Midterm 2 - food irradiation and browning reactions

Ionizing radiation

Radiant energy with some penetrating power which do not produce radioactivity in treated foods

Cold pasteurization

Radiation of food does not produce significant heat in foods

Radiant energy: invisible (long)

- radio

- infrared (heat)

Radio wavelength

Very long

Infrared wavelength

800 or more

red, orange, yellow, green, blue, violet wavelength

400-800

UV wavelength

13.6-400

Radiant energy: visible

Red, orange, yellow, green, blue, violet

Radiant energy: invisible

UV

X rays wavelength

100-150

A,b, delta rays wave length

Less than 100

Cosmic rays wavelength

Very short

UV light inactivates MO on the _________ of the food

Surface

X-rays are at

Experimental level

Alpha particles

Helium atoms minus 2 electrons (low penetration)

Beta particles

High energy electrons

Delta rays

Strong penetration power

In 1985, FDA allowed irradiation of

- strawbs

- poultry

- ground beef

- pork

RAD

radiant absorbed dose

- a measure of ionizing energy absorbed

Low RAD =

Up to 1 KGY

med RAD =

1-10 KGY

High RAD =

10-50 KGY

GRAY =

100 RADS

KRAD =

1000 RADS

MRAD =

1 000 000 RADS

The electromagnetic radiation differs in

- wavelength

- frequency

- penetration power

A light bulb emits visible energy; however, there are other forms of energy that cannot be detected by the human eye, like cosmic rays, ___________, and ____________

X-rays

Gamma rays

Ionizing radiations penetrate food materials to varying degrees, depending on the nature of food and ________

Density

Currently, radiation is used for 3 purposes

1. Control insects in food and spices

2. Inhibit spouting

3. Destroy vegetative cells

Sources of ionizing radiation

1. Natural radioactivity

2. Synthetic radioactivity

3. Flow of electrons

natural radioactivity

- uranium

- breakdown of atomic structure produce radiation energy

Synthetic radioactivity

- cobalt - 60

- high energy bombardment of atoms

Labelling requirements

Must carry the International Food Irradiation Symbol (RADURA)

Include a Written Statement:

Written statement

- treated with irradiation

- treaded by irradiation

- irradiated

Factors important in food radiation

1) SAFETY and Wholesomeness of the Treated Food

2) Resistance of Food to ORGANOLEPTIC Quality Damage

3) Resistance of MICROORGANISMS

4) Resistance of ENZYMES

5) COST

Commercial use of irradiation depends on

- demand for benefits provided

- competitiveness with alternative processes

- willingness of consumers to buy

Applications of irradiation

- increased shelf life

- decreases # of spoilage MO (1-10 KGY)

- inhibit sprouting

- decreased rate of ripening (5-15 days, 1 KGY)

Pathogenic reduction in...

- Salmonella

- Campylobacter

- Trichinella spiralis parasites

Disinfestation (insects)

As an alternative to chemical fumigation

- grains, spices, fruits, veg

Disadvantages of radiation

- Off-flavour and off-odour

- Destruction of B vitamins

- Degradation of protein and other nitrogen compounds

- Production of ammonia, hydrogen gas, CO2, H2S

- Rancidity of fats

- Tissue softness of vegetables

Radiation can cause off

Flavour and odour

Radiation causes destruction of

B vitamins

Radiation causes degradation of

Proteins and other N compounds

Radiation causes production of

Ammonia, h2, co2, H2S

Radiation causes rancidity of

Fats

Radiation causes ________ softness

Tissue

The most radiation-resistant MO is

Bacterial spores

Some elements, such as _____, are naturally radioactive: others can be radioactive by high energy bobmardment of their atoms, in the case of ______________

Uranium

Cobalt-60

____________ ____________ is a sensitive mixture of proteins and becomes thin and watery with a moderate radiation dose of 0.6 Mrad

Egg white

The most suitable emission for food irradiation have good ____________ power so that they will inactivate MO not only on the surface but deep within the food

Penetrating

T or F: in general, preservation by irradiation can be more costly the preservation by heat, refrigeration or freezing

T

Types of browning reactions

1. Non-oxidative

2. Oxidative

Non-oxidative browning reaction

- caramelization

- Maillard browning

Oxidative browning

Enzyme

Schematic of Maillard browning

Sugar compound + amino group = complex sugar-amine compounds

- uncoloured intermediates

- brown compound/flavouring substances

Maillard browning: Melanoids

Complex mixture of compounds giving colour/flavour

Impact of Maillard browning: nutritional loss of

Lysine

Impact of Maillard browning: undesirable

Colour and flavour

Browning can occur during both _______ __________ and food ________ at room temperature

Heat treatment

Storage

Browning can occur over range of

Product composition

Dried eggs are high in

Protein (83%)

Dried eggs are low in

Sugar (3% glucose)

Sugar refining:

Browning caused by traces of amino compounds

Most studies use model system of

Glucose-glycine

Factors affecting rate of reaction

1. Reactivity of sugars: Glucose > Lac > Mal

2. Water activity (aw): max at aw = 0.6-0.7

3. PH: max at higher pH

Reactivity of sugars

Glu > lac > mal

Water activity max

0.6-0.7

Ph max at

Higher ph

Enzymes: catalysts are

Not consumed

Enzymes are

Specific

Some enzymes mediate

Unidirectional reactions

Some enzymes are capable of encouraging both

Forward and reverse reactions

Enzymes used in food processing are derived from

- non toxic/edible plants + animals

- non-pathogenic MO

Majority of enzymes used are

Hydrolases

Hydrolases

Carbs (amylase hydrolyze starch)

Proteinase (pepsin)

Lipase

Inhibition of Maillard browning (ph, aw, sugar, other reactants)

Ph: low

Aw: high

Sugar: non-reducing

Other reactants: sulfite

Oxidative (enzymatic) browning: initial reactions

- oxidative

- enzyme catalyzed

Subsequent reactions

- non-enzymatic

___________ oxidize phenolic compounds into ___________

- phenolase

- O-quinones

Phenolic and phenolase causes

Exposure of cut surface to oxygen (apples, bananas, avocados, lettuce)

Exposure to cut surface to oxygen causes

Rapid oxidation of phenols to o-quinones

Rapid oxidation of phenols to o-quinones causes

Rapid polymerizaiton

Rapid polymerization causes

Brown pigment (melanins)

Undesirable browning effects

- on cut surface of fruits and veg

Desirable browning effects

- tea

- cocoa

- cider

Accepted browning effects

- prunes

- dates

- raisins

Prevention of enzymatic browning

- remove enzymes

- remove oxygen

How to remove enzymes

- reduce ph <3

- heat

How to remove oxygen

- vacuum

- brine/syrup

Not all food colour comes from true plant or animal pigments. One source of colour comes from the action of heat on sugars. This is referred to as ____________

caramelization

Browning reactions may be caused by enzymatic oxidations of __________ and other susceptible compounds if the oxidizing enzymes are not inactivated

polyphenols

T or F: Maillard browning generally proceeds most rapidly during drying when the moisture content is decreased to the range of about 15-20%

T

Enzymatic changes may take place in dried foods during drying, storage, or rehydration. Such changes are prevented by: ____________ of the food or by using sulfurous compounds to inhibit enzyme action

heating (blanching)