Assessing Fermentation Quality of Grain Sorghum for Fuel Ethanol Production Using Rapid Visco‐Analyzer

Abstract

The Rapid Visco‐Analyzer (RVA) was used to characterize the pasting properties of 68 sorghum grains with a standard 23‐min temperature profile. The results showed a strong linear relationship between ethanol yield and final viscosity as well as setback. Ethanol yield increased as final viscosity decreased. A modified RVA procedure (10 min) with an application of α‐amylase was developed to simulate the liquefaction step in dry‐grind ethanol production. There was a remarkable difference in mashing properties among the sorghum samples with the normal dosage of α‐amylase. The sorghum samples which were difficult to liquefy in the mashing step had much higher peak viscosities than the samples that were easily liquefied. The results also showed that the relationship between conversion efficiency and mashing property was significant. Tannins cause high mash viscosities. There was a strong linear relationship between tannin content and final viscosity as well as peak viscosity. The modified RVA procedure is applicable not only for characterization of mashing properties but also for optimization of α‐amylase doses for starch liquefaction.

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“…It is evident that addition of E2 beyond 2% was no longer beneficial. Although our results showed that increasing enzyme concentration did not lead to significantly greater sorghum starch degradation, Aggarwal et al (2001) and Zhao et al (2008c) 0.01% to 0.3%, v/w and when Zhao et al (2008c) increased Liquozyme SC DS (the same enzyme used in our study) dosage from 0.04% to 0.84% fwb. The contrasting results that we obtained may be because even the lowest enzyme dosage used in our study was more than double those used by Aggarwal et al (2001) and Zhao et al (2008c).…”

“…Possibly, the effects of increasing E2 were so slight that protein re-aggregation overrode any observable increase in digestibility brought about by raising E2. Furthermore, as discussed in the preceding section on the effects of E2 on PC, even the lowest levels of E2 used in this study were so much higher than those used in previous studies (Aggarwal et al, 2001;Zhao et al, 2008c) that probably any incremental improvements in digestibility were not significant. …”

Kinetics of starch digestion in sorghum as affected by particle size

“…In addition to other starch properties, the starch-protein interactions in sorghum are possibly responsible for the high pasting temperatures of sorghum, which from the present study, were generally higher than 80°C. These temperatures are within the range (76.7-89.6°C) of pasting temperatures of 68 Puerto Rican genotypes and elite hybrids of sorghum flours studied by Zhao et al (2008).…”

“…Hammer-milled and cryomilled With K 1 = 13.0 Â 10 6 S 2 P þ 1:9 Â 10 4 0.770 *** 0.8 a Level of significance: ** p 6 0.01; *** p 6 0.001. ies by Zhang and Hamaker (2005) and Zhao et al (2008) exhibited shear-thinning behaviours, with some varieties more marked than others. Although studies are in progress in our laboratories on the shear-thickening behaviours of sorghum during pasting, unpublished preliminary results revealed that water (1% sodium metabisulphite solution)-extracted sorghum starch exhibited shearthinning pattern during the 95°C-hold.…”

Particle size heterogeneity in milled barley and sorghum grains: Effects on physico-chemical properties and starch digestibility

“…1). In sorghum, all samples had low initial viscosity and gave typical starch-based viscosity profiles (Zhao et al, 2008). There was a systematic trend, with higher viscosity values obtained for smaller particles ( Fig.…”