Info

Thiamin retention c

Thiamin retention c

230 240 250 260 270 280 290 300 Temperature (°F)

Figure 3. Time-temperature sterilization curve for bacteria (F0 = 6 min) compared with time-temperature destruction curves for 1, 5, 10, 20, and 50% loss of thiamin. Source: Ref. 11.

230 240 250 260 270 280 290 300 Temperature (°F)

Figure 3. Time-temperature sterilization curve for bacteria (F0 = 6 min) compared with time-temperature destruction curves for 1, 5, 10, 20, and 50% loss of thiamin. Source: Ref. 11.

action applies to the destruction of thiamin, which may or may not be the case with other nutrients.

Currently, most aseptically processed products are of fluid nature, although studies are constantly under way to apply aseptic processing to fluid products containing solid particulates, such as soups or stews with chunks of meat and vegetables. These particulates would be the cold spots in the process. Until recently, there has been no way to actually monitor the temperature at these points, and, thus, food engineers have relied on mathematical models to predict temperature changes. Mathematical models to account for heat-transfer coefficients have been demonstrated by Sastry (12). A joint task between the National Center for Food Safety and Technology (NCFST) and the Center for Aseptic Processing and Packaging Studies (CAPPS) resulted in establishing a protocol for use by any company that wants to produce a low-acid aseptic product containing particulates; their aseptic process filing was accepted by the FDA in 1997 (13). This milestone opened a new market for aseptically processed particulate foods, resulting in higher quality and safety, and better color, texture, and overall quality products. To further ensure safety and quality of thermally processed foods, specific guidelines have been set forth by the U.S. Code of Federal Regulations. All plants producing low-acid canned foods must be registered with the Food and Drug Administration (FDA), indicating name and place of business, location, processing method, and list of food products processed. There are four operational levels for low-acid foods: (1) adequacy of equipment and procedures to perform safe processing operations; (2) adequacy of record keeping to prove safe operations; (3) justification of the adequacy of time/ temperature processes; and (4) qualifications of supervisory staff responsible for thermal processing and container closure operations.

Irradiation

Similarly to conventional thermal processing, the concept of irradiation is to temporarily raise the energy level of a system sufficient enough to result in the death of microorganisms, thus extending the shelf life of a product. In the case of irradiation, however, instead of raising the temperature of the system for a given period of time, the system is exposed to a source of radiation, resulting in ionization of individual atoms or molecules to produce an electron and a positively charged atom. The energy of radiation is often measured in electron volts (eV), where one electron volt is the energy acquired by an electron falling through a potential of 1 V (or 1/eV = 1.602 x 10"12 erg). The total effect of the radiation on a given material depends on the energy of each photon, its source, as well as the total number of photons impinging on the material. The relative ionization of electrons varies with the depth of absorption in a given material (absorber). Using irradiation as a technique for preservation allows the foods to be kept cold or frozen during treatment, thus potentially allowing greater stability of quality factors of the food product.

In looking at units of measurement for irradiation of foods from an historical perspective, a variety of different units have been proposed. Since the amount of energy absorbed by a material and the amount of ionization produced, as a result of the interaction of radiations with a given material, depend on a number of variables—including the number of particles passing through the material, energy of the particles, and the nature of the absorber— measurement of the radiation dose becomes a complex issue. Early references mention the roentgen (R) as a unit of measure or the amount of energy delivered by X-rays or y-rays to a gram of dry air or 83.3 erg. Since measurements in biological systems, however, were found to range from 93 erg/g in water or biological tissue up to 150 erg/g in bone, it was decided by the International Commission on Radiological Units that the term rad would be used. That is the quantity of radiation that results in the absorption of 100 erg/g at the point of interest (14). Now the radiation absorbed is conventionally reported in units of grays (Gy) or kilograys (kGy), where 1 Gy = 1 J/kg (1 J = 107 erg).

Although the concept of using ionizing radiation for the preservation of foods has existed since about 1945 and near-commercialization since the end of the 1950s, its actual practice as a common food processing technique still has not taken a strong hold in the United States even at the close of the twentieth century. One of the reasons contributing to this delay was the passage of the Food Additives Amendment to the Food, Drug and Cosmetics Act in 1958, which classified radiation as a food additive rather than a preservation processing technique. This legislation resulted in extensive and time-consuming testing before acceptance could be considered (15). Although the first actual approval of irradiation of a food product in the United States was for insect disinfestation of wheat flour in 1963, approval for the first meat product for the control of Trichinella spiralis in pork was not until 1985. This was followed by approval in the United States of irradiation of chicken in 1990 and beef in 1997 (Table 1). A review by Pauli and Tarantino (16) presents the FDA's standards by which they determine safety of proposed applications of radiation. The major areas that they pursue to ensure safety include radiological, toxicological, and microbiological safety and nutritional adequacy. From a radiological point of view, there is no concern since the currently approved radiation sources are of too low an energy level to induce radioactivity. Assessment of the toxicological safety of irradiated foods was accomplished through the Bureau of Foods Irradiated Food Committee, set up by the FDA. After going through a series of assessments based on animal feeding and mutagenicity studies, the group concluded that radiation doses below 1 kGy present no evidence of possible toxicological risk. For larger radiation doses it was determined to assess the process on a case-by-case basis, particularly foods consumed in significant quantities.

There has been a great deal of controversy over irradiation of foods and its safety to both workers in the plants conducting the treatment as well as the handling and consumption of irradiated food products. To a large extent these concerns are still present, but with the education of consumers regarding safety and benefits of irradiation, opinions are gradually changing. Hashim and coworkers (17) made recommendations for increasing consumer acceptance of irradiated foods, including: (1) development of educational programs to increase consumer understanding of the role of irradiation of foods; (2) preparation of informative irradiation labels and/or posters to assure consumers of the safety of irradiated products; (3) conduct television shows, promoting children interaction along with pamphlets and informational brochures; and (4) conduct in-store sampling surveys of cooked irradiated foods. Since the FDA acceptance of irradiation to control growth of microorganisms in red meat in December of 1997, there has been a great deal of changing of public opinion over irradiation as a means to preserve foods. Resurrección and Galvez (18) and Lusk et al. (19) have also discussed the need for consumer acceptance of irradiation as a safe processing method of preservation. At present the consumer's perception of this technique is still questionable but has been shown to greatly improve after conducting educational programs addressing the overall safety of the process.

From a microbiological safety viewpoint, some issues that are raised on the effects of irradiation of foods are whether irradiation may result in the mutation of microorganisms that may lead to more virulent pathogens and, if there is reduction of the spoilage microorganisms, whether, as a consequence, pathogens will be able to grow undetected without competition. The FDA, however, has indicated that radiation-induced mutation is not a concern with respect to increased virulence or increased heat resistance. In fact, Farkas (20) has indicated that radiation is more likely to reduce virulence of surviving pathogens. Other issues of concern involve losses of nutrients. There has been general evidence, however, that indicates conventional cooking alters the nutrient quality much more than irradiation. Macronutrients, including proteins, lipids, and carbohydrates, are not significantly affected up to doses of 10 kGy with only minor changes at sterilization doses of 50 kGy (21). There is evidence that vitamins may degrade with irradiation, which would be expected due to any process that elevates the energy level of the individual food constituents. The degree of degradation will depend on a number of factors such as the dose of radiation, the food type, the temperature at which irradiation occurs and the presence of oxygen. Generally, low-temperature radiation in the absence of oxygen reduces significantly the losses of vitamins as well as maintaining storage at low temperature and in sealed containers (22). Similarly to thermal processing, it has been found that thiamin is the most labile of the water-soluble vitamins in the presence of irradiation processing, whereas vitamin E has been shown to be the most susceptible of the oil-soluble vitamins to degradation from irradiation. The FDA requires that those vitamins most affected by irradiation are not a significant source from that particular processed food product in the overall diet.

Overall quality of irradiated foods may be affected by (i) radiation dose, (2) dose rate, (3) temperature and atmospheric conditions during irradiation (eg, presence of oxygen), (4) temperature and environmental conditions following irradiation during storage, and (5) development of radiolytic products (23). The presence of radiolytic products can result in oxidation of myoglobin and fat, which may result in discoloration and rancidity or other off-odor and/or off-flavor development. For instance, ozone, which is a strong oxidizer produced during irradiation in the presence of oxygen, may oxidize myoglobin, resulting in a bleached appearance. Color changes may be influenced by the packaging environment. It has been reported that irradiated vacuum-packaged meats develop a fairly stable bright pink or red color in turkey breasts, pork, or beef (2426). This stresses the importance of elimination of oxygen before irradiation. Irradiation in the frozen state minimizes movement of free radicals to react throughout the food system and, thus, can minimize sensory quality issues. According to Kropf et al. (27) and Luchsinger et al. (28), any irradiation-induced off-odors may be removed during conventional cooking; however, studies are ongoing to investigate. Another issue that should be considered is the effect of the type of packaging that is used to prevent the evolution of hydrogen, low-molecular-weight hydrocarbons, and halogenated polymers (29). Packaging materials must be approved by the FDA according to the 21 CFR 179.45.

Flavor-transfer problems to the food could occur as a result of using conventional fresh meat overwrap (eg, polyvinylchloride). The development of detection methods for irradiation of foods is currently an active area of investigation. This is important from a regulatory compliance view point (15). With the development of these methods, there should be an acceleration of approval of irradiated foods as well as new applications and enhancement of international trade. Since irradiation involves no major chemical, physical, or sensory changes in foods, minute changes must be focused upon. Glidewell et al. (30) prepared a comprehensive review on detection methods for irradiated foods. For example, detection of hydrocarbon formation from irradiated lipid-containing foods offers a potential method of detection. Crone et al. (31) detected the formation of 2-alkyl-cyclobutanone formed from fatty acids in irradiated but not cooked foods. Other methods of detection include measurement of cell membrane damage through measurement of electrical impedance, electron spin resonance, and thermal and near-infrared analysis.

From a microbiological point of view, the predominant spoilage organisms are Gram-negative psychrotrophic microorganisms, which are very susceptible to irradiation (32). It has been shown that doses of about 1 kGy virtually eliminate Gram-negative microorganisms. However, it is not as effective on Gram-positive lactic acid-producing microorganisms. Nevertheless, refrigerated storage of meats has increased dramatically as a result of irradiation. Lambert et al. (33) found pork loin slices packaged under nitrogen and irradiated to 1 kGy had an extension of 21 days beyond the control at 5°C. As with TDT in conventional thermal processing, the death of a microorganism resulting from exposure to radiation can also be evaluated by plotting the logarithm of the surviving fraction, in this case, against dose. With thermal sterilization, the effect of kill is not solely dependent on the quantity of heat absorbed by the cell but also on the intensity factor (temperature) and on time. Radiation sterilization, on the other hand, is actually less complicated since the intensity factor is called dose rate, or the amount of radiation absorbed by the cell per unit time. Although dose rate has some lethal effects, it is possible to relate radiation effects to dose alone according to the following equation: n = nge~D,D'>, where n = the number of live organisms after irradiation, n0 = the initial number of microorganisms, D = dose of radiation received, and D0 = constant dependent on organism type and environmental factors (Fig. 4).

Depending on the dose level of radiation energy applied, foods may be pasteurized to reduce or eliminate pathogens or they may be sterilized to eliminate all microorganisms. The approved sources of radiation for food use include y-rays (produced by radioisotopes cobalt-60 or cesium-137) and machine-generated X rays (with a maximum energy of 5 x 106 electron volts [eV]) or electrons (with a maximum energy of 10 MeV).

The Mediterranean Diet Meltdown

The Mediterranean Diet Meltdown

Looking To Lose Weight But Not Starve Yourself? Revealed! The Secret To Long Life And Good Health Is In The Foods We Eat. Download today To Discover The Reason Why The Mediterranean Diet Will Help You Have Great Health, Enjoy Life And Live Longer.

Get My Free Ebook


Post a comment