Mould spoilage and mycotoxin formation in grains as controlled by physical means

Sustainable Strategies to Counteract Mycotoxins Contamination and Cowpea Weevil in Chickpea Seeds during Post-Harvest

Mycotoxins contamination and pest infestation of foods and feeds represent a pivotal threat for food safety and security worldwide, with crucial implications for human and animal health. Controlled atmosphere could be a sustainable strategy to reduce mycotoxins content and counteract the vitality of deleterious organisms in foodstuff. Ozone treatment (O3, 500 ppb for 30, 60 or 90 min) and high nitrogen concentration (N2, 99% for 21 consecutive days) were tested in the post-harvest management of four batches of Cicer arietinum grains to control the presence of mycotoxigenic fungi and their secondary metabolites, as well as pest (i.e., Callosobruchus maculatus) infestation. At the end of the treatment, O3 significantly decreased the incidence of Penicillium spp. (by an average of -50%, independently to the time of exposure) and reduced the patulin and aflatoxins content after 30 min (-85 and -100%, respectively). High N2 concentrations remarkably reduced mycotoxins contamination (by an average of -94%) and induced pest mortality (at 100% after 5 days of exposure). These results confirm the promising potential of O3 and N2 in post-harvest conservation strategies, leading to further investigations to evaluate the effects on the qualitative characteristics of grains.

Antifungal activity of double Schiff bases of chitosan derivatives bearing active halogeno-benzenes

In this study, a series of chitosan derivatives bearing active halogenated aromatic imines were successfully synthesized via Schiff bases with the high degrees of substitution. Detailed structural characterization was carried out using Fourier transform infrared (FTIR) spectroscopy, solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy, and elemental analysis. Besides, the antifungal activity against three common plant pathogenic fungi, including Botrytis cinerea, Fusarium oxysporum f. sp. cucumerinum, and Fusarium oxysporum f. sp. niveum, was investigated using in vitro hyphal measurements. The results showed that double Schiff bases of chitosan derivatives exhibited enhanced antifungal activity compared with chitosan, especially at 1.0 mg/mL. The double Schiff bases of chitosan bearing halogeno-benzenes showed >95% inhibitory indices at 1.0 mg/mL against Botrytis cinereal since halogens had the stronger electron-withdrawing property. The higher degree of substitution was another positive effect to improve the antifungal activity. This study provides a practical strategy to synthesize new double Schiff bases of chitosan derivatives bearing halogeno-benzenes, which could be developed into stronger antifungal agents.

Inhibitory Effect of Moriniafungin Produced by Setosphaeria rostrata F3736 on the Development of Rhizopus Rot

Rhizopus rot is a serious postharvest disease of various crops caused by Rhizopus spp. and controlled mainly by synthetic fungicides. We detected the antifungal activity of a culture extract of Setosphaeria rostrata F3736 against Rhizopus oryzae. The active ingredient was identified as moriniafungin, a known sordarin derivative, which showed minimum inhibitory concentrations of 1-8 μg/ml against Colletotrichum spp. and 0.03-0.13 μg/ml against Rhizopus spp. in vitro. Moriniafungin showed protective control efficacies against Rhizopus rot on apple and peach fruits. Treatment with 25 μg/ml moriniafungin delimited the lesion diameter significantly by 100% on R. oryzae-inoculated apple fruits compared with the non-treated control. Treatment with 0.04 μg/ml of moriniafungin reduced the lesion diameter significantly by 56.45%, and treatment with higher concentrations of 0.2-25 μg/ml reduced the lesion diameter by 70-90% on Rhizopus stolonifer var. stolonifer-inoculated peach fruit. These results suggest moriniafungin has potential as a control agent of postharvest diseases caused by Rhizopus spp.

Synthesis of Submicrocontainers with “Green” Biocide and Study of Their Antimicrobial Activity

The synthesis and properties of submicrocontainers with a shell of nanoparticles of silicon dioxide and a core of polymerized 3-(Trimethoxysilyl) propyl methacrylate loaded with 5-Dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) are considered. The resulting containers were characterized by scanning electron microscopy SEM, laser correlation spectroscopy and thermogravimetric analysis. The obtained submicrocontainers show low polydispersity with a small increase in size in comparison with the initial droplet size of the Pickering emulsion. The Zeta potential of the final containers was sufficiently negative at pH7 to be stable. The maximum release of encapsulated biocide was observed over approximately 24–27 h with a lease of about 78% of the encapsulated biocide during 3.5 h. The effectiveness of the encapsulated biocide by the Pickering emulsion technique was studied by tests on the growth rate of a microfungi colony (Aspergillus niger, Aspergillus awamori) and the growth rate of the bacteria Bacillus cereus. The test shows that the submicrocontainers of DCOIT facilitate a growth inhibition of 70% against 52% for the free biocide after 5 days; this is due to the fact that free biocide loses its activity promptly, while the encapsulated biocide is released gradually, and thus retains its effectivity for a longer time.

Gamma irradiation of Aspergillus flavus strains associated with Indonesian nutmeg (Myristica fragrans)

The aims of this work were to investigate the effects of gamma irradiation on population, viability and aflatoxin B1 production of Aspergillus flavus strains isolated from nutmeg kernels. Thirteen strains of A. flavus were isolated and cultured in potato dextrose agar. Conidia were harvested, air-dried, and irradiated 0, 5, or 10 kGy with gamma rays using a Cobalt-60 source. Toxigenicity were determined using a coconut agar medium and thin layer chromatography. Genomes of strains were extracted from mycelia. Four sets of primers, regulatory (aflR) and structural genes (nor-1, ver-1, omt-1) were used to confirm the presence of the genes. Our results indicate that total fungal populations decreased significantly (P < 0.05) with increasing irradiation dose. However, doses of 5 and 10 kGy were insufficient to completely eliminate the viability of some A. flavus strains. Irradiation did not change toxigenicity and triggered surviving toxigenic strains to produce aflatoxin B1.

Microbiology neutralization of zearalenone using Lactococcus lactis and Bifidobacterium sp

The aim of the study was to neutralize zearalenone by lactic acid bacteria (LAB) such as Lactococcus lactis and Bifidobacterium sp. and investigate the mechanism of zearalenone (ZEA) binding. Neutralization of ZEA by LAB was confirmed by identification of binding kinetics and spectroscopic studies such as Fourier transform infrared spectroscopy (FT-IR) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). The obtained results showed that the kinetic process of zearalenone binding to L. lactis is not homogeneous but is expressed with an initial rapid stage with about 90% of ZEA biosorption and with a much slower second step. In case of Bifidobacterium sp., the neutralization process is homogeneous; the main stage can be described with about 88% of ZEA biosorption. MALDI-TOF-MS measurements and FTIR analysis confirmed the uptake of zearalenone molecules by bacterial species. Moreover, the assessment of dead and live lactic acid bacteria cells after zearalenone treatment was performed using fluorescence microscopy. Graphical abstract Microbiology neutralization of zearalenone using Lactococcus lactis and Bifidobacterium sp. was confirmed by identification of binding kinetics and spectroscopic studies such as FT-IR spectroscopy and MALDI-TOF-MS spectrometry. The mechanism of ZEA binding was also investigated.

Potential of essential oils for protection of grains contaminated by aflatoxin produced by Aspergillus flavus

Aflatoxin B₁ (AFB₁) is a highly toxic and carcinogenic metabolite produced by Aspergillus species on food and agricultural commodities. Inhibitory effects of essential oils of Ageratum conyzoides (mentrasto) and Origanum vulgare (oregano) on the mycelial growth and aflatoxin B₁ production by Aspergillus flavus have been studied previously in culture medium. The aim of this study was to evaluate aflatoxin B₁ production by Aspergillus flavus in real food systems (corn and soybean) treated with Ageratum conyzoides (mentrasto) and Origanum vulgare (oregano) essential oils. Samples with 60 g of the grains were treated with different volumes of essential oils, 200, 100, 50, and 10 μL for oregano and 50, 30, 15, and 10 μL for mentrasto. Fungal growth was evaluated by disk diffusion method. Aflatoxin B₁ production was evaluated inoculating suspensions of A. flavus containing 1.3 × 10⁵ spores/mL in 60 g of grains (corn and soybeans) after adjusting the water activity at 0.94. Aflatoxin was quantified by photodensitometry. Fungal growth and aflatoxin production were inhibited by essential oils, but the mentrasto oil was more effective in soybeans than that of oregano. On the other hand, in corn samples, the oregano essential oil was more effective than that of mentrasto. Chemical compositions of the essential oils were also investigated. The GC/MS oils analysis showed that the main component of mentrasto essential oil is precocene I and of the main component of oregano essential oil is 4-terpineol. The results indicate that both essential oils can become an alternative for the control of aflatoxins in corn and soybeans.

In vitro and in vivo activity of essential oils against major postharvest pathogens of Kinnow (Citrus nobilis × C. deliciosa) mandarin

The present study envisages the influence of essential oils namely lemon grass, eucalyptus, clove and neem on Kinnow mandarin with the objective to combat major post harvest diseases and to prolong its availability for longer time in the season. For this, in vitro and in vivo studies were conducted. Poisoned food technique was used for in vitro studies, and for in vivo studies, Kinnow fruit were pre-inoculated with pathogens (Penicillium digitatum and P. italicum), treated with different essential oils and then stored at 5 °C ±1 °C temperature and 85-90 % RH). Our results indicated that all essential oils inhibited the growth (colony diameter) of both pathogens over untreated PDA plates, but the inhibition was the strongest by lemon grass oil. Similarly, under in vivo conditions, all essential oils influenced decay incidence, decay loss, lesion diameter, respiration rate, ethylene evolution, overall acceptability and physiological loss in weight but lemon grass was the most effective. And also the incidence of Penicillium italicum was more noticed in fruits than P. digitatum, however, it was reverse under in vitro conditions. The decay rot at all stages of storage was less in EOs treated fruits than untreated fruits, thereby increasing their storage life significantly. Thus, it is evident from our studies that essential oils have the potential to control green and blue mold without causing any injury or harmful effects on Kinnow mandarin, and EOs can be recommended as a safe method for extending its storage life while maintaining fruit quality.

The antioxidant effects of pumpkin seed oil on subacute aflatoxin poisoning in mice

This study was aimed at the investigation of the antioxidant effect of pumpkin seed oil against the oxidative stress-inducing potential of aflatoxin. For this purpose, 48 male BALB/c mice were used. Four groups, each comprising 12 mice, were established. Group 1 was maintained as the control group. Group 2 was administered with pumpkin seed oil alone at a dose of 1.5 mL/kg.bw/day (∼1375mg/kg.bw/day). Group 3 received aflatoxin (82.45% AFB1 , 10.65% AFB2 , 4.13% AFG1, and 2.77% AFG2 ) alone at a dose of 625 μg/kg.bw/day. Finally, group 4 was given both 1.5 mL/kg.bw/day pumpkin seed oil and 625 μg/kg.bw/day aflatoxin. All administrations were oral, performed with the aid of a gastric tube and continued for a period of 21 days. At the end of day 21, the liver, lungs, kidneys, brain, heart, and spleen of the animals were excised, and the extirpated tissues were homogenized appropriately. Malondialdehyde (MDA) levels and catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px) activities were determined in tissue homogenates. In conclusion, it was determined that aflatoxin exhibited adverse effects on most of the oxidative stress markers. The administration of pumpkin seed oil diminished aflatoxin-induced adverse effects. In other words, the values of the group, which was administered with both aflatoxin and pumpkin seed oil, were observed to have drawn closer to the values of the control group.

Antifungal activity of plant extracts against Colletotrichum lagenarium, the causal agent of anthracnose in cucumber

BACKGROUND

Colletotrichum lagenarium is an important plant-pathogenic fungus that causes anthracnose of cucumber, a disease that is widespread under both greenhouse and field cultivation. To find a promising method for the control of this disease, extracts of eight plants from China were screened in the study presented here.

RESULTS

The results showed that the extract of Cinnamomum camphora (L.) Presl had significantly greater inhibitory activity against C. lagenarium than the other seven plant extracts tested in vitro. At 5 days after inoculation in a potted seedling experiment, C. camphora extract demonstrated 95% control of C. lagenarium at a concentration of 16 mg mL⁻¹, and the MIC₅₀ was 2.596 mg mL⁻¹. Microscopic observation showed that this extract had a significant impact on the morphology of the fungus, leading to shorter hyphae that were more branched; this observation was associated with the inhibition of mycelial growth. Stability assays revealed that the extract was relatively stable at 80 °C, under acidic conditions and when exposed to light and short periods of UV radiation.

CONCLUSION

These results demonstrated that the extract from C. camphora could be used as a potent phytochemical fungicide.

The influence of modified atmospheres and their interaction with water activity on the radial growth and fumonisin B1 production of Fusarium verticillioides and F. proliferatum on corn. Part I: The effect of initial headspace carbon dioxide concentration

The effect of modified atmospheres on the growth and fumonisin B(1) production of Fusarium verticillioides and Fusarium proliferatum on corn is presented in a series of two papers. In this, the first part, the effect of initial headspace (IH) carbon dioxide concentration and its interaction with water activity (a(w)) on growth and fumonisin B(1) production was evaluated. It was observed that at all a(w) values studied, increase in the IH CO(2) concentration generally resulted in a decrease in the colony growth rate (g, mm day(-1)) and maximum colony diameter (D(max), mm) and an increase in the lag phase duration (lambda, day). Although both a(w) and IH CO(2) concentration had significant and synergistic effects on g, a(w) had the largest effect. As little as 10% IH CO(2) completely inhibited the production of fumonisin B(1) by F. verticillioides. F. proliferatum was more resistant and required 40, 30 and 10% IH CO(2) at a(w) 0.984, 0.951 and 0.930, respectively, to completely inhibit fumonisin B(1) production. These results demonstrate that modified atmospheres containing high CO(2) levels could potentially be employed for the protection of corn from fungal spoilage and mycotoxin contamination during the post-harvest period.

The influence of modified atmospheres and their interaction with water activity on the radial growth and fumonisin B(1) production of Fusarium verticillioides and F. proliferatum on corn. Part II: The effect of initial headspace oxygen concentration

This paper is the second in a series of two that describe the effect of modified atmospheres on the growth and mycotoxin production of Fusarium verticillioides and Fusarium proliferatum on corn. In this part, the effect of initial headspace (IH) oxygen concentration and its interaction with water activity (a(w)) on growth and fumonisin B(1) production was investigated. In addition, the impact of vacuum packaging and in-cooperation of O(2) scrubbing sachets was also studied. It was observed that at all a(w) values studied, reduction of IH O(2) concentration from 20 to 2% had no significant effect on the colony growth rate (g, mm d(-1)) and lag phase duration (lambda, d). However, g and lambda were positively and negatively correlated to a(w). The IH O(2) concentration was determined to have a a(w) dependent effect on the oxygen consumption rate. Although the maximum colony diameter (D(max), mm) decreased with the reduction of the IH O(2) level, the greatest mycelial density occurred at 10% IH O(2) for both isolates. This observation was accompanied by a trend of a decrease in the value of the IH O(2) level at which the most fumonisin B(1) was produced from 15 to 5% when the a(w) was decreased from 0.976 to 0.930 for F. verticillioides. For F. proliferatum the optimum conditions for fumonisin B(1) production shifted from 20% at a(w) 0.976 to 10% at both 0.951 and 0.930. Vacuum packaging and the in-cooperation of O(2) absorbing sachets completely inhibited the growth of both isolates. These results together with those reported in Part I of the study indicate that O(2) should preferably be completely excluded from modified atmospheres that are employed to protect stored corn from fungal growth and mycotoxin production.

Fungicidal and anti-aflatoxigenic effects of the essential oil of Cymbopogon citratus (DC.) Stapf. (lemongrass) against Aspergillus flavus Link. isolated from stored rice

AIMS

To develop a natural fungicide against aflatoxigenic fungi, to protect stored rice, using the essential oil of lemongrass.

METHODS AND RESULTS

Aspergillus flavus Link. was isolated from stored rice and identified as an aflatoxigenic strain. Lemongrass oil was tested against A. flavus and the test oil was fungistatic and fungicidal against the test pathogen at 0.6 and 1.0 mg ml(-1), respectively. Aflatoxin production was completely inhibited at 0.1 mg ml(-1). The results obtained from the thin layer chromatographic bioassay and gas chromatography indicated citral a and b as the fungicidal constituents in lemongrass oil. During the fumigant toxicity assay of lemongrass oil, the sporulation and the mycelial growth of the test pathogen were inhibited at the concentrations of 2.80 and 3.46 mg ml(-1), respectively.

CONCLUSION

Lemongrass oil could be used to manage aflatoxin formation and fungal growth of A. flavus in stored rice.

SIGNIFICANCE AND IMPACT OF THE STUDY

Currently, fungicides are not used to control fungal pests or mycotoxin production on stored rice. Rice treated with the essential oil of lemongrass could be used to manage fungal pests as well as the insect pests in stored rice. The essential oil is chemically safe and acceptable to consumers, as synthetic chemical fungicides can cause adverse health effects to consumers.

Post-harvest storage of corn: effect of beginning moisture content on mycoflora and fumonisin contamination

The effect of storage on mycoflora profile was monitored bimonthly in 36 corn (Zea mays L.) samples, dividing the same sample into groups dried to 11 and 14% moisture content (1008 analysis). These groups were further subdivided based on the initial total count (moulds and yeasts) up to 10(4) CFU g(-1) (12 samples, range 1.6 x 10(4) to 9.0 x 10(4), mean 3.8 x 10(4) CFU g(-1)) and up to 10(5) CFU g(-1) (24 samples, range 1.0 x 10(5) to 5.0 x 10(5), mean 2.7 x 10(5) CFU g(-1)). In the corn group dried to 11%, the fumonisin content was analysed at the initial stage (freshly harvested) and at the end of 12-month storage. Fusarium spp. and Penicillium spp. prevailed at the freshly harvested stage (100%), maintaining this profile throughout 12 months, in corn dried to both 11 and 14%. Cladosporium spp., Aspergillus spp. and Phoma spp. were also detected at lower frequencies during the storage. Fusarium spp. and the total fungal colony count during 12-month storage carried out with samples dried to 11 or 14% moisture content were statistically evaluated using ANOVA for randomized complete block design. The correlation between storage time and Fusarium spp. and total fungal colony count data was analysed by Pearson's correlation test. There was no difference in Fusarium spp. and total counts in the 10(4) CFU g(-1) initial total count group throughout the storage time (p < 0.05). There was a negative correlation between fungal population and storage time (p < 0.05) in the 10(5) CFU g(-1) initial total count group. Fumonisins were detected in all freshly harvested corn, at a mean concentration of 9.9 +/- 6.0 micro g g(-1) (range 0.74-22.6 micro g g(-)1). These values did not change in the 12-month stored corn (mean of 9.9 +/- 5.8 micro g g(-1), range 0.81-23.7 micro g g(-1)). These post harvest data indicated the importance of moisture content at the crop harvesting/predrying stage to control fungal growth and further fumonisin production.

Effect of modified atmosphere packaging and water activity on growth of Eurotium amstelodami, E. chevalieri and E. herbariorum on a sponge cake analogue

The combined effects of water activity (aw), oxygen (O2) and carbon dioxide (CO2) levels on growth variables of three species of Eurotium (two isolates of each) on a sponge cake analogue were studied. The use of a multivariate statistical method (PLS) for the analysis of data showed that in general, the fungi had the same behaviour, according to their growth responses, to changes in the three tested factors. However, the maximal growth of E. herbariorum was somewhat more affected by the O2 level at lower CO2 levels. On the other hand, CO2, aw and the interaction between CO2 and O2 were found to be the most significant factors describing growth variables. In addition, the model found in this study had a good predictive power. There was a positive correlation between the CO2 concentration in the bags and the lag phase, and a negative correlation between the growth rate and maximum mycelial growth. In general, no isolates were able to growth when CO2 concentrations were higher than 60% under anaerobic conditions. At lower values of CO2, aw and O2 influenced growth variables. Low levels of O2 (0.02-0. 5%) did not affect the growth variables studied when levels of CO2 in the bags were high. However, when the CO2 concentration decreased, the different O2 levels had an influence on the growth variables, i. e., a small difference in the concentration of O2 can allow fungi to grow.

Effect of processing on Fusarium mycotoxins

Mycotoxins are secondary metabolites produced by a wide variety of fungal species that contaminate food or feed. Fumonisins (FUM), deoxynivalenol (DON) and zearalenone (ZEN) are examples of common mycotoxins in grains that have been shown to affect human and/or animal health. Physical, chemical and biological methods have been used for decontaminating grains containing these toxins. Some treatments reduce the concentration of mycotoxins while others are ineffective. For example, removal of damaged grain by density segregation can reduce DON and ZEN concentrations in corn and wheat. In contrast, thermal processing is usually ineffective for reducing the FUM and ZEN content of foods. More work is needed to identify effective methods for detoxifying mycotoxin contaminated food.

Influence of white light, near-UV irradiation and other environmental conditions on production of aflatoxin B1 by Aspergillus flavus and ochratoxin A by Aspergillus ochraceus

The effects of illumination, near-ultraviolet, incubation temperature pH and some minor elements on the growth rate and production of aflatoxin B1 by A. flavus and ochratoxin A by A. ochraceus were investigated. Aflatoxin B1 and ochratoxin A production was considerably higher in the light than in the dark. The greatest aflatoxin B1 and ochratoxin A production was occurred after 11 days of fermentation with light- and dark-grown cultures at 25 degrees C. The mycelial dry weight was also greater in the light than in the dark for both A. flavus and A. ochraceus. Exposure of conidia to near-UV irradiation increased mycelial dry weight and mycotoxins by both fungi more than white light. The greatest aflatoxin B1 and ochratoxin A was at 25 degrees C with UV-grown culture (24 h exposure) producing a mean of 400 and 260 micrograms/50 ml of medium, respectively. The maximum aflatoxin B1 and ochratoxin A yield was obtained at pH 5.5 and with increasing the initial pH to near neutrality, both mycotoxins yield decreased. Iron, copper and zinc were observed to stimulate aflatoxin B1 and ochratoxin A production and enhanced the growth rate of both A. flavus and A. ochraceus.

Effect of gamma-irradiation on the natural occurrence of Fusarium mycotoxins in wheat, flour and bread

A survey was carried out to obtain data on the occurrence of Fusarium mycotoxin in wheat and flour samples collected from local markets in Egypt and to study the influence of gamma-irradiation on controlling the occurrence of these mycotoxins in wheat, flour and bread. Deoxynivalenol (DON) was detected in five samples of wheat at levels ranging from 103 to 287 micrograms/kg and one sample each of flour and bread at concentrations 188 and 179 micrograms/kg. Zearalenone (ZEN) was detected in ten samples of wheat at levels from 28 to 42 micrograms/kg and four samples each of flour and bread at concentrations of 95 and 34 micrograms/kg, respectively. T-2 toxin was detected only in one sample each of wheat, flour and bread at concentrations of 2.9, 2.2 and 2.3 micrograms/kg, respectively. Gamma-irradiation at dose level of 6 kGy completely eliminated fungal flora in flour and wheat. DON, ZEN and T-2 toxin concentrations are reduced to 85, 20 and 2.0 micrograms/kg for wheat and to 125, 45 and 1.0 micrograms/kg for flour after 4 kGy exposure and a sharp drop in Fusarium toxin levels occurred at 6 kGy and as eliminated at 8 kGy. Bread prepared from 6 kGy was contaminated with Fusarium toxin at levels below 5 microgram/kg. It was noticed that gamma-irradiation reduce greatly the natural occurrence of Fusarium mycotoxins in bread.