As a chemist in a food lipids laboratory, you wish to determine the extent of li
ID: 105491 • Letter: A
Question
As a chemist in a food lipids laboratory, you wish to determine the extent of lipid oxidation in your company’s premier brand of potato chips. You have found that the soybean oil in which the potatoes are fried is oxidizing. A major fatty acid in soybean oil is linoleic acid (18:2, -6). Linoleic acid accounts for approximately 56% of total fatty acid methyl esters in soybean oil. Based on this situation, address the following questions: Gas chromatographic analysis of the oxidized soybean oil reveals the presence of the unsaturated, off-flavor aldehydes, 2-octenal and 2,4-decadienal. Select one of these aldehydes and clearly illustrate and explain in a mechanistic manner using step-by-step reactions through initiation, propagation, and decomposition stages its specific formation from the autoxidation of linoleic acid. Clearly label the stages of oxidation and the carbon numbers on all structures. Explain the chemical mechanism by which a phenolic antioxidant (e.g., BHA) can retard or inhibit the formation of the selected aldehyde via autoxidation of soybean oil.
Explanation / Answer
Lipids oxidation :- lipids(fatty acids,triglyerides,etc),undergo redox reaction,reacting with oxidising agents /oxidents,in general displaying with adding 'oxygen' or loosing 'hydrogen',and changes into 'oxidised form'.The existance of unsaturated fatty acids in oils and fats is the intrinsic reason for lipids oxidation.
Mechanism of lipids oxidation:-In general lipids oxidation,includes 3 phases,initiation(unsaturated fatty acids reacting with initiator to form radical),propagation(radical reacting with other fatty acids to propogate as chain reaction,)and termination(high concentrated radical interactingeach other for non-radical compounds).The primary oxidation product formed in the first stage can be further decomposed (from smaller volatile compounds such as aldehyde,ketones ,alcohols,etc.)or polymerized (from dimmer or oligomers).
By mechanism,lipid oxidation can be divided into auto-oxidation,photooxidation and enzymatic oxidation .
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