Effects of cross-pollination by ‘Murcott’ tangor on the physicochemical properties, bioactive compounds and antioxidant capacities of ‘Qicheng 52’ navel orange

Highlights

• The cross-pollinated fruit exhibited higher TSS content and lower TA content.

• The antioxidant capacities were increased due to higher phenolics content.

• ‘Murcott’ is a promising pollenizer for ‘Qicheng52’ navel orange.

Abstract

This study investigated the effects of cross-pollination by ‘Murcott’ tangor on the fruit quality of ‘Qicheng52’ navel orange, including the physicochemical properties, bioactive compounds and antioxidant capacities. There were no significant differences on the fruit weight, juice yield and pH value of juice between self- and cross-pollinated fruits. However, cross-pollination could significantly improve the fruit quality of ‘Qicheng52’ fruits by increasing the total soluble solid content from 11.12 ± 1.02 °Brix to 13.86 ± 1.17 °Brix. The results of high performance liquid chromatography analysis of three sugar components indicated that the increase of total sugar was mainly contributed by the increase of fructose and sucrose. Cross-pollination exhibited no effect on the flavonoids content, while the total phenolics content was increased from 210.09 ± 18.55 mg/L to 298.25 ± 29.10 mg/L, which contributed to the higher antioxidant capacity in the cross-pollination fruit juice.

Introduction

Citrus is an important crop worldwide, and the delicious flavor and beneficial health effects of citrus fruits are the important factors for their market values. Sugars and organic acids are the major components in citrus fruit juice, and their compositions and concentration largely affect taste characteristic and organoleptic quality (Liu, Yang, & Deng, 2015). Citrus fruits have been well accepted as an dietary source of bioactive compounds, such as ascorbic acid, phenolic compounds and flavonoids, which are found to be abundant in citrus fruits and associated with reduced risk of certain chronic diseases (Xi et al., 2014). In recent years, antioxidant properties of citrus fruits are becoming a major factor in determining consumer acceptance and preference (Loizzo et al., 2018, Zou et al., 2016). A large amount of evidence indicates that the antioxidant capacity of citrus fruits strongly correlate with bioactive compounds, such as phenolic compounds (Lagha-Benamrouche and Madani, 2013, Legua et al., 2014, Xi et al., 2014).

Currently, there are increasing interests in the fruit quality of citrus species, which appeared to be affected by farming methods and rootstocks combinations (Legua et al., 2011, Legua et al., 2014, Letaief et al., 2016). Cross-pollination has been used as an effective method to increase the yield or quality of crops (Fattahi et al., 2014, Shemer et al., 2014, Sulewska et al., 2014). In the recent literatures, cross-pollination between citrus species was proved to be an effective method to increase the yield of the citrus cultivars suffering from inadequate yield (Schneider, Goldway, Rotman, Adato, & Stern, 2009). However, the effects of cross-pollination on the citrus fruit quality, including weight, total soluble solid (TSS) content, total acids (TA), juice content and rind thickness, have not been comprehensively investigated in the previous research (Papadakis, Protopapadakis, & Therios, 2009). In our recent studies, ‘Murcott’ tangor (Citrus reticulata Blanco × Citrus sinensis Osbeck) trees, using as a pollenizer, were mix-planted with ‘Qicheng 52’ navel orange (Citrus sinensis Osbeck) trees. The fruit quality of ‘Qicheng 52’ could be significantly increased, especially for its TSS content.

‘Qicheng 52’ navel orange, developed from the fine mutation lines of ‘Newhall’ navel orange (Citrus sinensis Osbeck), is a new high-quality navel orange cultivar, which has become one of the main citrus varieties in southern China. The oval and seedless ‘Qicheng 52’ fruits have the TSS content ranged from 11.5% to 13.0% and the TA ranged from 0.46% to 0.73% (Zhao, Guo, Chen, Yu, & Xu, 2010). ‘Qicheng 52’ trees are always cultivated in isolated blocks, therefore little information is available about the effects of cross-pollination on its yield or fruit quality. By accident, we found that ‘Murcott’ tangor, a sweet orange with high TSS content, could be used as a potential pollenizer for ‘Qicheng 52’. The cross-pollination might not increase its yield, but could be an efficient and cheap method to increase the fruit quality of ‘Qicheng 52’, and thus significantly increase its market value.

In current study, the organic acids, sugars, phenolic composition and antioxidant capacity of the orange juice from the ‘Qicheng 52’ have been determined. The effect of cross-pollination by ‘Murcott’ tangor on the ‘Qicheng 52’ fruit qualities was investigated, focusing on the contents of bioactive compounds and the antioxidant capacities.