Mod. 10.docx

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Food, Nutrition and Health
FNH 200
Nooshin Alizadeh- Pasdar

MODULE 10: Preservation of Food with Ionizing Energy Introduction - food irradiation = controversial method of food preservation - controversy stems from unknown and unfamiliar – radioactive fallout, accidents at nuclear plants, confusion in minds of general public with radiation-related phenomena (nuclear war, weapons) Radiant Energy - radiation = emission and propagation of energy ( found within electromagnetic spectrum of radiation) through matter/space by electromagnetic disturbances - radio waves , microwaves, visible light, ionizing energy: different forms of energy vary in frequency, wavelength, energy value, penetrating power, effects on biological systems - long wavelengths, low penetrating power: microwaves, visible light, IR, UV rays  microwaves = heating properties; absorbed by food up to 5-7.5 cm depth; waves travel in straight lines through air, glass, paper, plastic, reflected by metals; absorbed by water => heat generated via intermolecular friction from vibrating water m/c in food  infrared energy = can generate heat; reach temperatures above 100°C; ovens, toasters, IR lamps to keep food warm - short wavelengths, high penetrating power, ionizing energy: x-rays, beta, gamma rays; energy sources in food irradiation Food Irradiation - food irradiation = application of radiation in form of ionizing energy to foods - Health Canada definition: “the treatment of food with ionizing radiation” from…  gamma radiation from cobalt-60 or cesium 137  x-rays from machine operated at or below 5 MeV  electrons from machine operated at or below 10 MeV - gamma radiation = electromagnetic radiation having short wavelengths, similar to short x-rays; cobalt-60 and cesium 137 emit gamma rays as disintegrate => does not induce radioactivity in food - x-rays = electromagnetic radiations highly energetic and short wavelength; produced by x-ray machines (only when turned on) emitting beam of fast electrons hitting metal target in vacuum - the gray = unit of energy absorbed by food irradiated with ionizing energy; 1000 Gy = 1kGy; most ionizing radiation processes worldwide allow doses less than or equal to 10kGy - Atomic Energy of Canada Limited (AECL) is Canadian federal crown corporation that is leading agency development of food irradiators using cobalt 60 - Canadian Nuclear Safety Commission (CNSC) regulates use of nuclear energy material in Canada - cobalt 60:  produced in Canadian-built Candu reactors  contained with stainless steel rods used to control rate of nuclear fission  irradiation process:  food pre-packaged in boxes loaded into pallet carrier where conveyor moves food in pallets  pallets carried into chamber with irradiation source (cobalt 60)  pallet carriers move through irradiator room and around cobalt 60 source at a speed that required absorbed dosage is attained  absorbed dosage depends on time food exposed to irradiation source  dosimeters placed with food to measure dose absorbed (kGy)  irradiated food pallets exit to unloading station physically separated from loading station so treated and untreated foods not mixed  used as energy source in food irradiators, irradiators for sterilizing medical supplies (bandages, specimen containers) and devices, or irradiators for cancer therapy Effects of Ionizing Energy Absorbed by Food Preserving Principle - basis of food irradiation is ability of absorbed quanta of energy to dislodge electrons from molecules with creation of free radicals without inducing radioactivity in food - free radicals = new molecular fragments possessing unshared electrons; extremely reactive, tend to react with other free radicals or molecules with unshared electrons - 1/6 billion chemical bonds in bacteria or food molecules broken by irradiation => as a result: formation of ion pairs and free radicals, reaction of free radicals with others => chemical and physical phenomena => form mechanisms for inactivation of microorganisms, enzymes, alterations of food during irradiation - changes in food by absorption of ionizing energy arise from both direct and indirect effects (ex. Hydrogen and hydroxyl – free radicals produced by gamma irradiation of water m/c; only exist for ~0.0001 sec but generate hydrogen peroxide (H2O2), an antimicrobial agent) - direct effect kills microorganisms directly – “the damage occurring from ionizing radiation can be random and extensive, making DNA repair near impossible” - even small DNA changes can destroy bacterial cells -disruption of DNA by irradiation: destruction of insects, inactivation of parasites, delay ripening, prevent sprouting  Free radical unique to irradiated food? - no; oxidative reactions in foods containing unsaturated fats also have free radicals + Maillard browning reactions + produced within human bodies and other living tissues during normal metabolism -mechanisms (chemical and enzymatic) for inactivation of free radicals within human body and other living tissues  Does irradiated food become radioactive? - no; approved irradiation sources provide enough energy to knock out electron from outer orbit but not enough to penetrate nucleus or eject neutrons, which induces radioactivity - radioactivity in food requires min of 15 MeV of energy; max energy outputs allowed are 5 or 10 MeV Changes that can occur in Food during Irradiation -molecular changes in irradiated foods similar to those in non-irradiated foods such as those treated by thermal processing - few unique radiolytic products found at trace levels but not of significance; no evidence of harmful effects - other indirect effects of irradiation: radiolysis of water m/c to produce hydroxyl radicals; reactions in foods of peroxides => peroxide free radicals with fats => lipid oxidation (rancidity) - some vitamins sensitive to radiation - extent of irradiation effects on macro/micronutrients dependent on dose of irradiation  3 methods of minimizing undesirable changes during food irradiation 1) Irradiation in frozen state - free radicals produced at lesser extent when water frozen - frozen state delays free radical diffusion and migration to food - D10 values change as water in product freezes 2) Irradiation in a vacuum - removing O2 from system may minimize reactions - removal of O2 may also have protective effect on microorganisms 3) Addition of free radical scavengers - ascorbic acid (vit. C) great affinity for free radicals - consumption of free radicals via reactions between scavengers and free radicals Irradiation Methods and Doses Dose (kGy) Purpose Examples <10 - inhibit sprouting of veggies Potatoes - kill insect eggs, larvae Wheat - delay ripening Bananas - inactivate parasites Pork
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