|dc.description.abstract||Increasing evidence from epidemiological studies has shown that vegetable consumption is an important determinant of health. These health benefits are attributed to the presence of phytochemicals in these vegetables or plants that fight and reduce the risk of diseases. Inadequate consumption of vegetables has been linked to increasing incidences of some chronic diseases like cancers and cardiovascular diseases.
Microgreens are edible seedlings of vegetables and herbs with quick production cycles. They are very tender and smaller in size, yet more colourful, flavourful and nutritious than their mature counterparts, thus explaining why they were used in this study.
The objective of this study was to examine the effect of light, in particular photoperiod and temperature on metabolite composition in four microgreens: beet greens, peppercress, lettuce, wheatgrass, and four herbs: basil, coriander, mint, and chives, with the main focus being on metabolites that affect the flavour of the plant and are health related. The analyses were carried out using a derivatisation technique in combination with gas chromatography (GC-MS) based metabolite profiling and a solid phase micro-extraction (SPME) technique for the detection of volatile compounds in the herb species. 208 compounds were identified from the GC-MS metabolite profiling of the species and 38 compounds, i.e. 28 aromatics, 2 terpenes, 3 sugars, 3 acids, and 2 amino acids were selected. Sugars and citric acid were also selected to show trends of changes in central metabolism related to the treatments across the species, while the phenolics play vital roles related to health and food flavour. 17 out of the 28 aromatics were further selected across all the species because they were identifiable by name. Using SPME, 29 volatile compounds were detected in basil, 29 compounds in coriander, 30 compounds in mint, and 35 compounds in chives.
Based on metabolite profiling data, temperature had a stronger effect on metabolite concentration in basil and wheatgrass compared to day length and interaction, while day length had a stronger effect on beet greens, peppercress and mint compared to temperature and interaction. Day length and temperature showed very strong effects on lettuce and under interaction, while chives and coriander showed no effect upon day length and temperature treatment. With SPME in general, day length and temperature had no influence on volatiles in chives and coriander, only (E)-2-hexenal in basil was affected by day length and temperature, while temperature influenced some terpenes in mint volatile composition.
The principal component analyses (PCA) was done on the 17 aromatics and on the whole data set. PCA on the 17 aromatics did not show clear differences across the treatments, but it depicted clear differences on the whole data set across the species clustering based on the treatments.
The overall outcome of this present study showed that metabolite concentration was strongly influenced by day length and temperature, differently across the species. The poor growth conditions of the plants also influenced metabolite concentration across the species.
Cold temperatures and long day lengths generally yielded higher phenolic levels. With the herbs, warm temperatures resulted in higher volatile levels, long day lengths yielded higher levels in coriander and basil, while short day lengths yielded higher levels in mint and chives.
Keywords: Temperature, Photoperiod, Microgreens, Herbs, Metabolites, GC-MS, SPME||