New solvents for extracting gallic acid from chestnut shells: deep eutectic solvents

Abstract Chestnut ( Castanea sativa Mill.) shell, a byproduct of chestnut processing, is a valuable source of phenolic compounds that have a range of industrial applications. This study investigated the optimization of gallic acid extraction from the outer shell of the chestnut using ultrasound‐assisted extraction (UAE) and deep eutectic solvents (DES). A Box–Behnken design (BBD) was employed to determine optimal extraction conditions, considering variables such as extraction time, temperature, water content, liquid‐to‐solid ratio, material treatment, and DES type. Results indicate that baked chestnut shell samples and choline chloride:ethylene glycol (1:2) DES yielded the highest gallic acid content, with optimal conditions of 70 °C, 35 min, 20% water content, and a 10:1 liquid‐to‐solid ratio. This study highlights the environmental and economic advantages of DES‐based UAE, supporting its use as a sustainable method for extracting bioactive compounds for application in the food, pharmaceutical, and cosmetic industries.