The microwave expansion of glassy, low-moisture and extruded
starch-based products has been widely studied in the industry. However,
there has not been much research on the microwave expansion of
high-moisture, non-extruded and multi-component foods.
The goal of Irish scientists was to study the microwave expansion
of a high-moisture, high-fiber and high-protein dairy-based matrix. They
found that it is possible to produce a novel, expanded, crispy, and
potentially healthy snack food by microwave-heating imitation cheese.
The researchers formulated an imitation cheese that contained about
20% w/w of protein and 60% w/w of moisture. The cheese was formulated to
contain 17.3% w/w of resistant starch, which was used to replace all of
the fat content of a typical cheese.
The cheese was stored at 5 C for four weeks. During the storage
period, 2-g-sized disks were bored from the cheeses which were
subsequently heated in a microwave at 2540 MHz for periods of 20 seconds
to 100 seconds at days 2, 4, 8, 10 and 22. The resulting expanded
products were characterized by the scientists who analyzed the degree of
expansion, the internal structure, any loss in weight, bulk density and
the maximum force required to puncture the samples.
Cheese expansion during microwave heating increased in the samples
exposed to prolonged storage. A 0.6-, 1.2-, 6-, 9-and 9-fold increase in
maximum expansion was observed after storing the samples for 2, 4, 8, 10
and 22 days, respectively. The rate of weight loss during the heating
process increased while the bulk density decreased with increasing
storage time.
The maximum force required to puncture the samples exhibited an
inverse relationship with expansion and storage time. At maximum
expansion, the samples stored for 2, 8 and 10 days required forces of
~47.36[+.or.-]34.53; 5.50[+.or.-]3.89 and 4.54[+.or.-]2.98 N to be
punctured, respectively. Heating samples for greater than 40 seconds
increased the jaggedness of the force-displacement curves, which
reflected the crisp texture of the products.
Further information. Michael O' Sullivan, College of Life
Sciences, School of Agriculture, Food Science and Veterinary Medicine,
University College Dublin, Agriculture and Food Science Centre, Belfield
Dublin 4, Ireland; phone: + 353 1 716 6100; fax: + 353 1 716 6104;
email: michael.osullivan@ucd.ie.
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