Seasonal variation in calcium and ascorbic acid content at harvest related to internal browning in ‘Braeburn’ apple during controlled atmosphere storage

Previous studies examining the causes of internal browning (IB) and strategies to reduce its incidence in ‘Braeburn’ apple grown in Southwest Germany have shown conflicting results. However, most studies have been conducted during only one season, requiring multi-seasonal evaluations to obtain robust data and information. IB has been associated with fruit mineral content in ‘Braeburn’ apple, and in other cultivars, ascorbic acid (AsA) is linked to IB. Few studies have investigated the possible role of the balance between mineral and AsA content on fruit susceptibility to IB. The objectives of this study were to use a four-year dataset to analyse the seasonal variation of mineral and AsA content at harvest and their relation to IB incidence in ‘Braeburn’ apple grown in Southwest Germany and stored under controlled atmosphere conditions. According to our results, the average seasonal IB incidence was highly associated with AsA and calcium contents in fruit. Fruit calcium content was positively correlated with IB incidence, whereas AsA content was negatively associated with IB. Seasonal variation in the AsA/Ca ratio at harvest followed the opposite trend to IB incidence, with a higher ratio occurring in years with lower IB incidence. Principal component analysis revealed that the relative humidity (RH) during the first 42 days after bloom (42-DAB) was positively correlated with AsA content and negatively correlated with fruit calcium content and IB incidence. Our results indicate that higher AsA and lower calcium content, due to higher RH during the first 42-DAB, are important to reduce ‘Braeburn’ apples’ susceptibility to IB during controlled atmosphere storage.