fungi from Grapes. Toxins (Basel) 2016; 8:toxins8110333. [PMID: 27845758 PMCID: PMC5127129 DOI: 10.3390/toxins8110333] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2016] [Revised: 10/24/2016] [Accepted: 11/08/2016] [Indexed: 11/16/2022] Open
Abstract
Ochratoxin A (OTA) contamination has been established as a world-wide problem. In this study, the strains with the ability of OTA production were screened by analyzing the green fluorescence of the isolates colonies from the grapes in Zhenjiang with 365 nm UV light and confirmed by HPLC with fluorescent detection (HPLC-FLD). The results showed that seven isolates acquired the characteristic of the fluorescence, of which only five showed the ability of OTA production as confirmed by HPLC-FLD analysis. The five OTA-producing strains were identified based on comparative sequence analysis of three conserved genes (ITS, BenA and RPB2) of the strains, and they are Talaromyces rugulosus (O1 and Q3), Penicillium commune (V5-1), Penicillium rubens (MQ-5) and Aspergillus aculeatus (MB1-1). There are two Penicillium species of the five OTA-producing strains and our study is the first to report that P. rubens, T. rugulosus and A. aculeatus can produce OTA. This work would contribute to comprehensively understanding the fungi with an OTA-producing ability in grapes before harvest and then take effective measures to prevent OTA production.
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Affiliation(s)
- Xiaoyun Zhang
- School of Food and Biological Engineering, Jiangsu University, 301 Xuefu Road, Zhenjiang 212013, China.
| | - Yulin Li
- Hubei Key Laboratory, Edible Wild Plants Conservation and Utilization, 11 Cihu Road, Huangshi 435002, China.
| | - Haiying Wang
- School of Food and Biological Engineering, Jiangsu University, 301 Xuefu Road, Zhenjiang 212013, China.
| | - Xiangyu Gu
- School of Grain Science and Technology, Jiangsu University of Science and Technology, 2 Mengxi Road, Zhenjiang 212003, China.
| | - Xiangfeng Zheng
- School of Food and Biological Engineering, Jiangsu University, 301 Xuefu Road, Zhenjiang 212013, China.
| | - Yun Wang
- School of Food and Biological Engineering, Jiangsu University, 301 Xuefu Road, Zhenjiang 212013, China.
| | - Junwei Diao
- School of Food and Biological Engineering, Jiangsu University, 301 Xuefu Road, Zhenjiang 212013, China.
| | - Yaping Peng
- School of Food and Biological Engineering, Jiangsu University, 301 Xuefu Road, Zhenjiang 212013, China.
| | - Hongyin Zhang
- School of Food and Biological Engineering, Jiangsu University, 301 Xuefu Road, Zhenjiang 212013, China.
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Han X, Chakrabortti A, Zhu J, Liang ZX, Li J. Sequencing and functional annotation of the whole genome of the filamentous fungus Aspergillus westerdijkiae. BMC Genomics 2016; 17:633. [PMID: 27527502 PMCID: PMC4986183 DOI: 10.1186/s12864-016-2974-x] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Accepted: 07/28/2016] [Indexed: 01/13/2023] Open
Abstract
BACKGROUND Aspergillus westerdijkiae produces ochratoxin A (OTA) in Aspergillus section Circumdati. It is responsible for the contamination of agricultural crops, fruits, and food commodities, as its secondary metabolite OTA poses a potential threat to animals and humans. As a member of the filamentous fungi family, its capacity for enzymatic catalysis and secondary metabolite production is valuable in industrial production and medicine. To understand the genetic factors underlying its pathogenicity, enzymatic degradation, and secondary metabolism, we analysed the whole genome of A. westerdijkiae and compared it with eight other sequenced Aspergillus species. RESULTS We sequenced the complete genome of A. westerdijkiae and assembled approximately 36 Mb of its genomic DNA, in which we identified 10,861 putative protein-coding genes. We constructed a phylogenetic tree of A. westerdijkiae and eight other sequenced Aspergillus species and found that the sister group of A. westerdijkiae was the A. oryzae - A. flavus clade. By searching the associated databases, we identified 716 cytochrome P450 enzymes, 633 carbohydrate-active enzymes, and 377 proteases. By combining comparative analysis with Kyoto Encyclopaedia of Genes and Genomes (KEGG), Conserved Domains Database (CDD), and Pfam annotations, we predicted 228 potential carbohydrate-active enzymes related to plant polysaccharide degradation (PPD). We found a large number of secondary biosynthetic gene clusters, which suggested that A. westerdijkiae had a remarkable capacity to produce secondary metabolites. Furthermore, we obtained two more reliable and integrated gene sequences containing the reported portions of OTA biosynthesis and identified their respective secondary metabolite clusters. We also systematically annotated these two hybrid t1pks-nrps gene clusters involved in OTA biosynthesis. These two clusters were separate in the genome, and one of them encoded a couple of GH3 and AA3 enzyme genes involved in sucrose and glucose metabolism. CONCLUSIONS The genomic information obtained in this study is valuable for understanding the life cycle and pathogenicity of A. westerdijkiae. We identified numerous enzyme genes that are potentially involved in host invasion and pathogenicity, and we provided a preliminary prediction for each putative secondary metabolite (SM) gene cluster. In particular, for the OTA-related SM gene clusters, we delivered their components with domain and pathway annotations. This study sets the stage for experimental verification of the biosynthetic and regulatory mechanisms of OTA and for the discovery of new secondary metabolites.
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Affiliation(s)
- Xiaolong Han
- State Key Laboratory of Organ Failure Research, Division of Nephrology, Nanfang Hospital, Southern Medical University, Guangzhou, Guangdong Province, People's Republic of China
- Department of Bioinformatics, School of Basic Medical Sciences, Southern Medical University, Guangzhou, Guangdong Province, People's Republic of China
| | - Alolika Chakrabortti
- School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore, Republic of Singapore
| | - Jindong Zhu
- State Key Laboratory of Organ Failure Research, Division of Nephrology, Nanfang Hospital, Southern Medical University, Guangzhou, Guangdong Province, People's Republic of China
- Department of Bioinformatics, School of Basic Medical Sciences, Southern Medical University, Guangzhou, Guangdong Province, People's Republic of China
| | - Zhao-Xun Liang
- School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore, Republic of Singapore.
| | - Jinming Li
- State Key Laboratory of Organ Failure Research, Division of Nephrology, Nanfang Hospital, Southern Medical University, Guangzhou, Guangdong Province, People's Republic of China.
- Department of Bioinformatics, School of Basic Medical Sciences, Southern Medical University, Guangzhou, Guangdong Province, People's Republic of China.
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Impact of postharvest processing on the fungal population contaminating African walnut shells (Tetracarpidium conophorum Mull. Arg) at different maturity stages and potential mycotoxigenic implications. Int J Food Microbiol 2015; 194:15-20. [PMID: 25461603 DOI: 10.1016/j.ijfoodmicro.2014.10.024] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2014] [Revised: 09/24/2014] [Accepted: 10/21/2014] [Indexed: 11/24/2022]
Abstract
African walnut (Tetracarpidium conophorum Mull. Arg) is commonly processed by boiling or toasting and consumed as a snack or used as a thickener in many West African soup preparations. The nuts are usually exposed to both high temperatures and high relative humidity in open markets which predisposes them to fungal growth. Hence, the dangers of spore inhalation and resultant mycosis cannot be over-emphasized as retailers and consumers are always in direct contact with these nuts during harvest, processing and consumption. So far, there is no reported research on potential mycotoxin contamination of African walnut and whether this risk might be accentuated by processing. African walnut, at early and late maturity stages, were processed by toasting, boiling or left unprocessed before being stored at 25°C and 37°C, respectively under controlled relative humidity for 7days. Nuts were cracked and shell pieces cultured in malt extract agar (MEA) and Dichloran Glycerol 18 (DG18) media and incubated at 25°C for 7days. Results revealed that potential mycotoxigenic species - Aspergillus section Nigri, Aspergillus flavus/parasiticus, Fusarium spp. and Penicillium spp. - were frequently isolated. When compared with unprocessed nuts, toasting completely prevented fungal contamination in shell pieces from nuts in the non-stored (NSN) group at the early maturity stage, while boiling significantly reduced the level of contamination to about 58% (p<0.05). In general, simulating open market conditions caused 100% fungal contamination in all boiled samples and toasted samples at early maturity. However, contamination in toasted samples at late maturity was increased to 90 and 70% at 25°C in DG18 and MEA, respectively, while at 37°C contamination was 40 and 60% in DG18 and MEA, respectively. Mycotoxin analysis using Yeast Extract Sucrose (YES) agar and High Performance Liquid Chromatography (HPLC)-Fluorescence detection (FLD) showed that Aflatoxins - G1 (AFG1), B1 (AFB1), G2 (AFG2), and B2 (AFB2) were produced by 20 isolates with both AFG1 and AFB1 being predominant at concentration ranges 4.33-32,200 and 4.20-22,700ng/g plug weight, respectively. No ochratoxin A (OTA) was detected out of 23 isolates analysed. From these findings, it is suggested that toasting of nuts, preferably at early maturity is a safer processing option than boiling in terms of prevention of possible fungal growth on nut shells and risk of mycotoxin contamination.
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