Short communicationEffect of thyme oil vapour exposure on the brown rot infection, phenylalanine ammonia-lyase (PAL) activity, phenolic content and antioxidant activity in red and yellow skin peach cultivars

- Thyme oil vapour exposure reduced incidence of brown rot disease in peaches.
- Thyme oil vapour increased activity of PAL and phenolic content in the fruit.
- Disease susceptibility is predetermined by biochemical composition of the fruit.
- Chlorogenic and caffeic acids content is associated with susceptibility to brown rot.
- Thyme oil is more suitable for reducing decay in red than yellow skin peaches.

Influence of thyme oil vapour on the incidence of brown rot (Monilinia laxa) was investigated in the yellow-flesh peach cultivars consisting of red skin 'Jim Dandy', 'Novadonna', 'Scarlet Rich' and 'Transvalia', and yellow skin 'Earli Gold', 'Kakamas', 'Kesie' and 'Summer Sun'. Fruit were exposed to thyme oil (96 μL L−1) vapour for 24 h, subsequently inoculated with the pathogen (105 spores mL−1), and stored for 14 d at 0 °C, followed by 6 d shelf-life conditions at 15 °C, 75% RH. Four varieties, i.e. 'Scarlet Rich', 'Transvalia', 'Earli Gold' and 'Kesie' were then selected to study the effect of thyme oil vapour on the phenylalanine ammonia-lyase (PAL) activity and hydroxycinnamic acids (chlorogenic and caffeic acids) content. The effect of thyme oil vapour on brown rot incidence, phenolic content and antioxidant activity was also investigated in naturally infected fruit. Thyme oil vapour reduced the incidence of brown rot by increasing the activity of PAL, the content of catechin, chlorogenic and caffeic acids, and via enhancing antioxidant scavenging capacity. However, the key finding from this study was that thyme oil vapour exposure is far more suitable for red skin peaches than their yellow skin counterparts.