Biomedical Engineering Reference
In-Depth Information
were completely inactivated by heating at temperatures above 70 °C for more than
1 min. According to Huang (
2005
), it is possible to reduce
L. monocytogenes
by
7-log in inoculated beef frankfurters using 600 W microwave oven for 12-15 min.
Huang and Sites (
2007
) demonstrated the feasibility of a proportional integral dif-
ferential controlled microwave heating process in the case of in-package pasteurized
frankfurters. Overall rate of inactivation of
L. monocytogenes
was 30-75 % higher
with microwave in-package pasteurization as compared to water immersion heating
at the same surface temperatures. Above fi ndings suggest that microwave thawing of
meat delays the meat spoilage while enhances thawing loss. Microwave used for
cooking of meat and meat products reduces the temperature and time required for
cooking thus makes it faster with either increased or decreased cooking loss and
acceptable toughness as well as tenderness. In the case of pasteurization, microwave
decreases the pathogenic microbial counts. Microwave cooking is also associated
with the non-uniform heating of foods, lack of colour and fl avour development.
Thus, combination of microwave with other heating methods can be used to over-
come these drawbacks.
10.2.1.4
Ohmic Heating
In recent decades, technologies that utilize the passage of electrical current directly
through food products are receiving attraction by the food industry. Some of these
like ohmic cooking technologies are now being used on a commercial scale for
processing a broad range of meat and other food products. Ohmic heating has been
developed two decades ago and now is in commercial scale operations for process-
ing a several food products, especially those containing particulates. Ohmic heating
(OH), also referred to Joule heating, electro-heating, and electro-conductive heating
and it is defi ned as a process wherein electric current is passed through materials
(Vicente et al.
2006
). The heat is generated in the form of internal energy transfor-
mation from electric to thermal within the material (Sastry and Barach
2000
). In
ohmic heating processes, foods are made part of an electric circuit through which
alternating current fl ows, where heat is generated within the foods due to the electri-
cal resistance. Therefore, in a liquid-particulate food mixture, if the electrical con-
ductivity of the two phases is comparable, heat is generated at the same or
comparable rate in both phases. Heat can be generated faster in the particulate than
in the liquid foods. Ohmic methods thus offer a way of processing food at the rate
of high temperature short time (HTST) processes without the limitation of conven-
tional HTST on the limited heat transfer to particulates.
Improved product quality and reduced processing times are the main advantages
of ohmic heating over other conventional processes (McKenna et al.
2006
). Ohmic
processing enables to heat materials at extremely rapid rates (Sastry
2004
) with
substantial reduction in processing time resulting in higher product quality (i.e.
product integrity, fl avour and nutrients retention) (Shirsat et al.
2004a
; Castro et al.
2003
; Tucker
2004
; Vicente et al.
2006
). Ohmic treatment has found a wide range
of applications such as preheating, cooking, blanching, pasteurization, sterilization,
