Chemical and functional properties of glandless cottonseed protein

Abstract

Glandless cottonseed protein isolates (CPI-I and II) were prepared using gel filtration chromatography. They contained large amounts of glutamic acid, arginine, and aspartic acid and had minimum solubilities at pH 4 and between pH 6 and 8, respectively. CPI-I showed higher emulsion capacity and stability and higher foam expansion and stability than CPI-II. The percent transmittance (%T) of 0.5% CPI-I solutions at all ionic strengths increased with increasing temperatures. However, %T of 0.5% CPI-II solutions increased with increasing temperatures at lower ionic strengths (0.01 and 0.1) but decreased at higher ionic strengths (0.5 and 1.0). On polyacrylamide gel electrophoresis (PAGE) and sodium dodecyl sulfate-PAGE (SDS-PAGE), band intensities of CPIs decreased with increasing ionic strengths as they were heated. The 7S and 11S protein fractions were isolated using Sephacryl S-300 HR column chromatography. These protein fractions had sedimentation coefficients of 6.8S and 10.7S and molecular weights of about 1.40 x 10^5 and 2.39 x 10^5 g/mole, respectively. Gossypol, phytic acid, -SH, and -SS- contents of these protein fractions were 2 a 0 ppm, 0.0091 and 0.0067%, 4.26 and 54.23 μM/g, and 2.57 and 40.26 μM/g, respectively. Both protein fractions showed minimum solubility at pH6. The 7S protein had greater emulsion capacity and stability than 11S protein. However, 11S protein showed greater foam expansion than 7S protein, but foam stability was almost the same. Unheated 7S and 11S proteins had two bands each on PAGE. The heated protein fractions also showed two bands each on SDS-PAGE. The 7S protein fraction and beef myosin were heated together to study their heat-induced interactions. At 80°C, the intensity of the protein bands of the mixtures was the sum of the corresponding 7S protein and myosin bands; however, at 90 and 100°C, the intensity of the bands for myosin heavy and light chains in the mixture decreased when compared to that of unheated myosin.