Biomedical Engineering Reference
In-Depth Information
the thawing time, thus reducing drip loss and improving product quality (Li and Sun
2002
). Thus, it seems that acoustic thawing is a promising technology in the food
industry if appropriate frequencies and acoustic power are chosen.
Application in ready
-
to
-
eat products
: Cooking of foods and meat products through
conventional methods exposes surfaces to elevated temperatures leading to over-
cooking at the outside while interior portion still remains undercooked. This leads
to a reduction in the quality of the product. Ultrasound has the ability to provide
improved heat transfer characteristics, which is a key requirement to avoid such
problems, and these have been utilized in cooking. Ultrasound cooking provides a
signifi cantly faster cooking rate and higher post-cooking moisture content and
greater myofi brillar tenderness. An additional advantage is that ultrasound-cooked
muscles have two to fi ve times less cooking losses than those cooked by boiling and
convection.
Thermal pasteurization and sterilization are the most common techniques cur-
rently used to inactivate microorganisms and enzymes in food products. Nevertheless,
the effectiveness of these methods has high time and temperature requirements,
which leads to deterioration of functional properties, sensory characteristics and
nutritional value of food products (Lado and Yousef
2002
; Piyasena et al.
2003
).
High power ultrasound is known to damage or disrupt biological cell walls resulting
in the destruction of living cells. The ultrasonic disruption of microorganisms has
been explained by acoustic cavitation and its physical, mechanical and chemical
effects that inactivate bacteria and deagglomerate bacterial clusters or fl ocs (Joyce
et al.
2003
). It is supposed to be cost-effi cient and environmental friendly approach
for supply of safe foods to the consumer. It has also been found that the microbial
mortality rate is highly dependent on ultrasound frequency, wave amplitude and
volume of bacterial suspension (Raso et al.
1998
). While a frequency of about
20 kHz is usually applied for microbial inactivation, the resistance of spores, Gram-
positive and coccal cells to ultrasound are higher than vegetative, Gram-negative and
rod-shaped bacteria (Feng et al.
2008
). Thus unfortunately very high intensities are
needed if ultrasound alone is to be used for permanent sterilization. However, the
use of ultrasound coupled with other decontamination techniques, such as pressure,
heat or extremes of pH is promising. Thermosonic, manosonic, and manothermo-
sonic treatments are likely to be the best methods to inactivate microbes, as they are
more energy-effi cient and effective in killing of microorganisms.
The advantages of ultrasound over heat pasteurization include, minimized fl a-
vour loss, greater homogeneity and signifi cant energy savings (Piyasena et al.
2003
).
In combination with heat, ultrasound can accelerate the rate of food sterilization,
thereby lessening the duration and intensity of thermal treatment and the resultant
damage (Piyasena et al.
2003
). According to Lillard (
1993
), salmonellae attached to
broiler skin were reduced upon sonication in peptone at 20 kHz for 30 min. Results
of research carried out by Dolatowski and Stasiak (
2002
) proved that ultrasound
processing was having a signifi cant infl uence on microbiological contamination of
meat. Thus high intensity ultrasound has found its application in meat industry to
improve meat tenderness, cooking performances, nutritional value and production
of safe meat and meat products.
