Beyond the Visible and Below the Peel: How UV-B Radiation Influences the Phenolic Profile in the Pulp of Peach Fruit. A Biochemical and Molecular Study

Abstract

In the last decades, UV-B radiation has attracted attention due to its potential to increase nutraceutical values of fruit and vegetables, especially by inducing the accumulation of phenolics in a structure-dependent way. However, most current studies have investigated the UV-B-driven changes only in the peel or focusing on individual phenolic classes. Adopting an "-omics" approach, this work aimed to deepen the knowledge about the effects of UV-B radiation on the phenolic profile in the pulp of peach fruit. Based on these considerations, melting flesh yellow peaches (Prunus persica L., cv. Fairtime) were subjected to either a 10-or 60-min UV-B treatment (1.39 and 8.33 kJ m −2 , respectively), and sampled at different time points from the exposure. A UHPLC-ESI/QTOF-MS analysis coupled with a phenolics-specific database for the annotation of compounds and a multivariate discriminant analysis revealed a marked effect of UV-B radiation on the phenolic profiles of peach pulp. Particularly, a general, transient increase was observed after 24 h from the irradiation, especially for flavanols, flavonols, and flavones. Such behavior diverges from what was observed in the peel, where an overall increase of phenolics was observed after 36 h from the irradiation. Concerning the flavonols in the pulp, UV-B exposure stimulated a specific accumulation of isorhamnetin and kaempferol derivatives, with variations imposed by the different sugar moiety bound. Anthocyanins, which were the second most abundant flavonoid group after flavonols, displayed a general decrease after 36 h that was not attributable to specific molecules. The UV-B treatments also increased the glycoside/aglycone ratio of flavonols and anthocyanins after 24 h, by increasing the glycoside concentration of both, flavonols and anthocyanins, and decreasing the aglycone concentration of anthocyanins. In support of the biochemical results, targeted gene expression analysis by RT-qPCR revealed an UV-B-induced activation of many genes involved in the flavonoid pathway, e.g., CHS,

Ultraviolet‐B exposure and exogenous hydrogen peroxide application lead to cross‐tolerance toward drought in Nicotiana tabacum L.

“…Furthermore, many research groups have reported that flavonoids have a function in defense against drought, when acting as free radical scavengers (Kumar et al, 2020; Nakabayashi et al, 2014; Ramakrishna and Ravishankar, 2011). Our data are in agreement with previous research which showed that UV‐B enhances accumulation of CHS transcripts, representing the first committed step of the flavonoid biosynthesis pathway (Brown and Jenkins, 2008; Rai et al, 2020; Rodríguez‐Calzada et al, 2019; Santin et al, 2020). It is well known that H 2 O 2 plays a role in regulation of genes associated with phenolic compound biosynthesis, of which CHS is one (Nyathi and Baker, 2006).…”

Anything New under the Sun? An Update on Modulation of Bioactive Compounds by Different Wavelengths in Agricultural Plants

“…Such an effect was particularly intense for flavanols, flavonols, and flavones, and, differently from what was observed in the peel, it occurred 24 h after the end of the treatment. As in the peel, however, flavonoid biosynthetic and regulatory genes were upregulated by UV-B after 6 h from the irradiation [ 227 ]. This finding is particularly interesting because it demonstrates the capability of UV-B treatments in improving the nutraceutical properties of peach pulp—that is the only part usually consumed due to the custom of peeling the fruit.…”

Primary and Phenolic Metabolites Analyses, In Vitro Health-Relevant Bioactivity and Physical Characteristics of Purple Corn (Zea mays L.) Grown at Two Andean Geographical Locations

“…Ultraviolet-B radiation and cold temperatures have been identified as key environmental factors that regulate the biosynthesis of flavonoids in plants at the transcriptional level [43]. The increase in the anthocyanin contents under cold stress was observed in strawberry fruits and purple head Chinese cabbage, while the UV radiation improved the levels of flavones, flavonols, and flavanols in the pulp of peach fruits [44][45][46]. In this current research, anthocyanins and especially quercetin derivatives, which are known to contain multiple hydroxyl groups with better reactive oxygen species (ROS) scavenging capacity, may have increased in highland purple corn to counteract oxidative stress induced by UV-B and cold temperature stress factors [47].…”