Potential of pre-and postharvest illumination of cherry tomato, a climacteric fruit, to reduce the ripening period and enhance yield and quality while maintaining shelf life.

Abstract

Tomato (Solanum lycopersicum) is the most-consumed horticultural commodity worldwide because it is diverse in use, attractive and contributes significantly to the health and nutrition of humans. There are many different types of tomato cultivars, such as the classic round, plum and baby plum, cherry, beefsteak, vine or truss and cocktail tomatoes. Baby tomatoes, also termed ‘cherry tomatoes’, have become particularly popular as fruit vegetables, due to their taste, particularly sweetness, high nutritional value and health benefits, as well as their attractive colour, particularly in the presentation of food.Many horticultural commodities are nowadays cultivated under supplemental lighting, such as ultraviolet C (UV-C), light emitting diodes (LEDs), and high-pressure sodium (HPS) so as to improve yield and reduce ripening period since the demand of tomato, particularly cherry tomato is increasing significantly which forces tomato growers to make use of controlled environment to meet the increasing demand. The use of LEDs in protected cultivation is gaining popularity as it can improve yields and enhance certain phytochemicals. Light-emitting diodes (LEDs) represent a relatively new technology for the greenhouse industry, as they emit light of narrow bandwidths. These lights are affordable and they do not contain unnecessary, low quality wavelengths. Therefore, LEDs can be employed to promote growth of fruit and vegetables in agriculture, particularly in horticulture, as they aid in plant development. Further, LEDs are easily controllable light sources and their use can improve the nutritional content of certain commodities, while improving or maintaining yield and giving high quality produce. Light affect the presence of phytonutrients in tomato fruit, such as carotenoids, vitamin C and phenolics. The general aim of this study was to determine if certain treatments are able to fast-forward colour change, while maintaining the fruit quality of cherry tomato. Two experiments were conducted, one in the glasshouse and another one in the post-harvest laboratory at the University of KwaZulu-Natal in 2017. The first experiment was designed to evaluate the effect of pre-harvest red and blue light treatment on colour, ripening, chlorophyll and carotenoid concentration as well as overall quality of the cherry tomato cultivars (‘Cherry Little Wonders’ and ‘Goldilocks’).When fruit were mature green, the a* values of the twelve trusses of the same age, six from each cultivar, were selected to receive light treatment. Six trusses, three of each cultivar, were illuminated with FLC-10W-R Red LED light (RL) and another six trusses, three of each cultivar, were illuminated with FLC-10W-BL blue LED light (BL). It was ensured that the distance from each light source to the truss was the same and it was also ensured that the light was equally distributed to every truss. Certain fruit were marked in each truss for analysis of quality parameters or measurements such as colour, size, firmness, TSS, chlorophyll and carotenoids. In this study pre-harvest red and blue light significantly affected the measured quality attributes of two cultivars (‘Cherry Little Wonders’ and ‘Goldilocks’), a red and yellow cherry tomatoes respectively. Light treatments did not have a significant effect on fruit size (P > 0.05) The size of all light-treated fruit was bigger than that of untreated fruit from day 15 to day 25, however there was no statistical significant difference between treated and non-treated fruits (P > 0.05). Yellow cultivar had a lower a* value and higher value of b*(green to yellow) from day 10 to day 25. A steady decrease in colour b* was observed in red cv while a sharp increase was observed in yellow cv, but fruits that were illuminated with red light had a higher b* value on both cultivars. Following treatment, L* (lightness) steadily decreased in treated and untreated tomato fruit for the first 10 days. Thereafter, a rapid decrease in L* was observed. A sharp decrease in chlorophyll concentration and a corresponding increase in carotenoid synthesis during the fruit ripening process was observed Chlorophyll a, b and carotenoid concentrations in tomato differed significantly (P < 0.01) between treatments, with the control maintaining the highest Chl a and Chl b values until day 25. There was a statistical significant difference between untreated and treated fruit in terms of changes in Chl a and b (P < 0.05). The red cv treated with BL and the yellow cv treated with RL showed a rapid decrease in Chl a. The accumulation of lycopene commenced in treated tomatoes 10 days after treatment, but for the first 10 days there was no statistical difference between the treated and non-treated fruit (P < 0.05). The lycopene concentration of yellow tomatoes was lower that of red tomatoes. The firmness of treated and non-treated fruit was similar the same in all fruit for the first five days postharvest, except in the yellow cv treated with BL. This treatment lost firmness most rapidly. Light also prevented the occurrence of diseases and disorder. The second study was conducted to investigate the effects of post-harvest red and blue LED light treatments on two cultivars of cherry tomatoes, red (‘Cherry Little Wonders’) and yellow (‘Goldilocks’) which received light at different stages of development, while on the plant as well as postharvest. The response of tomato cultivars that received post-harvest light treatment did not differ significantly with the cultivar that was treated and allowed to ripen on the tree. Light treatments were able to enhance colour development more on cherry tomato fruits treated at mature green compared to those treated at turning stage. The effect of light on chlorophyll a and b on fruits varied according to the cultivars. Fruit that were treated at turning stage had lower chlorophylls initially and then a steady rate of change was observed while a sharp/rapid degradation of chlorophylls was observed in fruits treated at mature green. Light effects on degradation of chlorophylls had no significant difference within the stage at which plants received the treatment. Lycopene was the major pigment in red cv of cherry tomatoes. It was influenced equally by red and blue lights, with fruit treated at mature green had more lycopene that those treated at turning stage. There was a significant difference between treatments and the control in terms of lycopene and β-carotene content which were higher in fruits treated at mature green. There was no significant difference (P < 0.05) in change in mass of fruit that received red and blue lights and non-treated fruits meaning that light did not have a negative effect on tomato fruits treated at mature green stage and at turning stage. Light treatments were able to prevent the occurrence of diseases on all the treatments.