July 1/Journal of Farming -- "The objectives of this work were to assess antioxidant activities and phenolic compounds of soymilk as affected by traditional and ultrahigh-temperature (UHT) processing. Three soybean varieties were processed into raw soymilk and then cooked soymilk by indirect and direct UHT methods (both at 143 degrees C for 60 seconds) and traditional cooking (stove cooking and steam injection) methods (both at 100 degrees C for 20 minutes)," scientists writing in the Journal of Agricultural and Food Chemistry report.
"Total phenolic content (TPC), total flavonoid content (TFC), phenolic acids, isoflavones, flavanols and anthocyanins were quantified. DPPH free radical scavenging activity, ferric reducing antioxidant power (FRAP), and oxygen radical absorbance capacity (ORAC) were analyzed. As compared to the raw soymilk, all thermal processing significantly (p < 0.05) reduced TPC values and significantly (p < 0.05) increased TFC values for all soybean varieties. All processing methods significantly (p < 0.05) increased DPPH and FRAP values in the soymilk processed from yellow soybean varieties Proto and IA 2032. UHT processing increased their ORAC values, but traditional and steam processing reduced their ORAC values. However, in the case of the soymilk from black soybean, all processing reduced ORAC values as compared to the raw soymilk. None of processing affected total phenolic acids, chlorogenic, and trans-cinnamic acid, as well as (+)-catechin. However, all processing significantly (p < 0.05) affected contents of total isoflavones and individual isoflavones. Thermal processing caused significant (p < 0.05) increases in 7-O-beta-glucosides and acetylglucosides but caused significant (p < 0.05) decreases in malonylglucosides and aglycones," wrote B.J. Xu and colleagues, North Dakota State University.
The researchers concluded, "Indirect UHT processing transformed more isoflavones from malonylglucosides into 7-O-beta-glucosides than the direct UHT did."
Xu and colleagues published their study in the Journal of Agricultural and Food Chemistry (Isoflavones, Flavanols, Phenolic Acids, Total Phenolic Profiles, and Antioxidant Capacities of Soymilk As Affected by Ultrahigh-Temperature and Traditional Processing Methods." Journal of Agricultural and Food Chemistry, 2009;57(11):4706-4717).
Additional information can be obtained by contacting S.K.C. Chang, North Dakota State University, Dept. of Cereal & Food Science, Fargo, ND 58105.
From the July 6, 2009, Prepared Foods E-dition