Assessing glycinin (11S) and β-conglycinin (7S) fractions of soybean storage protein by near-infrared spectroscopy

Soybean breeding programs underway today are addressing the goal of improving the protein profile to benefit the human diet as well as that of livestock. Glycinin, a globulin storage protein of the meal and designated as the 11S size fraction by ultracentrifugation, is desirable because of its relative abundance of sulfur-containing amino acids, such as methionine and cysteine. The current study examined the feasibility of near-infrared (NIR) measurement of glycinin and the other prevalent protein fraction, beta-conglycinin (7S size fraction), as well as the electrophoretically separable sub fractions that comprise these two components. From a population of 101 F-6-derived recombinant inbred lines in a field replicated trial, single whole soybeans were scanned in transmittance (800-1,798 nm, 24 beans/sample x 197 samples total). Additional scanning of the ground meal was performed in reflectance (1,100-2,498 nm). Partial least squares (PLS) calibrations were developed, using the 24-bean average log(1/T) spectrum for each sample, as well as the average spectrum from duplicate packs of log(1/R) spectra of the meal. The results indicate that NIR prediction of 11S and 7S, as well as the sub fractions thereof, is at best limited to screening purposes in soybean breeding programs for probable reasons of an inherent lack of spectral specificity of the protein fractions and a non-constant proportion of soluble-to-total protein.