3.1. Samples

Four varieties of celery (Apium graveolens L.) were investigated: “Elne”, “Magnum”, Torricella Peligna Black, and Trevi Black. The first two types are common varieties of celery, easily available in (super)markets in Italy, while the latter two are niche types of black celery, mainly grown in specific areas of central Italy (Abruzzo and Umbria). Black celery from Trevi is protected by the Slow Food Presidia, whereas black celery from Torricella Peligna is in the process of being registered in the regional Abruzzo registry of plant biodiversity, conceived for in situ or ex situ conservation of varieties at extinction risk.

Several plants of these four types of celery have been grown in an experimental field located in Torricella Peligna (Abruzzo). The seeds were planted on the 12th of May 2021 and harvested on the 1st of December 2021. It has to be noted that the plants of the different types of celery involved in the study were all grown in experimental fields close to the territory of Majella National Park, consequently, under the same soil and climatic conditions.

Eventually, petioles (including leaves) were collected from both the outside and the inside of the stalks and stored in a freezer at −18 °C. Prior to the analysis, each single leaf sample was left to thaw, and dabbed with absorbent paper. The leaves that showed imperfections, spots, or breakage of various kinds were discarded. Before proceeding with the analysis, a visual investigation was also carried out to ensure that there was no soil or mud on the leaves. Eventually, samples were analyzed by ATR-FT-IR. For each type of celery, 80 leaves (from different plants) were analyzed. The analysis took place as described in Section 3.2.