Interaction Between Sorghum Protein Extraction and Precipitation Conditions on Yield, Purity, and Composition of Purified Protein Fractions

Abstract

Sorghum proteins have the potential to be used as a bio‐industrial renewable resource for applications such as biodegradable films and packaging. This project was designed to evaluate the effect of interactions between sorghum protein extraction and precipitation conditions on the yield, purity, and composition of sorghum protein fractions. Proteins were extracted with 70% ethanol under nonreducing conditions, with ultrasound, or under reducing conditions using either sodium metabisulfite or glutathione as the reducing agent. Several conditions were used to isolate the extracted proteins through precipitation, including lowering ethanol concentrations alone or in combination with lowering to pH 2.5, or by adding 1M NaCl to the extract. Combinations of these conditions were also tested. All precipitation conditions effectively precipitated proteins and lowering the pH and adding 1M NaCl to the extracts enhanced precipitation in some cases. However, the conditions that precipitated the maxium amount of protein or highest purity of protein varied according to how the proteins were initially extracted. Precipitated proteins were characterized by RP‐HPLC, SEC, HPCE, and SDS‐PAGE to compare the protein fractions composition. Nonreduced and sonicated samples had a much wider Mw distribution than reduced extracts. Thus, extraction and precipitation conditions influenced the isolated proteins yield, purity, and composition. Because the extraction and purification processes influenced the composition, purity, and biochemical properties, it may be possible to prepare protein fractions with unique functionalities for specific end‐uses.

Characterization of Polymeric Proteins from Vitreous and Floury Sorghum Endosperm

“…On the basis of the elution times of standard M w marker proteins and by analyzing SEC patterns following reduction, peaks 1 and 2 were judged to contain mostly polymeric proteins while peaks 3-5 contain monomeric proteins, which was in agreement with the results of Bean et al (20) and El Nour et al (13). The results of the SEC analysis are shown in Figure 3.…”

“…RP-HPLC conditions were as described in Bean et al (19). Proteins were separated by SE-HPLC using a Biosep-3000 column (Phenomenx, Torrance, CA) with a 50 mM sodium phosphate, pH 7.0, buffer containing 1% SDS as mobile phase with a flow rate of 1 mL/min as described in Bean et al (20). HPCE was carried out as described in Bean et al (19) using a Beckman PACE 2100 instrument.…”

Sorghum Protein Extraction by Sonication and Its Relationship to Ethanol Fermentation

“…It is noteworthy that all nonmashed sorghum samples had fraction I, with M w much larger than individual kafirins (≈20-30 kDa). This result confirmed the fact that a few large polymeric proteins already existed in nonmashed sorghum and were solubilized in some solvents with or without sonication (EI Nour et al 1998; Bean et al 2006;Zhao et al 2008).…”

Isolation and Characterization of Protein Fractions Isolated from Camelina Meal

“…Size-exclusion chromatography (SEC) analysis was conducted as described by Bean et al (2006). A highperformance liquid chromatography (HPLC) system (1100, Agilent, Palo Alto, Cal.)…”