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
Chemestatic class of compounds:
non-volatile chemicals that are able to interact with nerve endings in the mouth and generate a pungent feeling
Capsaicinoids have an ________ group instead of an aldehyde, the degree of pungency of the capsaicinoid will depend on the chain
amide
The compounds responsible for the well-known hot sensation of chilli peppers belong to a family known as _________________. These consists of a __________, _____________ and a long chain fatty acids of variable lengths. All three of these segments are necessary for the trigeminal nerve endings to be stimulated; that is, a compound must have all three chemical moieties to be perceived as hot.
capsaicinoids
phenol
amide linkage
What is the scoville unit measurement for capsaicin:
16,000,000
An orally administered capsule of capsaicinoids claiming 100,000 scoville units will correspond to around _______ mg of capsaicinoids
6.6
Large or frequent doses of capsaicinoids reduce the _____________ of an individual to subsequent usage (adaptation). This has caused problems with reproducibility in sensory evaluations.
sensitivity
Capsaicinoids also affect __________ - body temperature actually drops with small doses. This hypothermia is associated with increased, ____________ which is why hot foods are usually eater in countries where the average temperatures are too high for comfort. Large doses of capsaicinoids, on the other hand, can cause desensitization and thus overheating.
thermoregulation
perspiration
SHU stands for:
Scoville Heat units
This measurement is the highest dilution of a chili pepper extract at which heat can be detected by a taste panel:
Scoville Heat Units
What is the active chemical in black pepper:
piperine
During storage, gingerol will be converted to _________
shogaol
T or F: There is a piperidine ring in piperine structure
T
The pungency in black pepper is due to _____________, which has a somewhat different structure from the capsaicinoids. it is not strictly a phenol, but instead contains a _______________ group attached to the aromatic ring. Because of this, piperine is much less pungent than the _________________, but gives a similar type of warming sensation.
piperine
methylenedioxy
capsaicinoids
T or F: Piperine si the only compound responsible for the pungency of black pepper
F (25 key pungent and tingling phytochemicals were found)
Different R groups are available in different peppers such as:
- piperidine ring structure
- pyrrolidine ring structure
- 4-carbon non-cylic amine
When it gets dehydrated during storage, gingerol becomes ___________
shogaol
When we process ginger, the threshold value becomes _______ and the pungency is ________
lower
higher
T or F: Gingerol can undergo retro-aldol reaction due to its B-hydroxy group
T
T or F: Shogaol has a lower threshold value compared to gingerol
T
The higher homologues of gingerols and shogaols have a __________ pungency which follows the same pattern as found among the capsaicinoids
lower
____________ are the main compounds we associate with the fruit flavors
esters
The typical flavors of fruit such as bananas, peaches, pears and cherries are not present during early stages of fruit formation, they entirely develop during a rather brief _____________________. During this period, the primary metabolites (lipids, carbs, proteins and amino acids) are enzymatically converted into secondary metabolites including _____________
ripening period
volatile flavors
Esters make the most important contribution to what we usually perceive as _____________, they are present in higher levels than any other class of compound and also they are present in a greater variety compared to any other class. Most of the esters contribute to the ____________ of the resultant aroma, certain esters have been associated with the aroma of specific fruits such as __________________ with apple, isopentyl acetate in __________ and ethyl butyrate with orange. Esters are biosynthesized by enzymatic esterification of carboxylic acids with alcohols through the action of such enzymes as esterases and acyl CoA-alcohol transacetylase; in general the most abundant alcohol in the volatile fraction of a fruit is usually present in the most abundant ester.
fruit flavors
character impact
methyl butyrate
banana
2,3-butanedione is important in dairy products such as _________
butter
Aromatic aldehydes sometimes constitute the main flavor component of certain fruits; ____________, for example is the principle flavor compound in bitter almond, it is also present in the volatiles of peaches, apricots, cherries and plums; they are generally produced from cyanogenic glycosides by the action of ________________ which hydrolyzes the glycoside into the free sugar and (R)-mandelonitrile, the latter, than undergoes an elimination reaction in the presence of hydroxynitrile lyase to produce benzaldehyde
benzaldehyde
B-glucosidases
Once cyanogenic glucoside encounters __________________ it produces glucose and ______________, this one also undergoes the action of _______________ enzyme which produces benzaldehyde + HCN (hydrocyanic acid)
B-glucosidase
mandelonitrile
hydroxynitrile lyase
T or F: HCN (hydrocyanic acid) is a very toxic gas
T
Lactone are considered ______________
cyclic esters
T or F: Alcohol part of the carboxylic acid can undergo esterfication in the same molecule and form a cyclic ester
T
T or F: Milk fron different animals have different proportions of the various precursors (carbs, proteins, amino acids and fats)
T
_________ is particularly the most important precursor in dairy products
Fats
During the cheese making process, we actually add the enzymes that we want (exogenous) because endogenous enzymes will generate ______________ - deactivation of endogenous enzymes by pasteurization needs to be done
bitter peptides
In contrast to vegetables and fruits in which the endogenous enzymes are responsible for the release of aroma compounds, dairy flavors are generated, in addition to endogenous enzymes. by added ________________ that play a predominant role in the formation of flavors. In general, the flavor of dairy products originates from microbial, enzymatic and _________________ (mostly oxidation) the relative importance of which is not always understood, these transformations give rise to a series of ___________ and _____________ compounds, some of which have been shown to correlate well with some typical dairy flavor notes and some have little indication of their real contribution.
microbial enzymes
chemical transformations
volatiles and non-volatile
For many dairy aroma, the total number of compounds identified is far less than in those foods subjected to thermal treatment, thousands of heterocyclic compounds present in such foods are missing in _______________, the characteristic dairy food flavors are usually related to the occurrence of relatively few key components
fermented ones
Endogenous lipases and proteases are not the ones we want to convert milk into _________ (production of bitter peptides is not what we want)
cheese
The effect of endogenous enzymes of the milk is usually __________ on the flavor of the resultant cheese, for example milk lipases tend to produce a combination of fatty acids which impart an ____________ aroma, milk proteases produce ___________ and branched aldehydes which do not contribute to the desirable aroma. Many of these enzymes are usually inactivated during _____________ of milk. Milk, however, supply the right combination of substrates and flavor precursors that are transformed mainly by the agency of the _____________ and added enzymes
negative undesirable bitter peptides pasteurization microbial
In the coagulation step of cheese making, what do we add to precipitate the protein to be able to separate the solid from the whey:
we add rennet
The methods of cheese manufacture depend greatly on the type of cheese being produced. However, certain steps are common:
1) The coagulation of milk protein
2) Separation of solids
3) Working on the solids to modify the flavor and texture
During aging there are ______________ that we add to affect the particular aroma of characteristic cheeses
aging enzymes
T or F: Aged cheeses are more expensive in terms of refrigeration cost
T
______________, proteolysis and fermentation each play significant roles in the development of cheese flavor. Differences between the milks of different species manifest themselves mainly as differences in lactose, protein and fat levels and in particular in differences in the chemical composition of fat triglycerides. This in turn gives rise to differences in the type and balance (profile) of volatile molecules liberated during fermentation.
Lipolysis
Most of the volatile components of cheese are universally distributed such as ____________, __________, _____________ and ketones. Besides these classes of compounds many cheeses do have in common certain volatiles not found so frequently in other foods. The include short chain fatty acids (__________) which impart the well known pungent notes; 2,3-betanedione (diacetyl) which imparts characteristic creamy note to most cheeses in addition, amines, lactones and ______________________ contribute to the overall flavor of cheese
aldehydes, alcohols, esters
C4-C10
2-methylketones
Without ________________ we do not have the yogurt taste
acetaldehyde
___________ acts as a nutrient for microbials and enzymes needed for the development of starter cultures
Sugar
Which sugar is the only sugar found in cows milk:
lactose
Milk furnishes the flavor precursors for all the fermented products (cheese, yogurt, etc) made from it; the milk lactose, in addition from being a __________ for the growth of the starter microorganisms it is also the the principle precursors of ________________ an important constituent of cultured products, it imparts the characteristic creamy note to most cheeses and other dairy products, it is found in butter, un-ripened soft cheeses such as cottage cheese and also in swiss cheese.
nutrient
2,3-butanedione (diacetyl)
During fermentation, lactose is also converted into ____________, acetic acid and acetaldehyde (important in yogurt flavor along with lactic acid), glyoxal and methylglyoxal (pyruvaldehyde)
lactic acid
What are the possible tastes of amino acids in aqueous solution (pH 6.0):
- sweet
- bitter
- umami
Name the 2 amino acids that have the umami taste:
glutamic acid
methionine
Proteins play an important role in the development of flavor in cheese. The action of proteases leads to the formation of ___________ and __________. Milk proteins (caseins) are the source of ___________ that contribute to the aroma of different cheeses; in cheese, bitterness results from the presence of low molecular weight ___________ peptides arising mainly from casein. _________-casein produces more bitter peptides than B-casein and since goat milk contains very little amounts of alpha-casein, goat milk derived cheeses (such as feta) are ______________.
amino acids peptides bitter peptides hydrophobic less bitter
What are other factors that contribute to the formation of bitter peptides in cheeses:
- cheese microflora
- the type of starter strains
- if the starter culture is deficient in peptidases that degrade peptides to non-bitter products and amino acids
- another source of bitterness in mould-ripened cheese is the presence of the mould itself such as Casecolum This is related to the amount of lactic acid present, since large amounts of lactic acid can stimulate the growth of the mould.
Oxidation of strecker aldehydes leads to the formation of _____________
carboxylic acids (small chain carboxylic acids are important to the aroma profile of cheeses and other dairy products)
On the other hand, the _______ flavor of Swiss cheese is due to a complex formed between _____________ and small peptides, the nutty flavor is also found to be related to the presence of small peptides and _____________; the burned note of __________ cheese to peptides complexed with ___________; these peptides and amino acids are produced during the ripening of cheese by the action of proteolytic enzymes on the _____________
sweet calcium/magnesium amino acids gruyere furanone milk caseins
Alanine conversion into ______________ is responsible for a part of aroma and taste of Swiss cheese.
propionic acid
Amino acids that react with carbonyl compounds can undergo strecker degradation in which ______________ is lost from the carboxyl group to produce strecker aldehydes, this reaction can be brought about at room temperature by _____________ produced during fermentation.
carbon dioxide
methylglyoxal
If the concentration of strecker aldehydes are too large it has been shown that they can cause ____________ in cheddar cheese.
off-flavors
Amino acids which can form intensely flavored strecker aldehydes are:
- methionine
- phenylalanine
- leucine
- valine
Methionine leads to _________ which has an intense brothy flavor. Phenylalanine gives rise to __________________ which has a floral, rose-like aroma.
methional
phenylacetaldehyde
T or F: In cheddar cheese or any other matured cheese, H2S and methanethiol (CH3-SH) which can be formed from the degradation of sulfur-containing amino acids are important contributors to the flavor
T
Amino acids can provide the _______ background characteristic of most cheeses
brothy
Amino acids can act as precursors of ________ by the action of amino acid decarboxylases
amines
T or F: Similar to strecker aldehydes, pyrazines can also be formed by enzymatic and non-enzymatic methods
T
Pyrazines in cheese can be generated by the reaction of _________ with alpha-hydroxyketones such as dihydroxyacetone at room temperature. Dimethylpyrazine is the major product of this reaction, trimethyl- and tetra-methylpyraxines can also be formed. These pyrazines have musty and ________ notes. Pyrazines in dairy products can also have ____________. Milk contaminated with ______________ contain dimethyl and 2-methoxy-isoporopylpyraxine which is responsible for strong ____________
lysine earthy microbial origin Pseudomonas taetrlens potato-like flavor defect
If you want to formulate and artificial blue cheese flavor, you have to add:
2-methylketones
While carbohydrates and proteins play an important role as precursors of cheese aroma, fatty acids are the _____ precursors for both desirable and undesirable aroma. C4-C10 fatty acids impart well known pungent notes to the cheese (some also act as source of off-flavors) while others are important precursors to other flavors such as ___________ (especially important in blue and roquefort cheeses). Fatty acid esters, lactones and dairy associates aldehydes such as cis-4-heptenal (creamy note); in addition they act as a medium (solvent) for the action of enzymes because of their _________ they control the activity of enzymes responsible for the formation of aroma.
key
2-methylketones
acidity
Fats can serve as a storage or repository for all the other ___________________ and as such they determine the relative composition of the aroma vapor above the cheese
aroma compounds
Triglycerides account for _____ of milk fat and by the action of lipases they are hydrolyzed into fatty acids. Lipases are the key enzymes for the desirable and undesirable flavor development in cheese. The lipases which produce the desirable aromas principally come from ______________ and to a smaller extent from the starter culture but not from milk, milk lipases are different in their _________ compared to lipases found in ripening microorganisms, however, not all microbial lipases give rise to desirable aroma. In order to produce those aromas, only lipases that are known to produce desirable aromas could be added.
98%
ripening microorgansims
specificities
What is the role of lipases:
Transform lipids into fatty acids
What is the role of lipoxygenase:
Add oxygen and form hydrogen peroxide
What is the role of the hydroperoxide lyase:
Transform the hydrogen peroxide into an aldehyde or ketone
What is the role of alcohol dehydrogenase:
convert aldehydes into alcohols
T or F: Decarboxylation is favored by heating
T
T or F: 2-keto fatty acids can be produced enzymatically by the oxidation of fatty acids.
T
The mold ___________, used in the manufacture of blue-veined cheeses, is particularly adept at this transformation. This mold can also reduce ketones to corresponding alcohols. Methyl ketones have very low threshold values (0.2-2.0ppm)
Penicillium roqueforti
T or F: Certain fatty acids are toxic to the mold Penicillium roqueforti which is why it can convert fatty acids into methyl ketones. By oxidative decarboxylation, these fatty acids are converted which are not toxic to the mold. This detoxifying mechanism generates the strong aroma of blue cheese.
T
In addition to 3-ketto fatty acyl groups, milk triglycerides also contain 4- and 5- hydroxyacyl groups which can cyclize to form ______________. Lactones have pleasant aromas and extensively used in imitation cheese flavors. Their aromas are described as _______, ______
gamma and delta lactones
fruity, peach, sweet, plum, butter and caramel like
Lipid _____________ mainly gives rise to off-flavors from small amount (3%) of polyunsaturated fatty acids in milk
autoxidation
