Changes in Chlorophyll Content of Selected Leafy Vegetables during Hydrothermal Processing

Abstract

Background: Chlorophyll is a pigment present in all green plants, and it is required for photosynthesis, which is a process by which light energy converts to chemical energy. Chlorophyll in leaf vegetables is highly susceptible to degradation during processing. This process occurs naturally with time, but can also be caused by enzymatic and non-enzymatic reactions influenced by several factors such as heat, pH, light, exposure to oxygen and processing procedures. Aim: This work aimed at studying the changes that occur in chlorophyll content of four selected leafy vegetables – Jatropha tanjorensis (tree spinach), Telfiaria occidentalis (fluted pumpkin leaf), Vernonia amygdalina (bitter leaf) and Celosia argentea (Lagos spinach) during hydrothermal processing. Method: Freshly harvested leaves were subjected to different hydrothermal treatments- 60, 65, 70, 75 and 80 °C for varying lengths of time --- 0, 5, 10, 15 and 20 minutes. Chlorophyll content was determined by the spectrophotometric method. Results: Degradation of chlorophyll during hydrothermal processing was dependent on temperature and time. An increase in temperature and time caused a high percentage decrease in the chlorophyll content of each of the vegetables during processing. The highest percentage decrease of 40.38% was recorded for Telfiaria occidentalis after 20 minutes at 80 °C. A percentage loss of 2.37% was observed for Jatropha tanjorensis after blanching at 60°C for 5 minutes. Blanching temperature and time have significant effects (P=.05) on the degradation of chlorophyll content of the selected leafy vegetables. Conclusion: As economic value and overall degree of acceptability of these vegetables are dependent on the greenness of the leaves, appropriate attention during processing should be paid to minimise loss of chlorophyll, a naturally occurring green pigment that has been reported to have a wide range of therapeutic properties. It is expedient that processing operations that can enhance the conservation of chlorophyll should be given adequate attention, as the green pigment is considered to have therapeutic properties. Moreover, the degree of consumer acceptability of these leafy vegetables depends on the greenness.