Adjusting photosynthetic photon flux density (PPFD) to improve the quality of leafy vegetables in vertical farms

Extending shelf life, improving quality, and reducing waste of leafy vegetables during transport and storage are key to tackling the global food challenge. Leafy vegetables – as the most popular crop grown in indoor vertical farms – are considered an important contributor to a healthy diet but generally have a short shelf life. In this chapter, we provide a comprehensive definition of quality and review studies on the effect of high photosynthetic photon flux density (PPFD) applied prior to harvest on phytochemicals in leafy vegetables. Increasing levels of phytochemicals (vitamin C, phenolics and carbohydrates) under high PPFD can directly improve health-related values at harvest, and more importantly, through their involvement in metabolic and redox homeostasis, ensure sufficient antioxidant capacity in leaves and suppress quality decay in storage. Increased PPFD during growth can be integrated with indoor vertical farming to improve quality and extend the shelf life of leafy vegetables.