Study of phytochemicals and morphological characteristics of selected leafy greens

Abstract

With the gaining momentum for industrial level agriculture, a new pivotal need emerges, the need to produce highly nutritious vegetables with minimal land and water requirements. The effects of light quantity and quality on selected lettuce, kale, or Swiss chard cultivars as well as the determination of relevant nutrients using both ultraviolet–visible spectroscopy (UV-VIS) and high-performance liquid chromatography (HPLC) assays were studied. This dissertation explores the morphological, photosynthetic, and nutritional benefits of varying blue light wavelengths (λpeak= 400, 420, and 450 nm) while maintaining a constant light recipe combination in leafy greens. Overall, lettuce cultivars grown under treatment 3 (blue λpeak = 450 nm) exhibited the most optimal light response curves (LRCs), with red leaf lettuce also showing increased morphological characteristics and nutrient content. The effects of varying the incident PPFD (photosynthetic photon flux density) (150, 250, and 300 µmol·m⁻²·s⁻¹) while maintaining a constant light recipe (blue λpeak = 450 nm) were also studied. This resulted in all three lettuce cultivars having a more optimal LRC when grown in treatment 1 (PPFD = 150 µmol·m⁻²·s⁻¹). However, larger morphological measurements were found in treatment 2 (250 µmol·m⁻²·s⁻¹) for Red leaf and Finstar lettuce, and in treatment 3 (300 µmol·m⁻²·s⁻¹) for Oakleaf lettuce. In terms of nutritional content, significant changes in nutrient (lutein, neoxanthin, violaxanthin, chlorophyll a, chlorophyll b) concentrations were found when growing Red leaf lettuce under treatment 3 (300 µmol·m⁻²·s⁻¹). A novel method for the determination of vitamin C using an extraction solution of water adjusted to pH 2.4 and 2.85 with hydrochloric acid is also investigated. UV-VIS results validated with HPLC demonstrated pH 2.85 to be the most suitable for kale and lettuce extractions. Additionally, five equation systems established by literature using acetone as the extraction solvent were compared to determine the concentration of available chlorophyll a, chlorophyll b, their sum, and total carotenoids in kale. Significant differences for chlorophyll content measured with UV-VIS and HPLC were found. For chlorophyll b and total carotenoids, all equations were suitable and comparable.