Chilling injury in pineapple fruit in response to calcium partitioning and allocation

Postharvest internal browning (PIB) represents a significant contributor to postharvest loss in pineapples. The role of calcium (Ca) within the fruit tissue has long been implicated as a potential factor associated with PIB. However, the reliability of this correlation has been questioned in recent years. In this study, an investigation was carried out to elucidate the distribution and subcellular-level localization of Ca in 'Pattavia' pineapple. Throughout the storage period, the formation of PIB was not observed in the flesh adjacent to the shell (FS) region, but became apparent in the flesh adjacent to the core (FC) region on the 21st day of storage. While total Ca and apoplastic Ca were lower in the FC region, these levels remained stable as PIB advanced. Conversely, a fourfold increase in calcium nitrate (Ca(NO3)2) and calcium chloride (CaCl2) levels was noted only in the FS region during storage. In addition, calcium-pectate levels in the FC region consistently surpassed those in the FS region throughout storage. Calcium ions (Ca2+) were distributed differently during storage, mainly in the apoplast and cell wall of the FS region, while in the FC region, Ca2+ was predominantly found in the vacuole. The findings from this study strongly suggest a significant correlation between the occurrence of PIB and calcium-related factors: low total Ca concentrations, reduced levels of Ca(NO3)2, CaCl2, Ca-organic, Ca-pectate, and apoplastic Ca, coupled with an increased presence of Ca2+ in vacuoles during low-temperature storage.