In preliminary tests for MW processing of Sysco sliced beef in
Nestle Trio gravy, it was observed that beef samples shrunk significantly
(about 35% area reduction and 40% weight reduction) after
MW sterilization. The shrinkage caused the beef samples to move,
and cold spots did not maintain fixed locations inside trays during
MW processing. This made it difficult to record the temperature
profiles of cold spots with temperature sensors. Therefore, precooked
or pre-shrunk beef was used for the development of MW
processing schedules.
Shrinkage of beef was studied by heating sliced beef samples in
boiling water with a 0.5% salt addition for different times between
0 and 40 min. The salt addition was to limit the change in dielectric
properties of the beef sample. Preliminary dielectric property tests
indicated that pre-cooking of beef in boiling water lowered both
the dielectric constant and the dielectric loss of the sample, and
that an addition of salt in the boiling water could reduce the decrease
in dielectric property data of the pre-cooked beef sample.
The weight and area of the sample were measured prior to and
after the heat treatment. The weight loss and area reduction of
the sample were then calculated. It was decided to use beef samples
treated for 4 min in the boiling water with 0.5% salt for MW
processing schedule development.