46F-13 |
Iron bioavailability and antioxidant activity of raisins |
C. K. YEUNG1, R. P. Glahn, X. Wu, R. H. Liu, and D. D. Miller. (1) Department of Food Science, Cornell University, Room 216 Stocking Hall, Ithaca, NY 14853
Raisins are rich in phenolic compounds and are perceived as good sources of iron and antioxidants. However, little is known about iron bioavailability from raisins or the effects of processing on their antioxidant activities.
Our objectives were to compare iron bioavailabilities and antioxidant activities in three common generic raisin types.
Three raisin types - Golden Thompson, Dipped Thompson and Sun-dried Thompson - were analyzed. Iron content was determined by atomic emission spectroscopy. Iron bioavailability was assessed with an in vitro digestion/Caco-2 cell culture model using cell ferritin formation as an index of iron bioavailability. Phytochemicals of the raisins were extracted using 80% acetone. Antioxidant activities of these raisin extracts were determined using the Total Oxyradical-Scavenging Capacity (TOSC) assay and results were expressed as median effective concentration (EC50). Lower EC50 values represent higher antioxidant activities. Data were analyzed by ANOVA and, when appropriate, means were separated by Fisher LSD procedures.
Iron concentrations (mean± SEM) in Golden Thompson, Dipped Thompson and Sun-dried Thompson raisins were 8.91± 0.50, 9.38± 0.55 and 11.18± 0.66 ppm respectively, or approximately 3-4% of the Daily Value for iron per ¼ cup serving. Ferritin formation in Caco-2 cells was undetectable for all three types, indicating low iron bioavailability. EC50 values were 0.19± 0.01, 0.55± 0.04 and 0.60± 0.05 mg raisin per mL assay buffer for Golden Thompson, Dipped Thompson and Sun-dried Thompson raisins respectively, indicating that antioxidant activity of Golden Thompson raisins was significantly higher than the other two types (p<0.0005).
Our results show, for the first time, that the bioavailability of raisin iron is low, presumably due to the inhibitory effects of phenolic compounds. In addition, Golden Thompson raisins are treated with sulfur dioxide in their production process to inhibit enzymatic browning. Hence the lower antioxidant activities in Dipped and Sun-dried Thompson raisins suggest that enzymatic browning causes a decrease in antioxidant activity.
Session 46F, Nutrition
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