Effect of harvest maturity on carbohydrates for ethanol production from sugar enhanced temperate × tropical maize hybrid

A northern adapted sugar maize (Zea mays L.) hybrid was bred by crossing temperate × tropical maize for bioethanol production. Temperate × tropical maize (TTM) has a prolonged vegetative growth and accumulates more sugar in the stalk compared to its respective tropical and temperature parents (White et al., 2012). In this study, the sugar concentration in the stalk was further increased by preventing pollination by shoot bagging (covering) ears. It was observed that starch content was eliminated and sugar content increased to 30.1% (w/w) in the stalks. The whole plant biomass (grain, sugars and stover) was evaluated for ethanol production. Ethanol produced from sugars and starch was comparable from milk (R3) to dent (R5) reproductive growth stages between pollinated and non-pollinated TTM, indicating that soluble sugar contents increased correspondingly with decreased starch contents. Temperate × tropical maize samples from both pollinated and non-pollinated treatments had high extractives. Glucan and xylan percentages were increased in non-pollinated extractive free samples. Ethanol produced from cellulosic material was similar for both treatments. The total ethanol yield (from starch, sugar and stover) was comparable from milk (R3) to dent (R5) stages and ranged from 0.20 to 0.22 g/g biomass. The pollinated TTM produced higher biomass in the field and resulted in 624.7 gal of ethanol per acre of land. Future research in TTM could be focused on increasing biomass yield of non-pollinated TTM.