Extraction of gallic acid from the chestnut husk growing in Bartin with deep eutecthic solvents

In our country, which ranks 2nd in chestnut production in the world, chestnut fruit is evaluated in different ways, but its outer shell, called the pericarp (husks), is unfortunately considered as waste. In recent studies, it has been determined that this inert source contains phenolic compounds with biological activity. It has been reported that organic solvents used for the separation of said phenolic compounds from plant material are harmful to the environment and human health and their use will be restricted in 2050. From this point of view, it is aimed to obtain and increase the yield of gallic acid, one of the phenolic compounds found in the chestnut pericarp, with environmentally friendly, non-toxic deep eutectic solvents. Within the scope of the study, chestnut fruit pericarp samples collected from Bartın Amasra-Yahyayazıcılar locality were treated with control, boiling in water and roasting in an oven at 150-200°C. It was then extracted with MeOH: water and acetone: water (90:10 v/v) solvents. These 3 different samples are also 3 different types of Deep eutecthic solvents (DES) (choline chloride: formic acid, choline chloride: ethylene glycol and choline chloride: lactic acid), 3 different extraction times (10, 35, 60 min.), 3 different extraction temperatures (30 Optimum conditions with Box – Behnken experimental design modeling by applying different parameters such as (30, 50, 70°C), 3 different liquid: solid ratio (10, 20, 30 mL/g), 3 different water amounts (10, 20, 30 %) determined. Samples were analyzed by HPLC. In addition, the amounts of holocellulose, α-cellulose and lignin in the inner shells of chestnut fruit were determined. When all sample groups were examined, it was seen that MeOH: water gave the best result. Within the sample groups, the amount of gallic acid was found to be 5 times higher in the baked samples compared to the other samples. It was thought that hydrolyzable tannins such as gallic acid and ellagic acid in the boiled samples, which gave the lowest amount, may have disappeared by mixing with the water. According to the data obtained, the amount of holocellulose is 45.3 %; α-cellulose 29.2 %; Klason lignin 42.5 %; the amount of extractive substance was determined as 3.2 % in the MeOH: water mixture. The presence of gallic acid was determined by analyzing MeOH: water and acetone: water samples in GC-MS. The purpose of using mass spectrometry within the scope of the thesis was to detect the presence of gallic acid. During these analyses, ellagic acid, which we planned to see in the samples, could not be detected. Because of the viscosity and water content of the DES samples, the analyzes were carried out in HPLC with a gallic acid focus after this stage. At the end of the 243 analyzes performed, when the highest amount of gallic acid obtained when each DES solution was evaluated in itself, and the results of the experiment performed with organic solvents in the Soxhlet device, it was seen that DES solutions significantly increased the amount of gallic acid in all three sample types. When the 6-hour extraction with organic solvents in Soxhlet extraction and the extraction results in the ultrasound bath using all three DES solutions were compared, it was observed that the DES solutions, especially the choline chloride: ethylene glycol (1:2) mixture, increased the gallic acid ratio in the baked crust 3 times compared to the methanol: water sample. In the thesis study, the variables that maximize the gallic acid value were determined and the optimum gallic acid value was estimated by solving the model with Minitab. Experiment conditions that give the best results, extraction time: 35 minutes, extraction temperature: 60°C, amount of water: 18 ml, liquid: solid ratio: 10 ml DES and 1 g sample, material: baked and DES: choline chloride: ethylene glycol determined. Under these conditions, the amount of gallic acid was estimated as 116 ppm (Loarithmic value: 4.75). The desirability function (d) was found to be equal to 1, indicating a perfect agreement between the predicted and experimental values. However, when we make predictions using the same model with the conditions that give the best results in our experiments (Extraction time: 30 minutes – Extraction temperature: 60°C – Amount of water: 20 ml – liquid: solid ratio 1 g sample 10 ml solution – Baked sample – choline chloride: ethylene glycol DES solution) gallic acid value with 115.07 and 0.99 ppm desirability ratio gave almost the same result with actual measurements.