A Semiyearly Study on the Effect of Light Quality on Flavor of Greenhouse Grown Tomatoes: LED Versus HPS

Seasonal variation in solar daily light integral (DLI) makes it logistically and financially burdensome to produce greenhouse-grown tomatoes during the winter in a northern climate. Two separate studies investigating interactions among light quantity and spectrum, fruit yield, flavor development, and composition of tomato fruit comparing supplemental lighting from energy-efficient LED intracanopy lighting vs. traditional overhead high-pressure sodium lighting vs. unsupplemented controls were performed during 2012. Two tomato cultivars, ‘Success’ and ‘Komeet’, were grown in soilless slab culture within a greenhouse using high-wire trellising. Tomato production experiments were conducted from July to December 2012 and from January to June 2013. In each experiment, supplemental DLI was determined on a monthly basis by subtracting solar DLI from 25 mol/m²/d. Fruits were harvested at the vine-ripe stage, counted, and weighed. Quality metrics were selected that are standard in the Horticultural and Food Science Industries. Objective measures of fruit quality included °Brix, titratable acidity, pH, electroconductivity, and chromatic index. These attributes were linked to consumer acceptance via subjective organoleptic taste panels. Both hedonic (indicating preference) as well as absolute scales of evaluation (without indicating preference) were used to evaluate tomato fruit for flavor characteristics including sweetness, acidity, texture, aroma, bitterness, aftertaste, color, and overall approval. Both subjective and objective metrics of fruit quality were correlated with type of supplemental lighting used, total DLI, cultivar, and time of year when harvested. Results from the first and second fruit-production experiment conducted in 2012 and 2013 will be presented. Additionally, the efficacy of testing heirloom fruits in the future will be presented. This project is supported in part by NIFA–SCRI grant 2010-51181-21369.