Chapter 8
Irradiation of Food and Packaging Downloaded from pubs.acs.org by UNIV OF NORTH CAROLINA on 10/23/15. For personal use only.
Irradiation Applications to Improve Functional Components of Fruits and Vegetables Bhimanagouda S. Patil Kingsville Citrus Center, Texas A&M University, Weslaco, TX 78596 and Vegetable and Fruit Improvement Center, Texas A&M University, College Station, TX 77843
Fruits and vegetable are part of our daily diet and it is important to understand the role of postharvest treatment effects on functional components including organoleptic characteristics. Irradiation has multiple benefits in food preservation through several processes such as disinfestations, delaying maturation, sprout inhibition, decontamination, and sterilization. Sensory evaluation studies in different commodities indicate that irradiation treatment does not affect quality and flavor. Quality retention, along with efficacy and efficiency, is critical for many postharvest treatments. Although irradiated fruit retained quality compared to control, very little information is available on the effects of irradiation on functional components. Accumulative evidences from epidemiological, case and cohort studies have shown that functional components such as flavonones, flavonols may prevent chronic diseases such as cancer and cardiovascular diseases. In this chapter, emphasis is given to onion and grapefruit to illustrate the effects of irradiation on functional components. In onion, our results have demonstrated that irradiation at 0.8 and 1.2 kGy doses significantly increased both free and total quercetin concentrations. During the last
© 2004 American Chemical Society
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118 four decades, ionizing radiation has been used as a quarantine treatment for eight fruit hosts that are shipped from Hawaii to the U S A mainland. Flexibility and effectiveness o f irradiation as a quarantine treatment have been demonstrated and proven to be appropriate for tropical fruits crops. However, several recent studies indicated the need of irradiation as an alternative for quarantine treatment in citrus to prevent infestation of Mediterranean (Ceratitis capitata (Weid), Mexican (Anastrepha ludens (Loew), and Carribbean (A. suspensa (Loew)) fruit flies. Our studies, in citrus, showed that low doses of ionizing radiation significantly increased flavonone concentrations. Potential use of irradiation to enhance the levels of functional components is discussed. To remain competitive in international and national markets, optimization of these components may be important for the processing industry.
Introduction Irradiation has been used in food industry for several purposes. Approximately, 40 different irradiated food products have been cleared by 28 countries; some countries such as Netherlands are approving 20 different foods. Irradiation sources are mainly from gamma rays (cobalt-60 and cesium-137), machine generated electron beams (P particles), and X-rays. While X-ray radiation is concentrated in the same direction as electron beams, y-rays from isotopes are emitted in all the directions uniformly (/). Traditionally, irradiation dose was measured in 'rad' (1 rad= 0.0 lGy) but it has been discontinued, and the current unit of measurement is gray (Gy) and it is equal to the absorption of 1 J/kg. A l l the irradiation sources including Cobalt-60's gamma energy can penetrate food, causing small harmless molecular changes to the food. The primary effects of ionizing radiation are ionization, dissociation, and excitation. When ionizing radiation passes through food, it loses energy (energy is absorbed). This absorbed energy or absorbed dose leads to ionization or excitation of atoms and molecules of the matter. Further it leads to chemical changes known to occur when food is irradiated. Free radicals produced as a result of these primary effects of ionization will lead to secondary effects that may interact with water to produce free radicals, which can diffuse far enough to
Irradiation of Food and Packaging Downloaded from pubs.acs.org by UNIV OF NORTH CAROLINA on 10/23/15. For personal use only.
119 reach and damage different important compounds of plant cell (2). Furthermore, radiolysis of water is therefore important in plants with higher water content because of its influence on temperature, p H , and dilution of solution by the presence or the absence of oxygen (3). However, the rise in temperature associated with radiation is minimal, and adverse changes in the food such as altered flavor, odor, color, texture and loss of nutritional quality are minimized (4, 5). Since there is no significant rise in temperature during irradiation, it is called as 'cold process.' Consumer acceptance of irradiated food is a major issue for the food industry. While there are claims that gamma rays would change the chemical structure of food and produce unique radiolytic products (chemicals) that might prove harmful are still in consumers mind, accumulative studies have demonstrated to the U S Food and Drug Administration (FDA) that no significant difference exists between irradiated and nonirradiated foods as far as safety is concerned (6). Initially, many investigations have been undertaken to study the potential use of ionizing radiation for several benefits like inhibition of sprouting (7, 8, 9, 10), disinfecting onions (7), and improving the storage quality (10, 11). Under the permitted irradiation doses, fresh onions did not show any significant changes in the aroma constituents, which are the most unstable flavor components in onion (12). Sensory quality of irradiated bulbs was observed to be better than unirradiated ones (13). Although there were doubts about the prospect for using gamma irradiation as a postharvest treatment for fresh produce (14), the F D A has approved the treatment of fruits and vegetables with gamma irradiation up to 1 kGy dose (15). Although irradiation was proposed as a treatment for fruit susceptible to fruit fly infestation in 1956 (16), only in the last four decades it has been used as a quarantine treatment for several fruits such as citrus (17, 18), mango (19, 20, 21, 22), and papaya (23). Gamma irradiation is used for quarantine treatment to control several fruit flies such as Oriental fruit fly (24) and Mediterranean fruit fly (25, 26, 27). Minimum absorbed doses suggested by U S DA-APHIS for quarantine security of different fruits flies vary from 150 Gy for Mexican fruit fly (Anastrepha ludens (Loew)) to 250 Gy for Oriental fruit fly (Bactrocera dorsalis (Hendel)) with different geographical distribution (28). These irradiation doses for the same insect vary for each host crop. For example, a speculative dose for achieving quarantine security of Mediterranean fruit fly third instars varies from 70 G y for grapefruit in Brazil to 215 Gy for papaya in the U S A (1). Although several species of Anastrepha and Bactrocera probit 9 efficacy can be achieved with 60-100Gy, additional research has been suggested to determine whether the Mediterranean fruit fly and Oriental fruit fly can be controlled with
