Enhancement of the antioxidant capacity of ripe tomatoes by the application of a hot water treatment at the mature-green stage

Authors: LOAYZA, FRANCISCO - University Of Florida; BRECHT, JEFFREY - University Of Florida; SIMONNE, AMARAT - University Of Florida; Plotto, Anne; Baldwin, Elizabeth - Liz; Bai, Jinhe; LON-KAN, ELENA - University Of Florida

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/24/2019
Publication Date: 12/10/2019
Citation: Loayza, F., Brecht, J., Simonne, A., Plotto, A., Baldwin, E.A., Bai, J., Lon-Kan, E. 2019. Enhancement of the antioxidant capacity of ripe tomatoes by the application of a hot water treatment at the mature-green stage. Postharvest Biology and Technology. 61:111054. https://doi.org/10.1016/j.postharvbio.2019.111054.
DOI: https://doi.org/10.1016/j.postharvbio.2019.111054

Interpretive Summary: Tomatoes are rich with lycopene and other carotenoids, vitamin C and other antioxidants, beneficial to human health. This study explored the potential of increasing the content of antioxidant compounds in tomatoes harvested at the mature-green stage ( standard commercial harvest) using a simple brief (5 minutes) hot water (52 °C or 125.6 °F) treatment. The results showed that this treatment could increase carotenoids and other antioxidant compounds in the ripe fruit without altering other quality attributes (sugars, acids, texture). Tomatoes ripened normally, with no firmness difference, but were darker red. This effect was more pronounced in varieties that already had a potential for developing darker color and having more lycopene content, such as Tasti-Lee. This study showed that a simple hot water postharvest treatment could increase the nutritional value of tomatoes.

Technical Abstract: Plants are constantly exposed to abiotic and biotic stresses, inducing the generation of reactive oxygen species (ROS). In response, the synthesis of antioxidants is upregulated to neutralize the deteriorating effects of ROS. We investigated whether promoting this response could enhance the nutritional and sensory quality of tomatoes. In preliminary experiments, mature green tomatoes were immersed in hot water (HW) at 50 °C for 5 min, 52 °C for 5 min, or 54 °C for 2.5 min (25 °C water for 5 min as control); subsequent experiments utilized 52 °C for 5 min. Following those treatments, we evaluated the changes in color, texture, soluble solids, titratable acidity, and the antioxidant system of the fruit during ripening at 20 °C and 85-90% relative humidity. The HW treatment of 52 °C for 5 min promoted higher accumulation of carotenoids and lipophilic phenolics, resulting in greater color development and slightly higher antioxidant potential, but did not otherwise affect the composition of ripe fruit; the tomatoes ripened normally after HW immersion, with no firmness differences, but were darker red and less yellow-orange with higher antioxidant potential. Futhermore, we observed that the beneficial effects were more noticeable at early stages of ripening, even in varieties that did not exhibit major differences after reaching full ripeness. In this sense, we found that ‘Florida 47’ and ‘Security 28’ tomatoes have a limited response to HW treatment compared with ‘Soraya’ and especially ‘Tasti Lee’ tomatoes, indicating that there might be genetic constraints on the response in the former varieties. The beneficial effect of immersing the tomatoes in HW was proportional to the heat penetration profile inside the fruit; for example, the 52 °C for 5 min treatment increased the temperature up to 45 °C in the peripheral tissues 4 mm below the fruit surface where the content of carotenoids and lipophilic phenolic compounds was mainly increased; whereas, the tissue temperature was 35 °C at the center of the tomato, where we did not observe any change in composition. In conclusion, the HW immersion used in this research promoted the synthesis of lipophilic antioxidants such as carotenoids in tomato fruit, enhancing red color development and antioxidant potential.