Effects of Agricultural Practices On Total Phenolics and Quality Attributes of Eight Selected Specialty Leafy Greens

Association between human health and bioactive compounds of leafy greens has been the focus of several academic and industry studies in recent years. Phenolic compounds, the largest group of plant phytochemicals, are of great importance both in plant physiology and human nutrition. Plants use these compounds as defense mechanisms against insects, pathogens, and photo-oxidation. The effects of phenolic compounds on human health have been investigated by various retrospective and prospective studies. Variation in agricultural practices may result in considerable change in nutritive value and quality attributes of leafy greens. This study investigated the effects of greenhouse, high tunnel, and open field cultivation methodologies on total phenolics, dry matter, total soluble solids, texture, and color profile of eight specialty leafy green vegetables (amaranth, huazontel, pac choi, tai sai, arugula, mizuna, komatsuna, and red iceberg lettuce) grown in Colorado.   

Huazontel, red iceberg, amaranth, Komatsuna  and tai sai had significantly higher levels of total phenolics when grown in high tunnels or under open field conditions compared to greenhouse production.  There was no difference in total phenolic content between plants grown under high tunnels and under open field conditions (P>0.05). Similarly, huazontel, red iceberg lettuce, amaranth, komatsuna, arugula, and mizuna had lower total soluble solids and dry matter in greenhouse grown plants. No significant difference was observed among color and texture attributes in the majority of samples.

This study indicated that although visual properties of the selected taxa were not detectable, the three production methods did produce significant changes in metabolites of leafy greens that may contribute to changes that impact nutritive value and quality attributes. Leafy greens planted in a high tunnel environment, in most cases, showed equivalent values when compared to open field samples, while greenhouse samples were lower in total phenolic compounds, total soluble solids, and dry matter relative to open field samples. Results of this study may contribute to a better understanding of plant responses to variation in agricultural methodologies, and may enhance the competitiveness of Colorado-grown vegetables, improving the profitability of local vegetable production.

Keywords: Specialty leafy greens; agricultural practices; total phenolics; quality attributes