High plant growth temperatures increase antioxidant capacities in strawberry fruit

The influence of four day/night growing temperature combinations (18/12, 25/12, 25/22, 30/22 °C) on phenolic acid, flavonol, and anthocyanin content and their antioxidant activities against peroxyl radicals (ROO ^•), superoxide radicals (O₂ ^•-), hydrogen peroxide (H₂O₂), hydroxyl radicals (OH ^•), and singlet oxygen (¹O₂,) in fruit juice of 'Earliglow' and 'Kent' strawberry (Fragaria × ananassa Duch.) were studied. The content of cyanidin- based anthocyanins, were much lower than pelargonidinbased anthocyanins. High day/night temperature conditions significantly enhanced pcoumaroylglucose, dihydroflavonol, quercetin 3-glucoside, quercetin 3-glucuronide, kaempferol 3-glucoside, kaempferol 3-glucuronide, cyanidin 3-glucoside, pelargonidin 3-glucoside, pelargonidin 3-rutinoside, cyanidin 3-glucoside-succinate and pelargonidin 3-glucoside-succinate content in strawberry juice. Plants grown at low day and night temperatures (18/12 °C) generally had the lowest anthocyanin contents. Plants grown at the highest day/night temperatures (30/22 °C) produced fruit with the most phenolic content as well as antioxidant capacity. Fruit of 'Kent' strawberry had higher contents of phenolic acid, flavonols, anthocyanins and antioxidant capacities compared to fruit of 'Earliglow' strawberry under all temperature regimes.