Effect of candying on microstructure and texture of plums (Prunus domestica L.)

The plums (Prunus domestica L.) of a specific 'Green Gage' variety, “Rainha Cláudia Verde”, are used to produce the candied product “Ameixa d'Elvas”. The candying process consists in boiling the intact plums in water and further immersion in sucrose syrup until 75 °Brix. Scanning electron microscopy of unprocessed plums revealed perfectly turgid parenchyma isodiametric cells with few intercellular spaces and the boiled plums showed a loss of intercellular adhesion of parenchyma cells and ruptures on the vascular strand structure. However, candied plums showed recovery of the turgidity and cell-to-cell adhesion of parenchyma cells. Texture analysis showed that the unprocessed plums had a fairly hard texture, improved by the presence of the skin. Firmness, rigidity, and deformation work had a sharp decrease upon boiling. However, after candying, an increase of firmness and deformation work was observed, also improved by the skin. Microstructure and texture recovery of the candying product suggests the formation of a jam-like structure in the middle lamella region promoted by the syrup. Nevertheless, cell adhesion recovery is limited by the extent of the disruption of the tissues during the boiling process. This is the first report concerning texture and microstructure changes of plums occurring during the candying process.