Enhancement of zeaxanthin in two-steps by environmental stress induction in rocket and spinach

- A two-step process to enhance carotenoid and tocopherol content in crops is proposed.
- Rocket seems to be a more sensitive crop for manipulating its nutritional value.
- By combining pre-harvest and post-harvest approaches, Z content can be enhanced.

Humans are continuously exposed to oxidative damage risk and in order to counteract it, the consumption of antioxidants and carotenoids of plant origin is recommended. Numerous studies show the need to include substantial amounts of the carotenoid zeaxanthin (Z) in the diet, because its deficiency provokes the development of macular degeneration, which leads to irreversible loss of vision. However, Z is a less-abundant carotenoid in plants, because most of its pool is rapidly converted to the carotenoid violaxanthin (V) via antheraxanthin (A), due to its involvement in the operation of the xanthophyll (V + A + Z) cycle. The aim of this paper, therefore, was to develop a protocol to enhance the Z content in spinach and rocket through two strategies: firstly, by applying stress (chilling, high light and drought) in order to enhance the total pool of V + A + Z and, secondly, by applying post-harvest treatments before consumption in order to enhance Z formation. The results showed that high light was the most beneficial stress, increasing the fresh weight production in rocket and showing the highest accumulation of V + A + Z and carotenoids in both species. An enhancement of α-tocopherol in rocket was, as well, accomplished by the environmental stress induction. Besides, with the second strategy (post-harvest treatments before consumption, such as boiling and vinegar dressing), both species showed Z enhancement. By combining both approaches in two-steps, the Z content can be enhanced up to 15-fold in spinach and 28-fold in rocket, increasing, as a result, the nutritional value of food.