Ontogenetic Variation in the Mineral, Phytochemical and Yield Attributes of Brassicaceous Microgreens

Marios C Kyriacou,Chrystalla Antoniou,Fabiana Pizzolongo,Raffaele Romano,Armando Zarrelli,Youssef Rouphael,Giulia Graziani,Antonio Pannico,Stefania De Pascale,Georgios A Soteriou,Angelos Kyratzis,Christophe El-Nakhel,Alberto Ritieni

doi:10.3390/foods10051032

Abstract

Microgreens constitute novel gastronomic ingredients that combine visual, kinesthetic and bioactive qualities. The definition of the optimal developmental stage for harvesting microgreens remains fluid. Their superior phytochemical content against mature leaves underpins the current hypothesis of significant changes in compositional profile during the brief interval of ontogeny from the appearance of the first (S1) to the second true leaf (S2). Microgreens of four brassicaceous genotypes (Komatsuna, Mibuna, Mizuna and Pak Choi) grown under controlled conditions and harvested at S1 and S2 were appraised for fresh and dry yield traits. They were further analyzed for macro- and micromineral content using inductively coupled plasma optical emission spectrometry (ICP-OES), carotenoid content using high-performance liquid chromatography with a diode-array detector (HPLC-DAD), volatile organic compounds using solid-phase microextraction followed by gas chromatography-mass spectrometry (SPME-GC/MS), anthocyanins and polyphenols using liquid chromatography-high resolution-tandem mass spectrometry (LC-MS/MS) with Orbitrap technology and for chlorophyll and ascorbate concentrations, well as antioxidant capacity by spectrophotometry. Analysis of compositional profiles revealed genotype as the principal source of variation for all constituents. The response of mineral and phytochemical composition and of antioxidant capacity to the growth stage was limited and largely genotype-dependent. It is, therefore, questionable whether delaying harvest from S1 to S2 would significantly improve the bioactive value of microgreens while the cost-benefit analysis for this decision must be genotype-specific. Finally, the lower-yielding genotypes (Mizuna and Pak Choi) registered higher relative increase in fresh yield between S1 and S2, compared to the faster-growing and higher-yielding genotypes. Although the optimal harvest stage for specific genotypes must be determined considering the increase in yield against reduction in crop turnover, harvesting at S2 seems advisable for the lower-yielding genotypes.

Highlights

Microgreens have gained a position over the past two decades initially in the upscale gastronomy market and subsequently in the mainstream horticultural supply chain as ingredients of outstanding gastronomic and nutritive value
Microgreens of four brassicaceous genotypes (Komatsuna, Mibuna, Mizuna and Pak Choi) grown under controlled conditions and harvested at S1 and S2 were appraised for fresh and dry yield traits. They were further analyzed for macro- and micromineral content by inductively coupled plasma optical emission spectrometry (ICP-OES), carotenoid content through HPLC-DAD, volatile organic compounds using Solid-Phase Micro-Extraction (SPME)-Gas Chromatography coupled to Mass Spectrometry (GC/MS), anthocyanins and polyphenols using Orbitrap LC-MS/MS and chlorophyll and ascorbate concentrations as well as in vitro antioxidant capacity by spectrophotometry
The developmental stage at harvest varies between different works, with certain researchers harvesting at the cotyledonary stage [23,24], others at the appearance of the first true leaf [6,8,25] and yet others at the second true leaf [3,7,24,26]

Summary

Introduction

Microgreens have gained a position over the past two decades initially in the upscale gastronomy market and subsequently in the mainstream horticultural supply chain as ingredients of outstanding gastronomic and nutritive value. They combine visual, kinesthetic and bioactive qualities derived from their rich mineral and phytochemical content. The phytochemical content of microgreens attributed bioactive value comprises phenolic compounds, encountered as flavonoids (including anthocyanidins) and nonflavonoids (mostly phenolic and hydroxycinnamic acids), carotenoids (β-carotene, lutein and violaxanthin), ascorbic acid, phylloquinone and tocopherols [4,5,6,7]. Microgreens of the Brassicaceae, which comprise the most extensive repository of genetic resources for commercial microgreens production [1,8], are significant sources of glucosinolates [9,10], encountered mostly in the form of isothiocyanates [11], which indicates an active glucosinolate metabolism in the early post-germination stages of development

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Conclusion