Kyriacou Marios C, El-Nakhel Christophe, Soteriou Georgios A, Graziani Giulia, Kyratzis Angelos, Antoniou Chrystalla, Ritieni Alberto, De Pascale Stefania, Rouphael Youssef
Department of Vegetable Crops, Agricultural Research Institute, Nicosia 1516, Cyprus.
Department of Agricultural Sciences, University of Naples Federico II, 80055 Portici, Italy.
Foods. 2021 Jun 9;10(6):1333. doi: 10.3390/foods10061333.
While imparting gastronomic novelty and sensory delight, microgreens also constitute rudimentary leafy greens packed with nutrients and phytochemicals. As such, they comprise an upcoming class of functional foods. However, apart from bioactive secondary metabolites, microgreens also accumulate antinutritive agents such as nitrate, especially under conducive protected cultivation conditions. The current work examined nutrient deprivation before harvest (DBH), applied by replacing nutrient solution with osmotic water for six and twelve days, as a strategy for reducing microgreen nitrate levels in different species (lettuce, mustard, and rocket). The three species were sown on a peat-based substrate, cultivated in a controlled climate chamber, and harvested 18 days after sowing, when the first two true leaves emerged. DBH impact on major constituents of the secondary metabolome, mineral content, colorimetric, and yield traits was appraised. Nitrate and mineral content were determined through ion chromatography, phenolic composition through UHPLC-Q-Orbitrap HRMS, and carotenoid composition through HPLC-DAD. Nutrient deprivation was effective in reducing nitrate content; however, effective treatment duration differed between species and decline was more precipitous in nitrate hyperaccumulating species such as rocket. Quercetin and kaempferol glycosides were the flavonol glycosides most abundant in brassicaceous microgreens, whereas lettuce microgreens were steeped in caffeoyl quinic acid. DBH interacted with species as it increased the total phenolic content of lettuce, decreased that of rocket, but did not affect mustard. Further research to link changes in phenolic composition to the sensory and in vivo bioactive profile of microgreens is warranted. Notably, brief (≤6 days) DBH can be applied across species with moderate or no impact on the phenolic, carotenoid, and mineral composition of microgreens. Brief DBH applications also have limited impact on microgreens' yield and colorimetric traits hence on the commercial value of the product. They can therefore be applied for reducing microgreen nitrate levels without significantly impacting key secondary metabolic constituents and their potential bioactive role.
微型蔬菜在带来美食新奇感和感官愉悦的同时，也是富含营养和植物化学物质的初级叶菜。因此，它们构成了一类新兴的功能性食品。然而，除了生物活性次生代谢产物外，微型蔬菜还会积累抗营养剂，如硝酸盐，尤其是在有利的保护栽培条件下。目前的研究考察了收获前养分剥夺（DBH），即通过用渗透水替代营养液6天和12天，作为降低不同物种（生菜、芥菜和芝麻菜）微型蔬菜硝酸盐含量的一种策略。这三个物种播种在泥炭基基质上，在可控气候室内栽培，播种18天后收获，此时第一对真叶出现。评估了DBH对次生代谢组主要成分、矿物质含量、比色法和产量性状的影响。通过离子色谱法测定硝酸盐和矿物质含量，通过超高效液相色谱-四极杆-轨道阱高分辨质谱法测定酚类成分，通过高效液相色谱-二极管阵列检测器测定类胡萝卜素成分。养分剥夺有效地降低了硝酸盐含量；然而，有效处理时间因物种而异，在硝酸盐超积累物种如芝麻菜中下降更为显著。槲皮素和山奈酚糖苷是十字花科微型蔬菜中最丰富的黄酮醇糖苷，而生菜微型蔬菜富含咖啡酰奎宁酸。DBH与物种相互作用，因为它增加了生菜的总酚含量，降低了芝麻菜的总酚含量，但对芥菜没有影响。有必要进一步研究将酚类成分的变化与微型蔬菜的感官和体内生物活性特征联系起来。值得注意的是，短暂（≤6天）的DBH可应用于所有物种，对微型蔬菜的酚类、类胡萝卜素和矿物质成分影响适中或无影响。短暂的DBH应用对微型蔬菜的产量和比色性状影响也有限，因此对产品的商业价值影响有限。因此，它们可用于降低微型蔬菜的硝酸盐含量，而不会显著影响关键的次生代谢成分及其潜在的生物活性作用。
