Optimization of protein isolation from sesame

Abstract

The use of salts, such as NaCl, Na(,2)SO(,3) and CaCl(,2), was examined as a means of improving yield and quality of protein isolates from sesame meal. Extraction conditions were identified as: 4% NaCl with Ca(OH)(,2) as extraction alkali at 45(DEGREES)C at pH 9. Laboratory data indicated that 77% of the protein could be recovered using the improved conditions versus only 38% using conventional practices. Although the flour contained 5% phytate, which has antinutritional effects by binding Ca, Zn, Mg and Fe, the improved isolate contained less than 0.1% phytate. The flour contained 4% oxalate which is known to impede calcium metabolism; but, the improved protein isolate contained less than 0.1% oxalate. Laboratory findings were scaled-up to pilot-plant level to determine commercial practicability. The yield of protein isolate was 55-58% of the total available protein versus 37% using conventional practices. The isolate of the improved process analysed: 78.8% protein, 0.1% phytate, 0.1% oxalate, 0.4% crude free fat, 2.9% total fat and 20.2% NaCl, while the isolate from conventional practices analysed: 90.2% protein, 0.2% phytate, 0.1% oxalate, 3.3% crude free fat, 7.3% total fat and 3.3% ash. Desalting methods for the improved processes were evaluated. Washing the isolate in the acid curd significantly reduced the salt level in the protein isolate, but resulted in high loss of protein. Ultrafiltration techniques resulted in protein concentrate with 20.6% NaCl. Functional property studies showed that conventionally processed protein isolate had better protein solubility profile than the isolate from the improved process. The former contains albumin protein, which is water soluble; while, the latter contains mainly globulin protein, which is less soluble in water. Amino acid analyses of isolated proteins indicated that sesame protein from conventional and improved processes are rich in sulfur-containing amino acids and tryptophan; but, are low in lysine.