Many citrus varieties are hybridized to improve their quality and to overcome the effects of climate change. However, there is limited information on the effect of the chemical profiles of hybrid varieties on their quality. In this study, we analyzed 10 citrus varieties and evaluated the correlation with their general characteristics and antioxidant activities. Chemical profiles, including the contents of sugars, organic acid compounds, flavonoids, limonoids, and carotenoids, which are related to taste, color, and health benefits, were significantly different depending on the citrus varieties, leading to different antioxidant capacities and general quality parameters. Based on these data, the correlations were investigated, and 10 citrus varieties were clustered into four groups—Changshou kumquat and Jeramon (cluster I); Setoka (cluster II-1); Natsumi, Satsuma mandarin, and Navel orange (cluster II-2); Kanpei, Tamnaneunbong, Saybyeolbong, and Shiranui (cluster II-3). Moreover, a metabolomic pathway was proposed. Although citrus peels were not analyzed and the sensory and functional qualities of the citrus varieties were not investigated in this study, our results are useful to better understand the relationship between citrus quality and metabolite profiles, which can provide basic information for the development and improvement of new citrus varieties.

Salt is one of the most important factors for fermented foods, but the effect of salt treatment time on the quality of fermented foods has rarely been studied. In this study, the effect of different salt treatment times (0, 48, and 96 h) after the start of fermentation on the quality of the soy sauce moromi extract (SSME) was investigated. As the salt treatment time was delayed, the population of Aspergillus oryzae, Lactobacillaceae, and Enterococcaecea in SSME increased, whereas the population of Staphylococcaceae and Bacillaceae decreased, leading to changes in the enzymatic activity and metabolite profiles. In particular, the contents of amino acids, peptides, volatile compounds, acidic compounds, sugars, and secondary metabolites were significantly affected by the salt treatment time, resulting in changes in the sensory quality and appearance of SSME. The correlation data showed that metabolites, bacterial population, and sensory parameters had strong positive or negative correlations with each other. Moreover, based on metabolomics analysis, the salt treatment-time-related SSME metabolomic pathway was proposed. Although further studies are needed to elucidate the salt treatment mechanism in fermented foods, our data can be useful to better understand the effect of salt treatment time on the quality of fermented foods.

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.