Henry Njapau - Academia.edu (original) (raw)

Papers by Henry Njapau

Journal of Chromatography B: Biomedical Sciences and Applications, 1982

BioControl, Apr 9, 2024

Through partitioning of ecological niches, several fungi are able to coexist on the same host cro... more Through partitioning of ecological niches, several fungi are able to coexist on the same host crop. In (partial) absence of niche partitioning, competitive exclusion among fungi can occur. Competitive exclusion is one of the bases for biocontrol. We investigated fungal correlations, in terms of relative abundance of the fungi, in pre-harvest maize, as a natural ecosystem model. Internal mycobiome fungal relative abundance of maize was used to establish correlations. The maize had been harvested from dry and wet agro-ecological zones of Zambia. The relative abundances of the fungal genera were determined using DNA amplicon sequencing. For this study, positive or absence of correlations between fungal genera signified good niche partitioning (co-existence), whereas negative correlations signified poor niche partitioning and potential for competitive exclusion. When species compete within one niche (competitive exclusion), we may expect to detect higher levels of mycotoxins-since mycotoxins are considered antagonistic agents aimed at defending or invading an ecological niche. To estimate the importance of mycotoxins in competitive exclusion, we measured the influence of the fungal correlations on levels of fumonisin-B1 (FB1) in the maize. FB1 data were derived from a previous study on the maize, determined by HPLC. Results showed that Sarocladium and Stenocarpella had the strongest significant negative correlation with Fusarium, suggesting poor niche partitioning and potential for antagonism of these genera with Fusarium. Furthermore, higher levels of Stenocarpella resonated with lower levels of FB1 and vice versa. It was also observed that, when Sarocladium was in low abundance (< 10%), the frequency of detection of higher levels of FB1 (> 100 µg kg −1) in the pre-harvest maize was highest.

Frontiers in sustainable food systems, Jan 30, 2024

Aflatoxin contamination in peanuts (Arachis hypogaea L.) by aflatoxinproducing Aspergillus spp. i... more Aflatoxin contamination in peanuts (Arachis hypogaea L.) by aflatoxinproducing Aspergillus spp. is a serious problem worldwide affecting human health and restricting trade. Recently, conservation agriculture practices such as minimum tillage, crop rotation, soil surface cover, intercropping, and planting in basins alongside trees that enhance soil fertility, have been introduced in Zambia as tools to conserve soil moisture, increase peanut yield, and reduce the risk of aflatoxin contamination. However, a limited understanding exists of the impact of conservation agriculture on Aspergillus population densities in the soil and aflatoxin concentrations in crops grown under conservation agriculture. This study assessed the impact of conservation agriculture on (i) Aspergillus communities profile in soil cropped to peanuts, (ii) peanut aflatoxin contamination levels, and (iii) influences of the practices on liver cancer risks as a result of consuming peanuts grown in basins, peanuts grown in basins in farms having Gliricidia sepium trees (agroforestry), and peanuts grown on ridges (conventional tillage). Densities of Aspergillus spp. in soils ranged from 10 to 7,400 CFU/g (mean = 295 CFU/g). The densities differed among farming techniques (p = 0.0011) with conventional tillage (357 CFU/g) supporting higher densities than agroforestry (296 CFU/g) and peanuts grown in basins (230 CFU/g). Aspergillus communities were dominated by fungi with S morphology (55%; which is composed of several morphologically similar species), followed by A. parasiticus (34%), and the L morphotype of A. flavus (11%). Over 60% of the peanut samples were contaminated but there were no differences among farming techniques. Mean aflatoxin contents in peanuts were 110, 99, and 87, μg/kg for agroforestry, conventional tillage, and peanuts grown in basins, respectively. Probable daily aflatoxin intake ranged from 12.7 to 767.1 ng/kg body weight/d, depending on the age of consumers. The estimated liver cancer risk due to consumption of raw peanuts (0.334 to 20.128 cases/100,000 persons/ year) was highest among children below 5 years and least for young adults. The results showed that growing peanuts in basins has the potential to reduce Aspergillus populations in soil. Possibly, planting in basins and agroforestry had minimal effect on water runoff and did not support sufficient moisture retention in the soil to reduce Aspergillus spp. densities and aflatoxin accumulation in the peanuts. Thus, more research is needed to improve the effectiveness of peanut

Journal of Fungi

Aflatoxins (AFs) are considered to play important functions in species of Aspergillus section Fla... more Aflatoxins (AFs) are considered to play important functions in species of Aspergillus section Flavi including an antioxidative role, as a deterrent against fungivorous insects, and in antibiosis. Atoxigenic Flavi are known to degrade AF-B1 (B1). To better understand the purpose of AF degradation, we investigated the degradation of B1 and AF-G1 (G1) in an antioxidative role in Flavi. Atoxigenic and toxigenic Flavi were treated with artificial B1 and G1 with or without the antioxidant selenium (Se), which is expected to affect levels of AF. After incubations, AF levels were measured by HPLC. To estimate which population would likely be favoured between toxigenic and atoxigenic Flavi under Se, we investigated the fitness, by spore count, of the Flavi as a result of exposure to 0, 0.40, and 0.86 µg/g Se in 3%-sucrose cornmeal agar (3gCMA). Results showed that levels B1 in medium without Se were reduced in all isolates, while G1 did not significantly change. When the medium was treated w...

Applied and Environmental Microbiology

Fungi contaminate various crops worldwide. Maize, an important human staple and livestock cereal,... more Fungi contaminate various crops worldwide. Maize, an important human staple and livestock cereal, is susceptible to contamination with fungi in the field.

a International Institute of Tropical Agriculture (IITA-Zambia), Lusaka, Zambia b IITA-Ibadan, Oy... more a International Institute of Tropical Agriculture (IITA-Zambia), Lusaka, Zambia b IITA-Ibadan, Oyo Road, Ibadan, Nigeria c Zambia Agriculture Research Institute, Mount Makulu Central Research Station, Zambia. d National Institute for Scientific and Industrial Research (NISIR), Lusaka, Zambia e The World Vegetable Center (AVRDC) Eastern and Southern Africa , Duluti, Arusha, Tanzania f USDA-ARS, School of Plant Sciences, University of Arizona, Tucson, USA.

a Deutsche Gesellschaft für Internationale Zusammenar beit (GIZ), Germany b International Institu... more a Deutsche Gesellschaft für Internationale Zusammenar beit (GIZ), Germany b International Institute of Tropical Agriculture (II TA-Zambia), Lusaka, Zambia c IITA-Ibadan, Oyo Road, Ibadan, Nigeria d Zambia Agriculture Research Institute, Mount Makul u Central Research Station, Zambia. e National Institute for Scientific and Industrial Re search (NISIR), Lusaka, Zambia f The World Vegetable Center (AVRDC) Eastern and Sou thern Africa , Duluti, Arusha, Tanzania g USDA-ARS, School of Plant Sciences, University of Arizona, Tucson, USA.

The removal of silicic acid, calcium phosphate and the sesquioxides is essential for the producti... more The removal of silicic acid, calcium phosphate and the sesquioxides is essential for the production of high grade raw sugars. Silicic acid and calcium oxalates are the major compounds causing hard and difficult to remove scale in evaporators. This study investigated the extent to which scale forming ions could be removed from clarified sugarcane juice by electro-coagulation (electro-clarification) using a novel Kaselco reactor fed with DC current. Observations from the study indicate that electro-coagulation can remove essentially all the silica, reduces Ca, P, Mg and Al although to a lesser extent and adds some iron to the treated juice. The direct operating cost of an electro-coagulating unit was estimated at <0.02 cents per pound of raw sugar.

Food, which ensures the sustenance o f life, has also been implicated in the development or preve... more Food, which ensures the sustenance o f life, has also been implicated in the development or prevention o f numerous diseases including cancer. Cancer may be a result o f hereditary factors or genomic instability induced by DNA damage, from the intrinsic chemistry o f cells or extrinsic factors like aflatoxin Bt. Aflatoxin B„ produced by Aspergillus flavus and Aspergillus parasiticus, is a common contaminant o f com and cottonseed and a proven mutagen and animal carcinogen. Increased scientific knowledge and establishment o f regulation have reduced but not eliminated exposure to aflatoxin Bt. Complete elimination may be uneconomical for producers and may deprive consumers of sources o f nourishment. Consumption o f substances that offset the deleterious effects o f aflatoxin, particularly those intrinsic to a commonly consumed foodstuff, may circumvent the problem. This study set out to isolate, substances that possess antimutagenic activity from com and cottonseed. A bioassay direc...

The characteristics of a conventional, 1-by 2-cm, N/P, gridded silicon solar cell when used n as ... more The characteristics of a conventional, 1-by 2-cm, N/P, gridded silicon solar cell when used n as a radiometer have been determined for solar intensity levels to 2800 mW/cm (20 solar constants). The short-circuit current was proportional to the radiant intensity for levels only to n 2 700 mW/cm (5 solar constants). For intensity levels greater than 700 mW/cm , it was necessary to operate the cell in a photoconductive mode in order to obtain a linear relation between the measured current and the radiant intensity. When the solar cell was biased with a reverse voltage of-1 V, the measured current and radiant intensity were linearly related over the comn plete intensity range from 100 to 2800 mW/cm .

Applied and environmental …, 2007

Maize contaminated with aflatoxins has been implicated in deadly epidemics in Kenya three times s... more Maize contaminated with aflatoxins has been implicated in deadly epidemics in Kenya three times since 1981, but the fungi contaminating the maize with aflatoxins have not been characterized. Here we associate the S strain of Aspergillus flavus with lethal aflatoxicoses that took more than 125 lives in 2004.

Copyright information:Taken from "Aflatoxin Contamination of Commercial M... more Copyright information:Taken from "Aflatoxin Contamination of Commercial Maize Products during an Outbreak of Acute Aflatoxicosis in Eastern and Central Kenya"Environmental Health Perspectives 2005;113(12):1763-1767.Published online 10 Aug 2005PMCID:PMC1314917.This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original DOI. Each dot represents the rate of aflatoxicosis by division, and dots are in the center of each division (divisions are not shown).

Copyright information:Taken from "Case–Control Study of an Acute Aflatoxi... more Copyright information:Taken from "Case–Control Study of an Acute Aflatoxicosis Outbreak, Kenya, 2004"Environmental Health Perspectives 2005;113(12):1779-1783.Published online 9 Aug 2005PMCID:PMC1314920.This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original DOI.

See next page for additional authors

In April 2004, one of the largest aflatoxicosis outbreaks occurred in rural Kenya, resulting in 3... more In April 2004, one of the largest aflatoxicosis outbreaks occurred in rural Kenya, resulting in 317 cases and 125 deaths. Aflatoxin-contaminated homegrown maize was the source of the outbreak, but the extent of regional contamination and status of maize in commercial markets (market maize) were unknown. We conducted a cross-sectional survey to assess the extent of market maize contamination and evaluate the relationship between market maize aflatoxin and the aflatoxicosis outbreak. We surveyed 65 markets and 243 maize vendors and collected 350 maize products in the most affected districts. Fifty-five percent of maize products had aflatoxin levels greater than the Kenyan regulatory limit of 20 ppb, 35 % had levels> 100 ppb, and 7 % had levels> 1,000 ppb. Makueni, the district with the most aflatoxicosis case-patients, had significantly higher market maize aflatoxin than did Thika, the study district with fewest case-patients (geometric mean aflatoxin = 52.91 ppb vs. 7.52 ppb, p...

OBJECTIVES: During January–June 2004, an aflatoxicosis outbreak in eastern Kenya resulted in 317 ... more OBJECTIVES: During January–June 2004, an aflatoxicosis outbreak in eastern Kenya resulted in 317 cases and 125 deaths. We conducted a case–control study to identify risk factors for contamination of implicated maize and, for the first time, quantitated biomarkers associated with acute aflatoxicosis. DESIGN: We administered questionnaires regarding maize storage and consumption and obtained maize and blood samples from participants. PARTICIPANTS: We recruited 40 case-patients with aflatoxicosis and 80 randomly selected controls to participate in this study. EVALUATIONS/MEASUREMENTS: We analyzed maize for total aflatoxins and serum for aflatoxin B1–lysine albumin adducts and hepatitis B surface antigen. We used regression and survival analyses to explore the relationship between aflatoxins, maize consumption, hepatitis B surface antigen, and case status. RESULTS: Homegrown (not commercial) maize kernels from case households had higher concentrations of aflatoxins than did kernels from...

See next page for additional authors

Journal of Chromatography B: Biomedical Sciences and Applications, 1982

BioControl, Apr 9, 2024

Frontiers in sustainable food systems, Jan 30, 2024

Journal of Fungi

Applied and Environmental Microbiology

Applied and environmental …, 2007

See next page for additional authors