Lipids of defatted soy-flours during storage

The objective of this study was to investigate the effect of storage on lipids present in defatted soy-flours (fully toasted, white and enzyme active).

Five replicates of each soy-flour were stored for 0, 60, 120 and 180 days at 23°C and then analyzed for lipoxygenase activity, nitrogen solubility index, thiobarbituric acid number, and percent extractable lipid. Both enzyme active and white flours had lipoxygenase activity; the enzyme active flour had the highest activity. Lipoxygenase activity of the enzyme active soy flour decreased at an increasing rate during storage. TBA number decreased during storage and thus was of little value in measuring the amount of oxidation that had occurred. The average percent of extractable lipid material decreased from approximately 3.0 to 2.8 percent during storage.

Lipid extracts were separated into three fractions by silicic acid column chromatography by eluting lipids with 300 ml portions of chloroform-methanol 20:1, chloroform-methanol 1:1, and methanol. The type of lipids in each fraction was analyzed by TLC and the fatty acid distribution was determined by GLC. Approximately 30, 57 and 14 percent of the lipids were eluted into Fractions I, II, and III, respectively. Fraction I lipids consisted mainly of glycerides, glycolipids, and steroids while Fraction II lipids consisted mainly of phospholipids, glycolipids, and steroids. As expected, lipid in Fraction III was almost pure lecithin. Of significance in the fatty acid analysis, the relative percent of linoleic acid in the fully toasted and white flour decreased during storage while the relative percent of linoleic acid in the enzyme active flour did not change. A considerably lower initial level of linoleic acid was found in the enzyme active flour than in the fully toasted and white flours.