Location: Grain Quality and Structure Research2009 Annual Report
1a. Objectives (from AD-416)
1) Determine the adhesive properties of sorghum proteins isolated from DDDGS, bran and flour, 2) Determine the chemical properties of sorghum proteins related to adhesive and bio-plastic quality, and 3) Improve the quality of sorghum protein based adhesives and bio-plastics.
1b. Approach (from AD-416)
Optimize the isolation of sorghum proteins from DDGS, bran, and/or sorghum flour and characterize the chemical properties of the isolated proteins and their functional properties in adhesives and bio-plastic production. Isolate proteins from sorghum grains with known attributes (e.g. hardness) to determine the factors that influence the quality of sorghum based adhesives and bio-plastics.
3. Progress Report
Sorghum DDGS with moisture content of 14.4% was used as protein source. Sorghum DDGS was milled into powder with particle size less than 1 mm. Three different protein extraction methods, including method developed by Taylor et al (2005), the procedure of Xu et al (2007), and extraction method described by Emmanbux and Taylor (2003), were used for sorghum protein extraction. Protein composition and chemical properties such as protein structure and molecular weight were analyzed using AOC standard method, FT-IR, lab-on-a-chip electrophoresis, size-exclusion chromatography (SEC), and reversed phase high-performance liquid chromatography. Thermal properties of extracted protein were analyzed using thermal gravimetric analysis (DSC) and differential scanning calorimetry. Extraction conditions (methods) had a significant effect on protein yield, purity, and thermal properties. Acetic acid and NaOH-ethanol produce protein with higher purity than protein extracted with HCl-ethanol protocol. Highest purity produced was 98.9% which was from the acetic acid extraction protocol. Investigation of secondary structure of sorghum protein showed that a helix dominates in all three protein samples extracted using different methods with a small portion of ß sheet. The ß kafirins have a lower Mw than a kafirins. SEC results showed that the chromatograms of the protein extracts were very similar between the 6.6-10 minute elution ranges. More proteins with Mw > 669 kDa were present in all three protein sample. Thermal properties of protein samples from different extraction procedures were studied. The degradation of samples went through three stages. The first stage (weight loss from room temperature to around 124°C) is ascribed to water evaporation. The second stage is corresponding to the degradation of sorghum protein. The degradation of protein undergoes multiple mass loss peaks suggests that the compositions of different thermal stability in protein. The degradation peak that started around 270-290°C is believed to protein thermal degradation, similar to the thermal degradation of zein and soy protein. Above 580°C, sample weight loss slowed and remained almost constant; the solids left were primarily ash. No peak was observed in DSC thermograms until around 230°C. There was no denaturation peaks (endothermic) detected, indicating the protein was denatured before being subjected to the test (denatured during distillation). Activities of this project are monitored by frequent personal meetings, emails and phone calls.