Effect on Color
The color variation in the aqueous solutions of anthocyanin crude extracts was studied in
different pH range and anthocyanin concentration. The results are shown in Fig 3a to 3e and
Fig 4. The color of the extract in the neutral pH was blue; but when the solution turned more
acidic, the color of the crude flower extracts was shifted into the red color region which the bright
red-pink color was achieved at pH 1.76. This is shown by a* values of both modes (Fig 3b and
3d) which their values increase as pH decrease. In contrast, when the extracts changed into a
basic condition, the color of the extract was shifted to green, a* values decrease as pH increase.
The color change of the extract is resulted from a change in structure of anthocyanins which
y = 0.5867x + 3.9222
R² = 0.8719
0
5
10
15
20
25
30
0 10 20 30 40 50
Anthocyanin Concentration (mg/100
mL)
Clitoria Ternatea Concentration (%)
Food and Applied Bioscience Journal, 2014, 2 (1): 31-46
© 2014 Agro-Industry, Chiang Mai University
38
support more or less conjugated system resulting in the shift of color in visible light spectrum
(Walkowiak-Tomczak & Czapski, 2007). Therefore, different color changes between basic and
acidic conditions reflect that structural change of anthocyanins in acidic conditions favored
conjugated system more than that of basic conditions. Therefore, the color of the extracts in basic
condition was shifted to green as indicated by b* value measured in reflection mode (Fig 3e). The
small L* values (Fig 3a and 3c) in both modes indicate that the crude extracts were turbid, so the
color of the extract were mostly resulted from the reflected light from the samples. Therefore, color
measured from the reflection mode is a preferable mode for color measurement in this study.
The coefficients in all color parameter equations (Table 4) suggest that the main factor
affecting the color of the extracts were the pH value of the solution. On the other hand, the effect
of anthocyanin concentration had shown a little impact on the color of the extract; thus, the result
implies that the main reason for color change was the different in anthocyanin structure from pH.