Proteins extracted from defatted wheat germ: Nutritional and structural properties

The main by-product of the wheat germ oil extraction process is a detailed wheat germ meal, which has a relatively high protein content, making it an attractive and promising source of vegetable proteins. Four protein fractions (albumin, globulin, prolamine, and glutelin) and protein isolate from detailed wheat germ flour (DWGF) were fractionated and then characterized by amino acid analysis, SDS-PAGE, and differential scanning calorimetry (DSC). Albumin was the major fraction (34.5%) extracted, followed by globulin (15.6%), glutelin (10.6%), and prolamine (4.6%). Protein isolate was mainly composed of albumin and globulin. These protein fractions and protein isolate showed an excellent balance of all essential amino acids, with a relatively high level of glutamic acid, arginine, leucine, and glycine, whereas cystine was lacking. All the estimated nutritional quality parameters based on amino acids composition showed that detailed wheat germ proteins had good nutritional quality. Nonreduced and reduced SDS-PAGE analyses showed that S-S bonds were deficient in the structure of wheat germ proteins. The albumin fraction consisted of 19 major polypeptide bands with M-r 14,000-84,000. The globulin fraction showed four distinct polypeptides or polypeptide group bands with M, 55,000, 37,000-43,000, 24,000, and 12,000-20,000, which may be the components of the 8S-type and I I S-like proteins. The prolamine fraction showed a predominant doublet-like band at M, 17,000-16,000, while the glutelin fraction showed five major polypeptide bands with M, 39,000, 20,000, 18,000, 17,000, and 14,000. Protein isolate and DWGF showed very similar SDS-PAGE patterns. Except for prolamine and glutelin fractions without detectable calorimetric response, the globulin fraction possessed the highest thermal stability (T-d = 83.80 degrees C, Delta H =1.36 J/g), followed by protein isolate (T-d = 80.05 degrees C, Delta H = 0.76 J/g), while the albumin fraction was lowest (T-d = 69.72 degrees C, Delta H = 0.53 J/g). The findings on defatted wheat germ proteins are important for their potential application as functional food ingredients.