Effect of refrigerated storage on betacyanin composition, antibacterial activity of red pitahaya (Hylocereus polyrhizus) and cytotoxicity evaluation of betacyanin rich extract on normal human cell lines

Red pitahaya fruit is rich in purplish-red color water-soluble betacyanins. The effect of refrigerated storage at 4 degrees C on the betacyanin composition of red pitahaya was monitored each day, for one week, using HPLC. The betacyanin content of red pitahaya had increased by 57.2% after storage for six days at 4 degrees C. From day 2 to day 7, the phyllocactin content decreased from 45.4 +/- 1.5% to 38.3 +/- 3.1%, whereas the betanin content increased from 37.9 L6% to 42.7 +/- 1.5%. Antimicrobial activity was determined using the broth microdilution assay and expressed as minimum inhibitory concentration (MIC). As compared to the freshly harvested fruits (MIC values: 50,000- > 50,000 mu g mL(-1)), fruits that were stored for six days at 4 degrees C demonstrated better antimicrobial activity (MIC values: 3130-6250 mu g(-1)) against 10 pathogenic Gram-positive and 6 Gram-negative bacteria. Betacyanin rich extract was also examined against normal human cell lines (HEK-293 and THP-1) and found to be not cytotoxic at the levels of 0.39-3.13 mu g mL(-1). In summary, refrigerated storage for 6 days increased the betacyanin content, changed the betacyanin composition in red pitahaya and contributed to higher antimicrobial activity.