|dc.description.abstract||Consumption of whole grains has been linked to reduced risk of colon cancer. This study determined estrogenic activity of sorghum phenolic extracts of different phenolic profiles and identified possible estrogenic compounds in sorghum in vitro, as well as evaluated the potential of estrogenic sorghum phenolic extracts to prevent colon carcinogenesis in vivo. The thermal stability of sorghum 3-deoxyanthocyanins was also studied, to determine their suitability as functional food colorants.
White and TX430 (black) sorghum extracts showed estrogenic activity in cell models predominantly expressing estrogen receptor-α (ERα) or ERβ at 5 and 10 µg/mL, respectively. The same treatments led to induction of apoptosis in cells expressing ERβ. The red TX2911 sorghum did not possess these activities. Compositional analysis revealed differences in flavones and flavanones. Flavones with estrogen-like properties, i.e. luteolin and apigenin, were detected in White and TX430 (black) sorghum extracts, but not in red TX2911 extract. Naringenin, a flavanone known to antagonize ERα signalling, was only detected in the red TX2911 extract. Additional experiments with sorghum extracts of distinct flavones/flavanone ratio, as well as with pure apigenin and naringenin, suggested that flavones are the more potent ERβ agonists in sorghum. On the other hand, 3-deoxyanthocyanins were probably not estrogenic.
Estrogenic white and black sorghum phenolic extracts (fed at 1% level in the diet) reduced the number of azoxymethane induced colon premalignant lesion (aberrant crypt foci) by 39.3% and 14.7%, respectively, in ovariectomized mice. Further studies are needed to elucidate the protective mechanisms induced by these sorghum extracts.
Sorghum 3-deoxyanthocyanins retained good color stability after 30 minutes of heat treatment at 121 °C under pressure: More than 80% of color retained in pH 1 and 2 HCl and citric acid solutions, and 39-84% retained from pHs 3-7. Formic acid negatively affected the color stability at pH 1 and pH 2 due to its reducing capacity. Methoxylation decreased the thermal stability of 3-deoxyanthocyanins. The heat stability of 3-deoxyanthocyanins indicates good potential for food use.
Overall, the inherent estrogenic activity of specific sorghum phenolic extracts is a likely mechanism for colon cancer prevention. Further studies are needed to assess physiologically relevant dietary level of sorghum phenolics for prevention of colon cancer, and effect of food processing on the activity and bioavailability of the chemopreventive components.||