Olive oil from the 79 A.D. Vesuvius eruption stored at the Naples National Archaeological Museum (Italy)

Pompeii and Herculaneum, buried by the 79 A.D. Vesuvius eruption, offer a unique glimpse into Roman life. Excavations, beginning in 1738, yielded numerous artifacts, including "edible items" now housed at the Naples National Archaeological Museum (MANN). These include charred seeds, fruits, bread, kitchen tools, and glass bottles—many believed to contain solidified olive oil. However, the authenticity and identity of these organic materials needed validation, as a previous radiocarbon dating of grape pomace from MANN revealed a modern origin. This study focuses on Mann-S1, a sample from an almost-full glass bottle, to determine if it is indeed olive oil from 79 A.D. and to analyze its molecular evolution over nearly 2000 years. Olive oil was a crucial part of Roman life, used extensively for food, lighting, cosmetics, and medicine. The Campania Felix region was known for high-quality olive oil production, though imports also existed. Previous analyses of organic residues in archaeological glass bottles used spectroscopic and chromatographic methods, but results were inconclusive. This work aims to definitively identify Mann-S1 using radiocarbon dating and the detection of analytical biomarkers, offering a rare opportunity to study the long-term chemical transformation of an ancient food.

Existing research on archaeological lipids often struggles to definitively determine the origin (plant or animal) and age due to significant chemical changes over time. The varying oxidation rates of fatty acids, depending on their degree of unsaturation, complicate analysis. Gas chromatography/mass spectrometry (GC/MS) of fatty acids and nuclear magnetic resonance (NMR) alone are insufficient for unambiguous identification. Studies have been hindered by the assumption of exceptional lipid time stability, ignoring the dramatic effects of the initial thermal shock and long-term storage. Previous attempts at characterizing the organic content of Vesuvius excavation bottles, such as Covelli's work in 1826, relied on sensory traits and lacked sophisticated analytical techniques. More recent spectroscopic and chromatographic analyses yielded inconclusive results, highlighting the challenges in authenticating and characterizing such ancient organic matter. While some studies have employed GC/MS and NMR to analyze prehistoric lipids, the profound chemical modifications occurring over millennia make precise identification difficult. The authors highlight the limitations of prior approaches that overlooked the extensive chemical alterations triggered by both the eruption's extreme heat and the prolonged storage period.

The study employed a multi-faceted analytical approach to characterize Mann-S1, the olive oil sample. Techniques included: Ultrahigh performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) to identify intact lipid components and their fragments; Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF/MS) to analyze fatty acids and their derivatives; NMR spectroscopy (¹H and ¹³C) to characterize the lipid nature of the sample; High-resolution gas chromatography (HR-GC) of fatty acid methyl esters (FAMEs) to determine fatty acid composition; determination of free fatty acids and peroxide value; Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy to identify functional groups; GC analysis of sterols; Solid phase microextraction (SPME)-GC/MS of volatile compounds; and radiocarbon dating to determine the age of the sample. Each method was rigorously applied, and detailed descriptions of the procedures and parameters are provided in the methods section of the original paper. The samples were prepared and analyzed under controlled conditions to minimize contamination and ensure data accuracy. Specific information on the preparation of the sample for each analysis is also provided in the methods section, emphasizing the rigorous process adopted to preserve the sample’s integrity and ensure accurate results.

UHPLC-ESI-MS analysis revealed a predominance of fatty acids, particularly palmitic and hydroxystearic acids, and surprisingly, estolides – oligomeric fatty acid esters of hydroxyl fatty acids. The absence of triacylglycerols indicated complete hydrolysis. MALDI-TOF MS confirmed these findings, showing high levels of hydroxystearic and hydroxyoleic acids, and also identifying estolides. ¹H and ¹³C NMR spectra also supported the absence of triacylglycerols and the presence of estolides, with characteristic signals for hydroxylated carbons and ester carbonyl carbons. The high free acidity (68.87%) confirmed extensive hydrolysis. No peroxides were detected, suggesting the sample was in the final stages of oxidation. HR-GC analysis of FAMEs showed a dominance of palmitic and stearic acids, with minimal oleic acid and its trans-isomer, elaidic acid, and no linoleic or linolenic acids. The low level of unsaturated fatty acids confirms their susceptibility to oxidation over such a long period. ATR-FTIR spectroscopy showed a similarity to EVOO but also revealed the presence of hydroxyl groups and a shift in the carbonyl absorption frequency consistent with free fatty acids and estolides. Radiocarbon dating placed the sample's origin with high confidence at the time of the 79 A.D. Vesuvius eruption.

The findings strongly support the authentication of Mann-S1 as ancient olive oil. The complete hydrolysis of triacylglycerols and the formation of estolides are consistent with the long storage time and the extreme thermal shock during the Vesuvius eruption. The presence of elaidic acid, the trans-isomer of oleic acid, further supports the impact of the high temperatures experienced during the eruption. The absence of more unsaturated fatty acids is expected given their greater susceptibility to oxidation. The unique composition, including the estolides, provides a valuable insight into the long-term chemical transformations of olive oil under extreme conditions. The data highlights the potential for studying ancient organic materials through this advanced chemical analysis for better understanding of past food production, preservation, and consumption practices. The high free acidity suggests that the oil underwent profound changes but retained a character consistent with olive oil. The preservation of the sample in its original glass bottle, relatively intact over millennia, provided unique conditions for the study.

This study definitively identifies Mann-S1 as a nearly 0.7 L sample of olive oil from the 79 A.D. Vesuvius eruption, likely the oldest known bulk sample of olive oil. The detailed chemical analysis reveals the profound changes the oil underwent over two millennia, including complete triacylglycerol hydrolysis and the unexpected formation of estolides. This research establishes a novel methodology for analyzing ancient lipid-based samples and opens new avenues for exploring ancient food history and preservation techniques. Future research could investigate the precise mechanisms involved in the formation of estolides under the conditions of the Vesuvius eruption.

The study is limited to a single sample. While radiocarbon dating and extensive chemical analysis provide strong evidence for the sample's origin and composition, analyzing additional samples from the same site could strengthen the conclusions. The possibility of microbial contamination during the long storage period, while considered, cannot be entirely ruled out. Further research using different analytical techniques may provide even more detailed information about the degradation process and potential sources of contamination.