Logan S. Logendra

Antioxidant activity and phenolic compounds of Swiss chard (Beta vulgaris subspecies cycla) extracts

The antioxidant activity (radical scavenging and thiocyanate method), total phenolic contents (gallic acid equivalents) and phenolic composition (coulometric array detection) in methanol extracts of different parts and tissue types of hydroponically grown Swiss chard (Beta vulgaris subspecies cycla) were determined. Significant differences (P <0.01) in the antioxidant activity were found between leaves and stems. Phenolic content and composition of the leaves and the stems also were found to be different. A positive linear correlation (R=0.943) was demonstrated between radical scavenging activity and total phenolic content of each extract. The major phenolic acid and flavonoid in leaves of Swiss chard were syringic acid and kaempferol. Coulometric array detection showed good reproducibility (CV, 0.06–1.05%) and sensitivity (1 ng/ml, detection limit) for simultaneous detection of 13 phenolics. Our data indicates that Swiss chard has potential as a good dietary source of phenolic antioxidants.

Effect of temperature perturbations on tomato (Lycopersicon esculentum Mill.) quality and production scheduling

Summary Controlled environment experiments were conducted to evaluate the effect of a 2-week change in air temperature imposed after first fruit-set on tomato production scheduling and on the quality of vine-ripened fruit. Experiments were conducted with hydroponically-grown tomato (Lycopersicon esculentum Mill., cv. ‘Laura’). Air temperature was altered from control day/night temperature values of 23°/18°C for a 2-week period starting 10 d after fruit-set. Plants were returned to the 23°/18°C temperature and a minimum of eight fruits per treatment were harvested at three ripening stages, breaker (when 25% of the fruit skin had acquired a red tint), breaker plus 3 d, and breaker plus 6 d. A perturbation of ± 5°C (28°/23°C and 18°/13°C) was used in two Experiments (E1 and E2) and ± 7°C (30°/25°C and 16°/11°C) was used in a third Experiment (E3). Fruits were more responsive to an increase than to a decrease in temperature. Reductions in days to harvest (from 3.1 – 8.5 d) and fruit fresh weight at later stages of vine-ripening were observed for the high temperature treatments. Colour indices, soluble solids contents (SSC), acidity and viscosity at each ripening stage were significantly affected by high temperature treatments. The results indicate that short-term temperature perturbations following first fruit-set can influence the rates at which changes occurred in the external appearance of fruit (colour) and in their internal characteristics. The results can be used to improve environmental control and management strategies for tomato growers.

Manipulation of Tomato Fruit Quality Through Temperature Perturbations in Controlled Environments

Quality factors such as size, color, taste, and nutritional content are important criteria for marketing of greenhouse tomato fruit. While the majority of the research on fruit quality factors focuses on effects of post-harvesting and storage conditions, the environmental conditions during plant growth and the time for which the fruit is allowed to ripen on the vine also influence fruit quality. Growth chamber experiments were performed with tomato (cv. Laura) aiming to study the influence of air temperature perturbations during fruit set on fruit quality at maturity, the time to harvest, and the harvest window. Plants were grown in 6” pots and pruned to the 2nd true leaf above the first fruit cluster. Nutrients were provided through a drip irrigation system. All plants were grown under the same environmental conditions except for a two week period beginning 10 days after fruit-set during which plants were assigned to one of three day/night temperature treatments, 28/23°C, 23/18°C, and 18/13°C. Five tomato fruits were harvested from each plant at three distinct physiological ages; breaker stage (taken as the point at which 25% of the fruit begins to turn red), breaker stage plus three days, and breaker stage plus six days. Harvested fruits were analyzed for mass, size, color, soluble solids content, pH, acidity, viscosity, and other quality parameters. Initial results show significant temperature effects on fruit size, mass, developmental rate, and fruit processing characteristics. The results are applicable towards the development of more efficient plant production strategies for greenhouse growers and for NASA’s advanced life support research program.