Green biotechnology for the valorization of sunflower ray florets as source of phenolic compounds with antioxidant properties

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In recent years, management of waste from sunflower (Helianthus annuus L.) plant processing (ray and disk florets, pollen, stem, leaves) is important for the environment protection. The valorization of agricultural waste and isolation of the bioactive compounds using ultrasound- and/or microwave-assisted extraction techniques present great interest, being green biotechnologies with several advantages for solving the environmental issues, over the traditional used methods. The aim of the present study was to optimize a lab biotechnology for a high extraction yield of phenolic compounds with antioxidant activity from sunflower ray florets, in view of their valorization as nutraceutical ingredients. The biological material was represented by sunflower ray florets harvested from Bacioi fields, Republic of Moldova, dried and ground to a powder. The powder was subjected to ultrasound-assisted extraction in ethanol, in a sonication bath at low frequency and high intensity, to enhance disruption of cellulosic walls and cell membranes in a short time, with low energy consumption. After filtration, the extracts were analyzed for total phenolic content by Folin-Ciocalteu method, to calculate the extraction yield, and their antioxidant activity by TEAC assay. The experimental design based on Design Expert software and response surface methodology was carried out on 20 extract variants obtained by varying the extraction parameters (independent variables): time, temperature, extraction ratio and ethanol concentration. The statistical analysis was conducted on the response variables: extraction yield and antioxidant activity.Based on the experimental data, the results’ representation as box plots, contour plots and 3D graphs for the variable parameters and their interactions led to the following observations: (i) the extraction yield significantly increased at higher ethanol concentrations and temperature; (ii) a high antioxidant activity was favored by lower extraction ratio and temperature, and their cumulative effect. Then, the parameters of ultrasound-assisted extraction were optimized to obtain cumulated high yield of phenolic compounds and strong antioxidant activity. The solution indicated the use of minimum temperature, in concentrated solutions and an average solvent concentration. HPLC analysis of the optimized sunflower extract showed high quantities of caffeic acid and quercetin, known as good antioxidant agents. In conclusion, the optimized green biotechnology applied to sunflower ray florets presented a high potential to be transferred to the economy. The obtained phenolics could be further used as valuable ingredients for the formulation of novel nutraceuticals

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