The effect of boiling method on phenolic compounds of some edible natural plants in Edremit bay (Balikesir) coastal region

In this thesis study, the edible parts of 10 plants (Asparagus acutifolius, Capsella bursa-pastoris, Erodium cicutarium, Malva sylvestris, Oenanthe pimpinelloides, Papaver rhoeas, Raphanus raphanistrum, Solanum americanum, Stellaria media and Urtica urens) consumed both raw and cooked by the indigenous people living in the coastal part of Edremit Bay were used fresh and boiled in water. In this context was investigated the effect of boiling process on the total amount of phenolic and flavonoid substances and antioxidant activities. Antioxidant activity determination methods (DPPH, ABTS, CUPRAC) were applied on the extracts obtained in ethanol. According to the results, the raw extract of the E. cicutarium showed the highest antioxidant activity compared to the other. It was determined as total phenolic substance 50.82 ± 0.58 µg GAE/mg, total flavonoid substance 154 ± 1.0 µg RE/mg, DPPH IC₅₀ = 0.23±0.004 mg/mL from antioxidant activity analysis, CUPRAC: 176.64±8.59 µgTE/mg, ABTS: 248.42 ± 4.95 µgTE/mg. It was statistically determined that the antioxidant activities increased or decreased after the boiling process applied to all extracts (p < 0,05). HPLC analysis was performed to determine whether they contain phenolic compounds such as gallic acid, catechin, chlorogenic acid, caffeic acid, epicatechin, p-coumaric acid, rosmarinic acid, rutin and cinnamic acid and the effect of boiling process on these phenolic compounds was revealed. It was observed that the amount of phenolic compounds contained in all extracts changed with the boiling process. The highest values of rutin (24310.1 µg/g) were determined in the raw extract of E. cicutarium, chlorogenic acid (32249.5 µg/g) in the boiled extract of Oenanthe pimpinelloides, and chlorogenic acid (51804.7 µg/g) in the raw extract of Urtica urens. Cinnamic acid was detected only in A. acutifolius and decreased from 17.47 µg/g in the raw extract to 5.66 µg/g after boiling. As a result, some of these plants exhibited higher antioxidant activity raw and some of them exhibited higher antioxidant activity after boiling and it was revealed that boiling method plays an important role in determining the plants that can be used as natural antioxidant source. KEYWORDS: Antioxidant, Raw and boiled extract, Edremit Bay, Phenolic, HPLC