Water Binding by Soy Flours as Measured by Wide Line NMR

Water was determined with a wide line NMR instrument. Three soy flours were studied: full‐fat Bonus variety; laboratory, chloroform‐methanol defatted from the same Bonus sample; and commercial, hexane defatted. In case of all three samples, a plot of moisture content vs NMR response at rf 28 db (total water) showed two straight lines; the break occurred at the Bound Water Capacity (BWC). At an instrument setting of rf 0 db (only bound water gives signal), a plot of signal against moisture content, both on a total sample basis, was a triangle; the first increment of water, 3 and 7% for full‐fat and defatted, respectively, did not give a signal and the apex of the triangle gave the BWC which was 27.9% for the full‐fat and 40.5% for the same soy flour after defatting. When laboratory and commercially defatted samples were compared, the ascending curves coincided but their BWC were 40 and 31%, respectively. BWC values obtained from full‐fat readings corrected for oil signal and from commercially defatted flakes were almost the same. Steam heating at 15 psig for 15 min and freezing to a temperature as low as ‐40°C did not change the water binding characteristics of commercial defatted dry flakes.