Hot water dipping of apple - not living up to its promise?

Apple is an important fruit commodity in Belgium. It represents the second highest production value by mass. The fruit can be stored year round using controlled atmosphere storage. During this storage, losses can occur due to fungal decay or physiological disorders. One approach that was previously studied to reduce these losses and better retain fruit quality is hot water treatment by dipping the fruit. In our study we investigated the effect of a hot water dip of 50°C for 4 min on the quality of Jonagored apples and their susceptibility for Botrytis cinerea and Penicillium expansum, using artificial wound inoculation. Fruit were hot water dip treated at harvest and stored under controlled atmosphere. Evaluation of quality, physiological parameters and disease susceptibility was carried out immediately after treatment, then after 1 week, 1 month, 3 months and 9 months. Our results show that the tested treatment had no protective effect against artificial wound inoculation with either pathogen. Furthermore, most quality (titratable acids, total soluble solids content, firmness) and physiological effects of the treatment disappeared after six months of storage. Treated fruit had a significantly higher mass loss throughout the 9 months of storage, which is in contrast to what has been reported in literature. Because this effect is already observed after 1 week we hypothesize that it is a direct effect of the hot water dip. After 9 months of storage, remaining fruit were placed in shelf-life for two weeks and the incidence of rot was recorded. The incidence rates were 17.45% and 7.63% for the control and treated fruit, respectively. This indicates that there may be a protective effect of the hot water dip against natural infections. Further research is ongoing to determine which factors explain this positive effect after 9 months of storage.