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United States Department of Agriculture

Agricultural Research Service


Location: Grain Quality and Structure Research

2009 Annual Report

1a. Objectives (from AD-416)
The objectives of this research are: (1) Evaluate starch and protein digestibility of select sorghum lines and (2) Develop rapid reference methods to assess amylose-amylopectin ratios as well as amylopectin branch ratios in wheat and sorghum starch.

1b. Approach (from AD-416)
Sorghum samples currently used for development of gluten-free foods will be analyzed for starch and protein digestibility using conventional pepsin digestion (protein) and the Englyst method (starch). The results will be used to evaluate rapid methods using specific labeling, gel permeation chromatography with pulsed amperometric detection (PAD) for determination of amylose amylopectin ratios and amylopectin branching. Digestibility will be performed using rapid fluoremetric methods.

3. Progress Report
Currently, most adhesives used in the wood industry are petroleum-based, such as phenol-formaldehyde and urea-formaldehyde adhesives. Many industries are seeking environmental friendly adhesives; however, the major challenge to switching from petroleum-based to biobased feedstocks is the high cost of biobased feedstocks and lacking of technologies to meet their requirements. The long-term goal of this project is to develop affordable, durable and biodegradable protein adhesives using low-cost sorghum DDGS to reduce reliance on fossil feedstocks. The short-term goal is to establish the feasibility of an innovative technology to produce affordable and durable biobased protein adhesive using sorghum protein from DDGS. The research will focus on 1) protein extraction from sorghum DDGS with high yield, high purity, and desirable functionality for industrial uses; 2) characterization of physical, chemical and structural properties of extracted proteins; and 3) evaluation of adhesion performance of sorghum protein and improved adhesion by chemical modification. Sorghum DDGS with moisture content of 14.4% was milled into powder with particle size less than 1 mm. Three different methods were used for sorghum protein extraction. Protein composition and chemical properties such as protein structure and molecular weight were analyzed, 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 had a significant effect on protein yield, purity, and thermal properties. Acetic acid and NaOH-ethanol produced protein with higher purity (> 94% purity) than the HCl-ethanol protocol (42% purity). Highest Investigation of secondary structure showed that a helix dominates in 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 due 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).

4. Accomplishments

Last Modified: 2/23/2016
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