Hazelnut (Corylus avellana L.) shells as a potential source of dietary fibre: impact of hydrothermal treatment temperature on fibre structure and degradation compounds.

BACKGROUND: Hemicellulose extraction from lignocellulosic biomasses has gained interest over the years, and hydrothermal treatment is one of the most common methods employed for this purpose. This work aimed to deeply study hazelnut (Corylus avellana L.) shells as a new source of dietary fibre, evaluating the effect of hydrothermal treatment temperatures on the type and structure of fibre extracted, but also on the formation of side-products derived from lignocellulose degradation. RESULTS: Different process temperatures led to diverse polysaccharides in the hydrothermal extract. Pectin was identified for the first time in hazelnut shells when experimenting with extraction at 125 °C, whereas at 150 °C a heterogeneous mixture of pectin, xylan, and xylo-oligosaccharides was present. The highest yield in terms of total fibre was gained at 150 and 175 °C, and then decreased again at 200 °C. Finally, more than 500 compounds from different chemical classes were putatively identified and they appeared to be present in the extracted fibre with a different distribution and relative amount, depending on the heat treatment severity. A generally high content of phenols, phenyls, oligosaccharides, dehydro-sugars, and furans was observed. CONCLUSIONS: Modulation of the hydrothermal treatment temperature allows fibre extracts with very different compositions, and therefore different potential end uses, to be obtained from hazelnut shells. A sequential temperature-based fractionation approach, as a function of the severity of the extraction parameters, can also be considered. Nevertheless, the study of the side-compounds formed from lignocellulosic matrix degradation, as a function of the applied temperature, needs to be fully addressed for a safe introduction of the fibre extract within the food chain. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

5-n-Alkylresorcinol Profiles in Different Cultivars of Einkorn, Emmer, Spelt, Common Wheat, and Tritordeum.

5-n-Alkylresorcinols (AR) are bioactive compounds found in the edible parts of many cereals. Here, saturated and unsaturated homologues, including the oxidized forms 5-(2'-oxo) AR and their plant metabolites, were profiled by ultrahigh-performance liquid chromatography-ion mobility separation-high-resolution mass spectrometry in 18 cultivars of einkorn, emmer, spelt, common wheat, and tritordeum, cultivated in two consecutive years under uniform agronomic conditions. The average content of AR ranged between 672.5 ± 129.8 and 1408.9 ± 528.0 mg/kg, exceeding 2380 mg/kg in some samples and highlighting a superior content in tritordeum and in modern cultivars with respect to old wheat genotypes. By evaluating the effect of environmental and agronomic factors on the different variables, the harvest year resulted to be always significant, while location and variety influenced AR abundance only for some homologues. Furthermore, the spatial distribution of AR was investigated by mass spectrometry imaging using transversal cross sections of wheat kernels. Our results show that AR homologues are mainly localized in the testa and in the outer pericarp of wheat kernels.