Py-GC/MS and HPLC-DAD characterization of hazelnut shell and cuticle: Insights into possible re-evaluation of waste biomass

- Py(HMDS)-GC/MS was used to study shell and cuticle wastes from hazelnut.
- Shell pyrogram mainly showed lignocellulosic products.
- Cuticle pyrogram also showed phenolic products not attributable to lignocellulose.
- HPLC-DAD of cuticle extracts revealed catechin, epicatechin and procyanidins.
- 1,3,5-trihydroxybenzene is proposed as pyrolysis marker for polyphenols.

The chemical characterization of shell and cuticle from Tonda Gentile Romana hazelnut was carried out using analytical pyrolysis in the presence of hexamethyldisilazane followed by gas chromatography-mass spectrometry analysis (Py(HMDS)-GC/MS) and high-performance liquid chromatography with diode-array detection (HPLC-DAD). The aim was to acquire a comprehensive picture of the chemical composition of shell and cuticle, which are produced as wastes by hazelnut confectionery industry, in view of a suitable exploitation strategy. Such waste biomass could be a promising substrate to produce value-added chemicals and biofuels. The pyrogram of the shell fraction showed the typical pyrolysis products of a lignocellulosic matrix. The cuticle pyrogram showed intense peaks that were attributed to fatty acids. Holocellulose-to-lignin (H/L) content ratios were determined both by Py-GC/MS and by a traditional wet-chemistry method. While the H/L values obtained by the two methods were similar for the shell fraction, those of the cuticle fraction were very different. To further investigate this behaviour, HPLC-DAD analyses were carried out on ethanol extracts of the two fractions. High concentrations of catechin, epicatechin and procyanidins were found in the cuticle fraction. The presence of phenolic compounds was hypothesised to determine the overestimation of the H/L ratio in the Py-GC/MS technique. 1,3,5-trihydroxybenzene was found to be a plausible marker for the presence of polyphenolic extractives in lignocellulosic materials. Based on the results obtained from the different analysis methods, possible exploitation strategies are suggested for the two waste fractions. The high lignin and carbohydrate content of the shell fraction could be used to produce value-added chemicals, biofuels and biochars. The high extractives content of the cuticle fraction, on the other hand, makes it a possible starting material to produce pharmaceutical and nutraceutical products, as well as cosmetic emulsions.