Effects of processing on kiwi fruit dynamic rheological behaviour and tissue structure

The effects of blanching and osmotic dehydration on the small deformation r heological properties and structure of kiwi fruit were determined. Kiwi fru it tissue behaved as an elastic solid with storage moduli (G') dominating t he viscoelastic response (G " /G'similar to0.2). Both storage (G') and loss (G " )moduli were frequency independent and a clear linear viscoelastic ra nge was evident. In general, G' and G " decreased upon blanching and osmoti c dehydration due to tissue damage. Structural changes caused by blanching included swelling of the cell walls and increases in the extent of cell-cel l separation in the middle lamella. For atmospheric osmotic dehydration, hi gh levels of solutes were observed within the cells which lead to a reducti on of freezable water. For unripe tissue, G' and G " increased with vacuum dehydration and it seemed that both cell wall integrity and cellular turgor were preserved to a greater extent than in ripe processed tissue. When cal cium was added to the osmoticum during osmotic dehydration under vacuum, no differences in dynamic rheological behaviour or tissue structure were dete cted. (C) 2001 Elsevier Science Ltd. All rights reserved.