Beyond Phytosterol Profiling in Greek Olive Oil: Biological Variability, Regulatory Interpretation and the Near-Threshold Sterolic Space

Phytosterols are key minor constituents of olive oil, contributing not only to its nutritional and bioactive properties but also to authenticity assessment, quality control, and regulatory classification. In Greek olive oils, particularly extra virgin olive oils from the dominant Koroneiki cultivar, sterolic composition is a critical yet complex marker, as total-sterol content and specific sterol fractions may naturally approach regulatory thresholds without indicating adulteration or quality loss. This review critically synthesizes current knowledge on phytosterol profiling in Greek olive oil, emphasizing sterolic composition, analytical methodology, stability, and the principal biological, geographical, technological, and methodological factors governing sterolic variability. Particular attention is given to the sterolic fingerprint of the Greek cultivars for which comparable data exist—principally Koroneiki, with Mastoides and Lianolia Kerkyras as comparators—dominated by β-sitosterol, Δ5-avenasterol, campesterol, stigmasterol, and Δ7-sterols, and to cultivar-dependent variation that may influence regulatory interpretation. The review further evaluates the official GC-FID analytical methodology, the complementary role of GC-MS and chemometric approaches, and the limitations of interpreting sterolic composition solely through fixed regulatory thresholds. It proposes a context-dependent framework for interpreting phytosterol composition in authentic Greek olive oils and introduces the concept of the Near-Threshold Sterolic Space, describing the natural clustering of authentic oils close to regulatory decision limits as a consequence of cultivar- and terroir-driven biological variability. Overall, phytosterol interpretation should evolve from a purely threshold-based regulatory exercise toward a biologically informed, method-aware and cultivar-sensitive framework that better reflects the natural complexity of authentic Koroneiki, and the other Greek cultivars examined here.