Consuming rice as the staple, 0.95 million tons of rice bran is produced annually in Japan as a by-product from the rice milling process. Bran is used in several applications such as animal feed and fertilizer for mushroom cultivation, but most of it has been discarded as an agricultural waste although it contains various functional substances, such as γ-oryzanol, ferulic acid, sterol, wax, ceramide, phytin, inositol and protein. It could be considered a scarcely used but promising resource. As such, continuous efforts have been dedicated to exploring its effective utilization. In this context, functionalities of the substances contained in the bran are summarized, and our attempts for improving functionality, improving ease of use, and exploring new applications are presented.
Shiikuwasha (Citrus depressa Hayata) is produced in the northern area of the main Okinawa island, the southern most region of Japan, and is a typical Japanese citrus along with Tachibana (Citrus tachibana). The seed of Shiikuwasha contains high concentration of limonoid glucosides, including limonin glucoside and nomilin glucoside, which has anti-tumor activity. Synephrine, a well-known enhancer of lipid metabolism, is also present in the fruit peel. The most notable feature of Shiikuwasha, among citrus fruits harvested commercially in Japan, is its high concentration of polymethoxylflavones, such as nobiletin (NBL), tangeretin and sinensetin. These are present in the peel, where NBL is predominant. Many studies have demonstrated that NBL possesses various biological properties such as anti-carcinogenic, anti-inflammatory and hepatoprotective activities. The ingestion of Shiikuwasha paste decreases plasma glucose level in laboratory animals, such as mouse and rat, as well as human volunteers. Study of the metabolism, by animal and human liver microsomes and cytochrome P450 of NBL shows the presence of 4’-OH, 7-OH, 6-OH metabolites, as well as the novel metabolites 3’ and 4’-diOH NBL. These results indicate that Shiikuwasha is an attractive foodstuff from the perspective of health promotion. Furthermore, in order to maintain Shiikuwasha authenticity, methods distinguishing between Shiikuwasha and Calamondin were developed using a unique phloretin glucoside and certain polymethoxyflavones as chemical markers, as well as Shiikuwasha chloroplast DNA.
Shiikuwasha (Citrus depressa Hayata) is a well-known traditional citrus fruit from Okinawa, with over 200 cultivars and varieties reported. The harvest season of Shiikuwasha is extensive, from August to February, and Shiikuwasha has a unique usage pattern. Unripe fruit, harvested in August and September, is used for cooking, while partially ripe fruit, available from October to December, is used for machining (mainly for juice) . Ripe fruit with reduced acidity is available in January and February and is used unmodified. Polymethoxylated flavones (PMFs) are characteristic components of Shiikuwasha. Depending on harvest time and variety, alterations in juice quantities, citric acid concentrations, and PMFs were observed. Most applications of Shiikuwasha involve juice processing. Notably, the efficiency of Shiikuwasha juice production is only about 50%. Many useful components are contained in the peel, and remain in the residue. A comparison of extraction methods revealed that a multi-stage extraction recovered more useful components. According to marketing research, consumer demand exists for products of Shiikuwasha as a seasoning. Therefore, we are developing applications (especially as seasonings) for juice residue containing essential oils and PMFs.