Meeting Abstract - Poster Presentation

Stability of colored compounds from black sorghum: Effects of pH and water activity
N. NJONGMETA (1), A. P. Cardenas-Hinojosa (1), L. Dykes (1), L. Cisneros-Zevallos (2), L. W. Rooney (1)
(1) Cereal Quality Laboratory, Department of Soil & Crop Sciences, Texas A&M University, College Station, TX, USA; (2) Department of Horticultural Sciences, Texas A&M University, College Station, TX, USA
Cereal Foods World 52:A54

Color is an important functional attribute of foods. Among cereals, special sorghums have the highest content of phenolic compounds, with unique 3-deoxyanthocyanins rendering them stable and thus natural food colorants. The objective was to determine the effect of pH and water activity on color stability of anthocyanins extracted from black sorghum bran, which is a rich source of 3-deoxyanthocyanins. After two hours of extraction, the supernatant was evaporated in a Speed Vac at low temperature. Dried extracts were reconstituted in aqueous ethanol and adjusted to 11 different pHs using 0.1-1N NaOH and 0.1-1N HCl. Sucrose solutions (a(w) 0.80 and 0.90), glycerol (a(w) 0.21) and distilled water (a(w) 0.100,) with fixed concentrations of extracts were evaluated for the effect of water activity on color stability. Color changes at different pHs and different water activities were measured over time using a Minolta CT-310 colorimeter to obtain the L*, a* and b* (CIELAB) color space coordinates, hue and chroma. The L*, a* and b* values, hue and chroma remained relatively stable over the pH range investigated. A major visual color difference was observed as the pH increased to > 6 from bright orange in acid pHs to burgundy in basic pHs. The L*, a* and b* values showed no significant change over time from pH 1-6 while showing changes from pH 6-11. The stability of 3-deoxyanthocyanins compared favorably with the standard red colors FD&C Red # 3 and FD&C Red # 40. The L*, a* and b* (CIELAB) color space coordinates, hue and chroma for samples at different water activities were also stable. The stability of the 3-deoxyanthocyanidins from sorghum is good. They have potential use as natural food colorants.