Polymethoxyflavones, Synephrine and Volatile Constitution of Peels of Citrus Fruit Grown in Okinawa

Quantification of Flavonoids, Phenols and Antioxidant Potential from Dropped Citrus reticulata Blanco Fruits Influenced by Drying Techniques

Physiologically dropped immature Citrus reticulata Blanco fruits are regarded as waste and discarded in the citrus orchard but are a good source of bioactive compounds including flavonoids, antioxidants and total phenols. A study was undertaken to identify and quantify these bioactive compounds and to investigate the influence of different drying techniques, namely freeze drying and hot air oven drying, on flavonoids namely flavanone glycosides, antioxidant potential and total phenol content in immature dropped fruits of Citrus reticulata Blanco. Flavonoids were quantified in high-performance liquid chromatography (HPLC). The antioxidant activity were investigated with three assays azino-bis [3-ethylbenzthiazoline-6-sulfonic acid]) (ABTS), 2,2-diphenyl-1-picrylhydrazyl radical (DPPH), Ferric Reducing Ability of Plasma (FRAP) and total phenol content was determined. Freeze dried samples of 12 and 14 mm size retained maximum hesperidin flavonoid content (27.03% and 27.20%) as compared to the hot air dried samples (17.99%) and retained higher phenolic content ranged from 50.54-54.19 mg GAEL^-1. The antioxidant activity in freeze dried fruits was from 12.21-13.55 mM L^-1 Trolox and 15.27-16.72 mM L^-1 Trolox with ABTS, DPPH assay and FRAP values ranging from 7.31-9.07 mM L^-1 Trolox. Significant positive correlation was found between the flavonoid hesperidin with antioxidant assays and total phenolic content (TPC). The results showed that waste citrus fruits can act as potential source of bioflavonoids, especially hesperidin, and antioxidants for pharmaceutical as well as nutraceutical industry.

Simultaneous determination of 14 bioactive citrus flavonoids using thin-layer chromatography combined with surface enhanced Raman spectroscopy

Citrus flavonoids consist of diverse analogs and possess various health-promoting effects dramatically depending on their chemical structures. Since different flavonoids usually co-exist in real samples, it's necessary to develop rapid and efficient methods for simultaneous determination of multiple flavonoids. Thin layer chromatography combined with surface enhanced Raman spectroscopy (TLC-SERS) was established to simultaneously separate and detect 14 citrus flavonoids for the first time. These target compounds could be characterized and discriminated when paired with SERS at 6-500 times greater the sensitivity than TLC alone. TLC-SERS exhibited high recovery rates (91.5-121.7%) with relative standard deviation lower than 20.8%. Moreover, the established TLC-SERS method was successfully used to simultaneously detect multiple flavonoids in real samples, which exhibited comparable accuracy to high performance liquid chromatography with shorter analytical time (10 vs 45 min). All the results demonstrated that this could be a promising method for simultaneous, rapid, sensitive and accurate detection of flavonoids.

Volatile Compounds in Citrus Essential Oils: A Comprehensive Review

The essential oil fraction obtained from the rind of Citrus spp. is rich in chemical compounds of interest for the food and perfume industries, and therefore has been extensively studied during the last decades. In this manuscript, we provide a comprehensive review of the volatile composition of this oil fraction and rind extracts for the 10 most studied Citrus species: C. sinensis (sweet orange), C. reticulata (mandarin), C. paradisi (grapefruit), C. grandis (pummelo), C. limon (lemon), C. medica (citron), C. aurantifolia (lime), C. aurantium (bitter orange), C. bergamia (bergamot orange), and C. junos (yuzu). Forty-nine volatile organic compounds have been reported in all 10 species, most of them terpenoid (90%), although about half of the volatile compounds identified in Citrus peel are non-terpenoid. Over 400 volatiles of different chemical nature have been exclusively described in only one of these species and some of them could be useful as species biomarkers. A hierarchical cluster analysis based on volatile composition arranges these Citrus species in three clusters which essentially mirrors those obtained with genetic information. The first cluster is comprised by C. reticulata, C. grandis, C. sinensis, C. paradisi and C. aurantium, and is mainly characterized by the presence of a larger abundance of non-terpenoid ester and aldehyde compounds than in the other species reviewed. The second cluster is comprised by C. junos, C. medica, C. aurantifolia, and C. bergamia, and is characterized by the prevalence of mono- and sesquiterpene hydrocarbons. Finally, C. limon shows a particular volatile profile with some sulfur monoterpenoids and non-terpenoid esters and aldehydes as part of its main differential peculiarities. A systematic description of the rind volatile composition in each of the species is provided together with a general comparison with those in leaves and blossoms. Additionally, the most widely used techniques for the extraction and analysis of volatile Citrus compounds are also described.

Immature Citrus reticulata Extract Promotes Browning of Beige Adipocytes in High-Fat Diet-Induced C57BL/6 Mice

Obesity has become a global public health issue. Promoting browning of white adipose tissue (WAT) helps to maintain energy homeostasis. Previous studies have found that citrus fruit exhibits a number of biological activities. Although most citrus fruit drop has been considered agricultural waste, the ability to use it may be desirable. In this study, we investigate the antiobesity effects of immature citrus fruits in high-fat diet (HFD)-fed mice. The main phytochemical components of immature Citrus reticulata in water extraction analyzed by HPLC are synephrine, narirutin, hesperidin, nobiletin, and tangeretin (16.0 ± 1.08, 4.52 ± 0.31, 9.14 ± 0.32, 2.54 ± 0.07, 1.67 ± 0.05 mg/g, respectively). Oral administration of 1% immature Citrus reticulata extract (ICRE) for 11 weeks markedly reduced body weight gain, epididymal fat weight, fasting blood glucose, serum triglyceride, and total cholesterol ( P < 0.05 for all). In addition, histological analysis revealed that dietary ICRE decreased adipocyte size and hepatic steatosis compared to the HFD group ( P < 0.05 for both). Furthermore, we found that mice treated with ICRE have improved cold tolerance during acute cold challenge. These effects were associated with increased expression of uncoupling protein 1 (UCP1) and thermogenic genes in inguinal WAT. Taken together, these results suggest that ICRE can prevent obesity and lipid accumulation through induction of brown-like adipocyte formation.

Extended aroma extract dilution analysis profile of Shiikuwasha ( Citrus depressa Hayata) pulp essential oil

Shiikuwasha pulp is an important raw material for producing citrus essential oils. The volatile aroma composition of pulp essential oil was evaluated using gas chromatography (GC) methods, and its aroma profile was assessed using GC-olfactometry with an extended aroma extract dilution analysis (AEDA) technique in regard to alterations of odor strength and sensorial perception throughout serial dilution steps. The essential oil comprised a mixture of 55 aroma compounds, including monoterpene hydrocarbon, sesquiterpene hydrocarbon, alcohol, aldehyde, ester, and oxide compounds. The predominant compounds were limonene [57.36% (4462.80 mg/100 g of pulp)] and γ-terpinene [25.14% (1956.21 mg/100 g of pulp)]. However, linalool was identified as one of the key aroma components providing the highest flavor dilution factor in AEDA, whilst three sesquiterpene hydrocarbons (δ-elemene, germacrene B, and bicyclosesquiphellandrene) and two esters (heptyl acetate and decyl acetate) had superior relative flavor activities. The extended AEDA profile identified variations in assessed odor perceptions, intensity, and duration of aroma components over dilution, whereas the 12 most odor-active compounds showed comparable odor strengths.

Infrared Drying as a Quick Preparation Method for Dried Tangerine Peel

To establish the most convenient and effective method to dry tangerine peels, different methods (sun drying, hot-air drying, freeze drying, vacuum drying, and medium- and short-wave infrared drying) were exploited. Our results indicated that medium- and short-wave infrared drying was the best method to preserve nutraceutical components; for example, vitamin C was raised to 6.77 mg/g (D.W.) from 3.39 mg/g (sun drying). Moreover, the drying time can be shortened above 96% compared with sun drying. Importantly, the efficiency of DPPH radical scavenging was enhanced from 26.66% to 55.92%. These findings would provide a reliable and time-saving methodology to produce high-quality dried tangerine peels.

Enhancement of Pentobarbital-induced Sleep by the Vaporized Essential Oil of Citrus keraji var. kabuchii and its Characteristic Component, γ-Terpinene

Kabuchii (Citrus keraji var. kabuchii hort. ex Tanaka, Rutaceae) is a peculiar Okinawan citrus fruit. Local farmers cultivating various Citrus fruits say that the fragrance of Kabuchii is the most relaxing, but, there are few reports on the biological effects of the essential oil of Kabuchii and its chemical components [1]. In this study, the sedative effects of inhalation of the vaporized Kabuchii essential oil in open field, Rotarod, and pentobarbital sleep tests are compared with diazepam, as a positive control. In the open field test, both Kabuchii essential oil and diazepam decreased the spontaneous motor activity dose-dependently. The reduction in spontaneous motor activity in the 0.3 mg/cage (ca. 0.0278 mg/L) Kabuchii essential oil group was greater than that in the 1 mg/kg diazepam group. In the Rotarod test, Kabuchii did not affect the motor performance, even at the highest dosage tested (3 mg/cage), whereas diazepam decreased it dose-dependently. The effects of the major or characteristic components of Kabuchii, d-limonene, γ-terpinene, thymol, and p-cymene, were also evaluated in the open field and Rotarod tests. γ-Terpinene and thymol significantly decreased spontaneous motor activity at a dosage of 0.3 mg/cage, without affecting motor performance. Thus, γ-terpinene was estimated to be the main active component. Reduction in spontaneous motor activity by γ-terpinene in the open field test was not observed in intranasal zinc sulfate irrigation-induced anosmic mice. In the pentobarbital sleep test, both Kabuchii essential oil and diazepam potentiated pentobarbital-induced loss of the righting reflex (LRR). The LRR duration prolonging effects of both treatments were inhibited by pretreatment with flumazenil, a benzodiazepine receptor antagonist. The LRR latency reducing effect of Kabuchii was not affected by flumazenil, while that of diazepam was suppressed by it. γ-Terpinene showed similar potentiating effects on pentobarbital-induced sleep. Thus, vaporized Kabuchii essential oil and its active component, γ-terpinene, have sedative effects comparable with diazepam without inducing motor incoordination, which is a well-known side effect of diazepam.

Phytochemical profile and antioxidant activity of physiological drop of citrus fruits

The phytochemical content and the antioxidant activity (AA) of physiological drop of the main citrus species grown in China were investigated. Among the flavonoids, hesperidin was found mostly in mandarin and sweet orange, naringin was found mostly in sour orange, pummelo, grapefruit and a hybrid (Gaocheng), narirutin was found in most varieties, neohesperidin was found in Gaocheng and Huyou, and nobiletin and tangeretin were found in most varieties. Hydroxycinnamic acids were the main phenolic acids present, ferulic acid and caffeic acid were the dominant in most cases. There was a greater amount of free (extractable) than bound (insoluble) phenolic acids. Levels of limonoids were higher in Foyou, Eureka lemon, and Gaocheng than those in the other cultivars. The highest level of synephrine was found in Ponkan and Weizhang Satsuma. AA was highest in Ponkan and Weizhang Satsuma and lowest in Huyou, pummel, and lemon. These results suggest that physiological drop of citrus fruits have good potential as sources of different bioactive compounds and antioxidants.

PRACTICAL APPLICATION

Physiological drop of citrus fruits may be a good resource of bioactive compounds including flavonoids, phenolic acids, limonoids, synephrine, and a good material of nutraceuticals.

Chemical markers of shiikuwasha juice adulterated with calamondin juice

Detection of shiikuwasha (Citrus depressa Hayata) juice adulterated with calamondin (Citrus madurensis Lour.) juice was investigated by the analyses of (1) phloretin dihydrochalcone glucoside, 3',5'-di-C-β-glucopyranosylphloretin (PD) detected by thin-layer chromatography and high-performance liquid chromatography (HPLC), (2) polymethoxylated flavones (PMFs), included nobiletin, tangeretin, and sinensetin, detected by HPLC, and (3) γ-terpinene peak percentage obtained by headspace solid-phase microextraction gas chromatography with cryofocusing. PD was detected in calamondin juice (25.5 mg/100 mL) but not in shiikuwasha juice. Shiikuwasha juice contained higher levels of nobiletin (48.8 mg/100 mL) than calamondin juice (2.4 mg/100 mL). Shiikuwasha juice was characterized by containing a higher percentage of γ-terpinene (12.3%) than calamondin juice (0.7%). A discrimination function obtained by a linear discriminant analysis with PMFs and a peak ratio of [nobiletin/tangeretin] and γ-terpinene detected the adulteration with accuracies of 91.7%. These three chemical markers were useful to detect shiikuwasha juice that is suspected of being adulterated with calamondin juice.

The composition of volatile aroma components, flavanones, and polymethoxylated flavones in Shiikuwasha (Citrus depressa Hayata) peels of different cultivation lines

Citrus peels are important sources of various pleasant aroma compounds and valuable bioactive substances. To investigate differences in the composition and content of Shiikuwasha (Citrus depressa Hayata) peels from different cultivation lines, the composition of volatile aroma components, flavanones, and polymethoxylated flavones (PMFs) in four Shiikuwasha cultivation lines was examined. The composition of volatile aroma components in cold-pressed extracts of Shiikuwasha peels was analyzed using gas chromatography-flame ionization detection and gas chromatography-mass spectrophotometry. The extracts contained mainly monoterpene hydrocarbons (93.40-97.25%), including limonene (46.52-68.26%) and γ-terpinene (21.48-30.52%). Differences in the composition of volatile aroma compounds in the Shiikuwasha cultivation lines were revealed using principal component analysis. Additionally, the composition of flavanones and PMFs was determined using high-performance liquid chromatography methods. Neohesperidin (96.58%) was the predominant flavanone in 'Izumi kugani' peel, while the other peels had high hesperidin contents (89.26-98.66%). Moreover, the PMFs of Shiikuwasha peels were composed of nobiletin (56.74-64.77%) and tangeretin (23.17-34.70%).