Lipids lecture 6 Flashcards
what is catalyst activity?
decrease in iodine number per unit of time during hydrogenation under a specific set of conditions
what is the iodine number?
iodine number:
- number of grams of iodine absorbed by 100 grams of fat
- iodine number indicates degree of unsat of the FA residues of the glycerides (b/c unsat FA reacts with iodine)
what is selectivity?
preferentially hydrogenating more highly unsaturated FA
what does SR= C(18:2)/C(18:1)-12.2 mean?
Selectivity ratio to produce C18:0
means that stearic acid is produced 12.2 times faster from linoleic acid than from oleic acid (b/c catalyst has a higher affinity for highly unsat FA)
2 types of hydrogenation?
partial and complete
what are factors that affect reaction rate of hydrogenation?
- nature of substance to be hydrogenated
- nature and conc of catalyst
- rxn pressure
- rxn temp
- degreeeo f agitation
steps in hydrogenation of oils?
1 transfer/diffusion 2 absorption 3 hydrogenation/isomerization 4 desorption 5 transfer
what are transfer/diffusion and adsorption critical for?
controlling the degree of isomerization and selectivity of rxns
what is transfer and diffusion?(hydrogenation)
what is it important for?
transfer: transferring reactants and products to and from liquid oil phase and outside surface of the catalyst
diffusion: diffusion of reactant into and out of the pores of the catalyst
both are important for controlling the degree of isomerization and selectivity of rxns
ratio to express selectivity?
K (lo) / K (o) = rate of hydrogenation of linleate relative to that of oleate
what determines selectivity for hydrogenation?
- geometric configuration of the catalyst
2. chemical/physical characteristics of catalyst
calculate iodine number of linoleic acid, C17H31COOH.
Molecular weight of linoleic acid = 18(12) + 32(1) + 2(16) = 280 g /mol
Molecular weight of iodine = 2(127) = 254 g/mol
Linoleic acid has 2 double bonds per molecule (from last problem).
280 grams of fat reacts with 2 x 254 g of iodine = 508 g iodine
100 grams of fat reacts with 508/280 = 181
0.01 moles of linoleic acid reacts with 5.1 g of iodine. Determine the number of double bonds present in the fatty acid.
Moles iodine = (5.1 grams)(1 mole iodine / 254 grams of iodine) = 0.020 moles I2
This implies a ratio of 0.01 mol linoleic acid : 0.020 mole I2
in hydrogenation of soybean oil, what does linolenic become?
what starts as the highest percent before hydrogenation?
linolenic –> linoleic –> oleic –> stearic
linoleic is highest percent
(refer to chart)
describe copper catalyst
- copper-chromium (CuO 50% + Cr2O3 40% + BaO 10%)
- high selectivity for linolenic acid (KLn / KLO = 10)
- almost infinite selectivity for linoleate
hydrogenation of FA in TG is not a function of….
their location
whether the DB is in 1st, 2nd, or 3rd position doesn’t matter
what is the lifetime of a catalyst
how long a catalyst will remain active and useful
what is AOCS
what is their method of determining catalyst activity?
american oil chemists society
catalyst activity is determined by the time required to hydrogenate soybean oil to an IV of 80 from 120 at 350 deg F, 20psig, 0.05% catalyst conc compared to time needed using AOCS standard catalyst under the same conditions
does olive oil of hydrogenated soybean oil have lower IV?
olive oil has lower IV b/c has more monounsaturates
what are factors affecting hydrogenation?
independent variables
- pressure
- temp
- agitation
- catalyst concentration
dependent
- trans FA
- selectivity ratio
- hydrogenation rate
how does increased pressure and temp effect trans unsaturation of soybean oil?
as pressure INCREASES, trans FA DECREASES
as temp INCREASES, trans FA INCREASES
how does pressure, temp and catalyst conc effect selectivity ratio?
as pressure INCREASES, selectivity ratio DECREASES
as temp INCREASES, selectivity ratio INCREASES
as catalyst conc INCREASES, sr INCREASES
how does agitation, pressure, temp affect selectivity ratio?
as agitation INCREASES, sr DECREASES
as pressure INCREASES, sr INCREASES
as temp INCREASES, sr INCREASES
how does agitation and catalyst conc affect rate of hydrogenation?
as catalyst conc increases, H rate increases
as agitation increases, H rate increases
another use for interesterification
production of monoglycerides used as emulsifiers
analytical methods for modified TG?
saponification value
iodine value
gas chromatographic analysis for FA
liquid chromatography
what is the saponification value?
number of milligrams (mg) of potassium hydroxide (KOH) to saponify 1 g of the fat/oil sample.
expressed by weight, not moles (b/c the substance is not always known or pure)
what is saponification?
hydrolysis of ester under alkaline conditions
how to determine saponification value?
- Weigh 5 g of fat in 250-mL Erlenmeyer.
- Add 50 ml KOH (0.5 N) to Erlenmeyer.
- Boil to saponify fat.
- Titrate with HCl (0.5 N) using phenolphthalein.
- Conduct blank determination.
Saponification value = 56.1 × (B – S) × normality of HCl / g of sample
B = mL of HCl required by blank to reach phenolphthalein endpoint.
S = mL of HCl required by sample to reach phenolphthalein endpoint.
Molecular weight of KOH = 56.1
how to calculate AMW of a simple TG?
AMW = 41 + 3 x (MWFA -1)
how to calculate AMW of simple and mixed type TG (has 2 FA: R1 and R2)?
AMWTG = 41 + 3 x [(xR1 x MWFAR1 + xR2 x MWFAR2 ) -1]
steps of GC analysis for FA?
- Extract fat.
- Saponify (hydrolysis under basic condition).
- Prepare methyl esters (CH3ONa).
- Chromatograph methyl esters.
- Determine peak areas of fatty acids.
Fatty acids are identified by retention time. - Compare with response curve of fatty acid standards.
what does higher IV usually indicate?
oils and lower value fats
approximate IVs of animal fats, non drying oils, semi drying oils, drying oils?
Animal fats (butter, dripping, lard): IV = 30 – 70
Non-drying oils (olive, almond): IV = 80 - 110
Semi-drying oils (cottonseed, sesame, soya): IV = 80 - 140
Drying oils (linseed, sunflower): IV = 120 - 200
what methods are used to determine IV?
Wijs or Hanus methods
describe Wijs method?
DB + ICl –> Cl-CH-CH-I
ICl + KI –> KCl + I2
I2 + 2 Na2S2O3 –> Na2S4O6 + 2 NaI
+KI
oils that prefer beta type?
beta prime type?
beta: Coconut oil Corn oil Olive oil Lard Palm kernel oil
beta prime: Cottonseed oil Herring oil Menhaden oil Milk fat Palm oil
what are important characteristics of shortenings?
what do they depend on?
- incorporation of air, plasticity and consistency
- solid-liquid ratio
depends on:
- polymorphic forms of the fats
- method of prep
what does plasticity, consistency, solid liquid ratio depend on?
melting range
needs proper tempering to form mixed crystals needed for a broad melting range
what size air bubbles do beta prime have vs beta?
beta prime: large amount of small air bubbles
beta: small amount of large air bubbles
describe beta prime crystal shortening
Small crystals
Whiter, creamier, more tender, smoother texture
Uniform and glossy texture
describe beta crystal shortening
Large clustered crystals
A waxy or grainy texture
role of beta prime crystal shortening in baking?
incorporation of an abundant quantity of small air bubbles in batters for good volume,
texture and tenderness of baked goods.
natural vs rearranged lard?
natural: palmitic acid is at 2 pos (64%)
rearr: palm acid at 2 pos (24%)
steps of lard conversion from beta to beta prime?
Interesterification
Interesterification and hydrogenation
Winterization (destearinization)
Addition of cottonseed oil and/or tallow flakes (beta- prime)
define plasticity
changes in consistency as a function of temperature.
define consistency
apparent hardness at a temperature
oils in margarine?
soybean (Beta) and hydrogenated cottonseed oil (beta prime)
what happens when beta prime becomes beta in chocolate?
white spots and dull surface
what is tempering?
A process which permits transformation to the proper polymorphic form.
During crystallization, the heat of transformation must be removed to avoid melting and a later conversion into large beta crystal.
how does the FA chain length affect MP of TG?
Melting point of TG increases as FA chain length increases
is natural and randomized lard beta or beta’ ?
natural: beta
randomized: beta’
what does randomization of lard improve?
plastic range
makes it a better shortening than natural lard
how to produce High polyunsaturated content and low-to-zero trans-acid containing margarines?
by interesterifying a blend of liquid oil and a fully hydrogenated oil.
describe hydrogenated palm kernal oil
hard butter melting at 46 C and produces a waxy feel in the mouth.
On randomization, its melting point is reduced to 35 C. By blending hydrogenated palm kernel oiland its randomized product, a whole series of hard butters with highly desirable melting qualities (rapid melt in mouth) are obtained
what happens to SCI of Hydrogenated Soybean Oil and Palm Stearine when temp increases? Before and after interesterification?
SCI decreases as temp increases
before: more gradual
what happens to SCI of cocoa butter when temp increases?
how does SCI compare before and after interesterification?
SCI decreases
before interesterification: sharper decrease
after: more gradual decrease
major uses of fats?
shortenings
margarines
confectionary fats
role of shortening in baking?
reduces elasticity of dough
makes pastry more tender/ flaky
fats w/ higher levels of unsat FA have… ____ shortening power
greater shortening power
what does lard shortening properties depend on?
dominant crystal form
solid fat content
describe margarine
water(~20%)-in-oil emulsions, with some milk solids, which have extensively replaced butter.
may consist of:
hydrogenated fats
• mixture of hydrogenated fat(s) and unhydrogenated oil(s)
• mixture of interesterified fat(s) and unhydrogenated oil(s), or
• mixture of unhydrogenated fats.
how is margarine made?
High polyunsaturated content and low-to-zero trans-acid containing margarines are produced by interesterifying a blend of liquid oil and a fully hydrogenated oil.
Mixture is fed into a scraped-surface heat exchanger, which partially solidifies the material.
Product may be tempered to allow for crystallization in a manner that gives good plasticity and spreadability.
properties of confectonary fats
Has narrow melting point range and contains about 80% disaturated triglycerides:
20% SOS - stearic, oleic and stearic 55% POS - palmitic, oleic and stearic
5% POP - palmitic, oleic and palmitic
advantage:
-solifidies fast = can be used as enrobing fats but melts at body temp
describe emulsions
properties of emulsions?
Emulsifiers stabilize and reduce the interfacial tension between the hydrophilic and hydrophobic constituents
properties: must have both hydrophilic and hydrophobic groups in its molecular structure. to reduce surface tension (seen on MonoGC and phospholipids)
properties of emulsions after emulsified
more viscous, opaque and thefattysensationis masked.
