Abstract
Culinary herbs such as parsley (Petroselinum crispum) and coriander (Coriandrum sativum) contain an abundance of bioactive polyphenol compounds with profound multi-targeted disease preventing actions. Given the current level of interest in bioactive research, the objective of many horticultural efforts is now focused on enhancing the health promoting potential of glasshouse crops like culinary herbs, all year round. Research has identified blue light (400-500 nm) as an effective driver of polyphenol accumulation in response to photo-oxidative stress. While this concept has proved promising in growth chamber experiments, more is still to be learned about the requirements for polyphenol accumulation without imparting negative returns on crop performance and yield. Additionally, few studies have applied this concept to real-world glasshouse sicarios which factor in the added impact of seasonal sunlight fluctuations. The primary aim of this thesis was to determine how short-term high-intensity light-emitting diode (LED) light supplementations consisting of different mixtures of red:blue light can enhance the health promoting potential of glasshouse grown parsley and coriander. The investigations conducted in this thesis clearly demonstrated that parsley and coriander would exhibit signs of photo-oxidative stress under a supplementary daily light integral (DLI) of 4.9 mol m-2 d-1 of 28.23% red and 68.82% blue light at 170 μmol m-2 s-1 for 8 hours during the natural photoperiod in the winter but not the spring. The oxidative stress induced by this same LED light supplementation in the winter did not impact markers of plant growth or photosynthesis over the 10-day treatment period but induced the most significant accumulation of total antioxidants and polyphenols with parsley seeing a 60% increase in apigenin. The use of INFOGEST in vitro digestion models and Caco-2 cell culture bioassays determined that this same LED light supplementation produced herbs that were significantly more potent to human cancer cells. Although LED light supplementation did not impact markers of oxidative stress or bioactivity in the spring, herbs grown in the spring had much higher polyphenol contents and were more potent than those grown in the winter. This study was the first of its kind to link the induction of low-dose photo-oxidative stress from blue rich LED light supplementations with changes to health outcomes in vitro and to compare these outcomes of light supplementation across contrasting seasons. Overall, the results of this thesis highlight the efficiency of LED technology at enhancing the health promoting potential of glasshouse grown culinary herbs, especially during the low sunlight conditions of winter.