Food Biochemistry and Food Processing (2 edition)

BLBS102-c39 BLBS102-Simpson March 21, 2012 14:20 Trim: 276mm X 219mm Printer Name: Yet to Come

754 Part 7: Food Processing

have been applied for pasteurization applications (Patterson and

Loaharanu 2000). Although high irradiation doses have intense

and effective microbial inactivation action, they are not pre-

ferred since they also destroy organoleptic features of the food

material. Thus, low doses of radiation that are severe enough to

reduce microbial populations and maintain sensorial and nutri-

tional quality of foods are generally applied. FDA regulations

specify the maximum radiation dose for control of food-borne

pathogens in fresh or frozen, uncooked poultry products (3 kGy);

refrigerated, uncooked meat products (4.5 kGy); and frozen, un-

cooked meat products (7 kGy) (FDA 2005, Komolprasert 2007).

Low dose (1 kGy maximum) is imposed for control of growth

and maturation inhibition in fresh foods. However, much higher

dose of 30 kGy is imposed for microbial disinfection of dry or

dehydrated spices.

Many studies have demonstrated that low-dose radiation is

useful in improving microbiological safety of fresh-cut fruits

and vegetables without significant change in appearance, tex-

ture, flavor, or nutrition quality (Kim et al. 2006, Niemira and

Fan 2009). Gamma radiation of broccoli, cabbage, tomatoes,

and mung bean sprouts at the dose of 1 kGy resulted in more

than 4 log reduction inListeria monocytogeneswithout signifi-

cant changes in appearance, color, taste, and overall acceptabil-

ity (Bari et al. 2005). Usage of low energy X-ray irradiation

(1 kGy surface dose) on lettuce caused 5 D reduction inE. coli

O157:H7 (Jeong et al. 2010). Reduction in theE. coliO157:H7

count without any effect on quality of spinach leaves was noticed

when gamma irradiation (doses of 0.3–1 kGy) was used (Gomes

et al. 2008). Along with the effect on microorganism, radiation

also denatures enzymes in foods. Latorre et al. (2010) reported

that when red beets were treated with 1–2 kGy gamma radia-

tion, peroxidase (POX) activity increased significantly with the

increasing radiation dose, whereas PPO activity increased only

for a radiation dose of 2 kGy. The trend was attributed to the

higher stiffness and to the rise in tissue elasticity after irradiation.

As a result, color pigments such as betacyanin and betaxanthin

did not change after 1 kGy radiation but decreased sharply at

2 kGy. A detailed review on the use of irradiation in the fruits

and vegetables has been given by Arvanitoyannis et al. (2009).

There are challenges associated with producing and market-

ing irradiated food products. Although it is well established that

food products processed using appropriate low dose of radia-

tion is safe to consume, there continues to be some widespread

hesitation by consumers. There is a strong opposition in the

European Union to irradiated foods, but as food safety takes

center stage internationally and people prioritize food safety,

these attitudes may shift. In the United States, a large number of

irradiated food products are available and without any significant

opposition from consumers. There are strict regulations limiting

the marketing of irradiated products in the United States. The

Federal Food, Drug and Cosmetic Act deems a food product to

be adulterated if it has been intentionally irradiated (unless the

irradiation is carried out in compliance with an applicable reg-

ulation under the prescribed conditions of use specified in the

regulation). Irradiated products are required to be adequately

labeled. Further, since most foods are generally prepackaged in

their final form before irradiation, there are serious constrains

on the type of packaging materials that can be used. Komol-

prasert (2007) discussed some of the constraints of irradiation

on packaging materials. To ensure that components of the pack-

aging materials that have been irradiated at a given level do not

migrate into the food, the regulation stipulates that the use of

packaging materials for irradiated food is considered a new use

and is subject to premarket safety evaluation and approval. In

general, development of new methods of irradiation detection

and chemical analysis of trace elements in foods could expedite

introduction of safe and quality irradiated products and enhance

consumer confidence in accepting the products.

Ultrasound

Ultrasound processing is the application of high-intensity sound

waves (20–100 kHz) on foods. The technology can be used

mainly in two ways: as a diagnostic tool for nondestructive

quality evaluation and as energy for processing (Mason et al.

2005). In the past, ultrasound has been used in quality assess-

ment of agricultural produce (preharvest and postharvest) but is

now increasingly being applied in processing. Ultrasound can

be applied for various operations such as cell disintegration, ex-

traction (phenolic compounds, pigments, lipids, proteins), mix-

ing, acceleration of enzyme activity and microbial fermentation,

emulsification, fruit juice processing, and many other uses. Fur-

ther, ultrasound has also been used for enzyme inactivation and

microbial reduction in food. The effectiveness of ultrasound in its

antimicrobial action is based on controlling critical factors such

as frequency and intensity of wave and time of exposure. Actual

application depends on the type of microorganism, temperature,

and the nature of the food. In fluid systems, ultrasound induces

rapid appearance, growth, and collapse of bubbles or cavitations,

leading to considerable agitation, localized “hot spots,” and in-

creased bulk transport within the mass (Mulet et al. 2003). In

solids, ultrasound produces series of rapid compression and ex-

pansions of the material comparable to repeated squeezing and

releasing of a sponge, which enhances mass transfer and creates

microchannels for fluid movement (Floros and Liang 1994).

Thus, when applied to solid–fluid systems, both internal and ex-

ternal resistances to mass transfer between the solid and liquid

phases are affected. The interaction of ultrasound in solid–fluid

interfaces can produce a microagitation in the immediate vicinity

of the solid surface, resulting in reduction of diffusion bound-

ary layer thickness (Mulet et al. 2010). It was reported that the

extractive value of herbs such as for fennel, hops, marigold, and

mint increased by 34%, 18%, 2%, and 3%, respectively, in water,

whereas in ethanol, there was an increase of 34%, 12%, 3%, and

7%, respectively, when ultrasound extraction was applied when

compared to conventional methods (Vinatoru 2001). Different

solvents may present varying effect on extraction effectiveness

of ultrasound. For extraction of carnosic acid from rosemary, ul-

trasound improved the relative performance of ethanol such that

it was comparable to butanone and ethyl acetate alone. Thus,

ultrasonication may reduce the dependence on harsh solvents

and enable use of environmentally benign solvents (Albu et al.

2004). Knorr et al. (2004) and Vilkhu et al. (2008) provided

good review of applications of ultrasound in the food industry.