What is shelf life?

What is shelf life?
 Length of time a product can be stored until degradation occurs.>Foodstuffs will gradually degrade, (growth of organisms) 
 >undesirable and unfit for consumption 
 >changes in flavour, smell, texture, and appearance

 Factors that affects the food shelf-
 1) Changes in water content (result of contact with the air) 
example : -moist foods becoming dry -dry food absorb water vapour from air, become moist, vulnerable to microbial degradation 
>Increase exposure to air , increase the rate of oxidation 
 -decrease in nutrient value, discolouration of the surface, rancidity. 

 2) Chemical reaction 
>result in pH changes, development of other undesirable flavours, colour changes in food, decrease in nutritional value. 

3) Light 
>provides energy for photochemical reaction to occurs. 
>rancidity, fading of the colour, oxidation of the nutrients (vitamins). 

4) Temperature 
>increase in temperature, increase in the rate of degradation of food. 
>water molecules will either chemically bonded to carbohydrate or protein polar group. 
>changes in temperature, change in the force of attraction between carbohydrates or protein chain with water molecules. 
>influence how much water molecules it can hold. Thus affecting texture, softness of the food.