Production of bioethanol from corn meal hydrolyzates

Bioethanol produced from renewable agricultural recourses is currently the most promising biofuel. In a lot of developed countries in Europe and in USA the use of bioethanol as an alternative fuel or a gasoline supplement in the amount of up to 15 % is highly recommended or even required as an ecologically favorable fuel oxygenate. Concerning EU, in November 2001 a new directive was accepted, that requires of members states to establish legislation about utilization of fuels from renewable resources. In 2005. this utilization should cover 2% of the total fuel consumption. This quota is expected to increase to 5.75% in 2010. and furthermore. In our country one of the most suitable agricultural raw material for bioethanol production is corn. Two-steps enzymatic hydrolysis of corn meal by commercially available a-amylase (Termamyl 120 L, Novozymes) and amyloglycosidase (Supersan 240L, Novozymes) and ethanol fermentation of the hydrolyzates by Saccharomyces cerevisiae yeast (culture collection BIB-TMF, Belgrade) was studied in this paper. The conditions of starch hydrolysis such as substrate and enzyme concentration and the duration of time required for enzymatic action were optimized taking into account both the effects of hydrolysis and ethanol fermentation. The results obtained showed that the corn meal hydrolyzates were good substrates for ethanol fermentation by Saccharomyces cerevisiae. The yield of ethanol of more than 80% of theoretical was achieved with a satisfactory volumetric productivity P (g /l ×h). No shortage of fermentable sugars was observed during simultaneous hydrolysis and fermentation. On this way, the savings in time and energy could be realized. By increasing the inoculum size form 1 % to 2 % of Saccharomyces cerevisiae the fermentation time could be reduced from 48 to 32 hours respectively. U radu je ispitivan postupak dvojno enzimske hidrolize kukuruznog brašna pomoću komercijalnih enzima a-amilaze (Termamyl 120L, Novozymes) i amiloglukozidaze (Supersan 240L, Novozymes) i fermentacija hidrolizata pomoću kvasca Saccharomyces cerevisiae (iz kolekcije kultura BIB-TMF Beograd). Uslovi hidrolize kao što su koncentracija supstrata i enzima i vreme dejstva pojedinih enzima su optimizovani sa aspekta oba procesa (i fermentacije i hidrolize). Dobijeni hidrolizati kukuruznog brašna su se pokazali kao pogodni supstrati za alkoholnu fermentaciju pomoću kvasca Saccharomyces cerevisiae, pri čemu je ostvaren prinos etanola od više od 80 % od teorijskog prinosa prinosa produkta po substratu YP/S (g /g) i zadovoljavajuća volumetrijska produktivnoost P (g /l ×h). U toku postupka uporednog odvijanja hidrolize i fermentacije nije primećen nedostatak fermentabilnih šećera u podlozi. Na ovaj način je moguće skratiti ukupno vreme procesa i ostvariti određene energetske uštede. Povećanje koncentracije inokuluma kvasca Saccharomyces cerevisiae sa 1 % do 2 % daje mogućnost da se skrati vreme fermentacije sa 48 na 32 sata, respektivno.