Effect of Drying Temperatures and Exposure Times on Aspergillus flavus Growth and Aflatoxin Production on Artificially Inoculated Hazelnuts.

ABSTRACT: Aspergillus flavus may colonize hazelnuts and produce aflatoxins in the field and during storage. The main purpose of this study was to investigate the influence of drying temperature and exposure times on the viability of A. flavus and its ability to produce aflatoxins during the drying process and storage. Hazelnuts were inoculated with A. flavus and dried at different temperatures to reach 6% moisture content and a water activity (aw) of 0.71, a commercial requirement to avoid fungal development and aflatoxin contamination. Hazelnuts were dried at 30, 35, 40, 45, and 50°C and subsequently stored at 25°C for 14 days. After drying at 30, 35, and 40°C, increased amounts of A. flavus were evident, with the highest concentration occurring after drying at 35°C ([6.1 ± 2.4] × 106A. flavus CFU/g). At these temperatures, aflatoxins were detected only at 30 and 35°C. Aflatoxins, however, were present at higher levels after drying at 30°C, with concentrations of 1.93 ± 0.77 µg/g for aflatoxin B1 (AFB1) and 0.11 ± 0.04 µg/g for aflatoxin B2 (AFB2). After 14 days of storage, the highest A. flavus concentration and the highest levels of mycotoxins were detected in samples treated at 35°C ([8.2 ± 2.1] × 107A. flavus CFU/g and 9.30 ± 1.58 µg/g and 0.89 ± 0.08 µg/g for AFB1 and AFB2, respectively). In hazelnuts dried at 45 or 50°C, no aflatoxins were found either after drying or storage, and a reduction of A. flavus viable conidia was observed, suggesting that a shorter and warmer drying is essential to guarantee nut safety. The lowest temperature that guarantees the lack of aflatoxins should be selected to maintain the organoleptic quality of hazelnuts. Therefore, 45°C should be the recommended drying temperature to limit A. flavus growth and aflatoxin contamination on hazelnuts.

Formation of by-products during chemical interesterification of lipids. Detection and characterization of dialkyl ketones by non-aqueous reversed-phase liquid chromatography-high resolution mass spectrometry and gas chromatography-mass spectrometry.

A new class of foreign substances present in the unsaponifiable fraction of vegetable oils undergone to chemical interesterification was systematically investigated. Their chemical structure, corresponding to dialkyl ketones (DAK) molecules, was elucidated both by gas chromatography-mass spectrometry (GC-MS), and liquid chromatography-high resolution mass spectrometry (LC-HRMS). An analytical protocol aimed to qualitative and quantitative detection of DAK molecules in vegetable oils of confectionery industry interest was developed. Being the range of concentration levels to be evaluated dependent on the technological task of interesterification process, the quantitation step was thoroughly examined. All the validation parameters were satisfactory and particularly the concentration determinations were made more reliable by the contemporary use of several quantitation standards. GC-MS and LC-HRMS analytical techniques exhibited comparable performances even if the second one shown better detection sensitivity.

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.

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% N2-1% O2) 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.