INCREASING IRRADIANCES INCREASE ANTIOXIDANT ACTIVITY, TOTAL PHENOLIC CONTENT AND AFFECT PHOTOSYNTHESIS OF ECONOMICALLY IMPORTANT MACROALGA SEA GRAPES Caulerpa lentillifera

Introduction

 Caulerpa lentillifera is a green ,  macroalga  of increasing economic interest, harvested as an aquaculture crop in several Asian countries

 . The alga is low-light adapted and its out-door culture takes place in shaded ponds (~ 50 µmol photons m-2 s-1) . In Europe, sea grapes are known as `green caviar´, due to the special texture of their edible fronds . Sea grapes contain significant amounts of polyphenols and vitamin C, resulting in high antioxidant activities

 .  Antioxidants can avoid cell damage by functioning as scavengers of reactive oxygen species (ROS) and are therefore recognized as essential parts in human diets to counteract the metabolic syndrome

. In plant s ROS form as a byproduct of photosynthesis, especially under excessive light introducing photooxidative stress

. I n this study  controlled light- stress is  applied as a tool to trigger  the antioxidant potential of sea grapes , while sustaining the healthy green color of the fresh sea grape fronds.

Material and Methods

Sea grapes were held in 2 L beakers (artificial seawater) in a water bath under irradiance s of 50, 100, 200, 400 and 600 µmol photons m-2 s-1 for 21 days . S amples for measurements of AOA (ABTS assay, following

, total phenolic content ( TPC, Folin–Ciocalteu assay , following

, chlorophyll a and b  content, maximum quantum yield of PSII (Fv/Fm )  and  pictures for color analysis  were taken regularly over the run of the experiment . Data processing of chlorophyll content and color measurements ( for a later processing using the image analysis software ImageJ) is still underway.

Results

 Sea grape fronds were significantly enriched in AOA and TPC when exposed to  excessive  irradiances (≥ 200 µmol photons m-2 s-1), compared to usual culture irradiances. However, AOA and TPC content of sea grapes were negatively correlated with Fv/Fm (Fig. 1 C) , implying an overall decrease of the algae’s physiological state with increasing antioxidant potential. Additionally, a  partial de-coloration of sea grape fronds under irradiances ≥ 200 µmol photons m-2 s-1 has been observed over the experimental run.

Discussion

The results confirm, that a ntioxidative compounds accumulate in sea grape fronds under light-stress. Light irradiances ≤ 100 µmol photons m-2 s- 1  seem to be too low to increase AOA and TPC significantly

 , however irradiances of ≥ 200 µmol photons m-2 s- 1 more than doubled AOA and TPC, respectively. Decreasing Fv/Fm values and de-coloration, possibly induced by chloroplast relocation movement

 or chlorophyll degradation

 , might have a negative impact on the product quality. Therefore, carefully controlled higher irradiances could be applied as a post-harvest treatment in order to keep a balance between triggering AOA and sustaining healthy appearance of sea grape fronds.

 References

Ainsworth EA, Gillespie KM (2007) Estimation of total phenolic content and other oxidation substrates in plant tissues using Folin–Ciocalteu reagent. Nat Protoc 2:875–877. https://doi.org/10.1038/nprot.2007.102

Chen X, Sun Y, Liu H, et al (2019) Advances in cultivation, wastewater treatment application, bioactive components of Caulerpa lentillifera and their biotechnological applications. PeerJ 7:e6118. https://doi.org/10.7717/peerj.6118

Guo H, Yao J, Sun Z, Duan D (2015) Effect of temperature, irradiance on the growth of the green alga Caulerpa lentillifera (Bryopsidophyceae, Chlorophyta). J Appl Phycol 27:879–885. https://doi.org/10.1007/s10811-014-0358-7

Horstmann U (1983) Cultivation of the green alga, Caulerpa racemosa, in tropical waters and some aspects of its physiological ecology. Aquaculture 32:361–371

John OD, Du Preez R, Panchal SK, Brown L (2020) Tropical foods as functional foods for metabolic syndrome. Food Funct 11:6946–6960. https://doi.org/10.1039/d0fo01133a

Kang L-K, Huang Y-J, Lim W-T, et al (2020) Growth, pigment content, antioxidant activity, and phytoene desaturase gene expression in Caulerpa lentillifera grown under different combinations of blue and red light-emitting diodes. J Appl Phycol 32:1971–1982. https://doi.org/10.1007/s10811-020-02082-8

Matanjun P, Mohamed S, Mustapha NM, Muhammad K (2009) Nutrient content of tropical edible seaweeds, Eucheuma cottonii, Caulerpa lentillifera and Sargassum polycystum. J Appl Phycol 21:75–80. https://doi.org/10.1007/s10811-008-9326-4

Nguyen VT, Ueng J-P, Tsai G-J (2011) Proximate Composition, Total Phenolic Content, and Antioxidant Activity of Seagrape (Caulerpa lentillifera). J Food Sci 76:C950–C958. https://doi.org/10.1111/j.1750-3841.2011.02289.x

Pospíšil P (2016) Production of Reactive Oxygen Species by Photosystem II as a Response to Light and Temperature Stress. Front Plant Sci 7:1–12. https://doi.org/10.3389/fpls.2016.01950

Re R, Pellegrini N, Proteggente A, et al (1999) Antioxidant activity applying an improved ABTS radical cation decolorization assay. Free Radic Biol Med 26:1231–1237. https://doi.org/10.1016/S0891-5849(98)00315-3