Polyphenol oxidase activity in harvest rhizome of lotus (Nelumbo nucifera Gaertn. ssp. nucifera) and its relationship with morphological characteristics

Abstract

Rhizome of lotus (Nelumbo nucifera Gaertn. ssp. nucifera) has become the most popular aquatic vegetables in the world. An important problem for its storage and process is easily browning and discoloration, which has been proved to mainly result from polyphenol oxidase (PPO) activity. Harvest rhizomes collected from 56 varieties including wild individuals, landraces and cultivars were investigated for their PPO activities as well as 19 morphological characteristics. Several correlations were found to exist in PPO activity values among different parts of all rhizome knots. Four out of 19 morphological characteristics were associated with PPO activity in different parts or knots. It was observed that the PPO activity was uniformly distributing neither in different parts within a knot nor in all knots. The PPO activity in heart part was lower than that in the periphery except for a special case that the 4th knot of red flower lotus rhizome. The PPO activity in former three knots with less number of stoma on skin of rhizome (SA) was lower than it in the same ones with more SA ones. The PPO activity in red-flower-lotus rhizomes was lower than that in white-flower plants. Our results also provide some clues for lotus rhizome processing. For red flower varieties, those with a few knot number of main stem of rhizome and the former three knots can be selected in priority, while the heart part of former four knots in white flower variety should be preferred. The periphery of former four knots in white flower variety that contained higher PPO activity would be beneficial for pest and disease resistance and for breeding medicinal and functional cultivars related with different phenolic compounds.