Author ORCID Identifier

Date of Award

Summer 7-31-2023

Degree Type


Degree Name

Master of Science (MS)



First Advisor

Rafaela G. Feresin

Second Advisor

Siming Wang


Due to poor soil practices, arable soil is estimated to significantly decrease over the next few years, and hydroponic farming is a sustainable alternative to traditional soil farming. Phytochemicals found in kale have antioxidant effects that can reduce the risk for chronic diseases. However, differences in nutritional quality of soil-grown and hydroponic kale, as well as phytochemical content and antioxidant capacity have not been previously evaluated. Thus, we aimed to compare the nutritional content, polyphenolic and glucosinolate content as well as the antioxidant capacity of hydroponic- versus soil-grown kale extracts. Hydroponic kale was grown in an indoor vertical hydroponic farm while soil-grown kale was purchased from a local grocery store. Macro- and micronutrient composition was analyzed by NP Laboratory Analytics. Kale was then dehydrated either with low-temperature oven-drying or freeze-drying prior to ethanolic extraction. Total polyphenol (TPC), flavonoid (TFC) and glucosinolate content (TGC) of kale extracts were determined using Folin-Ciocalteu, aluminum chloride, and palladium (II) chloride, respectively. Trolox equivalent antioxidant capacity (TEAC) and ferric reducing antioxidant power (FRAP) were used to measure antioxidant capacity, while 2,2-diphenyl-1-picrylhydrazyl (DPPH) and oxygen radical absorbance capacity (ORAC) measured radical scavenging capacity. The soil-grown kale contained higher carbohydrate, dietary fiber, iron, and vitamin C, whereas the hydroponic-grown kale contained higher sodium, calcium, and potassium. Irrespective of dehydration method, soil-grown kale had significantly more TPC and TFC than hydroponic-grown kale. However, oven-dried soil-grown (SO) and freeze-dried hydroponic-grown (HF) kale had significantly greater TGC compared to freeze-dried soil-grown (SF) and oven-dried hydroponic (HO) kale. Overall, soil-grown kale had significantly greater TEAC and FRAP compared with hydroponic-grown kale. Soil-grown kale also had significantly higher DPPH and ORAC compared with hydroponic-grown kale. In conclusion, soil-grown kale had a higher polyphenol concentration as well as antioxidant capacity compared to hydroponic kale. Future work should investigate methods to enhance phytochemical concentrations in hydroponic kale.


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