Extraction, identification, and quantification of antioxidant phenolics from hazelnut (Corylus avellana L.) shells

- A total of six factors were optimized for extracting phenolics from hazelnut shells.
- A third order polynomial model with transformed time was used for the optimization.
- Twice as much of total phenolics were extracted as reported in previous studies.
- A few phenolic compounds were identified from hazelnut shells for the first time.
- Two phenolic acids were quantified as abundant phenolics for the first time.

Hazelnut shells are the major byproduct of the hazelnut industry. The objectives of this study were to optimize the conditions for extracting phenolics and to identify and quantify the phenolics in hazelnut shells. Preliminary optimization showed that a high recovery of phenolics could be achieved with shell particle size less than 0.5 mm when extracted with acetone at 50 °C. Response surface experiments showed that a 10 g/l liquid to solid ratio, 58% acetone, and 12 h extraction time yielded the highest amount of phenolics. Twenty-seven phenolic compounds were identified in hazelnut shells by mass spectrometry. Coumaroylquinic acid, epicatechin gallate, quercetin, and six other phenolics were identified in hazelnut shells for the first time. The most abundant phenolics in hazelnut shells were catechin, epicatechin gallate, and gallic acid, as quantified by high performance liquid chromatography (HPLC). These results can be useful for the development of industrial extraction processes of natural antioxidants from hazelnut shells.