Chapter 5b: Impact of light, cultivar, and postharvest on nutritional value of plants Julian Verdonk Horticulture and Product Physiology, WUR

Presentation structure 5.5 Light 5.6 Cultivar 5.7 Postharvest

5.5 – Light quality and quantity 5.5.1 - Intensity Light intensity and amount Increase in photosynthesis and carbohydrates Damage to PSII and photo inhibition. Excessive energy cannot be channelled Surplus of energy - adaptation and defence Elevating concentration of phytonutrients, i.e. carotenoids, tocopherols, vitamin C, anthocyanins Increase of ROS quenching Increase of leaf nitrate levels Effects on quality Increased levels of antioxidants and phenolics can lead to increased shelf life and other quality improvements

5.5 – Light quality and quantity 5.5.2 - Spectrum Four main photoreceptors Phytochromes Cryptochromes UV-A receptors UV-B receptors Changes in light spectra can initiate biochemical response Addition of colour = Reduction of other colour Addition can lead to increased light intensity Examine if change is due to addition, or to increased intensity Correct for light intensity: change in light ratio Responses are genotype dependent

5.5 – Light quality and quantity 5.5.2 - Spectrum Some examples, very circumstantial, literature is very divided Blue light -> more B carotene in leafy greens, broccoli Red light -> more lutein in leafy greens, broccoli Far Red -> reduced carotenoids in lettuce Changes in ratio blue:red can be used to manipulate phenolic content Green light -> reduces anthocyanin in Arabidopsis Blue light -> increases anthocyanin in lettuce Green and Blue light -> increase vitamin C, E, in lettuce Etc... Possible applications of light treatments to increase phytonutrients are currently in the experimental phase

5.6 Cultivar choice Genotype and plant mineral content Genotype and phytonutrient concentration Grafting

5.7 Postharvest Living plant products and quality Preharvest and postharvest quality

Quality of living plant products is determined by physiological processes and metabolic content Plant products are alive: Physiological processes Respiration Transpiration Development, i.e. ripening senescence Metabolic processes Pigment, aroma, flavour Phytonutrients

Quality at harvest is determined by genotype and preharvest Shelf life is dependent on postharvest conditions Physiological processes are determined by genotype and preharvest conditions Low temperatures in the chain slow down these processes Risk of Chilling injury in products with tropical origin: Tomato, Mango, Avocado, Banana

Quality at harvest is determined by genotype and preharvest Shelf life is dependent on postharvest conditions Atmospheric conditions can be used to reduce respiration. Low O2 high CO2 Controlled atmosphere (CA) Modified Atmospheric Packaging (MAP) Long storage option possible Apples: 6-12 months Bagged cut lettuce: 1 weeks

Quality at harvest is determined by genotype and preharvest Shelf life is dependent on postharvest conditions Light: chain is often dark, practicality Light cannot reach full package Darkness can lead to yellowing of green tissues Most coloured fruit, no consequences Addition of light to postharvest chain has positive effect: longer shelf life (slide #3)

Quality at harvest is determined by genotype and preharvest Shelf life is dependent on postharvest conditions Deterioration: end of shelf life Determined by combination of: Physiological processes (same as slide #8) Mechanical damage Pathological deterioration Senescence: last developmental stage Product specific: Tomato -> softening Lettuce -> Browning Banana -> brown/black discoloration

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