Citrus reticulata Essential Oil as a Bioactive Food Ingredient: Composition Variability, Extraction, Functional Bioactivities, and Cross-Study Quantitative Analysis.

Citrus reticulata essential oil (CrEO) is a complex mixture of volatile and aroma-active phytochemicals mainly obtained from the peel oil glands of C. reticulata. Its chemical composition is dominated by monoterpene hydrocarbons, particularly limonene, together with other representative constituents such as gamma-terpinene, beta-myrcene, alpha-pinene, sabinene, terpinolene, oxygenated terpenoids, aldehydes, esters, alcohols, ketones, and minor aroma-active compounds. As a citrus-derived bioactive ingredient, CrEO has attracted increasing attention for its potential relevance to food preservation, functional product development, and the value-added utilization of citrus processing resources. This review comprehensively summarizes the chemical composition and volatile profile of CrEO and discusses the major factors responsible for compositional variability, including plant tissue, fruit maturity, cultivar identity, geographic origin, extraction method, processing conditions, and storage. In addition, a standardized, literature-derived secondary dataset is constructed to enable quantitative cross-study comparison, visualization, and multivariate analysis of CrEO composition despite differences in sample sources, extraction methods, analytical approaches, and reporting units. The effects of hydrodistillation, cold pressing, and emerging extraction approaches on essential oil yield, compositional stability, and functional quality are also discussed. Reported biological activities of CrEO, especially antioxidant, antimicrobial, antifungal, anti-inflammatory, and other food-relevant bioactivities, are critically reviewed in relation to their potential roles in food preservation, natural flavoring, functional food formulation, and bioactive ingredient development. Current evidence gaps are further identified, including the need for standardized compositional reporting, stronger activity validation in real food systems, improved safety and sensory assessment, and application-oriented studies. Overall, this review highlights the importance of integrating compositional characterization with standardized comparative analysis to support quality control, functional evaluation, and application-oriented development of CrEO.