Evolution of potent odorants within the volatile metabolome of high-quality hazelnuts (Corylus avellana L.): evaluation by comprehensive two-dimensional gas chromatography coupled with mass spectrometry

Abstract

Within the pattern of volatiles released by food products (volatilome), potent odorants are bio-active compounds that trigger aroma perception by activating a complex array of odor receptors (ORs) in the regio olfactoria. Their informative role is fundamental to select optimal post-harvest and storage conditions and preserve food sensory quality. This study addresses the volatile metabolome from high-quality hazelnuts (Corylus avellana L.) from the Ordu region (Turkey) and Tonda Romana from Italy, and investigates its evolution throughout the production chain (post-harvest, industrial storage, roasting) to find functional correlations between technological strategies and product quality. The volatile metabolome is analyzed by headspace solid-phase microextration combined with comprehensive two-dimensional gas chromatography and mass spectrometry. Dedicated pattern recognition, based on 2D data (targeted fingerprinting), is used to mine analytical outputs, while principal component analysis (PCA), Fisher ratio, hierarchical clustering, and analysis of variance are used to find decision makers among the most informative chemicals. Low-temperature drying (18-20 °C) has a decisive effect on quality; it correlates negatively with bacteria and mold metabolic activity, nut viability, and lipid oxidation products (2-methyl-1-propanol, 3-methyl-1-butanol, 2-ethyl-1-hexanol, 2-octanol, 1-octen-3-ol, hexanal, octanal and (E)-2-heptanal). Protective atmosphere storage (99% N-1% O) effectively limits lipid oxidation for 9-12 months after nut harvest. The combination of optimal drying and storage preserves the aroma potential; after roasting at different shelf-lives, key odorants responsible for malty and buttery (2- and 3-methylbutanal, 2,3-butanedione and 2,3-pentanedione), earthy (methylpyrazine, 2-ethyl-5-methyl pyrazine and 3-ethyl-2,5-dimethyl pyrazine) and caramel-like and musty notes (2,5-dimethyl-4-hydroxy-3(2H)-furanone - furaneol and acetyl pyrrole) show no significant variation. Graphical abstract Comprehensive two-dimensional gas chromatography (GC × GC) coupled with mass spectrometric detection captures hazelnut volatiles signatures while advanced fingerprinting approaches based on pattern recognition enable access to a higher level of information.

Combined Untargeted and Targeted Fingerprinting by Comprehensive Two-Dimensional Gas Chromatography to Track Compositional Changes on Hazelnut Primary Metabolome during Roasting

“…These data suggest that enzymatic (endogenous and exogenous enzymes) activation most probably occurred by inducing the release of amino acids and sugars from storage deposits and cell metabolism activation. Evidence of kernel viability was confirmed in a previous study aimed at comprehensively mapping hazelnuts volatilome along 12 months of shelflife [55].…”

“…Concerning the impact of drying conditions (E1 and E2), it was not possible to isolate, at this stage (i.e., at time 0 on fresh hazelnuts), a clear impact of drying although it is known to be decisive for long-term storage. In this case, and up to 18 months, low-temperature drying accompanied by low-temperature storage in an inert atmosphere, enables effective inactivation of enzymes and mold/bacteria development while reducing autoxidation of fats [55].…”

Volatile Profile of Nuts, Key Odorants and Analytical Methods for Quantification

“…As alcohols, linalool is representative of flowery odor and ketones such as 2-hepten-4-one and 5-methyl-(Z)-hepten-4-one are responsible for nutty and fruity odors and 2,3- butanedione of buttery. Other important volatiles in hazelnuts are pyrazines such as 3,6-dimethyl-2-ethyl pyrazine (roasted and earthy) among other compounds [ 8 ].…”

“…Even though oxidative rancidity should be avoided due to off-flavor formation, a mild oxidation reaction is sometimes desirable for the development of characteristic nut volatile odors. Frequently, equilibrium among them is important to define the characteristic volatile profile of a nut [ 8 ]. Additionally, it is important to know if there are differences in key odorants among different types of nuts, but also how the processing methods affect the volatile profiles.…”

The Blossoming of Technology for the Analysis of Complex Aroma Bouquets—A Review on Flavour and Odorant Multidimensional and Comprehensive Gas Chromatography Applications

“…Cocoa and hazelnut odorants were assessed by Cordero and co-workers [34,35], using GC×GC and MDGC approaches. The techniques allowed the determination of the volatile fingerprints, identification of potent odorants and correlation of datasets to the product’s origin and/or processing chain.…”