A hydroxypropyl methylcellulose (HPMC)-based coating inhibits ethylene-dependent quality changes and reduces superficial scald incidence and blue mould severity during postharvest handling of two apple varieties

Abstract

The search of new alternatives to substitute postharvest treatments based on synthetic chemicals has gained attention on recent years due to social pressure and stricter legislative policies. Consequently, edible coatings from natural sources have risen as potential solutions to retain postharvest fruit quality. Among these, coatings based on hydroxypropyl methylcellulose (HPMC) have shown potential in preserving fruit quality after harvest. However, scarce studies have explored into their effects on the physiology of climacteric fruits. In this context, the effect of a novel HPMC-based edible coating on fruit postharvest physiology and quality was evaluated in two apple cultivars: ‘Golden Reinders’ and ‘Granny Smith’. In both cultivars, the HPMC-based coating was able to preserve some initial quality attributes, such as firmness and colour, while reducing superficial scald and the severity of blue mould caused by Penicillium expansum. Coated fruit showed reduced ACS activity and ethylene production, delaying changes in ethylene-dependent parameters such as colour and firmness during two different postharvest scenarios: shelf life after harvest and after 3 months of cold storage. Other ripening-associated traits such as starch index, soluble solids content (SSC), and total titratable acidity (TTA) were not affected by the coating application. The coating altered the levels and composition of volatile organic compounds (VOCs), yet without affecting the overall consumer acceptance in most of the studied scenarios. Changes in fruit physiology promoted by the coating, including the decrease of α-farnesene levels and its oxidation products, together with enhanced accumulation of ethanol may reduce the superficial scald incidence in ‘Granny Smith’ and the severity of blue mould rot in the two studied cultivars. Overall, the use of the HPMC-based coating in apples could be useful for maintaining fruit quality and reducing postharvest losses related to mould development and physiological disorders without compromising taste perception.