Biomedical Engineering Reference
In-Depth Information
and Barbosa-Cánovas, 2004). Up to now, few studies have shown the effects of UV on
quality-deteriorative enzymes, and variable resistance has been found among them. For
example, while UV light caused 80% inactivation in PPO, the effect of UV on texture-
related enzymes such as pectinmethylesterase (PME) and polygalacturonase (PG) were
negligible (Barka et al ., 2000; Tran and Farid 2004; Guerrero-Beltrán and Barbosa-
Cánovas, 2006). Some food components are known to be “light sensitive”: carotenes,
tryptophan, certain food pigments, folic acid, vitamins B12, A, D, K, B2 and E, and
unsaturated fatty acid residues in oils, solid fats, and phospholipids (Spikes, 1981).
Riboflavin (vitamin B2) and beta-carotene seem to be the most sensitive in terms of
degradation; however, effects of UV light strongly depend on the wavelength used in the
treatment (Tran and Farid, 2004; Koutchma, 2009). It is well known that milk and milk
products are highly light sensitive and UV irradiation produces undesirable changes in the
sensory and chemical properties (Matak et al ., 2007) whereas in other products, such as
apple cider, no differences in sensory properties have been found (Tandon et al ., 2003 ;
Donahue et al ., 2004 ).
Recent advances in science and engineering of UV irradiation have led to the development
of continuous processing equipment, which rendered UV irradiation a viable alternative to
thermal pasteurization for a range of liquid foods and ingredients (fresh juices, soft drinks,
raw milk, liquid eggs, liquid sugars and sweeteners, etc.) (Koutchma, 2009). Currently,
several companies market continuous UV equipment, such as Dill Instruments Inc (USA),
manufactures an irradiator with a rotating cylinder with four LPM lamps that are able to
process up to 100 l/h of product, and Oesco Inc. (USA), which manufactures a UV processor
with 8 LPM lamps specifically designed to treat apple cider at around 1000 l/h.
13.2.6 Irradiation
Food irradiation is a physical means of food processing that involves exposing the pre-
packaged or bulk foodstuffs, such as tuber and bulb crops, stored grains, dried ingredients,
meat, poultry, fish and fruits, to gamma rays, X-rays, or electrons (Barbosa-Cánovas et al .,
1998). Foodstuffs are generally irradiated with gamma radiation from a radioisotope source,
energetic electrons from particle accelerators and X-rays emitted by high energy electron
beams (Cleland, 2006). The potential application of ionizing radiation in food processing is
based mainly on the fact that ionizing radiation damages the DNA very effectively so that
living cells become inactivated, therefore microorganisms, insect gametes, and plant
meristems are prevented from reproducing, resulting in various preservative effects as a
function of the absorbed radiation dose (Thayer, 1990). The choice of radiation source for
a particular food will depend on thickness and density of the material, dose uniformity,
ratio, minimum dose, processing rate and economics (Cleland, 2006). Gamma rays and
X-rays have high penetrating characteristics, thus they can be used to treat food even in
pallet-size containers (Farkas, 2006). These types of radiation do not induce radioactivity in
foods or packaging materials and are available in quantities and at costs that allow
commercial use of the irradiation processes which are considered safe by the World Health
Organization (WHO) and Food and Agriculture Organization (FAO) (El-Samahy et al .,
2000; Farkas, 2004). The most important parameter in the irradiation process is the absorbed
dose, which is proportional to the ionizing energy absorbed per unit mass of irradiated
material measured in gray (Gy) or 1J/kg (Cleland, 2006). Radiation treatment causes
practically no temperature rise in the product and can be used as a terminal treatment in the
packaged product (Borsa, 2006 ).
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