4. Interesterification + Hydrogenation + Winterization Flashcards
Interesterification vs intraesterification
- Inter: exchange of acyl groups among TG molecules
- Intra: acyl groups may also exchange position within a TG molecule
What characteristic (2) regarding FA position do you want in an oil after transesterification?
low GS3 and GS2U
3 step reaction mechanism for transesterification
- formation of enolate ion
- formation of beta-keto ester
- interesterification
What are the catalysts for interesterification?
- high temp vs low temp
- strong bases! usually
- high temp: KOH and NaOH –> KOH is favored bc weaker base, you don’t want to saponify
- low temp: sodium methoxide (NaOCH3) (weaker base)
how it an enolate ion formed? stable?
initial removal of proton from carbon adjacent to acyl group (alpha carbon) by the base catalyst –> leads to charge delocalized enolate anion
- anion is very unstable –> resonance to stabilize (negative charge shared between O and alpha carbon)
Random vs directed interesterification
- random: when interesterification carried out to equilibrium condition –> FA assume almost random distribution among TG
- directed: interesterification can be directed away from its usually random end-point if fat is allowed to crystallize during reactions (trisaturated glycerides crystallize first)
Lard interesterification:
- Crystal modified lard (CML)?
- Partially modified lard (PML)?
- Direct interesterified lard (DIL)
- CML: conditions favors intramolecular interchange
- PML: conditions favoring random distribution
- DIL: conditions favoring directed interesterification to control the GS3 content –> = highest unsat!
enzyme catalyzed interesterification in presence of water also used for manufacture of ________&________, extensively used by food industry as _____________
- mono and diglycerides
- emulsifiers
what is simple way to obtain glycerol and FFA?
- add NaOH to TG and boil
Hydrogenation super important to eliminate ?????
reliance on butter
-2 main purposes of catalytic hydrogenation?
+ Why is catalytic hydrogenation a very important reaction in organic synthesis? give example
- convert oil to fat (remove double bond)
- reduce susceptibility of oil to oxidative rancidity
in certain cases, isomerization of double bond is the desired outcome (ie pharmaceutical industry)
how is catalyst used in hydrogenation? 2 steps
- oil + catalyst –> oil-catalyst complex
- oil catalyst complex + H2 –> hydrogenated oil + catalyst
how is catalyst activity of hydrogenation defined?
- defined as decrease in iodine number per unit of time during a hydrogenation under specific set of conditions
iodine value defined as?
- what does it indicate?
number of grams of iodine (I2) absorbed by 100g of fat
- unsat FA residues react with iodine –> iodine number indicates degree of saturation of FA residues of glyceride
high degree of unsaturation = (high or low) iodine value
High!
how does I2 docks onto double bond?
1 I goes to each carbon = no double bond anymore
Iodine value of tristearin?
0!
if 0.01 moles of linoleic acid reacts with 5.1g of iodine. determine number of double bonds present in FA. Assuming 1 mol of iodine = 254g.
5.1g of iodine = 0.02 mol I2
0.01 mol linoleic acid = 0.01 mol I2
2 double bonds!
Calculate iodine number of linoleic acid C17H31COOH
181!
trans FA have higher or lower melting point that cis isomer?
higher!
Selectivity in hydrogenation? refers to?
- how can you vary selectivity?
- selectivity useful today?
refers to preferentially hydrogenating more highly unsaturated FA
- by varying catalysts/operating conditions
- Not in food industry! but useful in pharma
5 factors that affect reaction rate of hydrogenation
- nature of substance fo be hydrogenated
- nature and concentration of catalyst
- reaction pressure (ie concentration of hydrogen)
- reaction temperature
- degree of agitation (mix catalyst in solution)
5 steps in hydrogenation of oils
- which are critical steps in controlling degree of isomerization and selectivity of reactions?
- transfer and/or diffusion
- absorption
- hydrogenation/isomerization
- desorption
- transfer
- transfer/diffusion and absorption!
transfer vs diffusion
- transfer: transfer of reactants and products to and from the bulk of the liquid oil phase and outside surface of catalyst
- diffusion: diffusion of reactant into pores of the catalyst + diffusion of products out of the pores of catalysts
can conjugated double bonds go back to unconjugated? vice versa?
- conjugated can’t go to unconjugated
- unconjugated can go to conjugated
How do food chemists know about all the products that hydrogenation can yield?
they do hydrogenation –> then gas chromatography –> identify acids, and then find a mechanism to explain what happened
5 independent variables affecting hydrogenation
vs 3 dependant variables
independant:
- H2 pressure
- temperature
- agitation
- nature of catalyst
- catalyst concentration
Dependant:
- trans FA
- selectivity ratio
- hydrogenation rate
What is hydrogenation currently used for?
- to produce total saturation fat –> useful in interesterification OR in making blends with other natural oils to acquire plasticity or other functional attributes
Benefits of interesterified fats vs blends of fully hydrogenated sat fat with natural oils?
- interesterified fats have a wider plasticity range AND can also modulate polymorphism (beta prime)
Interesterification also used for manufacture of ________________ used as ______________ –> how?
- monoglycerides
- emulsifiers
- excess glycerol reacted with fat source to form mono and di glycerides
What was hydrogenation originally used for?
to decrease omega3 in soybean oil (maybe it inedible)
Double bonds are also capable of ___________ –> conversion of unconjugated to ________________ (more thermodynamically stable/unstable?) or _____________________ (3 words)
- wandering
- conjugated
- mixed bonding systems
what is winterization?
- process used to produce salad oils from oils not suitable for this purpose (using still liquid version)
- can also be used to produce natural hard vegetable fat (using the saturated portion)
how to do winterization? (concept + today)
- clouding of oil under refrigeration conditions –> fractional crystallization of more sat TG at fridge temp
- today: carried out with heat exchanger
