Biochemical and molecular traits underlying the quality preservation and defence enhancement by heat treatment in harvest-ripe strawberries

Abstract

Heat treatment is widely used as a postharvest strategy to extend the shelf life of fleshy fruits. Nevertheless, understanding the mechanisms by which heat stress exerts its effect continues to be a topic of interest. We studied the influence of heat treatment (3 h in an air oven at 45 ± 1 °C) on the modulation of defence mechanisms in ripe strawberry fruit (Fragaria x ananassa Duch). Whilst the thermal stress delayed the postharvest accumulation of anthocyanins, it did not cause changes in other quality parameters such as pH, percentage of titratable acidity, and total soluble solids concerning control fruit. Heat-treated strawberries showed a lower decay than controls during storage. The treatment was also effective in restricting the fungal pathogen Botrytis cinerea invasion. To explore the molecular and biochemical traits underlying the defence enhancement by heat treatment in ripe strawberries, we studied the effect on oxidative metabolism and classical hydrolytic and non-hydrolytic pathogenic-related proteins. Our findings revealed that heat treatment increases the activity of peroxidase, polyphenol oxidase, chitinase, and β-1,3-glucanase enzymes. Heat stress up-regulates the FaPAL1, FaCHS2, FaAPX42, FaPPO1, FaChi2–1, FaChi2–2, FaChi3, and FaβG2–3 gene expression. Moreover, the expression of genes involved in signal transduction (FaCDPK1) and a gene encoding a putative thaumatin-like protein (FaPR5) was induced in heat-treated fruit. These results provide insights into the basis of defence responses induced by heat stress in strawberries, offering information for potential strategies to improve fruit preservation and postharvest management practices.