2. Materials and methods
2.1. Rawmaterials and sample preparation
To determine the effect of rate of freezing on protein
functionality, m. semitendinosus muscles from 12 heifers
were hot-boned and held at 10 C until rigor. Each
muscle was divided into two equal portions (referred to
as front and back, each 170 mm long 110 mm diameter).
A Latin Square design to account for positional
effects was used to allocate the 48 portions to four
freezing treatments: (1) Slow blast-freeze (1.8 mm/h):
samples at 10 C were each vacuum packed, wrapped in
a single layer of 10 mm thick foam rubber and placed in
front of the fans in a20 C freezer until the temperature
reached 20 C, measured with a T-type thermocouple
inserted in the middle of the sample. (2) Fast
blast-freeze (7.8 mm/h): samples were frozen as in slow
blast, except that the samples were not insulated with
foam rubber, thus producing a faster freezing rate. (3)
Fast liquid nitrogen (49.8 mm/h; two treatments): samples
at 10 C were vacuum packed and frozen in a batch
liquid nitrogen freezer or samples were vacuum packed
and slow chilled from 10 C to 0 C, then frozen in a
batch liquid nitrogen freezer to 20 C. The batch liquid
nitrogen freezer was operating at a temperature of 80 C.
The air temperature in the batch freezer was controlled by
periodically spraying liquid nitrogen into the freezer—no
liquid nitrogen was directly sprayed onto samples.
The samples