accepted technique used for inactivating microorganisms in food,
however there can be a significant change in the functional properties
and contents of food, which tends to reduce the product quality
and freshness. In order to overcome the harmful effects of heat
in deteriorating the quality and aesthetic property of food,
non-thermal technologies for food processing are gaining popularity.
The focus is to lower the detrimental impact on the nutritional
content and quality of food. Therefore, a lot of effort has been
directed in developing new techniques for food processing using
lower thermal intensity and possibly ambient conditions. The technology,
at the same time, must give significantly reduced microbial
activity, ensuring safe consumption of food as well as higher shelf
life for the product [6]. An optimum approach might have to be
developed based on the balance of the microbial safety and
enhancement in the food nutrients and fresh like attributes. Use
of ultrasound (mostly over frequency range of 20–200 kHz) offers
good promise for many applications in food industries and it has
also shown potential in food sterilization achieving the desired
microbial safety levels. The microbial destruction effect of ultrasound
has been attributed to the cavitation phenomenon.
Passage of high power ultrasound through a liquid creates pressure
fluctuations based on the alternate compression and rarefaction
cycles and with sufficient intensity of ultrasound, cavities are generated
when the liquid molecules are stretched enough beyond the
critical distance [7]. These cavities/micro bubbles undergo different
stages of cavitation and subsequently collapse violently generating
hot spots with localized conditions of temperatures around
5000 K and pressures around 500 atm along with liquid turbulence
and high shear effects [8]. It is important to note that controlled
application of ultrasound is required so as to maximize the degree
of inactivation with as low as possible reduction in the nutrient
quality. A similar analogy can be given in terms of application for
intensification of enzymatic reactions where controlled application
is required as stimulus to the enzyme rather than deactivating the
enzyme. Thus there is also need to optimize the different parameters
such as power dissipation, treatment time and duty cycle that
critically decide the cavitational intensity in the processing.
Along with the ultrasound, use of ultraviolet irradiations is also
gaining momentum in food processing technology for its beneficial
anti-microbial properties and possible lower processing effect on
the nutrients as compared to thermal sterilization. The ultraviolet
irradiation affects the DNA of exposed microbial cells by causing
thymine dimer (peptide bonds) formation in the DNA molecules
of the microorganisms, thereby destroying the ability of microorganisms
to grow [9]. The inactivation mechanism depends on the
absorption of UV photons by the genetic materials and subsequently
the formation of dimers which inhibit the transcription and replication
of the cell [10,11]. UV light has already been used in food industries
for fruit juice disinfection [12] and vegetable surface
decontamination applications. FDA has also approved UV irradiation
technology as a safe food sanitation technology that could be used for
food and beverage sterilization applications. Ultraviolet light treatment
is a relatively new process that is becoming more common in
the food processing industry, as it holds considerable promise in food
processing as an alternative to traditional thermal processing [13]. It
is also important to note here that UV light offers some problems in
the processing based on lower penetration levels and inefficient distribution
especially for juices containing solids and at larger scale
operation. Several factors such as the type and length of lamp used,
density, viscosity, turbidity, absorbance coefficient of food material
being treated will help determine the efficiency of UV disinfection.
Ultrasound alone and/or in combination with other techniques
has been reported to be effective against Escherichia coli in model
fluids [14] as well as apple cider [15] and against Listeria monocytogenes
in apple cider [16]. Ultrasound has also been reported to
have lower effects on the quality of fruit juices such as orange juice