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Maize storage in termite mound clay, concrete, and steel silos in the humid tropics: Comparision and effect on bacterial and fungal counts
- Mobolaji O. Omobowale, Paul R. Armstrong, Yahaya Mijinyawa, Joseph C. Igbeka, Elizabeth B. Maghirang
- Transaction of the ASABE 2016 v.59 no.3 pp. 1039-1048
- clay, concrete, construction materials, corn, dry matter content, fungi, humid tropics, microbial activity, permeability, plate count, relative humidity, silos, steel, storage quality, storage temperature, storage time, stored grain, stored product protection, termite mounds, wet season, Nigeria
- Considering the inadequacy of grain storage structures in Nigeria, which has been partly attributed to high cost and unavailability of construction materials, this study investigated the suitability of using readily available termite mound clay (TMC) for grain silo construction in comparison to conventional reinforced concrete (RC) and galvanized steel (GS) silos for maize storage in the humid tropics. The extent to which temperature and relative humidity affected the quality of stored grain during 8-month unaerated storage, covering both dry and rainy seasons, was evaluated using bacterial and fungal counts as performance parameters. The initial bacterial count of 3500 colony forming units (CFU) per gram (CFU g-1) increased to 120000, 11000, and 8800 CFU g-1 for TMC, RC, and GS silos, respectively. There was no fungal activity at the beginning of storage, but fungal activity increased to 1500, 5500, and 350 CFU g-1 in TMC, RC, and GS silos, respectively. Fungal activity was noticed in the TMC silo in the fourth month of storage, which coincided with the start of the rainy season. Fungal counts exceeded the acceptable threshold of 1000 CFU g-1 in the TMC and RC silos. Relative humidity was of greater significance than temperature in affecting all maize quality parameters considered. TMC was found suitable for constructing silos for short-term grain storage under unaerated conditions. Modification of the current TMC silo design to address permeability issues is expected to improve its performance for longer-term maize storage.increased dramatically in the TMC silo compared to the RC and GS silos (120000, 11000 and 8800 cfus/g respectively). Fungal activity was observed in TMC silo on the fourth month of storage which coincided with the start of the rainy season. Fungal count exceeded the acceptable threshold of 1000 cfus/g (Nigerian Industrial Standards) in the TMC (1300 cfu/g) and RC silos (5500 cfu/g) after four and six months respectively. The GS silo remained at a safe level (350 cfu/g). Dry matter content, initially at 88.7%, was reduced to 84.0%, 84.9%, and 87.3 % in the TMC, RC and GS silos respectively. Based on dry matter loss reaching ~0.5% to 1.0%, the allowable storage time for TMC and RC silos was 4 to 4.75 months and for the GS silo was 6 to 7 months. Relative humidity was found to be of great significance compared to temperature in affecting all maize quality parameters considered. The TMC was found suitable for constructing silos for short-term grain storage (four months) under un-aerated condition. Modifications to the current TMC silo design need to address permeability issues to improve its performance for longer-term maize storage.