Physicochemical, Carotenoid, Metabolite, and Volatile Organic Compound Profiling of Okinawan Shiikuwasha (Citrus depressa Hayata) and Calamansi (C. microcarpa Bunge)

Shiikuwasha (Citrus depressa Hayata) and calamansi (C. microcarpa Bunge) are distinct citrus species with a strong sour taste that grow naturally in Okinawa, Japan. The present study aimed to characterize the physicochemical traits, total carotenoid content, and taste/nutrient-related metabolite and volatile organic compound (VOC) profiles of the mature fruits from three shiikuwasha cultivation lines (“Izumi kugani”, “Izumi kugani-like”, and “Ogimi kugani”) and calamansi. The shiikuwasha lines had higher ratios of soluble solids/titratable acidity but a lower total carotenoid content than calamansi. There were positive statistical correlations between total carotenoids with red, yellow, and orange indices (a*, b*, and a*/b* color spaces, respectively). Principal component analysis (PCA) revealed that shiikuwasha had higher sucrose and choline contents, while calamansi was richer in sourness-related metabolites such as citrate and malate. PCA plots displayed differences in the VOCs between the two citrus cultivars, wherein volatile accumulation was much richer in juices prepared from the whole fruits than in juices from the edible flesh parts. The plots also showed that monoterpenes and sesquiterpenes differentiated the VOC profiles of shiikuwasha and calamansi. This study reveals differences in the flavor components of the two citrus cultivars and highlights the potential uses of each in local and regional agro-business.