Studies on the Mycoflora and some Physical characteristics of Ghanaian Maize (Zea Mays L) Varieties and the Effect of Extracts of Zanthoxylum Xanthoxyloides Lam and Kigelia Africana Benth on some of the Contaminant Fungi

Abstract

Mycoflora of mixed maize grains and the newly developed Abeleehi and Obaatanpa varieties and airspora in the Warehouse of the Ghana Food Distribution, GFDC, at Balduzzi, Kumasi have been studied under normal and simulated ambient Environmental Relative Humidities (ERH’s) representative of the Ghanaian conditions. Some important physical and processing characteristics of ￡. and normal stackbumed white and yellow maize (seed water absorption, swelling index, 1000-seed weight, fermentation parameters) and gemination capacity of grains were also examined. To ascertain the ability of Abeleehi and Obaatanpa varieties to absorb and desorb moisture in relation to the development of attendant resident fungi, the moisture sorption isotherm at ERH’s 55-95% were determined in simulated humidity chambers. Finally results of the use of aqueous, acetone and methanolic extracts of the dry leaves of Zanthoxylum xanthoxyloides and the dry leaves and dry fruit of Kigelia africana as biofungicides to control vegetative growth and sporulation of important potential pathogenic fungi (Paecilomyces carneus, P.puntoni, P.varioti, Curvularia lunata, Fusarium moniliforme and Penicillium digitatum) resident in Abeleehi and Obaatanpa varieties are reported. Fifteen different fungal species (Aspergillus flavus, A.niger, A.sulphureus, A.tamarii, Penicillium brevicompactum, P.chrysogenum, P.citrinum, P.cyclopium, P. digitatum, P.glabrum, P.oxalicum, Cladosporium herbarum, Fusarium moniliforme, F.roseum andMucor haemalis) were isolated from maize grains obtained from the GFDC Warehouse at Balduzzi, Kumasi. Aspergillus species (A.flavus, A.niger, A. sulphur e-US', A.tamarii) and Penicillium species (Penicillium brevicompactum, P.chiysogenum, P.citrinum, P.cyclopium, P.digitatum) predominated. The initial fungal population in the mixed grain variety was 4.8 - 5.4 log |0 CFU/g but this decreased by 0.4 -1.3 log cycle after 2 months. There was no statistical difference (P< 0.05) between the population of fungi isolated from grains sampled from the top, middle and bottom of the bagstacks. Aspergillus flavus was Hie most predominant fungi encountered constituting 41.7- 44.0% of the species followed by Mucor haemalis (4.0 - 20.5%). Both A.flavus and M. haemalis occurred at all positions sampled. Twenty four different airspora of fungi (Aspergillus flavus, A.clavalus, A.fiumigatus, A.niger, A.ochraceus, A.parasiticus, A.sulphureus, A.tamarii, Penicillium chrysogemim, P.citrinum, P.cyclopium, P.digitatum, P. expansum, P.italicum, P.oxalicum Paecilomyces carneus, Ppuntonii, P.varioti, Cladosporium herbarum, Curvularia lunata, Fusarium moniliforme, Mucor haemalis, Neurospora sitophila, Rhizopus oryzae) were isolated from the Balduzzi Warehouse. Species of airspora that were not foundinthe grains wereA.clavatus, A.ochraceus, Aparasiticus, A.fumigatus, P.expansum, Paecilomyces carneus, Ppuntonij P.varioti, Curvularia lunata and Rhizopus oryzae. Generally mycological media used and the method used in isolation influenced the profile o f fungal species encountered. Thirty and 28 fungal species belonging to 13 genera were isolated from Abeleehi and Obaatanpa varieties respectively, and they are being recorded for the first time in Abeleehi and Obaatanpa varieties. The species diversity was influenced by grain variety, method of isolation, mycological media used, storage humidity and whether the grains were exposed in petri dishes or in woven polypropylene sachets. A.flavus was ubiquitous and was isolated from both Abeleehi and Obaatanpa stored at 55-95% ERH in both open Petri dishes and in woven polypropylene sachets; Fusarium moniliforme was encountered atERH’s 65-95% in open Petri dishes but not at 65 and 75 ERH in woven polypropylene sachets. Xerophilic species, like Aspergillus giganteus, P. carneus, P.puntoni and P.varioti were isolated at 55-65% ERH in both grain varieties. There was no statistical difference (analysis of variance P.< 0.05) between germination capacity of Abeleehi grains stored in woven polypropylene sachets at ERH 55- 85%; seed germination was drastically reduced at 90 and 95% ERH after 2 months storage period. Data on grains kept exposed in Petri dishes to the same ERH’s were similar. The same trend as above was observed for Obaatanpa grains. The storage ERH influenced the length of the emerging radicles of the germinating grains such that the higher the incubating ERH, the shorter the length of the emerging radicle. At ERH 95% radicle length was reduced by 39-69% (depending on the maize variety used). There was however a significant (P< 0.05) difference between the higher radicle length recorded in grains of both varieties stored in woven polypropylene sachets than same grains exposed in Petri dishes under the same ERH conditions. Abeleehi and Obaatanpa vai-ieties showed the characteristic sigmoid water absorption patterns o f macromolecules. The equilibration period of grains stored at 65-85% ERH was 8-12 days; those stored at 90-95% ERH continued rising while there was decrease in moisture content of grains incubated at 55% ERH for both grain varieties. Analysis of variance to ascertain the influence of ERH, Packaging material (P), incubation period (I) and maize variety (V) on moisture sorption as well as the interaction o f these factors showed that P, I and V significantly (P< 0.05) influenced moisture sorption. Moisture sorption by Obaatanpa was significantly higher than that of Abeleehi under the same environmental conditions. Obaatanpa variety had a higher density (1000 - seed weight o f273,9g) than Abeleehi (268.9g); stackbumed yellow (329.3 } 5.4g) and white grains (275.3 } 2. lg). The moisture content of stackbumed grains (13.0 -13.5 } 0.1 %) did not differ significantly (P< 0.05) from the normal grains of the same type (12.0-13.5 } 0.1). Seed length of normal white maize soaked for 48h. was 2-3% greater than that o f stackbumed white maize. Swelling of normal yellow maize initially lagged behind that of stackbumed samples but this was reversed after 24h. soaking resulting in 1 -2% increase in seed length over that o f the stackbumed yellow maize. Similar trends were observed for seed width and seed thickness. pH profile o f wet and dry-milled maize (normal and stackbumed) undergoing spontaneous fermentation was generally similar at least during the first 24-48 h. attended by a drop in pH from initial 5.0 - 6.5 to final pH 4.2 - 4.6. Steepwater of normal white maize was more acidic (pH 4.2 -4.3) than stackbumed grains (pH 5.1 - 5.2) of the same grain variety. Aqueous, acetone and methanolic leaf extract o f Zanthoxylum xanthoxyloides and leaf and fruit extracts of Kigelia africana obtained with the same solvents variably prevented or depressed vegetative growth and sporulation by pathogenic fungi (Paecilomyces carneus, P.puntonii, P. varioti, Fusarium moniliforme, Curvularia lunata, Penicillium digitatum) in maize meal media amended with the extracts. The efficacy of the extracts in depressing vegetative growth of the test fungi can be .. ng order: Methanol > acetone > aqueous (water) Extracts of leaf of Kqfricana was more potent at higher concentrations than extracts obtained from its own fruit or the leaf of Z.xanthoxyloides. P. puntonii appeared to be the most resistant fungus (among the other test fungi) to the biofungicides. Analysis of variance showed that the effectiveness of the plant extracts of Z.xanthoxyloides and K. africana in suppressing spomlation of the test fungi at high concentration differed significantly and can be ranked as follows in descending order: Leaves o f Z.xanthoxyloides > leaves o f K. africana > fruit of K. africana. Although each test fungus responded and behaved differently in vitro, a fortuitous condition is created in which especially the methanolic extract not only prevent vegetative growth at higher concentration but also prevent sporulation. The possible methods of application of the results from this thesis are discussed and further studies suggested.