Role of selenium in stress mitigation and enhancing Conilon coffee quality: a study of selenium sources and rates

Abstract

Selenium (Se) plays a crucial role in antioxidant metabolism and reduces oxidative stress under abiotic stress conditions (e.g., extreme temperatures, drought, salinity, and heavy metals). Furthermore, agronomic biofortification has emerged as an effective strategy to enhance the nutritional quality of food and address hidden hunger related to Se deficiency. The first chapter of this thesis aimed to evaluate the effectiveness of different sources and rates of foliar-applied Se in mitigating stress and Conilon coffee production during the ENSO phenomenon by measuring the crop's nutritional, physiological, and productive parameters. The second chapter aimed to assess the biofortification of Conilon coffee beans by testing the foliar application of different Se sources and rates and assessing their effects on the physicochemical attributes of the beans, yield, and beverage quality. Two experiments were conducted simultaneously using a randomized block design with a 2×5 factorial arrangement and four replications. Sodium selenate (Na₂SeO₄ – Se(VI)) and Se-bisglycinate (Se-Bis) were foliar-applied at five Se rates (0, 10, 20, 40, and 60 mg L⁻¹) during the small green fruit stage. In the first study, foliar application of Se(VI) and Se-Bis significantly increased foliar Se contents without causing toxicity or altering macronutrient and micronutrient contents. Selenium supply increased foliar proline concentration and antioxidant enzyme activity [superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT)], reduced lipid peroxidation, and improved photosynthetic performance, promoting starch accumulation in the leaves. Selenium applied at 20 mg L⁻¹ resulted in yield gains of 21.60% and 13.77% compared with the control. Furthermore, the findings suggest that foliar application of Se stimulates the conversion of total free amino acids (AA) into total soluble proteins (TSP) in plants under stress conditions. In the second study, foliar Se application at 60 mg L⁻¹ enhanced coffee quality and increased Se concentration in green and roasted beans, contributing to 3.11%–4.52% (3–4 cups day⁻¹) of the recommended daily intake for adults. Selenium application up to 60 mg L⁻¹, usingSe(VI) and Se-Bis, effectively biofortified coffee without inducing visual toxicity symptoms.On the other hand, significant Se losses occurred during roasting (38.92%–48.00%) and brewing (98.54%–99.00%). These findings indicate that the foliar application of Se(VI) and Se-Bis at 20 mg L⁻¹ of Se during the small green fruit stage proved to be a practical approach for reducing oxidative stress, enhancing photosynthetic performance, and ensuring higher yield of Conilon coffee during the ENSO phenomenon. Furthermore, foliar Se application enhances coffee quality in both sensory and nutritional aspects, offering a promising strategy for increasing Se intake in the diet.