Hue decreased with increasing pH for red sweet po-
tato (Table 1). However, for purple corn, hue decreased
from pH 3 to 5 and slightly increased from pH 5 to 7. At
pH 7, purple corn appeared dark purple-red. Hue for
red sweet potato extracts at pH 3 was lower than those
of red 3 and red 40, while hue for purple corn extracts at
similar pH approximated that of synthetic colorants,
especially red 3. The lower hue of red sweet potato
compared to purple corn, at all pHs, is most likely due
to a bluing effect conferred by acylation (Duhard et al.,
1997). The effect of pH on
L
* showed similar trend to
that of chroma values