Background: Plant foods, as functional foods, provide not only the essential nutrients needed to sustain life, but also bioactive compounds (phytochemicals) for health promotion and disease prevention.
Objective of the study: The aim of this research was to screen phytochemicals in commonly consumed fruits and vegetables in Malawi. The effect of processing vegetables on phytochemicals was also evaluated.
Methods: The potential of some commonly consumed fruits and vegetables in their raw and cooked forms as natural source of phytochemicals was evaluated in both aqueous and methanol extracts. These fruits and vegetables were screened for alkaloids, saponin, tannins, flavonoids, quinones, coumarins, terpenoids, steroids, glycosides and anthocyanins, total flavonoids content (TFC) and total phenol content (TPC) using standard procedures. TPC and TFC were also analyzed using spectrophotometric methods.
Results: Almost all the phytochemicals screened were found in some of the studied fruits and vegetables, with indigenous fruits and vegetables having the most, except for glycosides and anthocyanins. TPC in fruits ranged from 715.08mgGAE/g to 21,119.66mgGAE/g, while TFC ranged from 44.10mgQE/g to 434.74mgQE/g in vegetables. TPC of uncooked vegetables ranged from 522.22 mgGAE/g (pumpkin leaves) to 33, 684.66 mgGAE/g (ntoriro), while in cooked vegetables it ranged from 135.93 mgQE/g (bonongwe) to 6817.86 mgQE/g (chisoso). Overall, indigenous vegetables showed higher TPC values in comparison to exotic vegetables. It was also observed that processing of vegetables affected total phenolic compounds differently. In some vegetables, TPC values increased with cooking (pumpkin leaves, bonongwe and chisoso), while in others (cabbage, Chinese and rape) it decreased.
Conclusions: The results show that fruits and vegetables can serve as a cheap source of natural antioxidants that could help fight non-communicable diseases, such as hypertension, diabetes, and cancer. As might be expected, a single fruit or vegetable doesn’t contain all the necessary phytochemicals. Therefore, an intake of a mixture of fruits and vegetables is recommended for maximum benefit as functional foods.