Ascorbic acid enhances betacyanin stability by removing oxy-
gen from the surrounding environment; as oxygen is a factor
that accelerates the degradation of betacyanin (Attoe and von
Elbe 1982). A previous study has shown that ascorbic acid is
added to fruit juice to enhance its nutritional quality (Ozkan
et al. 2004). In this study, red-fleshed dragon fruit juice added
with 0.25 % ascorbic acid prior to thermal pasteurization gave
the highest betacyanin content (p≤0.05) (Table 3). Since low
level of ascorbic acid ranging from 7.0 to 11.4 mg 100 g−1 was
found in red-fleshed dragon fruit juice (Nerd et al. 1999), the
addition of ascorbic acid into red-fleshed dragon fruit juice in
the current study appears to be promising. The significant (p≤
0.05) decrease in betacyanin content as ascorbic acid was added
at 0.50–1.5 % (Table 3) could be due to the pro-oxidative effect
of ascorbic acid at a concentration of 1000 mg/kg as previously
reported in beet juice by Pasch and von Elbe (1979). The
concentration variation of the prooxidative effect of ascorbic
acid could be due to the difference in betacyanin concentration
and initial ascorbic acid content between red-fleshed dragon
fruit juice and concentrate in the current study and beet juice as
previously reported.