Optimization of phenolic compound extraction from goji berry (Lycium barbarum L.) fruit using ohmic heating process

Goji berry (Lycium barbarum L.) is a health beneficial medicinal plant that has an important place in both traditional medicine and modern food industry. Especially in recent years, with the increasing demand for functional foods, the fruits of this plant are included in different food products in raw form or extracted. Therefore, in this thesis, it was aimed to extract goji berries using ohmic heating-assisted extraction (OHAE) method, which is one of the innovative extraction techniques, and to optimize the extraction parameters. In this context, firstly, the operating conditions to be applied ort he OHAE method were determined using the Response Surface Method-Box Behnken experimental design. During the study, ohmic heating chamber temperature (40, 50 and 60 °C), holding time in the ohmic heating chamber (20, 40 and 60 min) and electric field strength (15, 30 and 45 V/cm) were determined as independent variables, while total phenolic compound (TPC), total flavonoid compound (TFC) and antioxidant activity (DPPH) parameters were selected as dependent variables. As a result of the optimization by Response Surface Method, the optimum conditions were determined as 60 ºC for temperature, 60 min for holding time and 45 V/cm ort he electric field strength and the desirability value (d) of the model was found as 0.90. The highest experimental results for TPC, TFC and DPPH were found to be 23.83 mg GAE/g, 7.33 mg QE/g and 24.53 mg TE/g, respectively. The predicted values for TPC, TFC and DPPH obtained under optimum conditions were 23.83 mg GAE/g, 7.13 mg QE/g and 22.65 mg TE/g, respectively. In addition, in the second stage of the thesis study, polyphenolic profiles of all extracts obtained under different process conditions were determined by LC-MS/M, and the highest amount of rutin phenolic compound (208.717-292.843 mg/kg) was detected in the extracts. Considering all the data obtained, it can be said that the OHAE method has a remarkable potential for maximum extraction of bioactive substances from goji berry fruit. Therefore, it can be suggested that this method should be preferred for future studies, especially in the extraction of goji berry fruit, and the potential of using the OHAE method in the extraction processes of different medicinal plants should be evaluated in detail.