Development of a Multiple-Headspace SPME and GC-MS method for the determination of white sturgeon (Acipenser transmontanus) eggs and caviar volatile profile at different stages of ripening

In a scenario where the global market becomes more and more competitive and challenging, the sensory evaluation and the identification of key compounds responsible for the aroma of caviar are relevant issues for its organoleptic quality. In this study, a method for the determination of caviar volatile organic compounds (VOCs) using MHS-SPME coupled to GC–MS was developed, optimized and validated. The method showed the ability to identify and quantify VOCs in caviar in a relatively short time, without any sample preparation avoiding the formation of artefacts before the analysis. This method allowed a reliable estimation of the VOCs quantity solving the issue of the nonexhaustive extraction due to the SPME working principle. The protocol of MHE involves an exhaustive extraction of targeted analytes by a series of consecutive extractions performed on standard calibration mixtures. This step allowed the determination of the exponential decay of the chromatographic area for each analyte under consecutive extractions, which enabled the estimation of the cumulative chromatographic area for each analyte. Consequently, the chromatographic area of each compound obtained after a single extraction on real samples was used to estimate the total area, which was interpolated in a calibration curve obtained by a linear regression model built by injection of external standard solution. White sturgeon (A. transmontanus) eggs and caviar samples were provided by an Italian caviar company (Agroittica Lombarda SpA). Each set of samples was collected at different stages of production: raw eggs (t0, n=4), 60 days (t1, n=4) and 120 days (t2, n=4) of ripening, for a total of 12 samples. The caviar analysed was salted with 3.6-3.8% of NaCl and canned before the storage. Twenty-two key volatile compounds were detected in eggs and caviar samples, mainly represented by 6-, 8- and 9-carbon atoms aldehydes and alcohols (hexanal, octanal, nonanal, 1-octen-3-ol, 2-ethyl, 1-hexanol as most represented) and nonanoic acid, with some significant differences among t0, t1 and t2 samples. The total amount of detected aldehydes decreased from t0 (34.4ng/g) and t2 (27.9ng/g). On the contrary, we found a lower amount of alcohols in t0 (5.6ng/g) than in t2 (13.2ng/g) samples. Caviar collected in our work was constantly stored at -1°C in specific cans practically under vacuum, so it might be suggested that the restricted number of compounds detected by the analytical procedure was due to a partial inhibition of lipid oxidation processes that usually lead to the formation of VOCs. The identification and the quantitative analysis of compounds responsible for caviar flavour described in this research represents an innovation in the field, adding knowledge and providing novelty in deficiency of data available in literature to date, giving a substantial contribution in the characterization of such a precious product.