Characterization and profiling of polyphenolics of Brassica microgreens by LC-HRMS/MS and the effect under LED light

An untargeted approach to profiling of polyphenolics of Brassicaceae microgreens was employed to characterize the phenolic composition in microgreens grown under 8 different treatments of combined amber (590 nm), blue (455 nm), and red (655 nm) LED, using full MS and HRMS/MS-ESI. Hydroxycinnamic acid (HCA) derivatives predominated the pool of phenolics in the microgreens, followed by free phenolic acids and flavonol glycosides/acylglycosides, with most of the HCA derivatives existing as malate esters. Most HCA malates in mustard (Barbarossa) and all HCA malates in mizuna (red kingdom)/ radish (red Rambo, organic) were significantly decreased under most treatments, whereas all malates were overall increased under combined lighting in radish (red Rambo), mustard (Garnet Giant), mizuna (organic), Pac choi (red Pac) and mustard (Scarlet Frills). The present study demonstrated that amber in combination with blue and red LED contributed to the altered phenolic profile and increase and/or decrease in quantity of certain phenolic compounds, particularly the HCA malates.

A Novel Graft between Pac Choi (Brassica rapa var. chinensis) and Daikon Radish (Raphanus sativus var. longipinnatus)

Vegetable grafting has primarily been used in the commercial production of high-value crops in the Solanaceae and Cucurbitaceae families. In this study, we explored the feasibility of making a novel graft between pac choi (Brassica rapa L. var. chinensis) and daikon radish (Raphanus sativus L. var. longipinnatus) to create a plant with harvestable pac choi leafy vegetable above-ground, and a daikon radish taproot below-ground. ‘Mei Qing Choi’ pac choi (scion) was grafted onto ‘Bora King’ daikon radish (rootstock). Grafted pac choi–daikon radish plants did not show a decrease in SPAD value, canopy size, leaf number, leaf area, or above-ground weight compared with self-grafted pac choi plants. However, taproot formation was reduced in grafted pac choi–daikon radish plants, as shown by decreased taproot length, diameter, fresh weight, and dry weight compared with non- and self-grafted daikon radish plants. Surprisingly, grafting with radish increased the photosynthetic rate of the pac choi. This pilot study demonstrated the potential of creating a new pac choi–daikon radish vegetable product to help save growing space and minimize waste at consumption, as pac choi roots are not eaten and radish leaves are usually discarded. The inter-generic grafting between B. rapa var. chinensis and R. sativus var. longipinnatus could also provide a unique model system to help elucidate scion-rootstock synergy and above- and below-ground sink competition in horticultural crops.

Nitrate-Nitrogen Sufficiency Ranges in Leaf Petiole Sap of Brassica oleracea L., Pac Choi Grown with Organic and Conventional Fertilizers

Greenhouse experiments were conducted to determine the response of Brassica oleracea L., pac choi to fertilizer rates and sources and to establish optimal soluble nitrogen (N) application rates and nitrate meter sufficiency ranges. Conventional soluble fertilizer was formulated from inorganic salts with a 4:1 NO3-N:NH4-N ratio. Phosphorus (P) was held at 1.72 mm and potassium (K) at 0.83 mm for all treatment levels. The organic soluble fertilizer, fish hydrolyzate (2N–1.72P–0.83K), was diluted to provide the same N levels as with conventional treatments. Both fertilizers were applied at N rates of 0, 32, 75, 150, 225, 300, and 450 mg·L−1. Seedlings were transplanted and fertilizer application began at 18 days. Plants were harvested at 7 weeks (5 weeks post-transplanting) after receiving 15 fertilizer applications during production. Samples of the most recently matured leaves were harvested weekly and analyzed for petiole sap NO3-N and leaf blade total N concentration. Leaf count, leaf length, and chlorophyll content were also measured weekly. Fresh and dry weights were determined on whole shoots and roots. Optimum yield was achieved at the 150-mg·L−1 fertility rate with both conventional and organic fertilizers. Field and high tunnel experiments were conducted to validate the sufficiency ranges obtained from the greenhouse studies. Sufficiency levels of NO3-N for pac choi petiole sap during Weeks 2 to 3 of production were 800 to 1500 mg·L−1 and then dropped to 600 to 1000 mg·L−1 during Weeks 4 through harvest for both conventional and organic fertilizers sources. Total N in leaf tissue was less responsive to fertilizer rate effects than petiole sap NO3-N. Chlorophyll content was not useful in evaluating pac choi N status. These guidelines will provide farmers with information for leaf petiole sap NO3-N to guide in-season N applications.

Effect of Nitrogen Source on Pac Choi (Brassica rapa L.) Chemistry and Interactions with the Diamondback Moth (Plutella xylostella L.)

Two greenhouse studies were conducted to examine effects of nitrogen source on primary and secondary metabolism of pac choi (Brassica rapa L. subsp. chinensis cv. Mei Qing Choi) and diamondback moth (Plutella xylostella L.) consumption, development, survival, and body weight. Applications of a liquid organic source of nitrogen (fish hydrolysate fertilizer) were compared with a conventional fertilizer to determine whether nitrogen source directly impacts pac choi chemistry (elemental composition and phenolics) and biomass and indirectly affects diamondback moth fitness parameters. There was no significant effect of fertility treatment on pac choi chemistry or biomass with the exception of percent leaf phosphorus, which was significantly higher in the conventional fertility treatment, and p-coumarin, which was significantly higher in the organic fertility treatment. Diamondback moth also affected plant chemistry. Both calcium (Ca) and magnesium (Mg) were significantly higher in plants infested with larvae compared with uninfested plants. Fertilizer affected diamondback moth fitness with percent survival and cohort development significantly reduced on pac choi associated with the organic fertilizer. However, pac choi receiving the organic treatment was similar in regard to primary nutrients and secondary compounds compared with plants that received a conventional fertilizer.

Fertilizer Source and High Tunnel Production Environment Affect Antioxidant Levels of Pac Choi

An experiment was conducted at Olathe, Kan., in Spring 2004 to investigate the influence of organic and conventional fertilizer sources and application rates on antioxidant levels of pac choi (Brassica rapa L. cv. Mei Qing) in open fields and poly-covered high-tunnel plots. Organic plots received pre-plant application of composted cattle manure and alfalfa (Hu-More 1–1–1) at 0 kg/ha N, 156 kg/ha N, or 314 kg/ha N, and conventional plots received preplant application of 13N–13P–13K at 0 kg/ha N, 78 kg/ha N, or 156 kg/ha N. Antioxidant levels were measured using the oxygen radical absorbance capacity (ORAC) assay. There were significant effects of fertilizer source and high-tunnel environment on the antioxidant capacity of pac choi. Organic fertilization significantly increased hydrophilic ORAC of pac choi in open field plots, but not in high tunnels. Regardless of the fertilizer source, pac choi grown in the open field had significantly higher hydrophilic ORAC than that grown in tunnels. Lipophilic ORAC was significantly increased by organic fertilization but was not affected by high-tunnel production. Total ORAC (hydrophilic + lipophilic) was significantly higher in pac choi from organic or open-field plots, compared to conventional and high-tunnel plots, respectively. Although fertilizer rate did not show significant impact on antioxidant level of pac choi, hydrophilic and total ORAC seemed to decrease as the fertilizer rate increased, especially under conventional fertilization, while lipophilic ORAC reached the highest level at the medium fertilizer rate. Differences in antioxidant levels were likely associated with the enhanced phytochemical content of pac choi from organically fertilized and open-field plots.

(473) Influences of Fertilizer Source and Insecticide Application on Phenolic Compounds in Pac Choi (Brassica rapa L.)

Implications of dietary phenolic compounds for human health and disease prevention have been indicated by a body of literature. A greenhouse pot study was performed to investigate the impacts of fertilizer source and preventive insecticide application on phenolic compound levels in pac choi [Brassica rapa (L.) cv. Mei Qing]. A two-way randomized complete-block design with five replications was used in this experiment. Fertilizer source consisted of two levels: conventional fertilizer (pre-plant application of Osmocote slow-release fertilizer), and organic fertilizer (pre-plant application of vermicompost and fertigation with compost tea and fish emulsion). Insecticide application consisted of three levels: organic (pyrethrin) vs. conventional (permethrin), and a plain water control. At harvest, total phenolics and individual phenolic compounds in pac choi leaves (blades) were analyzed by Folin assay and HPLC, respectively. Head weight of pac choi was significantly higher under conventional fertilizer treatment, while it was not affected by insecticides. Total phenolic content of pac choi was significantly increased by organic fertilizer treatment. HPLC results indicated that organic fertilizer treatment resulted in significantly higher levels of individual phenolic compounds, including chlorogenic acid and ferulic acid. In contrast, preventive insecticide application showed little effect on the phenolics in pac choi. Correlation analysis excluded the influence of plant size (head weight) on phenolic content in pac choi. Differential N-forms, rates of nutrient release, and/or variable nutrient content in organic and conventional fertilizer treatments may contribute to elevated phenolic content in organically fertilized pac choi.