Vinegar extraction from unripe shikuwasa (Citrus depressa L.), an Okinawan citrus fruit

Introduction. Nakamoto Seedless, a variety of shikuwasa (Citrus depressa L.) in Okinawa, can be used to produce vinegar extracts because it has no seeds causing bitter taste. However, Nakamono Seedless is hardly cultivated commercially in Okinawa. This research was aimed to develop vinegar extract from Ogimi Kugani, another major variety of shikuwasa, and compare its characteristics with those of extracts from Nakamoto Seedless. Study objects and methods. The study featured vinegar extracts from the whole shikuwasa of Nakamoto Seedless (20% fruit) and Ogimi Kunagi (5, 10, and 20% of fruit) varieties. The fruit was harvested in June, July, and August. We tested the samples for limonin and polymethoxyflavones content and sensory attributes, especially bitterness. Results and discussion. Vinegar extracts with 20% of Ogimi Kugani harvested in June and July tasted bitter compared to those from Nakamoto Seedless harvested in August, but extracts from Ogimi Kugani harvested in August were not bitter. In addition, 5 and 10% vinegar extracts from Ogimi Kugani harvested in June had lower bitterness. The vinegar extracts from both shikuwasa varieties contained polymethoxyflavones ‒ bioactive compounds ‒ and similar flavor. Conclusion. The whole shiluwasa fruit can be used to produce vinegar drinks, Ponzu soy sauce, salad dressings, etc.

Extraction of Nobiletin and Tangeretin From Peels of Shekwasha and Ponkan Using [C2mim][(MeO)(H)PO2] and Centrifugation

The polymethoxyflavonoids nobiletin and tangeretin are isolated from peels of shekwasha ( Citrus depressa Hayata) and ponkan ( Citrus reticulata Blanco). These natural products possess biological activities, including anticancer and anti-inflammation properties. This report describes an efficient method for the extraction and isolation of nobiletin and tangeretin from citrus peels using 1-ethyl-3-methylimidazolium methylphosphonate ([C2mim][(MeO)(H)PO2]) and centrifugation/decantation. The results showed that the extraction yield of nobiletin and tangeretin using [C2mim][(MeO)(H)PO2]/organic solvent (1:1 w/w) was 1.4 to 1.6 times higher than that using organic solvent. This extraction method is expected to be applicable for obtaining other organic compounds from natural sources.