Lakdas N. Fernando

Changes in the Profile of Genistein, Daidzein, and Their Conjugates during Thermal Processing of Tofu†

Profiles of genistein, daidzein, genistin, daidzin, and their acetyl- and malonyl-beta-glycosides were determined in tofu as affected by temperature and time. Tofu was heated in water at 80, 90, and 100 degrees C for 0 (control), 10, 20, 30, and 40 min, and the contents of the isoflavones of interest were quantified using reversed-phase HPLC. Total isoflavone content decreased most likely due to leaching of isoflavones into the water. Because the content of the isoflavones of the genistein series was little affected by the treatments, the decrease in the total isoflavone content was almost exclusively due to a decrease of the daidzein series. Changes in the profile of the daidzein series suggest little decarboxylation of the malonylglycoside to the acetylglycoside, but considerable de-esterification of the malonyl- and acetylglycoside to the beta-glucoside. Strongly temperature dependent decreases of the aglycon suggest possible thermal degradation of daidzein in addition to losses due to leaching.

Quantitation of hexanal by automated SPME for studying dietary influences on the oxidation of pork

Automated headspace solid-phase micro-extraction gas chromatography (auto-HS-SPME-GC) was employed to determine the hexanal content of ground pork shoulders from pigs raised on a normal corn diet and a corn diet high in oil and monounsaturated fatty acids. This external standard method showed good linearity (R2=0.999) and acceptable reproducibility (rsd=6.7%). Samples were stored refrigerated under light and analyzed on days 0, 3, 5, 7 and 9. Although no significant differences were observed between treatments in hexanal concentration, color, odor, or thiobarbituric acid-reactive substances (TBARS) value, TBARS and hexanal values increased over time, which became significant on days 7 and 9 for TBARS and on day 9 for hexanal. TBARS and hexanal concentration were correlated with R2 values of 0.992 and 0.804 for the treatment and control group, respectively. Auto-HS-SPME-GC provided a rapid and convenient method for monitoring the hexanal content of raw ground pork. HS-SPME using Carboxen/PDMS stable flex fiber provided the required sensitivity, linearity and reproducibility for measurement of hexanal in the headspace of raw ground pork.