Effects of harvest techniques and drying methods on the stability of glucosinolates in Moringa oleifera leaves during post-harvest

Moringa oleifera (Lam.), an edible plant found to have high nutritional value, has recently attracted intense research interest due to its high glucosinolate (GS) content giving the plant its chemoprotective attribute. The plant grows well in dry environments, but is also found in moist tropical or subtropical climates. Thus, it is widely cultivated in Asia, Africa, South and North America. However, the plant’s leaf compartment harvested for food, and post-harvest technologies used to process the leaves in developing countries where long transportation routes and high fluctuating temperatures are inevitable, can influence the stability of GS contents. Therefore, the present study investigated the influence of different harvesting techniques and commonly used traditional drying-methods on the stability of GS in M. oleifera leaves during post-harvest. Leaves were subjected to either of the following drying methods: sun-, oven-, solar- and shade-drying and GS analysis was conducted. Results revealed that sun- and oven-drying of M. oleifera leaves retained significantly higher GS contents (101.54 and 84.67 µmol/g dw, respectively) compared to solar- and shade-drying (64.46 and 45.30 µmol/g dw, respectively). To test for effects of harvest technique on GS contents and stability of GS during post-harvest, two leaf compartments, i.e. pinnae and leaflets were harvested separately. Leaf compartments were subjected to either oven- or freeze-drying methods. The samples from each drying method were divided into two portions, where GS were immediately analyzed in one portion and the other analyzed after one month storage at ambient temperature. Results showed that factors such as harvest technique (harvesting pinnae or leaflets of the plant) and the storage time influences GS content of M. oleifera leaves significantly.