Optimization of the Folin–Ciocalteu method for measuring phenolic antioxidants in the shoots of Crataegus pinnatifida Bunge

Objective. To optimize the Folin–Ciocalteu (FC) method for estimating phenolic antioxidants in the shoots of Crataegus pinnatifida Bunge using surface response methodology and the Box–Behnken design. Materials and methods. The shoots of Crataegus pinnatifida Bunge were harvested in 2025 at the beginning of flowering from a natural population in Khabarovsk Krai. The measurements were performed using a UV-1700 spectrophotometer (Shimadzu, Japan). The response surface tool and the Box–Behnken design were applied to identify the combination of phenolic compound extraction factor levels that would yield the optimal response. Statistical processing of the results was carried out in accordance with the State Pharmacopoeia of the Russian Federation, 15th edition, OFS.1.1.0013 “Statistical processing of the results of physical, physicochemical, and chemical tests” using the Microsoft Office Excel 2010 and Statistica 6.0 software packages. Results. For the shoots of Crataegus pinnatifida Bunge, the optimal parameters for the FC reaction have been determined as 0.5 ml of FC reagent and 5 ml of a 20% sodium carbonate solution, which ensure the accuracy, reproducibility, and stability of the reaction products. The response surface methodology and Box–Behnken design revealed that the highest yield of phenolic compounds occurs when the following extraction parameters are combined: extractant is 54.87% ethyl alcohol; raw material to extractant mass ratio is 1:783, and extraction time is 65.99 min. Conclusion. Extraction conditions are optimized; a method for quantitative spectrophotometric determination of phenolic compounds in the shoots of Crataegus pinnatifida Bunge is developed, which is necessary for standardization of this type of raw material.