Jan '25 • Accountability
Light Source and Spectra Influence the Phytochemical Profile of Amaranth Microgreens Why Does Light Matter for Microgreens?
Read a new article on the effects of lighting on microgreens. This study focused specifically on Red Garnet Amaranth, but had some great observations! Here's a breakdown of the basics:
Light Is Key: Different light spectra (colors) can drastically change the color, taste, and nutritional qualities. Controlling light opens opportunities for crafting a premium microgreen that fits market demands—whether that’s vibrant color for garnishing or a nutrition-packed product to stand out with customers.
Key Terms
- Phenolic Compounds: Plant chemicals that often have antioxidant properties (potential health benefits like anti-inflammatory effects).
- Carotenoids: Natural pigments (e.g., beta-carotene, lutein) that give oranges, yellows, and reds to plant tissues—many are associated with eye health and antioxidant benefits.
- Vitamins: Essential compounds (like C, E, and various B vitamins) that support immunity, metabolism, and other bodily functions.
- Antioxidants: Help reduce or neutralize free radicals (unstable molecules that can damage cells).
- Amino Acids: The building blocks of proteins; crucial for growth, repair, and metabolic processes in both plants and humans.
Overview
Researchers used ‘Garnet Red’ amaranth microgreens (Amaranthus cruentus).
Light Treatments:
- R:B (80:20) – 80% red + 20% blue LED.
- R:G:B (70:10:20) – Red, green, and blue LEDs (with 10% green).
- White (W) – A broad-spectrum “daylight” LED (5700 K).
- Ambient (Natural Solar) – Standard greenhouse sunlight (control).
Light Intensity & Photoperiod:
- LED setups provided 300 µmol m−2·s−1 of light for 13 hours a day.
- Ambient light varied (11 hours of sunlight on average, intensities ranged ~255–299 µmol m−2·s−1).
Measurements & Methods:
- Growth & Color: Hypocotyl (stem) length, yield (fresh weight), color properties (L*, a*, b*, hue, chroma).
- Total Assays: Antioxidant activity, total anthocyanins, total phenolics, chlorophyll, total carotenoids.
- Advanced LC-MS/MS: Detailed profiling of vitamins, carotenoids, phenolic compounds, amino acids, sugars, organic acids, and nucleosides.
Main Findings
A. Growth & Appearance
- Stem Length: Shorter under R:B, R:G:B, and White LEDs (~3.6–4.1 cm) vs. Ambient (~5.6 cm).Practical Benefit: Shorter stems can look sturdier and are often easier to handle or package, which many chefs prefer.
- Yield: No big statistical difference among the LED treatments, though Ambient was slightly higher (~50 g m−2).Takeaway: You can still get good yields using red/blue-based LEDs, while controlling coloration and other traits.
B. Leaf Color
- R:B and R:G:B increased redness (a*) and lowered hue angle, resulting in a more intense red. Customer Appeal: Deeper color often implies higher “visual” value—especially in a restaurant or premium retail setting.
C. Basic Phytochemical Assays
- Antioxidant ActivityHighest under R:G:B (62.5%) and R:B (57.5%), then White (53.2%), and lowest in Ambient (48.6%).
- AnthocyaninsSurprisingly no major differences among treatments; a bit unexpected, as red+blue can stimulate anthocyanin.
- Total PhenolicsSlightly lower in R:B and R:G:B vs. Ambient. Some phenolics actually went down with more red/blue light.
- ChlorophyllNo significant changes. The 13-hour photoperiod at 300 µmol m−2·s−1 didn’t create big differences.
- Total CarotenoidsR:G:B showed the highest total carotenoids (0.52 mg g−1), followed by R:B (0.37 mg g−1), indicating a color/nutrition bump when adding some green light.
Detailed Nutrient & Phytochemical Findings (LC-MS/MS)
They identified and measured 65 different compounds, including vitamins, carotenoids, phenolics, amino acids, sugars, acids, and nucleosides.
Some highlights:
- VitaminsVitamin C: Highest in R:G:B (834 µg g−1 vs. 279 µg g−1 in Ambient).Vitamin E: Increased in R:B and R:G:B (~1.0 µg g−1 vs. 0.84 µg g−1 in Ambient).B Vitamins (B1, B3, B6, etc.): Generally lower under R:B/R:G:B than under White or Ambient.
- CarotenoidsLutein: Higher in R:G:B compared to Ambient.Zeaxanthin: Also increased with added blue/green elements.
- Phenolic CompoundsSome (like rutin) went up with R:B/R:G:B. Others (like mangiferin) were higher in Ambient.
- Amino Acids & NucleosidesMost amino acids were lower in R:B/R:G:B, but tryptophan went up in R:G:B.Sugars (glucose, fructose, sucrose) were higher in R:B, potentially contributing to a sweeter taste. Organic acids like malic acid increased in R:G:B, possibly giving a slight tang.
Key Takeaways for Microgreens Businesses
- Red/Blue & Red/Green/Blue LEDsPlus:Vibrant red color (eye-catching presentation).Boosted antioxidants, vitamins C and E, certain carotenoids, and sugar/acid content (potentially better flavor).Minus:Slight drop in B vitamins, phenolic compounds, and many amino acids.If your product emphasizes B-vitamin content or certain phenolics, you might lose some of that.
- Shorter HypocotylsMicrogreens look more compact and sturdy. Many chefs prefer this aesthetic for plating.
- Yield Not Significantly AffectedYou’re not sacrificing much in total harvest weight by switching to these custom LED spectrums.
- Market DifferentiationGrowers can label or promote: “High in Vitamin C and E” or “Slightly Sweeter, More Colorful Microgreens.” This can boost perceived value.
- Tailor the Light to Your GoalsIf your brand demands intense flavor and color, R:B or R:G:B is beneficial.If you prioritize certain B vitamins or phenolics, consider balancing with white or natural light, or tweaking your ratio.
6. Conclusion / Take-Home Message
Different LED “recipes” (ratios of red, green, blue light) let you dial in color and specific nutrients in red amaranth microgreens. By using R:B or R:G:B:
- You gain better color, higher antioxidants, and more vitamins C/E and sugars/acids.
- You lose some B vitamins, phenolics, and amino acids.
Ultimately, no single light spectrum is perfect for everything. It depends on your customers’ priorities: vibrant, “sweet” microgreens vs. ones with a broader range of B vitamins or phenolics.
For most microgreens businesses seeking that bright color and strong antioxidant profile, R:B or R:G:B would be a solid choice.
Reference:
Trandel-Hayse, M., Bai, J., Jeffries, K., Poole, G., Hensley, M., Schonborn, W., Di Gioia, F., & Rosskopf, E. (2025).Light source and spectra influence the phytochemical profile of amaranth microgreens. Food Bioscience, 105839.https://doi.org/10.1016/j.fbio.2025.105839
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Light Source and Spectra Influence the Phytochemical Profile of Amaranth Microgreens Why Does Light Matter for Microgreens?
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