Storage performance of Fortune mandarins following hot water dips

Commercially ripe ‘Fortune’ mandarins were dipped in water at 50 °C (Dip50), 52 °C (Dip52), 54 °C (Dip54), 56 °C (Dip56), or 58 °C (Dip58) for 3 min before storage at 6 °C for 30 days and 3 additional days at 20 °C (simulated shelf-life). Untreated fruits were used as control. Scanning electron microscopy of untreated fruit revealed rough and granular wax surface structures with a number of deep surface cracks. In contrast, fruits dipped at 50–54 °C did not exhibit similar fractures and the fruit surface appeared relatively homogeneous. Dip56 resulted in parts of the surface with no apparent epicuticular wax and zones with an accumulation of waxy deposits. With Dip58, the fruit surface appeared as if the treatment had melted and completely removed epicuticular waxes. Dip50–54 reduced chilling injury and levels of decay, both during cold storage and simulated shelf-life. Dip56–58 showed no advantages compared with untreated fruit. Neither Dip50 nor Dip52 caused adverse effects to rind surface, either during or after simulated shelf-life. Conversely, higher dip temperatures induced heat damage in the form of rind browning, the extent and number of fruits affected increasing as bath temperature increased. Water loss was consistently lower in untreated fruit. Peel water loss was consistently higher in Dip56 and Dip58 fruit. Differences in external appearance, physiological behaviour and internal quality attributes between untreated and Dip50–54 fruit were minimal. Dip56 and especially Dip58 had negative effects on the external appearance of fruits. The off-flavour found in Dip58 was probably due to increased levels of ethanol in the juice.