Color stability of black sorghum bran extracts under different conditions
Abstract
The color stability of 3-deoxyanthocyanins extracted from Tx430 Black
and Black tannin sorghum brans were exposed to different pHs, temperatures,
water activities, and concentrations for comparison with synthetic colorants Red
No. 3, and Red No. 40 for 13 weeks. Dry extracts were solubilized using 0.5%
citric acid in 70% aqueous ethanol. The color parameters of lightness, chroma,
and hue of samples and synthetic standards were measured at pH ranging from
1 to 11; temperatures of -8, 4, 25, and 50°C; water activities of 1.00, 0.95, 0.85,
and 0.20; and extract concentrations of 0.5, 1.0, 5.0, 10, 20 and 40 mg/mL for
Tx430 Black and 0.1, 0.5, 1.0, 5.0, 10, and 20 mg/mL for Black tannin sorghums.
The absorbance values for thermal stability of the pigments from different
pH levels of both black sorghum extracts were stable over time, especially at pH
levels above 3. Lightness, chroma, and hue of Black PI Tall sorghum bran
extracts at all pHs were more stable over time than those from Tx430 Black. The Black PI Tall extracts were red, and closer in color to synthetic Red No. 40, while
the orange colored extracts of Tx430 Black were more similar to those from
synthetic Red No. 3. Color of both sorghum bran extracts and Red No. 40 were
stable at all temperatures except 50°C; however, Red No.3 color was unstable
at all temperatures over time. As water activity and extract concentrations of
both sorghum brans increased, the color became more red. At low extract
concentrations, the color of both black sorghum bran extracts was similar to
synthetic Red No. 3, i.e. orange.
Sorghum bran extracts had better stability than natural fruit and vegetable
anthocyanins. The condensed tannins present in Black tannin sorghum
enhanced the stability of its extracts.
Overall, Black PI Tall and TX430 Black sorghum bran extracts have
excellent potential for use in the food industry as natural colorants with
significantly more stability than other natural pigments. The sorghums can be
grown, stored and processed easily into bran concentrates which should reduce
their cost and availability.
Citation
Cardenas Hinojosa, Ana Paola (2008). Color stability of black sorghum bran extracts under different conditions. Master's thesis, Texas A & M University. Available electronically from https : / /hdl .handle .net /1969 .1 /174178.