The Quality Parameters of Hazelnuts: A Literature Review on Physical and Nutritional Properties

Hazelnuts rank among the most widely cultivated tree nuts globally and are valued for their distinctive sensory profile and extensive applications across the food industry. This literature review synthesises current knowledge on hazelnut quality, encompassing varietal differences in physical characteristics and nutritional composition, and identifies significant knowledge gaps in aspects such as dietary fibre content and protein digestibility. We reveal substantial variations in kernel weight, colour, texture, proximate composition, amino acid profile and fatty acid profile exist among hazelnut varieties. Additionally, processing methods are found to have important effects on quality attributes. This information is important for recognising the variability in quality parameters among varieties and for the selection of optimal hazelnut varieties and processing methods tailored to specific end-uses. By-products from components such as shell, skin and oil cake are increasingly recognised as valuable sources of nutritional, nutraceutical and pharmaceutical products with significant economic potential. However, methodological inconsistencies in the analysis of hazelnut quality across different research groups hamper development of by-products and traditional primary products. This review identifies key methodological variations, and advocates for standardised protocols to support the development of international quality benchmarks for hazelnuts.