New highly stable dimeric 3-deoxyanthocyanidin pigments from sorghum bicolor leaf sheath.

The growing interest in natural alternatives to synthetic petroleum-based dyes for food applications necessitates looking at nontraditional sources of natural colors. Certain sorghum varieties accumulate large amounts of poorly characterized pigments in their nongrain tissue. We used High Performance Liquid Chromatography-Tandem Mass Spectroscopy to characterize sorghum leaf sheath pigments and measured the stability of isolated pigments in the presence of bisulfite at pH 1.0 to 7.0 over a 4-wk period. Two new 3-deoxyanthocyanidin compounds were identified: apigeninidin-flavene dimer and apigenin-7-O-methylflavene dimer. The dimeric molecules had near identical UV-Vis absorbance profiles at pH 1.0 to 7.0, with no obvious sign of chalcone or quinoidal base formation even at the neutral pH, indicating unusually strong resistance to hydrophilic attack. The dimeric 3-deoxyanthocyanidins were also highly resistant to nucleophilic attack by SO(2); for example, apigeninidin-flavene dimer lost less than 20% of absorbance, compared to apigeninidin monomer, which lost more than 80% of absorbance at λ(max) within 1 h in the presence of SO(2). The increased molecular complexity of the dimeric 3-deoxyanthocyanidins compared to their monomers may be responsible for their unusual stability in the presence of bisulfite; these compounds present new interesting opportunities for food applications.

Sorghum phenolics demonstrate estrogenic action and induce apoptosis in nonmalignant colonocytes.

Evidence indicates sorghum may be protective against colon cancer; however, the mechanisms are unknown. Estrogen is believed to protect against colon cancer development by inducing apoptosis in damaged nonmalignant colonocytes. Three sorghum extracts (white, red, and black) were screened for estrogenic activity using cell models expressing estrogen receptor α (ER-α; MCF-7 breast cancer cells) and ß [ER-ß; nonmalignant young adult mouse colonocytes (YAMC)]. Black and white sorghum extracts had significant estrogenic activity mediated through both estrogen receptors at 1-5 and 5-10 µg/mL, respectively; but red sorghum did not. Activation of ER-ß in YAMC reduced cell growth via induction of apoptosis. Only the black and red sorghums contained 3-deoxyanthocyanins; however, these compounds were non-estrogenic. Flavones with estrogenic properties, luteolin (0.41-2.12 mg/g) and apigenin (1.1-1.4 mg/g), and their O-methyl derivatives (0.70-0.95 mg/g) were detected in white and black sorghums, but not in the red sorghum. On the other hand, naringenin, a flavanone known to interfere with transcriptional activities of estrogen, was only detected in the red sorghum extract (as its 7-O-glycoside) at relatively high concentration (11.8 mg/g). Sorghum flavonoid composition has important implications on possible modes of chemoprotection by sorghum against colon carcinogenesis.