Changes in the radical-scavenging activity of bitter gourd (Momordica charantia L.) during freezing and frozen storage with or without blanching

The effects of blanching, freezing, and frozen storage on the retention of radical-scavenging activity (RSA), total phenolics, and ascorbic acid in bitter gourd were investigated. Blanching of sliced bitter gourd resulted in considerable losses of RSA and total phenolics, and most extensively, of ascorbic acid. In the subsequent frozen storage at -18 degrees C, RSA and total phenolic content of unblanched and blanched bitter gourd underwent little change for 90 d then gradually declined, but at -40 degrees C, they practically remained unchanged throughout the entire storage period. On the contrary, ascorbic acid content of both unblanched and blanched bitter gourd decreased abruptly at the early stage in frozen storage. The results show that blanching of bitter gourd improves the retention of RSA and total phenolics during subsequent frozen storage but markedly aggravated loss of ascorbic acid. Finally, it is to be noted that RSA, total phenolics, and ascorbic acid originally contained in the raw bitter gourd were overall best retained by quick freezing followed by frozen storage at -40 degrees C without preceding blanching.