peels Determination of the lignin content of apple peels was madeaccording to the method of Li et al. (2006). Apple peel dry pow-ders were extracted in 0.5 mL 25% bromoacetyl-acetic acid solution(25% acetyl bromide in glacial acetic acid, v/v). After 0.02 mL per-chloric acid was added, nozzle was sealed for 70◦C water bath for30 min. Then, the reaction mixture was shifted into volumetric flaskcompletely, which had been equipped with the mixture of 1 mL2 mol L−1NaOH and 2.5 mL of glacial acetic acid. Lignin content wasmeasured on a UV spectrophotometer at 260 nm, with glacial aceticacid as the blank. Lignin content was indicated with OD260