Rancidity in fats and oil

Rancidity

Rancidity can be defined as the spoilage of food in a way that it changes its color and flavor to the form which is unpleasant to smell and taste. This mostly occurred in foods which are stored for extended period of time in conditions that is not suitable to that specific food. The term rancidity can be applied to such changes in fats and foods containing these odorous compounds. oils are more susceptible to rancidity.

Following are some characteristics of rancidity.

·        Undesirable changes in odor, flavor, color and consistency

·        Inactivate vitamins A and E

There are three types of rancidity

1.     Oxidative rancidity

2.     Hydrolytic rancidity

3.     Microbial rancidity
                                         

                              Oxidative rancidity

·        Oxidative rancidity occur due to oxidation of fatty acid chains, especially by the addition of oxygen at C=C bond mostly in unsaturated fatty acids.

·        Oxygen, which is imported in this reaction initiate the reaction across triacylglyceride molecules.  

                     

                                  

·        Oxidative rancidity is catalyzed by inorganic elements such as copper and iron in the presence of light and high temperature.

·        The process proceeds by the free radical mechanism which is catalyzed by light in the presence of enzymes and metal ion

·        The fatty acid free radicals generated at the onset of the oxidative process yield peroxides and hydroperoxides which later breaks up into odorous, compounds such as aldehydes, ketoses, alcohols, etc having unpleasant taste and smell. 

 Hydrolytic rancidity:

·        Hydrolytic rancidity is caused by the breakdown of lipid into fatty acid and glycerol.

·        Mostly occur as a result of lipase hydrolysis of oils and fats. 

·        Occur more rapidly in the presence of enzymes, heat and moisture.

·        The water present in the food and high temperature will increase the rate of hydrolysis to fatty acids.
                        

·        Lipases occur naturally in fats and oils but may come from microbial source.

·        Efforts are usually carried out to destroy these enzymes during processing.

·        Lipases are sensitive to heat and denatured during heat treatment.

·        When fats and oils are stored in airtight containers in a dark, cool place, deterioration by oxidation is minimized.

·        Addition of antioxidants such as Tocopherols helps in the retention of natural characteristics of fats and oils.

           
                                Rancidity of oil