Unit 7 - Flavor formation by enzymes and microorganisms Flashcards
T or F: Most aroma compounds generated by enzymes are not heterocyclic compounds
T
Thermally produced flavor compounds are rich in _______________ compounds
heterocyclic
In vegetables, substrates and enzymes are compartmentalized in different parts of the __________ - harder for enzymes to react with substrates ex: if onion is not damaged physically you will not smell it
tissues
____________ enzymes in plants and vegetables act on the precursors or substrates during maturation
endogenous
Flavors generated by enzymes in vegetables and fruits consist mainly of:
aldehydes ketones alcohols esters terpens terpenoids S-containing aliphatic and aromatic volatile compounds
Alternatively, flavors can be produced by the action of ______________ enzymes or microorganisms during fermentation
exogenous
T or F: Phytochemicals are considered secondary metabolites
T
The characteristic aromatic profiles of plants used as a source of flavoring materials depends on a complex mixture of chemicals which have been formed in the plant during the __________________ and remain there more or less intact after harvesting
normal growth cycle
The biogenesis and synthesis of aromatic compounds in live tissue which are metabolically active is a ___________ process which depends on the plant, its variety, its environment during growth, maturation and fruiting
dynamic
T or F: Not all the chemicals found in plant tissue contribute to a desirable aromatic profile, some are odorless and tasteless, others give rise to objectionable attributes or may be even toxic
T
T or F: We can induce stress in the plant to create the secondary metabolites that we want to have
T
In peppers capsaicinoids are ________________ (some peppers have a lot of them and others have a lower amount) - stress the plant more if you want the pepper to be considered very hot and contain a lot of capsaicinoids
antimicrobials chemicals
What are the 2 levels of plant metabolism:
Primary and Secondary metabolism
Covers the growth and development of the individual:
Primary metabolism
Covers the interactions of the individual with its environment
Secondary metabolism
Plants are exposed to severe environmental stresses that induce them to biosynthesize _________________, such as antioxidants, anti-feedants, antibiotics, and others. Without those reactions, they will be exterminated by the stressors.
secondary metabolites
The chemicals produced by plants include flavors, fragrances, pigments, sweeteners, pharmaceuticals and pesticides. These seemingly unrelated collection of chemicals can be grouped together under plant _____________________
secondary metabolites
Secondary metabolites can be functionally distinguished from primary metabolites such as amino acids, nucleic acids, carbohydrates in that they do not seem to have any direct physiological function related to _____________
life and death
Secondary metabolites often seem to act as an interface between the producing organism and its surrounding _______________ such as bright colorful pigments and sweet or pleasant tasting compounds might serve to attract pollinator insects, or bitter chemicals can act to discourage predators that might damage the plant.
environment
Phenylalanine can be converted in different metabolites, it is the primary precursor of ______________
vanillin
Secondary metabolites are often biosynthesized from primary metabolites in specific tissues such as ________, _________ and roots
flowers
leaves
From the metabolism of phenylalanine, we can obtain:
- caffeic acid
- ferulic acid
- eugenol
- vanillin
The flavor compounds of fruits are developed during the:___________________
ripening period
Why can vegetables be well paired with meat products?
They can be paired with meat flavors because meat contained a lot of sulfur aroma compounds in their profile
The flavor compounds of vegetables are developed during the:
- cellular disruption
- no ripening period
- sulfur containing
Esters are the most common character impact compounds in _______
fruits
This fruit ________ has a very potent smell and contains lots of sulfur volatiles compounds, can cause inconvenience to people sitting next to you and the smell is considered a chemical weapon
durian
Flavor formation in vegetables is quite different than in fruits. Vegetables do not have a __________________ as fruits do. While some vegetables will develop partial flavor during growth and the remaining flavor during _____________, most vegetables develop all flavor constituent during ______________. Cellular disruption may be due to cutting a vegetable (garlic or onion) prior ro use or to chewing, this permits the mixing of separated enzymes and substrates. A few examples of vegetables which contain flavor prior to cellular disruption are _________________, ___________ and bell pepper
ripening period cellular disruption cellular disruption celery asparagus
T or F: Similar to flavor formation in fruits, fatty acid, carbohydrate and amino acid metabolism serve to provide the precursors of vegetable flavors. The action of lipoxygenase on linoleic and lenolenic acids to produce volatile carbonyls and alcohols is similar to that of in fruits.
T
The major difference in flavor development lies in the importance of ____________________ ro vegetable flavor
sulfur containing flavor precursors
What are the 3 precursors if aldehydes in vegetables:
- amino acids
- esters
- lipids
Strecker aldehydes can be generated with enzymes and not only ___________
thermally
Aldehydes containing less than 5 carbon atoms usually are associated with the development of ___________, however, unsaturated alkenals containing 5-10 carbon atoms impart desirable flavor attributes to fresh vegetables.
off-flavors
Cis- and trans-2-hexenals are both potent aroma compounds of __________ character
green leaf
The melon-like odor of cucumbers are due __________________
cis-2-nonenal
Aliphatic aldehydes may arise and accumulate in vegetables from precursors such as esters, amino acids and free fatty acids; esters can be hydrolyzed by ______________ and followed by enzymatic oxidation (NADP dependent dehydrogenases) of the resulting alcohols to produce aldehydes; amino acids can be converted to _______________ by the action of transaminases, followed by enzymatic decarboxylation to produce flavor aldehydes; triglycerides in plant tissue can be hydrolyzed by ___________ to produce free fatty acids which in turn can produce long chain aldehydes by the action of __________________ and lyases
esterases
alpha-keto acids
lipases
lipoxygenases
Garlic, Onion, Leek, Chives and Shallots:
Alliaceous plants
Cabbage, Mustard, Horseradish, Broccoli, Brussel Sprout, Turnip and Radish:
Cruciferous plants
The origins of sulfur containing compounds in vegetables (2):
- cysteine sulfoxides
- thioglucosides
From cysteine sulfoxides in alliaceous plants (garlic, onion, leek, chives, shallots)from glucosinolates in cruciferous plants - genus brassicacea (cabbage, mustard, broccoli, brussel, horseradish sprouts, etc). Alliaceous vegetables produce ____________ and related volatiles, whereas, cruciferous vegetables generate ____________
disulfides
isothiocyanates
What are the 2 proposed origins of cysteine sulfoxides:
cysteine or glutathione
Alliin is an example of ___________ found in large amounts in garlic
cysteine sulfoxide
The main precursor of disulfides in alliaceous plants (onion, garlic, leek, chives, shallot) are _________________ l-cysteine sulfoxides which upon the action of allinases produce __________________, the principal component responsible for the odor of fresh alliaceous plants, upon heating, the thiosulfinates are converted into corresponding disulfides which are responsible for the _______________
S-substituted
thiosulfinates (allicin)
cooked flavor
The major thioallyl compound in fresh garlic is ___________. However, when garlic is chopped or crushed, the action of the enzyme alliinase converts alliin to allicin, which is unstable and decomposes to form strong smelling, oil soluble sulfur compounds. Similar type reactions initiated by alliinase occurs in chopped onions to yield the lacrimator ____________________ and other compounds
alliin
propanethiol-S-oxide
The method by which onions and garlic are cooked results in various ____________. In the presence of water during heating, many di, tri, and poly sulfides are formed from thiosulfinates. If, on the other hand, very little amount of water is present and the alliums are in lipids, more complex poly-sulfur compounds could be formed
flavor profiles
The pungent taste of cruciferous vegetables on the other hand are caused by _________________, they have considerable antimicrobial activity, the enzymes responsible for the release of these compounds are __________________ which act upon different thioglucosides (glucosinolates) found in these vegetables to produce the corresponding isothiocyanates.
isothiocyanates
thioglucosidases
The enzymes and the substrates in these vegetables are compartmentalized, the tissue of the plant should be _____________ to bring the substrate close to the enzyme for the generation od the flavor compounds
disrupted
Black and brown mustards and horseradish mainly contain _____________, white or yellow mustards usually contain ____________.
sinigrin
sinalbin
Both types of thioglucosides (sinigrin and sinalbin) can be hydrolyzed by thioglucosidases such as _____________ in the mustard seeds to produce isothiocyanate, the _______________ compound
myrosinase
flavor producing
Thioglucosidases such as myrosinase need ________ for their activation
water
Heating brussel sprouts will release an active anti-cancer agent which is called:
sulforaphane
