Influence of pre-harvest calcium application on the concentration and distribution of ascorbic acid and mineral content in apple cultivars at harvest and during storage

This study investigated the effects of pre-harvest calcium (Ca) application on apple fruit ascorbic acid (AsA) concentration and mineral contents in the cultivars ‘Braeburn’, ‘Fräulein’, ‘Pinova’, ‘Topaz’ and ‘Elstar’, and core browning (CB) susceptibility in ‘Braeburn’ and ‘Fräulein’ during controlled atmosphere (CA) storage (1 °C, 1 kPa O2 plus ≤ 1 kPa CO2). Approximately eight pre-harvest Ca applications were applied during the growing season for ‘Braeburn’ and ‘Fräulein’ cultivars and one application in “spring” for ‘Pinova’, ‘Topaz’ and ‘Elstar’. In addition, data from five consecutive harvest seasons was used to assess the relationship among AsA, mineral content, and CB for ‘Braeburn’. Results showed that the impact of pre-harvest Ca was variable among cultivars; fruit Ca concentration was increased and the K/Ca ratio was reduced only in ‘Fräulein’ fruit, and AsA was increased only in ‘Braeburn’ fruit, especially in the inner cortex tissue where CB occurs. For ‘Pinova’, ‘Elstar’ and ‘Topaz’, Ca concentration was slightly higher in untreated fruit compared to Ca-treated fruit (p < 0.07). AsA increased after storage, remaining higher in ‘Braeburn’ fruit treated with Ca, especially in the outer cortex tissue. Pre-harvest Ca reduced CB in ‘Fräulein’, but CB incidences in ‘Braeburn’ were too severe (> 84%) and unaffected by Ca application. Analysis of the data from five consecutive harvest seasons showed that ‘Braeburn’ CB incidence related positively with Ca (r = 0.97, p < 0.05) and negatively with the AsA/Ca ratio (r = −0.71, p > 0.05). Our results suggest that the positive effect of pre-harvest Ca application in reducing CB incidence in ‘Braeburn’ apple, as reported by previous studies on ‘Braeburn’ apple, may be associated with increased AsA concentration, possibly due to higher synthesis and/or reduced degradation, rather than due to higher total fruit Ca concentration.