Page 33 - FoodFocusThailand No.165 December 2019

SMART PRODUCTION

This system has been continuously developed by TOPS Food
(Belgium) and Otsuka Chemical Co. (Japan) to produce chilled and
frozen packaged foods including spaghettis and chicken satay which
can be kept at 7 C for 35 days. Recently, Micvac (Sweden) has developed
o
the new concept of a package with valve for microwave pasteurization.
When food inside the package is heated and evaporation then occurs,
the internal pressure opens the valve due to steam pressure. The valve
is subsequently closed during cooling in which condensation creates
vacuum inside the package. The food package with valve can be kept
at 8 C for 30 days (Barosa-Canovas et al., 2014; Tang, 2015; Tang
o
et al., 2018).
For sterilization of the packaged foods, non-uniform electromagnetic
field distribution and edge overheating as well as the difficulty of cold
spot identification are concerned. The technique which involves
microwave heating of foods and water as well as heat transfer from water
to internal foods can produce more even heating than microwave heating
alone.
From this concept, microwave assisted thermal sterilization (MATS)
is developed by a team from Washington State University (WSU). The
application of 915 MHz single-mode cavity coupled with water immersion
results in more heating uniformity and temperature distribution can be
predicted. MATS system is composed of 4 sections: 1) preheating
2) microwave heating 3) holding and 4) cooling in which the food packages
are transferred to mesh pockets attached to conveyor and conveyed
through the 4 sections without the application of overpressure. The mesh
pockets lock the packages and prevent their swell. Mashed potatoes,
salmon filet in sauce and chicken dumplings contained in the container
processed by MATS were approved by USFDA (Barbosa-Canovas
et al.,2014).

time compared with conventional retorts. For example, ohmic
heating of soup containing chicken chunks and vegetables in
pouch takes less than 15 min from room temperature to 121 C
o
, accounting for better quality and higher microbial inactivation.
In addition, post pasteurization of vacuum packaged
sausages with OH at 75 C for 30 sec could destroy Listeria
o
monocytogenes higher than 5 log reduction whereas
conventional heating with hot water could inactivate L.
monocytogenes only 3 log reduction. In addition, from sensory
evaluation consumers could not detect the difference of sensory
attributes of the sausages between ohmic and conventional
heating (Inmanee et al., 2019).
• Microwave Heating Microwave heating is the process
wherein high frequency electromagnetic waves pass through
and generate heat within food products due to dipole rotation
and ionic polarization. Besides domestic microwave oven,
microwave heating is utilized in food industries in the combination
of microwave and other processing methods such as drying,
meat precooking, roasting, pasteurization of ready-to-eat meal,
blanching, frying, thawing and extraction to reduce processing
time and increase throughput.
Pasteurization of packaged food products using microwave
heating is an interesting technology. In the 1980s at least 5
European companies developed this technology including Alfasta
(Sweden), Berstorff (Germany), APV-Baker and Microwave
Systems (England). OMAC company (Italy) is a leading company
which develops horizontal cylindrical chambers wherein the
packaged food products move through 5 working sections:
1) compression 2) microwave heating at 2,450 MHz 3) holding
4) cooling and 5) decompression.

DEC 2019 FOOD FOCUS THAILAND 33

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