BAEN-625 Advances in Food Engineering

Induced activityHeating effects of radiationBiochemical effectsOganoleptic changes

Radiation may also affect the food itself by inducing radioactivityHeavy particles (protons, deuterons, alphas, neutrons, etc) cannot be used Above certain threshold energy, γ radiation can also induce activity

The products from γ radiation of most elements found in foods have short-livesException is iodine-126 (12 d) from iodine-127For food containing iodine – minimum storage time

Induced activity from electrons is well bellow the maximum concentration permitted in foodsExcept with carbon and chlorine, the half-lives are short (20-33 min)

10 kGy is equivalent to 10 kJ/kg of irradiated materialThe rise in temperature being inversely proportional to the specific heatPossibility that certain foods of low Cp may be damaged by heating effects Cp

DoseT

TmQCp

mED

=Δ

Δ=

Δ=

Biological or nutritive value and the digestibility of food may be concluded to be unaffected by radiationOr slightly lowered if compared with other treatment methodsMore studies are neededUndesirable by-products of radiation action make the food unacceptable

SugarsStarchesMonosaccharide

GlucoseFructose

DisaccharidesSucroseLactoseMaltose

PolysaccharidesStarchfiber

Complex carbos break down into simpler sugarsMonosaccharide break down into sugar acids and ketonesA general reaction is oxidation of alcoholic to carbonyl groups

Responsible for the development of brown color in milk

Polysaccharides are depolymerized and oxidized leading to softening of the food

Large compounds that contain nitrogenSome contain iron, phosphorus, and sulfurThey consist of long chains of amino acids connected by peptide bonds

Most are affected by high doses

LeucineValineLysineArginine

Possible source of objectionable odors and flavors after radiation

Lucine yields isovaleraldehyde which has a strong ‘goaty’ odors, and tryptophan yields indole or related compoundsThese and the sulphur compounds from radiation of methionine and cytine also smell unpleasant

Fast and oils composed of the same element as carbohydrates (C, H, O)Triglycerides -glycerol plus fatty acids

Undergo peroxidation

And carbonyl groups formation (in the presence of O2)Ingestion of carbonyl compounds can produce toxic effects but not proved

OH

O

OCCOOH −−−→−||

All seen susceptible to break down by radiationParticularly vitamins C and EMore sensitive when in pure state than when incorporated in food

Radiation often indices undesirable changes in taste and/or appearance in foodsSome foods are nor suitable for radiationMeat – limiting factor is the development of rancidity in its fat, and the development of bitter, metallic, or burnt flavors

Fish in general appears to be less sensitive to changes than meatsRefrigeration shelf-life of all fishes can be extended by up to 1 to 2 months by dose of 5 kGy(pasteurization)Higher dose levels cause burnt flavors and discoloration

Fruits are very prone to spoilage by radiationSoftening is the most difficult problemGood results obtained with apple juice and strawberries

5 kGy will destroy mould on strawberries and double their shelf-life

Causes mushroom caps to remain closed longer and kills microorganisms that cause spoilage; Thus irradiated fruits and vegetables have longer shelf lives

Milk gives very disappointing resultsQuickly development of unpleasant taste, odor, and color