Optimizing Growth And Nutrient Properties Of Red Amaranth Microgreens Through Blue Light Duration And Calcium Ascorbate Application

Optimizing Growth and Nutrient Properties of Red Amaranth Microgreens through Blue Light Duration and Calcium Ascorbate Application

Leal, Jeraldine¹ and Tan, Romil²

¹Department of Horticulture, Central Mindanao University, Maramag, Philippines

²Professor, Department of Horticulture, Central Mindanao University, Maramag, Philippines

DOI: https://dx.doi.org/10.47772/IJRISS.2025.9010169

Received: 05 January 2025; Accepted: 09 January 2025; Published: 10 February 2025

ABSTRACT

The experiment involved blue light exposure durations (4 hours, 8 hours, and 12 hours) and white light as control. Calcium ascorbate was applied at varying concentrations (10 ppm, and 15 ppm) and water as control. The results revealed that the combination of 4 hours of blue light exposure and 10 ppm calcium ascorbate application significantly increased plant height. Furthermore, 12 hours of blue light exposure led to a thicker and wider cotyledon area, resulting in a deep purple color characteristic of red amaranth microgreens. Fresh weight and dry weight were highest on red amaranth microgreen exposed to 12-hour blue light duration. Shelf life analysis indicated that microgreens grown under 12 hours of blue light exposure with 10 ppm calcium had an extended shelf life at room temperature. Analysis of nutrient content revealed that nitrogen levels were highest in the control group. However, phosphorus content was highest in microgreens exposed to 4 hours of blue light, potassium content was highest in microgreens exposed to 12 hours of blue light. Overall, the combination of 12 hours of blue light exposure and 10 ppm calcium ascorbate application resulted in quality red amaranth microgreens with desirable growth and nutrient properties.

Keywords: Red amaranth microgreens, blue light duration, calcium ascorbate, nutrient content

INTRODUCTION

Red amaranth microgreens (Amaranthus cruentus) have gained popularity in recent years due to their nutritional richness and culinary versatility (Thakur et al., 2020). These young seedlings are not only visually appealing with their vibrant red and purple hues but also pack a nutritional benefit, containing high levels of vitamins, minerals, and antioxidants (Rustic wise, 2021). The cultivation of microgreens has become a focus of research aimed at optimizing their growth and enhancing their nutrient properties (Zhang et al., 2021). One significant factor that influences plant growth and development is light quality, with studies increasingly exploring the effects of different light spectra on microgreen production (Rehman et al., 2017; Singh et al., 2015). Additionally, the application of micronutrients such as calcium ascorbate has been investigated for its potential to improve plant growth and nutrient content. Blue light, known for its role in photosynthesis and photomorphogenesis (Cryptochromes) has been studied extensively for its effects on plant growth, leaf morphology, and pigment accumulation (Wang et al., 2014). By varying the duration of blue light exposure, ranging from 4 hours to 12 hours, the study aims to determine the optimal light regime for enhancing the growth and quality of red amaranth microgreens. Furthermore, calcium is an essential micronutrient that plays a crucial role in cell wall structure, enzyme activation, and overall plant health. The application of calcium ascorbate, a form of calcium supplemented with ascorbic acid, has shown promise in improving plant vigor and nutrient uptake (Gallie, 2013). By applying calcium ascorbate at different concentrations, seeks to elucidate its influence on the growth, nutrient content, and shelf life of red amaranth microgreens. Understanding the interactions between blue light duration, calcium ascorbate application, and the resulting effects on red amaranth microgreens is not only valuable for optimizing microgreen production but also for enhancing their nutritional value. This research contributes to the growing body of knowledge aimed at sustainable and nutrient-rich food production, with implications for both commercial growers and consumers seeking healthy and flavorful culinary options. In this article, methodology, results, and discussion are presented highlighting key findings and insights into the cultivation of high-quality red amaranth microgreens.

PLANT MATERIALS AND METHOD

Red amaranth seeds are precured at Condor. Blue light and white light (for control) are all precured at Citi Hardware, Valencia City, Bukidnon. 5 grams seeds are sown in a 10*12 cm container with 1*1 cm holes underneath for water drainage, arranged in growing rack by 25*25 cm distance in a 3*4 spit-pot CRD study design replicated 3 times (Treatment 1 to T12), under blue light (4, 8, and 12 hours) and white light (control) as artificial light on the study. Coco peat are used as soil medium on the study. LUX meter was used prior to planting for light measurement. Sown seeds are subjected to blackout method in an average of 28^oC room temperature. After 2 days, covers are removed, germinated seeds were sprayed with Calcium ascorbate in a 10 and 15 ppm concentration, water was used for control plants. Spraying with calcium ascorbate and water lasted until 13 days, microgreens are harvested at 14 days early morning, sharp sterilized scissors and 2 decimal calibrated weighing scale was used to harvest and weigh the microgreens. Harvested red amaranth microgreen was subjected to drying and tissue analysis for total N,P and K at Soil and Plant Tissue Analysis (SPAL), Musuan, Maramag, CMU. Atomic absorption spectroscopy (AAS) was used to analyzed the tissue samples.

RESULT AND DISCUSSION

Plant Height

For proper growth, red amaranth microgreen grows under blue light having an average of 4000 LUX wherein 4237 LUX is used in the research while white light needs an average of 5000 LUX and 5177 LUX is used in the study. Plant height was significantly affected by the combination of blue light duration and calcium ascorbate concentration. The highest plant height was observed in microgreens exposed to 4 hours of blue light with 10 ppm calcium ascorbate, indicating a positive synergistic effect on vertical growth. Although, microgreen exposed to 4 hours blue light has weak and fragile stems, plants exposed to shorter light tends to have a frail stem, long and thin, it is also due to etiolation. Interestingly, microgreens grown under 12 hours of blue light with 10 ppm calcium ascorbate showed optimal growth without compromising yield and quality, suggesting a potential balance between light exposure and calcium quantity. As calcium considered as essential element which greatly needed for the growth and development of plant thus further increases plant growth (Brahmakshatriya et al., 2022). The combination of blue light and calcium ascorbate gives positive impact towards the increase of red amaranth microgreen height. Similarly, in the application of Goble (2018), Kou et al., (2018) shows a positive response of varying microgreen varieties and species upon the application of calcium. The figure below was the actual picture of the red amaranth microgreen which is subjected to blue light exposure and calcium

Graph 1. Plant height at 7 and 14 DAP

Figure 1. Red amaranth microgreen treatments comparison

Cotyledon Area and Color

Cotyledon area, an indicator of leaf development, was notably larger in microgreens exposed to 12 hours of blue light, leading to thicker and wider cotyledons. This characteristic, coupled with the deep purple color observed in microgreens under 12 hours of blue light exposure, underscores the importance of light duration in influencing both structural and pigment-related attributes of red amaranth microgreens. Treatments under white light, 4- and 8-hours blue light exposure shows thin and smaller cotyledons in comparison to 12 hours blue light exposure, wherein the average of cotyledon area is 2cm while other treatments range from 0.8 cm to 1 cm. In Lobiuc et al. (2017) study shows that subjecting blue light on plants could increase cotyledon area. In addition, Ying et al. (2020) and Hogewoning et al. (2010), study on the blue-light exposure of various microgreen, shows, that blue light has positive connotation on the increase of hypocotyl and the cotyledonary area of a plant, thus increasing thickness of plant leaf index. On this study, the application of calcium and blue light give rise on the increase of red amaranth cotyledonary area. Figure 2 shows the gap between each treatment upon the varying cotyledon area of the 4 treatments, as blue light was seen to be significant on the increase of cotyledon area of red amaranth microgreens.

Figure 2. Red amaranth microgreen cotyledon comparison

Fresh Weight, Dry Weight, and Shelf Life

Significant differences in fresh weight and dry weight were observed between microgreens exposed to 4 hours and 12 hours of blue light, with the latter showing higher weights on average. This indicates that longer blue light exposure durations contribute to increased biomass accumulation. Moreover, microgreens grown under 12 hours of blue light with 10 ppm calcium ascorbate demonstrated an extended shelf life at room temperature, suggesting a potential preservation effect associated with the light and nutrient combination. Highest fresh weight recorded is 74.41 grams this is under 12 hours blue light exposure with 10 ppm calcium ascorbate application, least weight recorded is 26.90 grams (T4) under 4 hours blue light and water (control) application. This result is also been justified by Wang et al. (2022), Zheng et al. (2018) and Takemiya et al. (2005) wherein an increase in the exposure of microgreens to blue light could help increase the photosynthetic activity of the plant thus giving bigger rate on its weight.

Graph 2. Red amaranth microgreen fresh and dry weight

Highest dry weight is recorded at treatment T11 followed by T12 (12 hours BL exposure and 15 ppm) wherein dry weight range from 4.81 to 3.53 grams, lowest dry weight is recorded at T4 wherein it has a mean of 1.01 grams dry weight.  Khwankaew et al. (2018) revealed that exposure of blue light to water spinach obtained the highest dry weight among their study, which also seen to have similar effect on red amaranth microgreen. In addition, Ying et al. (2020) and Terfa et al. (2013) also stated in their various  study that the use of blue light leads to the increase of dry weight on different varieties and species on their study. Dry weight data shows that there is a significant effect of blue light and calcium application.

Microgreens are delicate plant which are highly perishable which can deteriorate fast if not stored properly (Amin et al., 2015). Among the treatments, T11 shows the ideal result for the longer shelf life of the red amaranth microgreen, it last at least 4 days being viable from harvest at room temperature, moreover, T2 deteriorate faster than the other treatments. Microgreens under 12 hours blue light exposure, microgreens subjected 4 hours BL exposure deteriorate fast almost last for 1 day only. Moreover, Ying et al. (2020) and Di Gioia et al., (2015) find out that the use of blue light towards the plant could increase cotyledon thickness and dry matter, thus, potentially increase the microgreen shelf life.

Nutrient Content

Nitrogen analysis result shows that there is no significant result on the application of blue light, T1 which is the control is seen to have the highest nitrogen content, followed by 4 hours of blue light exposure. High phosphorus content is seen on the control (T5) with 0. 96%, followed by the 4 hours BL exposure, (T4) with 0.94%. The least phosphorus content seen is the T8 having a 0.74%. On total potassium analysis, the highest potassium content is seen in 12 hours BL exposure T10 having 4.123%, followed by T12 with 3.75%, least potassium is seen on 4 hours BL exposure (T4) with 2.40%.  Brazaityle et al. (2021); El Haddaji et al. (2023), the use of blue light on the microgreen shows higher mineral content, with the exception of nitrogen, the use of blue light also leads to the decrease of nitrates and osmoprotectant content in microgreens. Acton (2013) wherein lower blue light dosage leads to higher phosphorus and other nutrients. The study of Brazaityle et al. (2021), Zhang et al. (2021) shows similar results on this study, wherein the increased exposure of blue light (LED) leads to the increase of macronutrients on their various microgreens studied. Analysis of nutrient content revealed intriguing patterns. While nitrogen levels were highest in the control group, indicating minimal impact from the treatments on nitrogen uptake, phosphorus content showed variation based on blue light exposure duration. Microgreens exposed to 4 hours of blue light exhibited higher phosphorus content compared to those exposed to 8 hours of blue light, suggesting a potential role of light duration in nutrient assimilation. Notably, potassium content was highest in microgreens exposed to 12 hours of blue light, highlighting the positive correlation between extended light exposure and potassium accumulation.

Figure 2. Red amaranth N, P, and K content comparison

CONCLUSION

The study’s findings underscore the importance of optimizing light duration and nutrient supplementation for the cultivation of high-quality red amaranth microgreens. The synergistic effects observed between blue light exposure and calcium ascorbate application offer valuable insights into sustainable and efficient microgreen production practices. Wherein, study shows the treatment combination of blue light exposure and calcium ascorbate gives a positive connotation upon the overall growth and nutritional content without compromising the quality of red amaranth microgreen. Further research could delve into the mechanistic aspects of nutrient uptake and light signaling pathways to enhance our understanding of plant responses to environmental stimuli.

ACKNOWLEDGEMENT

The author would like to thank DOST-STRAND for funding her study journey, to her study adviser Prof. Romil Tan, her panelist Prof. Myrna Pabiona and Prof. Andrew Melencion for the valuable insight and unending guidance towards her.

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