Although many aspects of scald have been investigated, we are still far away from a general understanding of the disorder. Here, we tried to elucidate the role of the phenolic compounds and their fate during scald development. The study was performed on 'Granny Smith' apples. After 5 months in cold storage, scald developed rapidly at room temperature, giving us the opportunity to study unaffected, partly scalded, and fully scalded apple peels. We analyzed the phenolic content, enzyme activity, and gene expression of the flavonoid pathway as well as peroxidase and polyphenol oxidase activity. We demonstrate that scald incidence is mostly dependent on hydroxycinnamic acids, namely, chlorogenic acid and its increased accumulation during scald development, while other phenolic compounds do not seem to be relevant. Expression of genes of the flavonoid pathway was strongly increased during disorder development, whereas a decreased activity of most analyzed flavonoid pathway enzymes was observed. The results presented here help elucidate the role of phenolic content during scald development, which will be useful for future studies of scald development.
In the last few years, spring frosts have become more of a rule than an exception. There are several prevention measures available for growers and numerous are being tested; however, fruitlets are often affected to some extent. One of the more common phenomena is the development of frost rings. The aim of our study was to evaluate how the occurrence of frost rings affects sugar, organic acid, and phenol content in the flesh and phenol content in the peel of cv. ‘Gala’ apples. The results show that the frost damage from spring frost affects compounds in the peel, as well as in the flesh of ripe apples. The flesh of fruits with frost rings contained higher content of fructose and in the flesh directly under the rings there was higher sorbitol and malic acid content. Additionally, the hydroxycinnamic acid and dihydrochalcone content in apple flesh was also altered by frost. The frost-affected peel had a completely different ratio of phenolic compounds content in comparison to healthy apples. While there was a significantly higher content of hydroxycinnamic acids and dihydrochalcones in the corky peel in comparison to the unaffected peel, the flavonol and anthocyanin content was considerably lower.
The reaction of two apple cultivars ('Braeburn' and 'Golden Delicious') on dissimilar temperature conditions (SD1 -extremely high temperatures and SD2 -regular summer temperatures) was evaluated in terms of their phenolic accumulation. Total and photosynthetically active radiation as well as air and fruit temperatures were higher on SD1. Fruit temperature was approx. 10°C higher on SD1 in comparison to SD2. Significant differences in phenolic content levels were detected between the two sampling days. Higher amounts of hydroxycinnamic acids, flavonols, flavanols and dihydrochalcones were measured in sunburned (SB) and healthy sun exposed (HS) 'Golden Delicious' apples on SD1 compared to SD2. The differences in phenolic content were less prominent in 'Braeburn' peel sampled on both sampling dates. Differences in phenolic accumulation were also determined between morning (7 am) and afternoon (1 pm) samplings but the changes were less uniform and only significant in 'Braeburn' HS peel and 'Golden Delicious' SB peel. No changes in phenolic content levels have been detected in apples inside the tree crown on different sampling dates and hours of the day.
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