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Yellowball (Citrus hybrid cv. Yellowball ) is a new citrus hybrid between Haruka (C. tamurana × natsudaidai ) and Kiyomi (C. unshiu × sinensis) and is known to possess strong antioxidant activity. However, detailed information on the antioxidant components of its peel has not yet been reported. This study evaluated the antioxidant activity of the peel and identified the antioxidant components by fractionating a methanolic extract of Yellowball peels using liquid-liquid extraction with n-hexane, ethyl ether (ether), ethyl acetate (EA), butanol, and water. The phenolic contents and antioxidant activities of the n-hexane, ether, and EA fractions were higher than those of the other fractions, and these fractions were further separated by semi-preparative high-performance liquid chromatography (HPLC). Four antioxidant peaks, EA1, EA2, EA3, and He1, were isolated and analyzed using ultra-performance liquid chromatography–quadrupole-time- of-flight mass spectrometry (UPLC-Q-TOF MS). Sinapoyl glucoside and hesperidin were identified in EA2 and EA3, respectively, and a polymethoxylated flavone (PMF) complex (5-hydroxy-3,6,7,8,3’,4’-hexamethoxyflavone, natsudaidain, tetrameth- oxyflavone, and tangeretin) was identified in He1. A compound in EA1 with m/z 223.0246 [M-H] could not be identified and was named unknown2. The antioxidant activity of unknown2 (IC50=69.17 μg/mL) was similar to that of Trolox, which was noted as a major antioxidant in Yellowball peel. Further studies on the antioxidant capacity of Yellowball peel are required; however, these results provide a foundation for using Yellowball peel as an antioxidant.

Background Citrus ‘Minihyang’ is a novel citrus cultivar created through the hybridization of Citrus kinokuni and Citrus poonensis. This domestic cultivar has a small fruit size and high sugar content, making it highly valuable in the niche market both for ornamental and commercial purposes. Additionally, as a genetic resource, ‘Minihyang’ is highly valuable. However, the lack of a tissue culture system for ‘Minihyang’ could potentially constrain the utilization of bioengineering techniques for its cultivation. Therefore, in this study, we aimed to develop a regeneration system for ‘Minihyang’ using cultured cells of unfertilized and undeveloped seeds in mature fruits.Results Somatic embryogenic cells were obtained on somatic embryogenesis induction modified Murashige and Tucker (SIME) medium, and the propagated cells were obtained through subculture at 4-week intervals in a modified Murashige and Skoog (EMS) medium. Rather than normal cotyledon-stage embryos, abnormal globular embryos were observed after 4 weeks of culture in an EMS medium containing 70 g·L− 1 lactose and 16 g·L− 1 agar. Through the regeneration of plants from these abnormal globular embryos, somatic embryos with developing shoots and roots were obtained within 3 weeks of culture in an EMS medium containing 0.05 M sorbitol and 0.05 M galactose as carbohydrate sources, 0.5 mg·L− 1 GA3, and 2 g·L− 1 gelrite. These embryos were transferred to and cultured in a basic MS medium enriched with 500 mg·L− 1 malt extract, 50 g·L− 1 sucrose, and 8 g·L− 1 agar to produce normal plants.Conclusions ‘Minihyang’ can serve as a promising genetic resource for developing bioactive cultivars using biotechnological techniques and can be used to breed cultivars that can be consumed whole.

This study aimed to genetically verify whether Citrus aurantium L. (sour orange) plants grown using anther culture were obtained from somatic embryos or haploids. The ploidy of the individuals was assessed using ploidy measuring instruments and simple sequence repeat (SSR) molecular markers. The anthers of sour oranges were cultured onto a medium supplemented with 0.44 mg/L thidiazuron (TDZ), 0.8 mg/L 6-benzylaminopurine (BA), 0.43 mg/L Zeatin, 0.44 mg/L Kinetin, 0.2 mg/L a-naphthalene acetic acid (NAA), 0.2 mg/L 2,4-dichlorophenoxyacetic acid (2,4-D), and 500 mg/L malt extract. Somatic embryos and callus were obtained using dentin in N6 medium supplemented with malt extract (500 mg/L) and N6 liquid medium supplemented with spermidine (200 µM), and gibberellic acid (GA3, 1 mg/L) was added to the anther surface. Regenerated plants were obtained from Murashige and Skoog medium supplemented with 0.5 mg/L TDZ, 1.0 mg/L GA3 (or single use 0.5 mg/L) and 500 mg/L malt extract. For the genetic verification of the obtained plants, haploid-derived plants were investigated by polymerase chain reaction using two SSR markers. In addition, verification with a ploidy meter confirmed that approximately 80–90% of the regenerated plants were triploids, and two plants among the investigated plants were haploids. This study was the first to report these results among haploid and triploid studies obtained from an anther culture of sour oranges. The study findings suggested that the anther culture technique can produce seedless triploid cultivars of domestic citrus varieties.