Solubilized wheat protein Proteins

Wheat Protein Isolate occurs as a powder. It is produced by acidic deamidation of gluten that converts glutamine and asparagine to their nonamidated derivatives, glutamic acid and aspartic acid, followed by several purification measures. Alternatively, gluten can be solubilized in an acidic or alkaline medium, and the dissolved protein is then separated and purified by filtration or centrifugation. 

Some cereal proteins are quite soluble in aqueous solution (albumins, globulins) but the functional proteins—prolamins and glutelins—are difficult to solubilize. This is important because, for example, we do not want wheat gluten proteins to be soluble in a dough system. However, in order to characterize proteins, it is usually necessary to have them in solution. Because the property of solubility is such an important one with respect to cereal proteins, we will dedicate this chapter to the topic. In keeping with the objectives of the book, we will attempt to approach the subject from the most general and fundamental basis. 

High-performance liquid chromatography (HPLC) was first applied to cereal proteins by Bietz (1986). Size-exclusion HPLC (SE-HPLC) has been used to quantify cereal proteins it separates proteins according to molecular size. Wheat proteins have been the most studied of the cereals. The preferred solvent has been dilute sodium dodecyl sulfate (SDS)/buffer. A wheat flour suspension (-1.0 mg/mL) is sonicated under conditions (time, intensity) that solubilize almost all, if not all, of the protein without altering quantitation of the main protein classes (see discussion in Chapter 9). 

Figure 10, Glucoamylase digestion releases proteins complexed with starch and results in essentially complete solubilization of proteins in wheat flour extrudates. Other extrusion conditions (see Figure 11) show comparable behavior. Adapted from (4) with permission. Copyright American Assoc, of Cereal Chemists, 1996,...

Succinic anhydride, a reagent frequently used to solubilize proteins (I), has been studied for its effect on the properties of wheat flour by... 

Phenol/aceticth acid/water. PAW desorbs residual intracellular proteins, some starch, adsorbed deoxycholate, lipids, and pigments from the SDC-residue. The amount of cell wall polysaccharides solubilized is approximately 1% of the dry weight of the purified CWM for potatoes, runner beans, wheat bran, and oats. 

Extraction of Unreduced Glutelins. Protein molecular sizes or size distributions often influence functional properties, necessitating extraction and characterization of native proteins. Various procedures have solubilized and fractionated unreduced wheat glutenin using dilute acetic acid [34], solutions differing in HCl concentration [35-37], or 50% and 70% I-propanol [38]. 

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