Rocket science: phytochemical, postharvest, shelf-life & sensory attributes of rocket species

Rocket species are increasing in popularity with consumers, and in the last ten years scientific interest has also increased due to the potential health benefits of consuming leaves. They are known for pungent and bitter taste components, and the chemical compounds largely responsible for these sensations are also health beneficial. These compounds are called isothiocyanates (ITCs), and they are ubiquitous in the plant family Brassicaceae. Precursor compounds called glucosinolates (GSLs) are converted to ITCs via the action of myrosinase enzyme. This thesis presents data relating to numerous aspects of rocket species, such as differences in GSLs and ITCs. Other phytochemical constituents (flavonols, volatile organic chemicals (VOCs), free amino acids, free sugars, polyatomic ion content, and organic acids) are explored to determine their impacts on human sensory perceptions and consumer acceptance. The data presented highlight significant differences between ‘wild’ accessions of rocket and commercially available varieties, in terms of flavonol and GSL content and sensory attributes. There is great potential to develop underutilised genetic resources in breeding programs, and through collaboration with a breeding company (Elsoms Seeds Ltd., Spalding, UK) and a commercial salad supplier (Bakkavör Group Ltd., Spalding, UK), several accessions were selected for detailed analyses. Analysis of VOC profiles further demonstrated the differences between the selected cultivars, and by combining these data with sensory and consumer studies, it was observed that the diversity of phytochemical components fundamentally underpins taste, flavour, and consumer acceptance. The same accessions of rocket were also tested under commercial growth, processing and storage conditions. It was hypothesised that this would negatively impact GSL and ITC content of leaves, but in fact increased concentrations up to five fold from the point of harvest in all accessions analysed. We also observed a previously undocumented link between GSL, ITC and free amino acid content with bacterial load