Unit 7 - flavor formation by enzymes and microorganisms Flashcards
flavor generated by enzymes
aldehyde, ketone, esters, OH, terpene, terpenoid, S containing compounds, aromatic volatile compounds
origin
can be form volatile precursors. before harvest or due to disruption of cell tissue or by enzymes during fermentation
dynamic processes
biogenesis and synthesis = process depends on plant, variety, environment, maturation and fruiting
other components of flavors
some chemicals are odorless and tasteless
some metabolic by products
secondary metabolites
environment stress biosynthesize 2nd metabolites like antioxidants
metabolism levels
primary = growth and development = aa, nucleic acid, carbs (thermally generated) secondary = interaction of individual with its environment which results in flavor, fragrance, pigments, sweet, Pharma, pesticide
fruits flavor origin
ripening period
vegetable flavor origin
flavor form sulphur compounds and cellular disruption
action of lipoxygenase on linoleum and linolenic acid to produce volatile carbonyl and alcohol similar to ripening in fruits
veg: aldehyde for esters, aa, fatty acids
aldehydes are under 5C = develop off flavors
alkenols = 5 to 10 C = desirable flavors = fresh veg
cis trans 2 hexenals = green leaf
cis 2 nonenal = melon like odor of cucumber
aliphatic aldehyde form ester which are hydrolyzed by esterase + enzymatic oxidation
aa into alpha kept acid by transaminase and enzyme decarboxylation = flavor aldehyde
triglyceride hydrolyzed by lipase produce free fatty lipoxygenase + lyase produce aldehyde
sulfur in which plants
alliaceous and cruciferous
sulfur origin
cysteine sulfide and thioglucoside
sulfur volatiles
cysteine sulfide in allicaneous plants which produce disulfide
glucosinate cruciferous plants which produce isothiocyanate
alliaceous plants
main precursors are S substitues I-cysteine sulfoxide which produce thiosulfinate
heating of thio converts it into disulfide = cooked flavor
garlic = thiallyl compound which when chopped Allin (major thio) is converted to allicin by allinase
allicin = unstable + decompose = strong flavor/smell
allinase in chopped onion yields lacrimator propanethiol S-oxide
method of cooking of garlic and onion five different flavors. if water present it forms di-, tri- poly- sulphide from thio. if very little water present = allium in lipids = many poly sulfur compounds formed
skin in garlic inhibit garlic allinase
onion allinase is sensitive to acid
cruciferous vegetables
pungent taste caused by isothiocyanate = released by enzyme thioglucoside
tissue of plant need disruption to bring substrate close to the end = flavor
mustard, horse radish = sinigrin
yellow mustard = sinalbin
sinalbin and sinigrin are both types of thioglucosides which can be hydrolyzed to give tyrosinase which produce isothiocyanate
important = need water for activation
non volatile flavor compound causing pungency
chilipepper
black pepper
ginger
chilipepper = capsaicinoid = phenol + amide linkage + fatty acid and all 3 are needed to stimulate nerve to be perceived as hot
dose of capsaicinoid decrease sensitivity of individual at fq usage = adapt = cause pb in reproduction of sensory test
caps affect thermo regulation = body temperature decrease with small dose = eat in warm countries so perspiration doesn’t happen (hypothermia)
large dose can cause desensitization = allows over heat
black pepper
pungency of black pepper = piperine
has different structure than caps and is not a phenol
contains a methylenedioxy gp attach to the aromatic ring = less pungent than caps
piperine not only one in pepper –> has 25 pungent phytochemical among which has 8 amides
ginger
pungency from gingerol and shogaol
fresh ginger = gingerol mostly
in commercial oleoresins = shogoals prominent one
100x less pungent than piperine
shoal and zingerone are formed by gingerol during process + storage or by distillation
shogaols formation by dehydration of gingerol = pungency doubles = aged ginger strong
when gingerol transform via retroaldol reaction –> zingerone (sweet) and hexanol (off flavor) = no pungency because need H bond in middle and phobic at opposite ends to stimulate nerve ending
fruits
typical flavor develop during ripening period
fruit volatile = esters, aroma aldehyde, lactones, alcohols, terpenoids and thirsters
usually aroma preformed and arise directly from fruits
fruits esters and aromatic aldehydes
esters = most important = high levels + variety = character impact aroma
methyl butyrate = apple
isopentyl acetate = banana
ethyl butyrate = orange
ester biozynthezied by enzyme esterification of carboxylic acid with OH through action of enzyme like esterase and acyl CoA alcohol transacetylase
aromatic aldehyde sometimes more flavor
benzaldehyde = bitter almond
volatiles in peach, apricot, cherry, from cyanogenic glycosides by action of beta glucosidase which hydro glycol in free sugar and mandelonitrile than undergo elimination reaction in presence of hydroxynitrile lyase which produces benzaldehyde
dairy products
F&V = endogenous enzymes
dairy = microbial enzyme + oxidation = volatile and non volatile products
less number of compounds in thermal treatment products
dairy flavor related to occurence of relatively few key components
role of endogenous enzyme
effect in milk -= negative on flavor
milk lipase produce fatty acid = undesirable aroma
milk protease = bitter peptides
usually inactivated during pasteurization
but milk gives good substrates + flavor precursors tranformed by microorganisms and added enzymes
flavor components of cheese
fundamental steps = coagulation of milk, separation of solids, work on solids to modify flavor/texture
lipolysis, proteolysis, fermentation –> important components of development of cheese flavor
volatile component of cheese = aldehyde, alcohol, ester, ketones
short fatty = pungent
diacetyl = creamy note
amine, lactone, 2 methylketone =overall flavor contribution
role of lactose
nutrient for growth of micro + precursor for dactyl (in butter, soft cheese)
lactose convert to lactic acid, acetic acid, acetaldehyde, glyoxal, methylglyoxal
role of protein
protease form aa + peptide
prot = bitter peptide = presence of low mol phobic peptide form casein alpha> beta for bitter
sweet = calcium + small peptide
nutty flavour = small peptide + aa
burn note = peptide complex produced during ripening by proteolytic enzyme casein. aa oxidation into carbo acid via strecker = flavor of dairy
mature cheese flavor = H2S + methanethiol
flavor with aa = brothyl flavor and precursor of amine
pyrazine = reaction of lysine with alpha hydroxyketone at RT –> dimethylpyrazine = musty + earthy note
factors for bitter peptide
cheese microflora
type of starter strain
presence of mould (more lactic acid increase mould)
pyrazine in dairy
pyrazine = reaction of lysine with alpha hydroxyketone at RT –> dimethylpyrazine = musty + earthy note
micro origin = strong potato flavor defect
taste of aa in aq solution pH=6
bitter = tryptophan, tyrazine, Valine, Arginine, Asparagine, aspartic acid, histidine, isoleucine, leucine sweet = alanine, glutamine, glycine, proline, serine, theorine umami = glutamic acid, methionine
role of fat
key precursor to aroma
C4-C10 = pungent notes
other precursor to 2-methylketone = blue cheese, fatty ester, lactose + serve as medium for action of enzyme + with acidity control enzyme
serve as storage = determine relative components of aroma vapor of cheese
lipase = undesirable or desirable flavor
desirable = ripening of micro (not from milk, milk lipase is different)
microlipase is unwanted so dont add them
lactone can cycle –> pleasant aroma = fruity, sweet, peach, plum, butter, caramel
lipid oxygen = off flavor from poly unsaturated fatty acids
methylketone very important = characterization of milk fat
3 keto fatty lose CO2 favored by heat
penicillium likes it –> mold decrease ketone to OH + MEKs key
by oxidation decarbo fatty convert to methyl ketone not toxic to mold
this detoxyfying mechanical gives strong aroma to blue cheese
