Quality of soy fortified bread as affected by soy flour lipids and water dispersibility of soy protein

The effects of defatted soy flours with different protein dispersibility index (PDI 10-25 and 65-75) alone and in combination with added lipids (polar and/or neutral at concentrations present in full fat soy flour) and a full fat soy flour (PDI 15-25) were investigated on quality of 12 and 24 percent (on full fat soy flour or its lipid free, dry material equivalent basis) fortified bread. The following characteristics were measured: specific loaf volume, crust and crumb color, total solids, and texture during staling (compressibility at 0, 2, 4, and 6 days). Bread was prepared according to the K-State Process, and the flavor and acceptability of 12 percent soy level were evaluated by a 25-member untrained sensory panel on a 6-point hedonic scale. Addition of neutral lipids to defatted soy flour caused greater loaf volume and more total solids than polar lipids. The addition of neutral and polar lipids to defatted soy flour gave bread the greatest loaf volume and highest level of total solids. PDI of defatted soy flour did not affect the specific loaf volume of bread significantly. Therefore, reported differences between loaf volume of bread fortified with full fat soy flour and with defatted soy flour and made by K-State Process (addition of sodium stearoyl-2 lactylate) would seem to be due to the lipid content of the full fat soy flour rather than protein quality, particularly the neutral lipids. The combined neutral and polar lipids also caused bread to have a lighter and less yellowish crumb color. Toasted defatted soy flour (TN, PDI 10-25) caused bread to have darker and more yellowish crumb color than a white defatted soy flour (BN, PDI 65-75). A consumer panel generally preferred the flavor of bread fortified with TN more than that of bread fortified with BN. The addition of neutral lipids to defatted soy flour caused bread to be softer than the addition of polar lipids and the combined lipids caused the softest texture of bread at 0, 2, 4, and 6 days storage, especially at the 24 percent soy level.