Preharvest application of ethephon and postharvest UV-B radiation improve quality traits of beetroot (Beta vulgaris L. ssp. vulgaris) as source of colourant

Abstract

BackgroundBetanins have become excellent replacers for artificial red-purple food colourants. Red beet (Beta vulgaris L. spp. vulgaris) known as beetroot, is a rich source of betalains, which major forms are betanin (red to purple) and vulgaxanthin (yellow). Betalains and phenolic compounds are secondary metabolites, accumulation of which is often triggered by elicitors during plant stress responses. In the present study, pre-harvest applications of ethephon (an ethylene-releasing compound) and postharvest UV-B radiation were tested as elicitors of betalains and phenolic compounds in two beetroot cultivars. Their effects on quality parameters were investigated, and the expression of biosynthetic betalain genes in response to ethephon was determined.ResultsEthephon was applied as foliar spray during the growth of beetroot, resulting in increased betanin (22.5%) and decreased soluble solids contents (9.4%), without detrimental effects on beetroot yield. The most rapid accumulation rate for betanin and soluble solids was observed between 3 and 6 weeks after sowing in both untreated and ethephon-treated beetroots. Overall, the expression of the betalain biosynthetic genes (CYP76AD1, CYP76AD5, CYP76AD6 and DODA1), determining the formation of both betanin and vulgaxanthin, increased in response to ethephon treatment, as did the expression of the betalain pathway activator BvMYB1. In the postharvest environment, the use of short-term UV-B radiation (1.23 kJ m− 2) followed by storages for 3 and 7 days at 15 °C resulted in increased betanin to vulgaxanthin ratio (51%) and phenolic content (15%).ConclusionsThe results of this study provide novel strategies to improve key profitability traits in betalain production. High betanin concentration and high betanin to vulgaxanthin ratio increase the commercial value of the colourant product. In addition, lowering soluble solids levels facilitates higher concentration of beetroot colour during processing. Moreover, we show that enhanced betanin content in ethephon-treated beetroots is linked to increased expression of betalain biosynthetic genes.

Ethephon foliar application: Impact on the phenolic and technological Tempranillo grapes maturity

“…In 2016, °Brix in treated grapes was not significantly different when compared with the control, although the °Brix values of ethephon‐treated berries tended to be slightly lower than those of the control (Figure 1). The decrease in the accumulation rate of soluble solids has been observed after preharvest treatments of ethephon in other species such as Beta vulgaris L. (Barba‐Espin et al., 2018) or Capsicum annuum L. (Yang, Luo, Tan, & Kan, 2020). However, other authors have reported no significant differences in sugar accumulation in V. vinifera L. (Kok & Bal, 2018) or Solanum lycopersicum L. (Martínez‐Damián, Cano‐Hernández, Moreno‐Pérez, Del Castillo, & Cruz‐Álvarez, 2018).…”

Environmental effects of stratospheric ozone depletion, UV radiation, and interactions with climate change: UNEP Environmental Effects Assessment Panel, Update 2020

“…In most studies where UV-B radiation has been manipulated, it has been applied prior to harvest (i.e., preharvest), or following harvest (i.e., postharvest). Species studied in this context include beetroot [ 200 ], broccoli [ 201 ], ginseng [ 202 ], prickly pear [ 203 ], blueberry [ 204 ], and even mushrooms [ 205 ]. In certain varieties of peach, these treatments have helped maintain the weight, firmness, and vitamin C content of the fruit, which increases its quality, value, and shelf-life [ 206 – 208 ].…”

Nutritional and Physiological Effects of Postharvest UV Radiation on Vegetables: A Review

“…87 However, after three and seven days of storage, vulgaxanthin I content in beets decreased, regardless of whether the samples were control or UV-B treated. 87 Betalain pigments may also play some role in protecting against UV stress, but further evidence is needed to support this hypothesis.…”

“…They contain two groups of water-soluble pigments: red-purple betacyanidins and yellow betaxanthins. Betacyanidins are conjugates of cyclo-dihydroxyphenylalanine and betalamic acid, and betaxanthins are conjugates of amines or amino acids and betalamic acid …”