Combined Effect of Salinity and LED Lights on the Yield and Quality of Purslane (Portulaca oleracea L.) Microgreens

Abstract

The present work aims to explore the potential to improve quality of purslane microgreens by combining water salinity and LED lighting during their cultivation. Purslane plants were grown in a growth chamber with light insulated compartments, under different lighting sources on a 16 h d−1 photoperiod—fluorescent lamps (FL) and two LED treatments, including a red and blue (RB)) spectrum and a red, blue and far red (RB+IR) LED lights spectrum—while providing all of them a light intensity of 150 µmol m−2 s−1. Plants were exposed to two salinity treatments, by adding 0 or 80 mM NaCl. Biomass, cation and anions, total phenolics (TPC) and flavonoids content (TFC), total antioxidant capacity (TAC), total chlorophylls (Chl) and carotenoids content (Car) and fatty acids were determined. The results showed that yield was increased by 21% both in RB and RB+FR lights compared to FL and in salinity compared to non-salinity conditions. The nitrate content was reduced by 81% and 91% when microgreens were grown under RB and RB+FR, respectively, as compared to FL light, and by 9.5% under saline conditions as compared with non-salinity conditions. The lowest oxalate contents were obtained with the combinations of RB or RB+FR lighting and salinity. The content of Cl and Na in the leaves were also reduced when microgreens were grown under RB and RB+FR lights under saline conditions. Microgreens grown under RB light reached the highest TPC, while salinity reduced TFC, Chl and Car. Finally, the fatty acid content was not affected by light or salinity, but these factors slightly influenced their composition. It is concluded that the use of RB and RB+FR lights in saline conditions is of potential use in purslane microgreens production, since it improves the yield and quality of the product, reducing the content of anti-nutritional compounds.

Light Spectrum Differentially Affects the Yield and Phytochemical Content of Microgreen Vegetables in a Plant Factory

“…Brassica carinata microgreens produced greater amounts of phenolics when treated with monochromatic blue compared to red and 50% red/ 50% blue light [29]. As with the green basil used in this study, Lobiuc et al [42] found a higher phenolic content in green basil (Ocimum basilicum) under increased red light portion, while Gimenez et al [40] reported greater total phenolic content in purslane microgreens treated with red-blue light compared to fluorescence and red-blue, including far-red. Romaine baby leaf lettuce had significantly higher phenol, but lower anthocyanin, and tocopherol amounts under supplemental light with a peak at 622 nm, and less ascorbic acid and tocopherols under supplemental light, with a peak at 595 nm [43].…”

“…On the contrary, Pennisi et al [30] reported significantly greater antioxidant capacity (ferric reducing antioxidant power: FRAP) in basil plants treated with a red/blue ratio of 2 units compared to those treated with 0.5 or 1, while total flavonoid concentration was promoted under a red/blue ratio of 3 units compared to ratios ranging from 0.5 to 4 units. In a study with purslane (Portulaca oleracea) microgreens, antioxidant capacity was not affected by fluorescent, red-blue, or red-blue, including far-red lights [40].…”

“…In the present study, it was clear that increasing blue light portion induced the accumulation of decreased phenolic compounds in six microgreens. Blue, red, and far-red wavelengths have the ability to regulate the biosynthesis of phenolic compounds in a direct or indirect manner through signaling, which leads to the expression of key enzymes, or through increasing shikimic acid, a precursor of phenolic compounds [39,40]. Moreover, the activity of a major enzyme participating in the phenolic biosynthesis, phenylalanine ammonia lyase (PAL), is known to be regulated by light quality [41].…”

Red Light Enhances the Antioxidant Properties and Growth of Rubus hongnoensis

“…Zheng and Van Labeke [34] reported that total phenol content in the leaves of Dendranthema morifolium was suppressed under B light, although this effect depended on the cultivar. B, R, and FR wavelengths also regulate the biosynthesis of phenol contents in a direct or indirect manner through signaling, which leads to the expression of key enzymes, or through upregulating the production of shikimic acid, which is a precursor of phenol contents [35]. Moreover, the activity of phenylalanine ammonia lyase (PAL), a major enzyme involved in phenolic biosynthesis, is known to be regulated by light quality [36].…”

By-Products Revalorization with Non-Thermal Treatments to Enhance Phytochemical Compounds of Fruit and Vegetables Derived Products: A Review

“…The application of UV-B, alone or in combination with UV-C, has not been widely studied as a revalorization tool for maintaining and/or increasing the main key compounds in F&V by-products [ 69 ]. Although light-emitting diodes (LEDs) are increasingly adopted for the production of several vegetable modalities and for quality preservation during storage [ 70 ], influencing the metabolic pathways (biosynthesis of several bioactive compounds) [ 71 , 72 , 73 ]. No published information is already available concerning the effect of this light stress in F&V by-products.…”