Quality analysis of fruits bore from summer and spring blooms of Orah mandarin (Citrus reticulata Blanco) in Yunnan province

Abstract: 【Objective】China has energetically developed late-ripening citrus over the last decade. Late-ripening citrus also has a great impact on the market. Orah mandarin (Citrus reticulata Blanco) is a late-ripening citrus variety which has been widely planted in China in recent years, and it is extensively cul-tivated in Yunnan province, China. The climate of Yunnan province is characterized by longer day-length, high diurnal temperature variation, drought spring and rainy summer, under which Orah manda-rin is more easily to bloom and bear fruits in the Summer . Fruits derived from the spring blooms(spring fruits) usually mature in January to March of the following year, and fruits derived from the summer blooms (summer fruits) usually mature in June to July of the following year. In China, June to July is the off-season for fresh citrus in fruit market. Therefore, utilization of Orah mandarin summer fruits could not only reduce labor cost for removing summer flowers but also increase fruit incomes and benefit fruit market.【Methods】In this study, 5-7 years old Orah mandarin trees grafted on Ziyang sour orange [Citrus junos (Sieb.) Tanaka] rootstocks in Faping orchard of Jinghong city (FP), Wangsi or-chard of Menghai county (WS), Chuancheng orchard of Xinping county (CC) and Lizhi orchard of Xin-ping county (LZ) in Yunnan province were used as materials, and their summer fruits and spring fruits were investigated and measured in 2019—2021. Twelve external quality indicators, seven conventional  internal quality indicators and sugar as well as acid metabolites indicators were used to assess the fruit quality of the fruits. Single fruit weight, edible rate and juice rate were determined. Fruit shape index and peel thickness were measured by a vernier caliper. Peel firmness was measured by GY-4 fruit firm-ness meter. Peel smoothness and oil gland were evaluated according to NY/T 2435—2013 (China na-tional industry standard). The soluble solids (TSS) content was measured by the ATAGO PAL-1 digital sugar meter. Vitamine C (Vc) content was measured according to GB 5009.86—2016 (China national standard). Titratable acidity was (TA) measured according to GB/T 12293—1990 (China national stan-dard). The fruit color was measured by Konica Minolta CR-400, and the C, h, L, a* and b* were calculat-ed. Sugar metabolites were determined and analyzed by GC-MS. Microsoft Office Excel 2016 was used to organize and draw the data; SPSS IBM SPSS Statistics 23.0 was used for variance analysis and multi-ple comparisons, and the LSD was analyzed by univariate ANOVA to compare the significance level of the differences.【Results】Compared with the spring fruits, the summer fruits of Orah mandarin were more oblate, the single fruit weight was heavier, the peel was harder and thicker, and the peel surface was more coarse. The seed number, juice rate, edible rate, Vc content and solids acid ratio of the summer fruits had no regular change, but the edible rate was over 62% and the juice rate was over 46%. The summer fruits also had significant lower a* value and higher h value; The summer fruits had higher TSS and TA than those of the spring fruits. The analysis of sugar metabolites showed that the soluble sugars in Orah mandarin fruits mainly included sucrose, glucose and fructose, of which the sucrose were the highest. All kinds of sugars in the summer fruits from WS and most kinds of sugar in the summer fruits from FP were significantly higher than those of the spring fruits in 2019—2020. All kinds of sugars in the summer fruits from LZ were higher than those of the spring fruits, while there was no significant dif-ference in 2019—2020. All kinds of sugars in the summer fruits from CC did not significantly regularly changed in 2019—2020. The sucrose content in the summer fruits from all tested orchards was higher than that of the spring fruits in 2020—2021, and most of them had significantly difference. Except for WS, the contents of glucose, fructose and galactose in the summer fruits from other orchards were high- er than those of the spring fruits in 2020—2021. The citric acid and malic acid were the two most impor-tant acids, which accounted for more than 80% of the total acids in the summer fruits and the spring fruits. The content of citric acid in the summer fruits from all tested orchards was higher than those of the spring fruits in 2020—2021. The contents of oxalic acid, quinic acid and aminobutyric acid in the summer fruits from all tested orchards were not significantly different but most of them were signifi- cantly higher than those of the spring fruits in 2020—2021. The content of proline in the summer fruits was higher than that of the spring fruits and the content of other substances had no significant and regu-lar change. More than 78.6% of the consumers expressed good taste for the spring and the summer fruits, and there was no peculiar smell in the summer fruits after 30 days storage at room temperature.【Conclusion】The summer fruits had lower external quality. The contents of TSS, TA and most of sugar and acid components of the summer fruits were higher than those of the spring fruits. The summer fruits had good taste and would be valuable for research and utilization.