Food Analysis- FScN 4312W

Laboratory: characterization of various and

Key to Questions

Page 188: 1) What is meant by unsaponifiable matter in lipid samples? Give an example of such a type of compound. Unsaponifiable matter is a group of lipids that don’t break down to and free fatty acids in alkaline solutions. They consist of hydrocarbons, sterols, and aliphatic alcohols with high molecular mass, or can be imitation fat. Specific examples of unsaponifiable matter include cholesterol, paraffin , and olestra.

2) What does a high versus low value tell you about the nature of the sample? A high saponification value indicates that the sample has a shorter chain and a lower molecular weight. A low saponification value indicates that the sample has a longer fatty acid chain and a higher molecular weight. The molecular weight of the fatty acid chain has an inverse relationship to the saponification number this is because the longer the average fatty acid chain is the fewer the number of carboxylic groups per unit mass.

Page 190: 1) In the determination, why is the blank volume higher than that of the sample? In the iodine value determination, the blank volume is higher than that of the sample, because the iodine in the blank (which does not contain fat) will not react with anything (no double bonds). Therefore the iodine is not “used up”, and more titrant is required to reach equilibrium.

2) What does a high versus a low iodine value tell you about the nature of the sample? Iodine value measures degree of unsaturation. A high iodine value indicates that the sample is has a high % of unsaturated fatty acids (mono and poly unsaturated, whereas a low iodine value indicates that the sample constitutes mostly saturated fatty acids.

Page 191: 1) What is a high FFA value indicative of relative to product history? The might have gone through hydrolytic rancidity due to lipase activity, or the oil might not have been adequately refined. High free fatty acid content is an indication of the age of a frying oil. During frying presence of water and heat will result in the hydrolysis of .

2) Why is the FFA content of frying oil important? Free fatty acids in frying oil will cause off flavors. Also FFA are prone to oxidation resulting in the production of secondary metabolites such as malonylaldehydes, which have adverse health effects.

3) In a crude fat extract, FFA are naturally present, but they are removed during processing to enhance the stability of the fat. State and describe the processing step that removes the FFA naturally present. Refining is the process that removes free fatty acids from crude oil. NaOH is used, which reacts with FFA, generating and water that are separated from the oil by centrifugation, and repeated washing with water.

Page 110-111: 1) What are some cautions in using peroxide value to estimate the amount of autoxidation in foods? When using peroxide to estimate autoxidation in foods, you should be careful to prepare the samples in an environment void of oxygen, light, and high temperatures, as these conditions will induce oxidation. Additionally, when reading and analyzing peroxide values, keep in mind that peroxide values of oils and fats tend to start low (for fresh oil) and increase over time (with exposure to oxygen, light, and high temperatures), yet eventually with lots of exposure to these factors, the peroxide value will decrease to near zero, as the primary oxidation products convert to secondary oxidation products as oxidation proceeds. Therefore, a low peroxide value does not necessarily mean that it is fresh.

2) The peroxide value method was developed for fat or oil samples. What must be done to a food sample before measuring its peroxide value using this method?

Before measuring a food sample’s peroxide value with this method, one must extract the fat (for example using an organic solvent such as ethyl ether, or chloroform) and add (to prevent the sample from oxidizing during preparation). Also samples must be prepared in an environment void of oxygen, light, and high temperatures, as these conditions will induce oxidation.