Contents lists available at ScienceDirect Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti Optimal red light irradiation time to increase health-promoting compounds in tomato fruit postharvest Lachinee Panjai a,b, ⁎ , Georg Noga a , Mauricio Hunsche a,c , Antje Fiebig a a Institute of Crop Sciences and Resource Conservation (INRES), Horticultural Sciences, University of Bonn, Auf dem Hügel 6, 53121, Bonn, Germany b Department of Agro-industry, Rajamangala University of Technology Lanna Lampang, Thailand c COMPO EXPERT GmbH, Research and Development. Krögerweg 10, 48155, Münster, Germany ARTICLE INFO Keywords: Lycopene β-carotene Antioxidant activity LED Postharvest Tomato ABSTRACT The impact of postharvest red light irradiation via LED modules on the content of health promoting compounds was evaluated on green tomatoes stage 1 exposed to intermittent or continuous irradiation. The first experiment studied the overall effects of different duration periods of red light radiation (darkness, continuous red light for 10 d, continuous red light for 15 d and continuous red light for 20 d) while the second experiment focused on effects of intermittent red light (darkness, red light for 30 min per day, red light for 6 h per day, red light for 12 h per day and continuous red light). In both experiments, tomatoes exposed to darkness served as control. Continuous red light irradiation accelerated ripening of green tomatoes. In addition, continuous red light also significantly increased lycopene, β-carotene, total phenolic content, total flavonoid concentration and anti- oxidant activity compared to all other treatments, suggesting that continuous red light exposure positively in- fluences metabolic processes and contributes to a higher content of health promoting compounds in tomatoes. 1. Introduction Recently, interest in nutritional value of food has rapidly increased due to associated positive health effects (Prasad and Chakravorty, 2015). Together with their derived products, tomatoes are one of the major food sources of carotenoids, providing roughly 80% of daily in- take of lycopene, as well as folate, ascorbic acid, flavonoids, a-toco- pherol and potassium in the Western diet (Willcox et al., 2003). These health promoting compounds of tomato fruit have mainly been attrib- uted to the significant amount of natural antioxidants, especially ly- copene (Ilić et al., 2012). In the past decades, considerable work has been conducted to in- crease levels of carotenoids in tomatoes through breeding programs or ripening intervention technologies. In particular, during post-harvest storage irradiation with different light spectra has been tested (Alba et al., 2000; Liu et al., 2003; Rosati et al., 2000). Light is one of the most important environmental factors affecting the pigment metabolism of vegetables and fruit (Lado et al., 2015). As shown, light has a positive effect on nutritional quality of butterhead lettuces (Lactuca sativa L.) (Charles et al., 2018). Continuous light (around 35 μmol -2 s -1 ) can maintain the level of soluble sugars and ascorbic acid in post-harvest fresh-cut romaine lettuce (Zhan et al., 2013). In spinach leaves, the endogenous pool of some vitamins including ascorbic acid and folate is higher when leaves are stored under visible light than in the dark (Lester et al., 2010). Therefore, the aim of this study was to investigate the effect of postharvest red light radiation schemes (intermittent or continuous) on heath promoting compounds in tomatoes. The guiding work hypothesis was that different red light irradiation time per day lead to a differ- entiated synthesis of heath promoting compounds in tomatoes. In order to reach the objectives, simple chlorophyll fluorescence ratio, lycopene, β-carotene, total phenolic concentration, total flavonoid concentration, as well as hydrophilic and lipophilic antioxidant activity were mon- itored during a storage period of 20 and 14 d in experiment 1 and 2 respectively. https://doi.org/10.1016/j.scienta.2019.03.019 Received 19 November 2018; Received in revised form 7 March 2019; Accepted 8 March 2019 Abbreviations: USDA, The United States Department of Agriculture; PAR, photosynthetic available radiation; SFR, simple chlorophyll fluorescence ratio; FRF_R, far- red fluorescence; RF_R, red fluorescence; HPLC, high performance liquid chromatography; QAE, quercetin equivalents; TE, mMTrolox equivalents; ABTS+, 22′- azino-bis (3-ethylbenzthiazoline-6-sulphonic acid) ⁎ Corresponding author at: Institute of Crop Sciences and Resource Conservation (INRES), Horticultural Sciences, University of Bonn, Auf dem Hügel 6, 53121, Bonn, Germany. E-mail addresses: lachineep@gmail.com, lachinee@uni-bonn.de (L. Panjai). Scientia Horticulturae 251 (2019) 189–196 0304-4238/ © 2019 Elsevier B.V. All rights reserved. T