Unit 8 - Enzymatic and Thermal degradation products of lipids: Formation of flavors and off-flavors

T or F: Enzymatic reactions of lipids can create flavors and off-flavors

Lipids occur in all _____________ in varying concentrations, and are associated with ___________ and ____________ functions, In addition they function as long-term storage _____.

T or F: With a few exceptions lipids occur in all types of food

Oils and fats are pure lipids which in practice contain one lipid class, the ______________.

Major components of lipids are _________ and ________ fatty acids

Lipids can undergo 3 types of reactions that lead to the formation of compounds able to modify flavor properties of food.

What is the main fatty acid found in olive oil:

T or F: Saturated fatty acids require much more energy to react with oxygen to break the carbon - hydrogen bond to replace the hydrogen with oxygen

T or F: Most of the fatty acids present in butter are saturated so it is harder to make it react with an oxygen

Sugars cannot undergo ____________as quickly as fatty acids with allylic groups. Fatty acids are the only ones that can do that at room temperature.

T or F: Once fatty acids are oxidized, they will start breaking down and this is why we should have enough antioxidants in our diet to prevent such oxidation from happening in our bodies

Among the major components of the food, the ______________________ are the only class of compounds which even in physiological conditions are rapidly degraded by a _________________ reactions to a great number of volatile compounds which, in part, exhibit very low ___________________ thresholds

In saturated and unsaturated lipids, all positions of the hydrocarbon can be attacked by ____________ with the formation of a large number of volatile compounds. The minor components of lipids such as _____________ and _________ fatty acids and sterols must not be forgotten when considering lipids as flavor precursors. In various foods such as tomatoes, butter, peaches, it is from these that the volatile substances arise which are important for the typical aroma.

T or F: If we do not have free radicals initially, no chain reaction will occur

The familiar rancid odors of deteriorated fats and oils result from ____________________________________. The course of the reaction is the same whether the acids are esterified or free and occurs in 3 steps: initiation stage, propagation stage and termination reactions

The ______________ produces small numbers of highly reactive free radicals, molecules with unpaired electrons

In the _________________ oxygen reacts with the free radicals produced in the initiation stage to form fatty acid _____________. These hydroperoxides break down to generate more __________ which can either attack more fatty acids and/or cycle with more oxygen to maintain a chain of reactions.

When sufficiently high concentrations of free-radical species are formed, they tend to react together in ____________________ to give polymers or decompose to form stable end-products characteristic of rancid fat: (3)

Cis-hex-3-enal, butanedione, pentane-2,3-dione, and penta-2,4-dienal give the the characteristic odor of ______________________

When a lower dissociation energy is needed, the initiation step will occur more _________

The free radical lipid oxidation reactions involved both during ___________ and in ______________ follow the same basic pathways (described above) and result in similar types of volatile products

In food the futur of hydroperoxides depends on the______________

Hydroperoxides are extremely heat _________. At lower temperatures, they are more stable, and more may build up before ___________ occurs. This leads to different proportions of the various radical intermediates, resulting in different levels of volatile products in heated vs stored foods.

Hydroperoxide formation at the gamma or delta positions is believed to be responsible for the formation of gamma and beta _________ via cyclization of the resulting hydroxy acids. Most gamma and delta lactones have flavor thresholds in the 7-500 ppb range. These compounds are typically used as flavorings in __________, hazelnut and other nut flavor formulations and in a number of ________ formulations