Effects of Maize Weevil Infestation on Corn and Utilization of Infested Corn for Ethanol Production

EFFECTS OF MAIZE WEEVIL INFESTATION ON CORN AND UTILIZATION OF INFESTED CORN FOR ETHANOL PRODUCTION

Abstract

The maize weevil, Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae), is a cosmopolitan pest of stored cereal grains, especially maize in tropical and subtropical regions. The focus of our laboratory study was to characterize physical and chemical damage caused by S. zemais to corn over a six month period, and to determine ethanol yield from infested corn.

Clean, certified organic whole yellow corn (5 kg) of 11.9% moisture in 20-L round plastic with ventilated lids was infested with 20 unsexed adults of mixed ages of S. zeamais. There were a total of 36 buckets, of which 18 were infested and 18 were uninfested (controls). It was stored for periods of 1, 2, 3, 4, 5 and 6 months. The moisture content, test weight, dead and live insects, and proximate analysis were conducted using the AOAC (Association of Official Analytical Chemists) and Ankom methods, were measured monthly. The ethanol production was evaluated using two procedures, the enzyme digestion and fermentation processes, to measure the amount of glucose at initial time of the experiment and evaluated the glucose complete conversion into ethanol and its amount, respectively. The amount of glucose and ethanol was analyzed using the High Performance Liquid Chromatography (HPLC) technique.

The corn moisture content of uninfested corn fluctuated between 10.6 and 11.9% during the six-month study period, whereas that of infested corn increased from 11.9 to 14.8% at the end of the study. The number of live insects increased exponentially in infested corn and reached a maximum of 6,985 by the end of the study. Dockage in 1000 g of uninfested corn was 1.2 to 2.2 g but steadily increased in infested corn from 1.2 g to a maximum of 154 g at the end of six months. The weight of 100 uninfested corn kernels normalized to 11.0% wet moisture basis remained unchanged (35.8 g) but this weight in infested corn decreased gradually to 22.6 g at six months. However, dry matter losses were marginal for both uninfested and infested corn over the study period. The crude protein, crude fat, crude fiber, and ash of uninfested and infested corn over time showed minor variation that are not biologically significant. The starch content of uninfested and infested corn ranged from 58 to 61%, and these values were lower by about 10%, probably due to the official standard method used (glucoamylase method) or use of aged enzymes. It was demonstrated that during the first four months with a high level of infestation it was possible to obtain a profitable level of ethanol production, and it begins to decline after the fifth month, and over the sixth month it was not profitable because the amounts of glucose declined dramatically. In conclusion, it was possible to obtain profitable levels of ethanol from infested corn even under a high density of infestation by maize weevil, and it will optimize the use of corn as raw material for worldwide ethanol production.