Abstract
Early ripening apples are usually used for fresh marketing because of short storage life, although they are with high acid and low sugar contents. Understanding the malate metabolism in fleshy fruit and underpinning process during ripening is crucial for particular crop improvement where acidity is a concern for direct consumption or further processing. In this research, a traditional Chinese apple cultivar ‘Hongyu’, which belongs to early ripening apple cultivar, were freshly harvested at commercial maturity stage (120 Days after full bloom) and used for different storage temperature (4°C, 20°C) and UV-C treatment (following storage at 20°C after treatment). Simple sugars (glucose, sucrose, and fructose) and organic acids (malic, and oxalic) were assessed after 14 d of storage. Compared to fruits stored at 20°C, the malate content in fruits stored at 4°C significantly higher, while it was decreased significantly in UV-C treated fruits stored at 20°C after 14 d of storage. The sugar content was almost similar throughout the UV-C-treated fruits and fruits stored at different temperature. The higher ratios of total sugars to total organic acids in UV-C treated fruits after 14 d suggest that UV-C treatment has the potential to improve the taste of early ripening apple cultivars. Considering the significant difference in malate the samples at 14 d of storage were subjected for RNA-seq analysis. Transcriptome analysis revealed that the phenomena underlying this change were governed by metabolism of malate by the regulation of NADP-malic enzyme (NADP-ME) and phosphoenolpyruvate carboxylase kinase (PEPCK) in apple during postharvest storage. This transcriptome profiling results have specified the transcript regulation of malate metabolism and lead to possible taste improvement without affecting the other fruit quality attributes.
Highlights
Apple (Malus domestica Borkh.) is an economically important and popularly grown fruit crop all over the world due to high nutritive value, good taste and availability throughout the year
Acidity has been considered as an important factor of fruit harvesting due to its direct influence on fruit quality where acidity is crucial for further processing
Following different effects observed in different horticultural produce, important things must be taken into consideration to achieve successful implementation such as plant parts used for treatment, dose, cultivar specificity, developmental stages, harvesting date, pre-harvest factors and postharvest storage conditions [49]
Summary
Apple (Malus domestica Borkh.) is an economically important and popularly grown fruit crop all over the world due to high nutritive value, good taste and availability throughout the year. Summer apple cultivars or early harvested apple cultivars have been in sale for fresh market but not for long-term storage [1]. Acidity has been considered as an important factor of fruit harvesting due to its direct influence on fruit quality where acidity is crucial for further processing. Fruit flavor largely depends on a multifaceted interaction of several metabolites, the ratio of sugars and acids are considered as a key determinant factor of fruit taste and sensory evaluation [7,8]. The early ripening apples are usually of high acidity and low sugar contents, which results in a low ratio of total sugars to total organic acids and reduce the market preference for fresh consumption. Many studies elucidated a prominent influence on the variation of organic acids and sugars in post-harvest fruit quality and shelf life [12,13,14]
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