Chemical and ATR-FTIR characterisation of olive oils from small-scale producers in San Lorenzo Maggiore, Southern Italy

Olive oil is more than a kitchen staple; it is a liquid record of a specific place, a season, and the care taken by the people who grow and press the fruit. Its quality depends on a chain of events that begins long before the bottle reaches the shelf: the health of the tree, the timing of the harvest, the speed of the milling, and how the oil is stored afterward. When olives are damaged or left too long before processing, their chemical makeup changes, often in ways that are invisible to the eye but detectable through careful measurement. Scientists use specific tests to check these changes, looking for signs of spoilage or oxidation that might affect the oil's taste, nutrition, and shelf life. For large industrial producers, these checks are routine, but for the many small, family-run farms scattered across the hills of Southern Italy, the scientific picture is often incomplete. These smaller operations preserve unique local varieties and traditional methods, yet their oils rarely appear in the broad scientific studies that define what "good" olive oil looks like.

In the hills of San Lorenzo Maggiore, a small municipality in the province of Benevento, a team of researchers set out to change that silence. They wanted to understand the true chemical character of the olive oil produced in this specific corner of Italy, not by selecting only the perfect samples, but by capturing the full reality of what the local farmers were making. The researchers worked directly with forty-five different small-scale producers, collecting their oils and running them through a series of standard chemical tests. They measured the free acidity, which indicates how much the oil's fats have broken down, and the peroxide value, which tracks the early stages of oxidation. They also used a technique called ATR-FTIR spectroscopy, a rapid method that shines infrared light through the oil to create a molecular fingerprint, revealing the overall structure of the fats without needing complex preparation. The goal was not to grade the oils for sale, but to build the first reliable baseline of data for this territory, showing both the strengths of the local production and the natural variations that occur in real-world farming.

The results painted a picture of a diverse and generally healthy local production, though one that was not without its imperfections. Out of the forty-five samples collected, forty-one fell within the acceptable limits for both free acidity and peroxide value, suggesting that the majority of the oil produced in San Lorenzo Maggiore is of good quality. However, four samples exceeded the limits for one of these two measures, with free acidity reaching as high as 1.01 percent and peroxide values climbing to 40.5. These outliers were not dismissed; instead, they were treated as important clues. They highlighted that in a landscape of small, independent farms, the quality of the oil can vary significantly from one producer to another, often depending on how quickly the fruit was processed after harvest or how it was stored. The study did not assign a formal commercial label like "extra virgin" to the collection, because that requires a sensory tasting panel which was outside the scope of this campaign, but the chemical data provided a clear snapshot of the territory's current state.

When the researchers looked at the data as a whole, they found that the oils did not fall into neat, separate groups based on who made them. Instead, the chemical profiles formed a continuous spread, with the samples that had higher acidity or oxidation levels sitting at the edges of the group. This pattern suggests that the variations are not due to a single cause, such as a specific type of olive tree, but rather to the many small differences in how each farm handles its crop. The spectral fingerprints taken by the infrared machine confirmed this, showing the classic chemical signals of olive oil across all samples, yet with subtle shifts in intensity that reflected the unique history of each bottle. The researchers also noticed that the time of day or the period when the samples were measured influenced the spectral readings, a reminder that even the way a sample is handled in the lab can leave a trace on the data.

One part of the study tested whether this rapid infrared scanning could replace the traditional, slower chemical tests for measuring acidity. The researchers tried to use the spectral patterns to predict the acidity levels, but the results showed that the method was not accurate enough for this purpose. The infrared light sees the bulk of the oil, which is made of stable fats, while the acidity comes from a tiny fraction of broken-down molecules that are harder to spot against that background. This finding is not a failure of the technology, but a clear boundary: the infrared scan is excellent for quickly checking the overall identity of the oil and spotting major differences, but it cannot yet replace the precise chemical titration needed to measure acidity.

Ultimately, this work provides a foundational map for the olive oil of San Lorenzo Maggiore. It proves that the local production is capable of high quality, while also documenting the natural variability that comes with small-scale farming. By capturing forty-five different oils from a network of family farms, the study offers a realistic starting point for future monitoring. It shows that while the region's oils are generally sound, there is room for improvement in how some producers manage their harvest and storage. The data serves as a reference for local farmers to understand their own production better and for scientists to track how the quality of this specific territory evolves over time, ensuring that the unique character of these Southern Italian oils is preserved and understood.