Using Light to Manipulate the Nutritional and Sensory Properties of Greenhouse Tomatoes with Red, Blue, and Far-red Supplemental LEDs

Greenhouse tomatoes tend to have a reputation of inferior nutritional and sensory quality compared to their field-grown counterparts. It has been long known that light is a critical mediator of secondary metabolism in plants; signaling the production of nutritionally important phytochemicals and regulating the emission of volatile organic compounds that may influence the sensory attributes of edible tissues. By leveraging photobiological principles, we are using supplemental light from light-emitting diodes (LEDs) to determine if supplemental red, blue, far-red, or various combinations of those wavebands can improve the quality of greenhouse tomatoes. We hypothesize that enriching the amount of blue light tomatoes receive will positively impact the amount of carotenoids and phenolic compounds that accumulate in tomato fruits through cryptochrome and/or phototropin-dependent signaling pathways. On the contrary, we hypothesize that additional far-red light will decrease these phytochemicals by increasing the amount of inactive phytochrome in leaf and fruit tissues, thereby down-regulating secondary metabolic pathways related to the nutritional content of tomato fruits. To test these hypotheses, tomato fruits were subjected to a battery of physicochemical metrics that include total soluble solids, citric/ascorbic acid content, pH, and electrical conductivity. Phenolic compounds were broadly quantified using the Folin-Ciocalteu method and specific flavonoids in fruit tissues (e.g. quercetin-3-O-rutinoside) were quantified using HPLC-ESI(-)-MS. Two major tomato carotenoids, lycopene and β-carotene, were quantified spectrophotometrically. Lastly, consumer sensory panels were used to assess the impact of supplemental light quality on the flavor and overall quality of tomato fruits.