Effect of Sorghum Decortication and Use of Protease Before Liquefaction with Thermoresistant α‐Amylase on Efficiency of Bioethanol Production

Abstract

Cereal Chem. 85(6):792-798The aim was to study the dual effect of sorghum decortication and protease treatment before liquefaction with α-amylase on the performance of subsequent steps of saccharification and fermentation. A bifactorial experiment with a level of confidence of P < 0.05 was designed to study differences among grains (maize, whole, and decorticated sorghum) and the effectiveness of the protease before liquefaction. Sorghum was decorticated to remove most of the pericarp and part of the germ and increase starch concentration of the feedstock. The decorticated sorghum had significantly higher starch hydrolysis during liquefaction compared with the whole kernel. These hydrolyzates contained ≈50% more reducing sugars than the untreated counterparts. At the end of saccharification, the final glucose concentration in hydrolyzates treated without protease was the highest for maize (180 mg/mL), followed by decorticated sorghum (165 mg/mL), and whole sorghum (145 mg/mL). Decortication and protease treatment had a significant effect on fermentation times. In decorticated sorghum mash treated with and without protease, fermentation times were 22 and 60 hr, respectively. The decorticated sorghum treated with protease yielded similar amounts of ethanol compared with maize and 44% more ethanol compared with the untreated whole sorghum. Both sorghum decortication and protease treatments before hydrolysis with αamylase are recommended to increase ethanol yields, lower yields of distilled grains, and save liquefaction, saccharification, and fermentation times.

Detrimental effect of increasing sugar concentrations on ethanol production from maize or decorticated sorghum mashes fermented with Saccharomyces cerevisiae or Zymomonas mobilis

“…The proximate compositions of grains were within values reported in the literature (Perez-Carrillo et al 2008) ( Table 1). As expected, sorghum decortication decreased the amounts of ash, crude protein and crude fiber approximately 23, 12 and 34%, respectively.…”

“…However, ethanol production was different in Z. mobilis and S. cerevisiae. Fermentations with S. cerevisiae showed the typical behavior of ethanol production (Perez-Carrillo et al 2008;Chuck-Hernandez et al 2009) where most of the alcohol was produced between 12 and 24 h. With Z. mobilis, the highest ethanol production was at the end of the 72 h fermentation. The delay could be attributed to fermentation temperature.…”

“…Mashes were treated with Neutrase 0.5 and Termamyl 120L (Novozymes, Denmark) according to the process described by Perez-Carrillo et al (2008). After liquefaction, the suspension was filtered and pH adjusted to 5.5.…”

“…However, sorghum typically yields less ethanol than maize mainly due to a tougher protein matrix and compounds present in the pericarp that lower and delay starch conversion into fermentable carbohydrates. The sorghum decortication process improves biocatalysis and fermentation efficiencies downstream and yields value-added and shelf-stable bran (Corredor et al 2006;Wu et al 2007;Perez-Carrillo et al 2008). Recent investigations have demonstrated that sorghum can match maize bioethanol yields when treated with proteases after decortication or steam-flaked before liquefaction (Perez-Carrillo et al 2008;ChuckHernandez et al 2009).…”

Evaluation of Waxy Grain Sorghum for Ethanol Production

“…Yeast can only utilize FAN and short peptides, not large intact proteins. Much research has been conducted on the effects of protein and protein digestibility on ethanol fermentation of various cereal grains such as wheat and barley (Lacerenza et al 2008), sorghum and maize (Perez-Carrillo and Serna-Saldivar 2007;Perez-Carrillo et al 2008;Zhao et al 2008), and different varieties of maize (Wu 1989;Wang et al 2005), but little research has been conducted on the effect of FAN on the conversion efficiency of sorghum varieties in ethanol fermentation.…”