Unit 8 - enzymatic and thermal degradation product of lipids = flavor and off flavor

Question 1

lipid reaction to modify flavour

Answer 1

autoxidation and thermal oxidation 
thermal degradation at high T
enzymatic oxidation 
saturated chain = hard to oxidize 
in unseat allyl gp = highly susceptible to free radical reaction 
O2 may increase break of fatty acid 
unsat = very low odor/taste threshold 
minor components of lipid flavor = hydroxy oxo fatty acid , sterol --> important in tomato, peach, butter

Question 2

autoxidation

Answer 2

rancid odor from autoxidation of unsat
initiation = small number of free radical
propagation = O2 reacts with free R form hydroperoxide = break and increase number of free R continuously and when enough
termination = reacts to give polymers = rancid fat = aldehyde, alcohol, ketone
free radical reaction during cooking + rancid flavor formation

Question 3

thermal reaction

Answer 3

difference in mechanism between refrigeration and thermal condition
cooking radical reaction = desirable flavor
in a stale rancid product = radical reaction = off flavor

Question 4

hydroperoxide reaction

Answer 4

heat labile
at low T = stable = build up leads to different proportion of Radical intermediate = difference level of volatile product in heat vs stored food
hydroperoxide formation responsible for gamma and alpha lactone = 7-500 ppm threshold = coconut, nut flavor in dairy
hydro formation at beta –> form methyl ketone
aldehyde + ketone go second reaction with aa

Question 5

lipid oxidation

Answer 5

at cooking = develop meat aroma in lightly grilled/boiled meat
long storage of meat = undesirable

Question 6

warmed over flavor WOF

Answer 6

appear when cooked meat kept in fridge then reheated due to oxidation of phospholipids (usually unsaturated) during initial heating during initial heating disruption + dehydration of meat cell membrane
disruption is catalyzed by trace metals ion (iron) made available by break of team pigment during cooking

Question 7

thermal degradation (frying oil)

Answer 7

of saturated under oxidation = dehydration, decarboxylation, hydrolysis of ester…
intensity of thermal treatment depend on chain length
above 200˚C alkane = main hydrocarbon formed with other micro constituents

Question 8

enzymatic oxidation

Answer 8

enzyme convert unsaturated in presence of O2 are widely in plants = beneficial or not depends on [] and compo, type of plant
in fresh plants breakdown = odor threshold so low amount = positive influence on aroma
storage of fresh non heat material = promote enzyme reaction so volatile cp accumulate in [] = off flavor
only 2 unsaturated (linoleum and linolenic in all plants
the difference in mechanisms with F&V might be caused by the nature and properties of enzyme involved in oxidative degradation if unsaturated lipids
key reaction = hydroperoxidation by lipoxygenase or lipase oxidizes free fatty acid
cell breakdown = ox of unsaturated enzyme convert poly unsaturated in hydroperoxide –> gives aldehyde, alcohol esters
each plant have own lipoxy
factors influence breakdown of volatiles

Question 9

biotechnology and production of flavor compounds

Answer 9

1st synthetic flavor = short chain fatty esters
had some drawbacks
- more expensive than extraction and low yield
- consumer prefer natural

Question 10

raw materials pb for extraction

Answer 10

contain low [ ] so expensive
seasonal variations + weather
sociopolitical stability
which makes technology more attractive than extraction

Question 11

steps for biotech process

Answer 11

raw materials
biological transformation
bio reactors
product recovery

having intact cells is a key and catalyst helps produce it consistently

Question 12

genetic manipulation

Answer 12

increase purity and yield = decrease cost

microbial cell can continuously synthesize pdt form inexpensive nutrients

Question 13

plant cells

Answer 13

large = rigid + grow slow so need more precautions= do not excrete their chem product but can be done by controlling pH. also enzyme in isolated form can transform substrates who are present in high [ ]
in both cases product is natural = plant or genetic

Question 14

process consideration

Answer 14

many flavors not soluble in aq solution so enzyme transformation in non aq environment = very interesting = resolve problem + stabilzize enzyme
many flavors = toxic to producing cell so removal of solvent from product must be efficient because final level of solvent must be very low for it to be natural