A Comparative Study on the Phytochemical Constituents of Selected Plant Species in Relation to Their Leaf Maturity Stages

Abstract

Secondary metabolites are essential in the therapeutic value of medicinal plants and their amounts significantly vary depending on the environment and their developmental stage. This comparative study aimed at understanding how the maturity of the leaves affects the quantitative phytochemical profile of eight medicinal plant species namely Syzygium cumini, Calotropis procera, Tamarindus indicus, Parkia biglobosa, Mangifera indica, Eucalyptus camaldulensis, Azadirachta indica and Psidium guajava. The phytochemicals analysed were Total Phenolic Content (TPC), Total Flavonoid Content (TFC), saponins, and alkaloids, in three different stages of leaf maturity (young, matured and senescent). Standardised extraction procedures were used and colourimetric and gravimetric assays were used to quantify. The analysis showed that the content of TPC and TFC had the same ontogenetic pattern across all eight species (matured leaves > young leaves > senescent leaves), and that the content in matured leaves was always the highest and significantly different (P < 0.05) from the other leaves. Nitrogenous compound and total alkaloid content showed high level of species-specific variation. The matured leaves contained maximum amount of alkaloids in six species (T. indicus, P. biglobosa, M. indica, E. camaldulensis, S. cumini, A. indica) while the senescent leaves contained maximum amount of alkaloids in C. procera and P. guajava, which corresponds to specialized nitrogen remobilization strategies. The saponin content was generally highest in young leaves (P < 0.05), as it is in the initial tissue defense, except in A. indica which reached its peak at maturity. It was observed that these results highlight the importance of maturity level of leaves as an important criterion to consider when harvesting medicinal plants for phytochemical production, therefore the need to establish uniform and standardized harvesting procedure based on the morphology of the plants to ensure phytochemical consistency and efficacy.