A review about health & sensory properties of rocket species

Rocket species (Eruca?spp. and?Diplotaxis?spp.) are becoming increasingly important leafy salad crops across the world.? Numerous scientific research papers have been published in recent years surrounding the potential health benefits associated with phytochemicals contained in leaves, such as flavonoids and isothiocyanates. Other research of note has also been conducted into the unique taste and flavour properties of leaves, which can be hot, peppery, bitter, and sweet depending upon the genotype and phytochemical composition. While research into these aspects is increasing, some studies lack cohesion and in-depth knowledge of commercial breeding and cultivation practices that makes interpretation and application of results difficult. This review draws together all significant research findings in these crops over the last five years, and highlights areas that require further exploration and/or resolution. We also advise on experimental considerations for these species to allow for more meaningful utilisation of findings in the commercial sector. ConclusionsRocket species are excellent candidates for health-related and sensory improvement through selective breeding. The diversity of morphological, phytochemical and sensory traits evidenced by previous research is an excellent resource for breeders to utilise to that end. As with broccoli GSL, glucosinolate, and GHP, glucosinolate hydrolisis products, formation could be enhanced to produce cultivars with demonstrably greater health effects than regular types. That being said, rocket breeding is much farther behind?B. oleracea species, as it has only come to prominence within the last 25?years. Commercial and packet rocket seed are not typically the products of dedicated breeding programs; rather they are simply the result of bulk propagation of landraces, with little intensive selection placed upon them for advanced traits. The resultant cultivars lack morphological uniformity, as well as phytochemical. Some breeding companies have active breeding programs and have produced some morphologically improved cultivars, but this has not yet extended to health beneficial or sensory components with any environmental stability. In order to achieve this, much more research into the genomics and transcriptomics of the species is required, and not just simply cherry-picking analogous genes from other, better-studied crops. Many genes may indeed be homologous, but the GSL profile of rocket is also very different from?Arabidopsis?and?Brassica, with several unique compounds present. Novel gene discovery will therefore be needed in order to fully understand rocket GSL biosynthesis. The effects of the growth environment, nutrient application, and endemic soil and leaf bacteria may also need to be considered in greater detail in future studies. Breeding selections should be conducted based on information from within the commercial supply chain, wherever possible. It is clear that harvest time, growth environment, processing and storage have significant impacts upon GSL and GHP concentrations. The end consumer should be the primary focus of selections for phytochemical traits and health benefits, as it is ultimately they who will consume the final product. This may seem an obvious statement, but researchers have not made this an overt consideration to-date. An experimental aspect that is prevalent within the literature is the assumption that one rocket cultivar is reflective of whole species. This is clearly not one that can withstand scrutiny, as evidenced by studies of more than one accession. If shelf life VOC, volatile organic chemical, markers are to be identified, for example, several varieties must be tested, as the variation of volatile production has also been demonstrated to be high between genotypes. This is applicable to all aspects of rocket species evaluation, as there is no representative cultivar of all traits and environmental responses. This is well established for major commercial crops and needs to be adopted to avoid generalization about these highly diverse species. The scope for improvement of rocket is huge, as consumer demand and increased interest in health beneficial foods is consistently rising. Research could benefit from adapting the roadmap set out for broccoli GSL improvement, and potentially be even more efficacious in producing health benefits due to its consumption as a raw, uncooked product. Increasing the health-related properties of rocket can only be achieved through consideration of the supply chain and shelf life conditions, and selecting for specific compounds such as glucoraphanin, glucoerucin, and their respective ITCs, Isothiocyanates. Selecting for total GSL content is likely to adversely affect sensory profiles, and so should not be adopted without careful consideration of the preferences of the end consumer. Finally, clinical trials are needed to test any beneficial health effects of rocket, and to quantitatively compare these with other Brassicaceae species. Nutritional interventions and studies utilising relevant quantities of leaves in a form that is compatible with a daily diet (i.e. as leaves, not as a beverage) are also needed to properly assess their health-promoting effects. SourcesRocket science: A review of phytochemical & health-related research in Eruca & Diplotaxis speciesLuke Bell & Carol WagstaffFood Chemistry X Volume 1, 30 March 2019, 100002The original source contains quotes. Picture by?Whiterose