SHELF LIFEWho’d want to spend life

on a shelf anyway?

LOOK AT THE SHELF LIFE LIST.

WHAT CHANGES SEEM TO INCREASE A FOOD’S SHELF LIFE?

Try this first…

WHAT IS SHELF LIFE? A food reaches its shelf life when it no

longer maintains the expected quality desired by the consumer because of changes in FlavourSmellTexture Appearance (colour, mass) or because ofMicrobial spoilage

FACTORS THAT AFFECT S.L. Water content

pH

Light

Temperature

Oxygen contact

More water= more microbial growth

Low/High pH= less microbial growth

Light exposure= rancidity, color change, loss of nutrients

Higher temp= higher rate of spoilage… but cooking temps can kill microbes

Oxygen= oxidation which spoils food

RANCIDITY What does “rancid” mean? Chemical decomposition of a fat which

creates an unpleasant smell and/or tasteHydrolytic= breaking a fat back into

glycerol and its component fatty acids Also called ester hydrolysis Fatty acids can taste bitter, sour, or even soapy

Oxidative= oxygen breaks the double bonds, creating aldehydes or ketones Can be catalyzed by light Can be suppressed with antioxidants

SIDE NOTE… Putrefaction= usually anaerobic

microbial decomposition of proteins into amino acids, ammonia (yuck-o) and hydrogen sulfide (super yuck-o)

Fermentation= decomposition of sugars into acid, alcohol, and CO2

HOW IS RANCIDITY PREVENTED?

Processing, Packaging, Additives

See Examples...

PROCESSING Storing at low temperatures

refrigeration + freezing High temperature processing

Pasteurization= heating food to kill bacteria Cooking

Storing with reduced light Opaque packaging Colored glass

Keeping moisture low Drying Salting Sugaring Smoking

Irradiation

PACKAGING Low Oxygen

Packaging with an inert gasVacuum seal (with or without inert

gas) Special Permeable Packaging Little Headspace

Jams, canned goods, oils

Packaging with Modified

Atmosphere

ADDITIVES Ethanoic acid (vinegar)

Pickling delays mold + adds flavor Sulfites or citric acid

Delay browning Nitrates or nitrites

Keep color Sodium benzoate or benzoic acid

Antimicrobial (in juices) Propanoates or propanoic acid

Delay mold + bacteria growth (in breads + cheeses) BHA, BHT, ascorbates

Antioxidants

Find any of these in the food packages at your table?

Supersize Me Part 1

Supersize Me Part 2

MORE ON ANTIOXIDANTS… An antioxidant

a substance that delays the onset or slows the rate of oxidation.

It is used to extend the shelf life of food. Antioxidants are added to foods such as oils, fats and butter as they react with oxygen-containing free radicals and so prevent oxidative rancidity.

Can reduce the formation of free radicals which can lead to cancer or heart disease.

Synergists, so they form complexes with metals, preventing them from catalyzing oxidation

Natural: vitamins E & C, Se, beta-carotene, flavonoids

Synthetic: often have phenols (benzene with a –OH) or tertiary butyls (3 –CH3 on 1 C) (see

data booklet for more structures)

TRADITIONAL FOODS… Pemmican (Native American) Haggis (Scotland) Hangikjöt (Iceland) Century eggs (China) Lutefisk (Norway) Beer Kishke (Russia) Stinkhead (Alaskan Indian) Kimchi (Korea)