Fennema's Food Chemistry · Chapter 4 · 6-hour Edition

Lipids

From a single fatty acid to the snap of chocolate

Fatty Acid Nomenclature Polymorphism Lipid Oxidation Antioxidants 26 slides · 6 minigames

Why does good chocolate
"melt in your mouth, not in your hand"?

Butter softens at 35°C,
chocolate melts at 32°C,
yet peanut oil still flows at −18°C?

The key is fatty acid saturation and crystal polymorphism.
We start from FA geometry, TAG packing, to crystal transitions.

99%

natural FAs esterified to glycerol

3

polymorphs: α, β', β

3 steps

oxidation: initiation, propagation, termination

3 strategies

antioxidants: FRS, chelate, quench

Chapter Map · From Structure to Health

Six topics across 6 hours

01

Structure & Classification

FA nomenclature, TAG, phospholipids, sterols, waxes, composition

⏱ ~60 min

02

Physical & Crystallization

SFC, supercooling, nucleation, α/β'/β polymorphs

⏱ ~50 min

03

Lipid Oxidation Mechanism

Initiation → propagation → β-scission off-flavors

⏱ ~70 min

04

Prooxidants

Singlet O₂, LOX, transition metals, light, heat

⏱ ~50 min

05

Antioxidant Systems

FRS, tocopherol, BHT/BHA, chelators, synergy

⏱ ~60 min

06

Food Lipids & Health

Trans fat, ω-3, CLA, phytosterols, low-cal fats

⏱ ~50 min

+ Refining & TAG modification (interesterification, hydrogenation) · ⏱ ~20 min

Topic 1a · Saturated FAs

Saturated FAs: straight, tightly packed, high melting

Common	Systematic	Abbrev	mp °C	Source
Caproic	Hexanoic	6:0	−3	Goat fat
Caprylic	Octanoic	8:0	17	Coconut
Capric	Decanoic	10:0	32	Coconut
Lauric	Dodecanoic	12:0	44	Coconut, palm kernel
Myristic	Tetradecanoic	14:0	54	Palm kernel, nutmeg
Palmitic	Hexadecanoic	16:0	63	Nearly all fats
Stearic	Octadecanoic	18:0	70	Animal fat, cocoa

★ Even-carbon dominant (2-C biosynthesis)

Notation: C-count : double-bonds, e.g., 16:0
Mp linearly increases with C-count (vdW)
Saturated FAs are straight → tight pack → solid at RT
Coconut/palm kernel: lauric (12:0) rich → solid but easy to melt
Butterfat: contains 4:0–6:0 short chains (ruminant only)
Implication: cooking oil vs baking fat vs candy fat

Long-chain SFA & cardiovascular: palmitic, myristic ↑ LDL; stearic neutral (converts to oleic in body).

Topic 1b · Unsaturated FAs

Double bonds: change geometry → change melting point

Common	Systematic	Abbrev	ω	mp
Oleic	cis-9-octadecenoic	18:1 Δ9	9	5°C
Elaidic (trans)	trans-9-octadecenoic	18:1 Δ9t	9	44°C
Linoleic	cis-9,12-octadecadienoic	18:2 Δ9	6	−5°C
Linolenic	9,12,15-octadecatrienoic	18:3 Δ9	3	−11°C
Arachidonic	5,8,11,14	20:4 Δ5	6	−50°C
EPA	5,8,11,14,17	20:5 Δ5	3	−54°C
DHA	4,7,10,13,16,19	22:6 Δ4	3	−44°C

Three naming systems
① Δ: count from COOH end (18:1 Δ9)
② ω (n): count from methyl end
③ IUPAC: explicit cis/trans

cis bond: kinks chain ~30°, disrupts packing → low mp
trans bond: stays linear → like saturated → high mp
Pentadiene system: two cis bonds with CH₂ between (positions 9, 12)
PUFA bonds are not conjugated (except CLA)
Same chain length, more bonds → lower mp
e.g., 18:0 = 70°C; 18:1 = 5°C; 18:2 = −5°C

Essential FAs

Linoleic (ω-6): humans can't synthesize
α-Linolenic (ω-3): same
EPA, DHA from ω-3 (low efficiency) → eat fish oil

Topic 1c · Triacylglycerols (TAG)

99% of food lipids are TAG; sn position determines biology

Structure: glycerol + 3 FA (ester bonds)
"Tuning fork" conformation: sn-1 & sn-3 one way, sn-2 opposite
Stereospecific numbering (sn):
→ sn-2 OH on left (Fischer)
→ sn-1 (top), sn-2 (middle), sn-3 (bottom)
sn-2 FA has special biology
Pancreatic lipase only cleaves sn-1, sn-3 → leaves sn-2 monoacylglycerol
Long-chain SFA at sn-2 → higher absorption

Cocoa butter secret: 85% oleic at sn-2; palmitic + stearic evenly at sn-1, sn-3. Symmetric → narrow melt range → 32°C all melts → "melt in mouth".

Topic 1d · Phospholipids

Two tails, one head: natural emulsifiers

Structure: TAG sn-3 replaced by phosphate + polar head
sn-1 usually saturated, sn-2 unsaturated (fluidity)
Common phospholipids by head group:

Phospholipid	Head X	Source/Use
PA	-OH	Simplest (phosphatidic acid)
PC (lecithin)	-O-CH₂CH₂-N⁺(CH₃)₃	Soybean, egg yolk; W/O emulsion
PE	-O-CH₂CH₂-NH₂	Soybean, brain
PS	-O-CH(NH₂)-COOH	Brain
PI	-O-inositol ring	Cell signaling

Surface-active: polar head + nonpolar tails → bilayer, micelle
lysophospholipid: lost one FA, stronger emulsifier
Food lecithin: commercial is PC + PE + PI mixture

Topic 1e · Sterols & Waxes

Sterols & waxes: small but critical

🐮 Sterols

Structure: 4 fused rings (3 hexa + 1 penta), OH on C3
Cholesterol: dominant animal sterol; precursor to bile acids, vit D₃
Phytosterols: β-sitosterol, stigmasterol
Phytosterols lower cholesterol absorption (competitive) → functional food (Benecol, Take Control)
Cholesterol-rich: animal foods; phytosterol: plants
High blood LDL → atherosclerosis risk

🐝 Waxes

Definition: long-chain FA + long-chain alcohol (ester)
Often includes sterol esters, ketones, aldehydes
Classification by source:
→ Animal: beeswax
→ Plant: carnauba, candelilla
→ Mineral: petroleum wax
Food uses:
→ Fruit-skin coating → water loss inhibition
→ Candy shell glossing
→ Chocolate thin shell

🍃 Sphingolipids

Sphingosine backbone (not glycerol). In nerve cell membranes; minor in food.

Topic 1f · FA Composition + Refining

Food lipid fingerprints & purification

Food	16:0	18:0	18:1	18:2	Sat%
Olive oil	14	3	71	10	16
Canola	4	2	61	19	5.5
Corn oil	12	2	28	57	14
Soybean	11	4	23	53	15
Linseed	5	5	20	16	10 (18:3=53)
Coconut	8	3	7	2	92
Cocoa butter	26	35	35	3	60
Butterfat	26	13	28	2	63
Lard	26	12	45	10	39
Salmon	16	3	21	1	23 (DHA+EPA)

★ Ruminants (cow, sheep) have rumen biohydrogenation → high SFA + trans / CLA

Refining (4 steps)

1. Degumming
1-3% water, 60-80°C → phospholipids hydrate → filter
Soybean byproduct = lecithin
2. Neutralization
NaOH neutralizes free FA → soap stock removed
3. Bleaching
Bleaching earth / silica / carbon adsorbs pigments
(chlorophyll, carotenoids) 80-110°C, vacuum
4. Deodorization
180-270°C vacuum steam distillation → removes volatiles
⚠️ Side effect: produces trans FAs

Topic 2a · Physical Properties

TAG vs Water: opposite in almost every way

Property	Triolein	Water
MW	885	18
mp °C	5	0
Density kg/m³	910	998
Viscosity mPa·s	~50	1.0
Thermal cond. W/m·K	0.170	0.598
Heat cap. J/g·K	1.98	4.18
Dielectric constant	3	80.2
Surface tension mN/m	~35	72.8
Refractive index	1.46	1.333

⭐ Oil floats, viscous, non-conductive, low ε (no ion dissolving)

Liquid oil: Newtonian, viscosity 30-60 mPa·s @ 25°C
Exception: castor oil (-OH groups, H-bonds) → very high viscosity
Solid fat "plastic" behavior:
→ τ < τ₀ → behaves like solid
→ τ ≥ τ₀ → behaves like liquid
→ "Bingham plastic"
Cause: fat crystal network dispersed in oil

τ = G·γ (when τ < τ₀)
τ − τ₀ = η·γ̇ (when τ ≥ τ₀)

Thermal

Smoke / flash / fire points: thermal stability markers
Pure TAG more stable than free FAs

Topic 2b · Solid Fat Content (SFC)

Why does chocolate melt sharply but butter slowly soften?

SFC: % of solid fat at a given T
Food fats contain many TAGs → no sharp mp, melt over a plastic range
Pure TAG (POP, SOS): sharp curve (narrow range)
Mixed fat (butterfat): wide range, multi-stage
Cocoa butter: concentrates at 32°C → mouth melt
Butter: 4-40°C gradual softening → spreadable
Measurement: DSC, dilatometry, NMR (preferred)

Food implications

Spread: 4°C SFC ~50% (spreadable), 20°C ~30% (no flow)
Chocolate: 25°C SFC > 60%, 32°C → 0%
Candy: bloom related to SFC changes

Topic 2c · Crystallization

Supercooling → Nucleation → Growth: 3 steps that decide everything

① Supercooling

Pure oil can stay liquid 10°C+ below mp
ΔT = T_mp − T bigger → easier nucleation
Reason: nucleation needs activation energy (interfacial)

② Nucleation

ΔG = (4/3)πr³·(ΔH_fus·ΔT/T_mp) + 4πr²γᵢ
r* = 2γᵢ·T_mp / (ΔH_fus·ΔT)
J = A·exp(−ΔG*/kT)

Homogeneous: pure oil
Heterogeneous: with impurities / seeds → easier (lower ΔG*)
Greater supercooling → smaller r* → higher J
But too much supercooling → viscosity ↑ → diffusion-limited → J falls
→ J has optimum T

③ Crystal Growth

Once r > r*, molecules continue adding
Rate controlled by diffusion & surface integration
High supercool → many nuclei → small crystals
Low supercool → few nuclei → large crystals

Food Applications

Chocolate tempering: control supercool → form β → mouth melt
Margarine: fast cooling spray → small crystals → smooth spread
Ice cream: fat crystals + ice → multi-stage control
Fat bloom: storage polymorph transition → surface crystals → whitening

⭐ Cooling rate decides all: fast → many small → smooth; slow → few large → coarse

Topic 2d · Polymorphism

Same TAG, 3 crystal forms, different fates

α form (Hexagonal)

Least stable, lowest mp
From fast cooling (kinetic)
e.g., SSS α 55°C

Use: starting form, spontaneously transitions

β' form (Orthorhombic)

Intermediate stability/mp
Moderate cooling + agitation (margarine)
e.g., SSS β' 63°C

Use: margarine, shortening
Needle-like → smooth

β form (Triclinic)

Most stable, highest mp
Slow cooling or long storage
e.g., SSS β 73°C

Use: cocoa butter (chocolate form V/β₂)
Plates → shine, snap

Chocolate 6 polymorphs (form I-VI):
Form V (β₂): 32°C melt, ideal → "snap", shine, mouth melt
Form VI: 35°C, too stable → poor texture → bloom (fat fluorescence)

Chocolate Tempering

① Heat to 45-50°C, fully melt
② Cool to 27°C (form all polymorphs incl. β)
③ Reheat to 30-32°C (melt α, β', leave β)
④ Mold and cool → only β remains

Topic 3a · Hydrolytic Rancidity

Free fatty acids: the "sour" of dairy

Mechanism: H₂O + lipase → cleave TAG → free FA (FFA)
Results:
→ Off-flavor (short-chain FFA volatile; milk → "rancid")
→ Lower smoke point
→ Foaming
→ Accelerates oxidation
Sources:
→ Endogenous enzymes (milk lipase activates on homogenization)
→ Microbial lipase
→ High-T hydrolysis (frying)

Control

Pasteurize to inactivate lipase
Regular oil filtration (FFA adsorption)
Prevent water in oil systems
Low pH or antimicrobials

Exception: hydrolytic rancidity can be "desired"
★ Cheese ripening (Cheddar, Parmesan)
★ First-press olive oil (flavor)
★ Cocoa butter aging

Key: controlled & specific FA release = flavor; uncontrolled = defect

FFA in oil refining

Crude oil contains FFA 0.5-5%
NaOH neutralization → soap → removed
Commercial refined oil FFA < 0.05%

Olive oil grades:
Extra Virgin: FFA < 0.8%
Virgin: FFA < 2%
Lampante: FFA > 2% (needs refining)

Topic 3b · Oxidation: Initiation (180 min break)

First step of lipid oxidation: H abstraction → free radical

Reaction: L-H + initiator → L· + H·
L·: alkyl radical (C-centered)
Easily abstracted H locations:
→ pentadiene middle C (-CH₂- between two double bonds)
→ C-H bond energy 80 kcal/mol (vs alkyl 98 kcal/mol)
Unsaturation ↑ → easier oxidation:
→ 18:1 (oleic) baseline 1×
→ 18:2 (linoleic) 10-40×
→ 18:3 (linolenic) ~80×
→ 20:4 (arachidonic) ~160×
After formation: radical delocalizes → double-bond shifts, trans formation

Initiators: metal ions (Fe²⁺), light, heat, ·OH, lipoxygenase (LOX), radiation

Topic 3c · Propagation + Termination

Oxidation's autocatalytic nature

② Propagation

L· + ³O₂ → LOO· (peroxyl)
LOO· + L'H → LOOH + L'·
LOOH = hydroperoxide (odorless "bomb")

① L· + O₂ is diffusion-limited (very fast)
② LOO· is high-energy radical, abstracts another L'H
③ Produces new L'· → chain reaction
1 initiation event → infinite LOOH
Hence free-radical chain = autoxidation

③ Termination

LOO· + LOO· → LOOL + O₂ (atmospheric)
L· + L· → L-L (low O₂, frying)

Radicals recombine to non-radicals. Frying produces C-C crosslinks (polymers).

⚠️ Key insight:
LOOH itself is odorless! It's the "bomb" intermediate.
True rancid flavor comes from β-scission of LOOH (next slide).

Oxidation kinetics & lag phase

★ Antioxidants "extend" lag phase; can't reverse oxidized oil

Topic 3d · β-scission → Flavor Aldehydes

True rancid smell: low-MW aldehydes, ketones

LOOH decomposes: by Fe²⁺, heat, light
LOOH → LO· (alkoxyl) + ·OH
LO· higher energy → attacks C-C bonds
β-scission: cleaves C-C beside LO· → :
→ Low-MW aldehydes (volatile, smelly)
→ Rancid / fishy / oxidized flavor
e.g., linoleic 9-LOOH decomposition:
→ Carbon-end cleave: octanoate + 2,4-decadienal (fry aroma)
→ Methyl-end cleave: nonanoic + 3-nonenal

Source	Typical aldehyde	Sensation
ω-6 (corn, soy)	hexanal, 2,4-decadienal	grassy, beany
ω-3 (flax, fish)	3-hexenal, propanal	fishy
Butter	diacetyl, butanal	oxidized cream
Frying oil	2,4-decadienal	"french fry aroma"

Topic 4a · Prooxidants Overview

Three classes of prooxidants, distinct mechanisms

🌟 Direct LOOH generation

Singlet O₂ (¹O₂): 1500× faster than ³O₂
Source: photosensitization (chlorophyll, riboflavin, myoglobin + light)
"ene" addition directly to double bond
Lipoxygenase (LOX): enzyme-catalyzed
Source: soybean, vegetables (released on disruption)
Non-heme iron enzyme

⚡ Free radical generation

Ionizing radiation: H₂O → ·OH (strongest H abstraction)
Side effect of food irradiation
UV / visible light: directly excites LOOH decomposition
Heat: accelerates all reactions

🔬 LOOH decomposition

Transition metals: Fe, Cu
Fenton: Fe²⁺ + H₂O₂ → Fe³⁺ + ·OH + OH⁻
Fe²⁺ vs Fe³⁺: 10⁵× faster
Heme proteins: myoglobin, hemoglobin, cytochrome, peroxidase
Heat denaturation → more active

💡 Typical food LOOH: 1-100 nmol/g in high-quality oil (vs ~1 pmol/g in biology) → 40-1000× higher, due to extraction/refining oxidation.

Topic 4b · Singlet O₂ + LOX

Two "accelerators" with special mechanisms

🌞 Singlet O₂ (¹O₂)

³O₂ (ground state): two unpaired electrons, same spin (biradical) → can't directly attack double bonds
¹O₂ (excited): opposite spins → can directly react with double bonds
Generated by photosensitization:
→ Chlorophyll, riboflavin, myoglobin + light → excited state
→ Energy transfer to ³O₂ → ¹O₂
Products: LOOH at every double bond (linoleic → 4 species)
Contrast: free-radical only 2 species (C9, C13)

Food example: "sunlight flavor" in milk powder, butter ← riboflavin generates ¹O₂

Control: avoid light, add β-carotene (¹O₂ quencher)

🌱 Lipoxygenase (LOX)

Sources: soybean, legumes, potato, tomato, apple
Contains non-heme iron (Fe³⁺)
Catalyzes double-bond FA → site-specific LOOH
Soybean LOX-1: 13-LOOH (high specificity)
Soybean LOX-2: 9-LOOH + 13-LOOH
Food significance:
→ Soy/soymilk "beany flavor"
→ Cut-fruit flavor generation
→ Bread dough "slack" (loss of strength)
Control: heat inactivation, low T, breeding

⭐ Pasteurized soymilk: 80°C 5 min first to inactivate LOX before extraction → much less beany.

Topic 4c · Transition Metals + Chelation

Fe, Cu: strongest prooxidants

Fenton reaction:

Fe²⁺ + H₂O₂ → Fe³⁺ + ·OH + OH⁻
Fe²⁺ + LOOH → Fe³⁺ + LO· + OH⁻
(Fe²⁺ vs Fe³⁺: 10⁵× faster)

Haber-Weiss cycle: Fe³⁺ + O₂·⁻ → Fe²⁺ + O₂; ascorbate can reduce Fe³⁺→Fe²⁺ → prooxidant
Cu 50× faster than Fe (decomposes H₂O₂), but lower food content
Sources:
→ Raw material (myoglobin in meat, plant Fe)
→ Processing equipment (steel, copper)
→ Water, additives
Low water activity → metals more active (no water shell protection)

Chelators

Chelator	Mechanism	Food use
EDTA	Strong, full coordination	Dressings, cans
Citric acid	Multi-coord + oil-soluble	Oil refining (0.01%)
Polyphosphates	Multi-P coord	Meat, seafood
Phytate	Endogenous in grains	Grain naturally
Proteins	Transferrin, casein, ferritin	Dairy endogenous

⚠️ EDTA ratio matters:
EDTA/Fe < 1 → prooxidant (partial bind, more active)
EDTA/Fe > 1 → antioxidant

Topic 5a · Free Radical Scavengers (FRS)

Tocopherol, BHT etc.: "tame" high-energy radicals with low-energy ones

LOO· (high E) + FRS-H → LOOH + FRS· (low E)
Key: FRS· is resonance-stabilized, no longer abstracts H

Why FRS targets LOO·? (not ·OH)
→ Propagation is slowest step → LOO· accumulates
→ LOO· lower energy than ·OH; FRS-H can't handle ·OH
FRS reduction potential must be below LOO· (1000 mV):
→ α-tocopherol 500 mV
→ catechol 530 mV
→ ascorbate 282 mV
Each FRS neutralizes 2 radicals (LOO· then FRS· termination)

FRS types

FRS	Property	Use
α-tocopherol (Vit E)	Natural, lipid-soluble	Vegetable oils
BHA / BHT	Synthetic, lipophilic	Animal fat, oil
TBHQ	Synthetic, more polar	Frying oil
Propyl gallate	Synthetic, polar	Water + oil
Rosemary extract	Natural (carnosic acid)	Clean-label foods

Topic 5b · Synergism + Paradox

1+1 > 2: three synergies + the antioxidant paradox

🤝 Three synergies

① FRS + FRS regeneration: α-tocopherol + ascorbic acid
tocopherol-· + ascorbate → tocopherol + ascorbate-·
Tocopherol is recycled
② FRS + chelator: BHT + EDTA
EDTA chelates Fe → less initiation → BHT preserved
③ FRS + singlet quenching: tocopherol + β-carotene
Different oxidation pathways

Natural vs Synthetic

Natural	Synthetic
tocopherol, ascorbic, rosemary, tea polyphenol	BHT, BHA, TBHQ, PG
Consumer preferred (clean label)	Stable, cheap
Limits: volatile, discolors	Gradually phased out (consumer concern)

⚠️ Antioxidant Paradox

"Hydrophilic antioxidants are ineffective in O/W emulsions, and hydrophobic antioxidants are ineffective in bulk oils"
→ the antioxidant paradox

O/W emulsions (oil droplets in water):
→ Oxidation happens at oil-water interface
→ Nonpolar antioxidants concentrate at interface → effective
→ Hydrophilic ones partition to water, useless
Bulk oils:
→ Oxidation happens in reverse micelles (trace water + metals)
→ Polar antioxidants concentrate there → effective
→ Nonpolar ones disperse evenly, less effective

⭐ Practical: match antioxidant to matrix. e.g., ascorbyl palmitate (amphiphilic): oil-soluble but enriches at water interface.

Topic 6a · Trans Fat + Hydrogenation (300 min · final hour)

The health shadow of partial hydrogenation

🔧 Hydrogenation

Goal: turn liquid oil (unsaturated) into semi-solid (saturated)
Process: oil + H₂ + Ni catalyst @ 150-200°C
Result: 18:2 → 18:1 → 18:0
Side effect: incomplete hydrogenation → cis → trans
Produces trans-18:1 (elaidic acid), mp 44°C like SFA

⚠️ Trans fat health effects

↑ LDL (bad cholesterol)
↓ HDL (good cholesterol; unlike SFA)
↑ Cardiovascular risk (worse than SFA)
2018 US FDA banned, Taiwan followed
Label: per serving < 0.5 g can be labeled 0 g

🔄 Alternatives

① Full hydrogenation + interesterification:
→ Fully saturated oil + liquid oil mix
→ Enzyme or chemical redistribution
→ No trans, solid fat function
② Fractionation:
→ Temperature-controlled crystallization separation
→ Palm oil → stearin + olein
③ Breeding:
→ High-oleic soybean / sunflower
→ Replaces partial hydrogenation

Ruminant natural trans (CLA in milk, beef): different from industrial trans, possibly beneficial (anti-cancer, fat reduction).

Topic 6b · Functional Lipids

Lipids can be functional food ingredients

🐟 ω-3 Fatty Acids

EPA (20:5), DHA (22:6)
Source: deep-sea fish (salmon, mackerel, sardine)
Benefits: ↓ TAG, anti-inflammatory, brain
α-linolenic (flax, chia) → body converts to EPA/DHA (< 5%)
Recommend: 500 mg/day EPA+DHA
Food fortification: algal oil, fish oil capsules

🐄 CLA (Conjugated Linoleic)

Source: ruminant products (beef, lamb, dairy)
Rumen bacteria isomerize linoleic
Benefits: fat reduction, anti-cancer (animal studies)
Human studies mixed
Commercial CLA supplements common

🌱 Phytosterols

β-sitosterol, stigmasterol, campesterol
Source: vegetable oils, nuts, seeds
Mechanism: compete cholesterol absorption
2 g/day → LDL ↓ 10%
Functional food: Benecol, Take Control spreads
FDA-approved cholesterol-lowering claim

🥕 Carotenoids

> 600 species, yellow-red-orange
β-carotene: vitamin A precursor
Lycopene: antioxidant, anti-prostate-cancer
Lutein, zeaxanthin: eye health
Main function: potent ¹O₂ physical quencher (dissipates as heat)
9+ conjugated double bonds → effective

🥄 Low-cal lipid mimetics

Salatrim: short-SFA + long-FA at sn-2 → 5 kcal/g (vs 9)
Olestra: sucrose + 6-8 FA esters (not absorbed) → 0 kcal
Drawback: lipid-soluble vit absorption ↓; potential diarrhea
Diacylglycerol oil: reduces fat accumulation

Topic 6c · TAG Modification

Five methods of lipid modification

Technique	Principle	Product
Blending	Mix different oils	Salad oil
Fractionation	Temperature-controlled crystallization	Palm oil → stearin + olein
Hydrogenation	+ H₂, saturate	Margarine, shortening
Interesterification	Redistribute FA randomly	Zero-trans shortening
Genetic engineering	Breed plants with new FA profile	High-oleic soybean

★ Interesterification is the key zero-trans alternative to partial hydrogenation

Interesterification detail

Chemical: NaOCH₃ catalyst, random rearrangement
Enzymatic: sn-1, 3 specific lipase → preserves sn-2 FA
Applications:
→ Palm stearin + soybean oil → interesterified → zero-trans bakery fat
→ Coconut + high-oleic → cocoa butter replacer (CBR)
→ Infant formula (mimics human milk TAG, palmitic at sn-2)

⭐ Cocoa butter equivalent (CBE): from shea + palm mid-fraction interesterified, mixes with cocoa butter (stable price & supply).

Chapter Wrap-up · 360 minutes covered

From one fatty acid,
to the fate of a chocolate bar

What you learned

• FA nomenclature, cis/trans → mp
• TAG structure, sn position biology
• SFC & plasticity, α/β'/β polymorphs
• Chocolate tempering principle
• Oxidation 3-step, β-scission flavors
• Prooxidants (¹O₂, LOX, Fe/Cu)
• Antioxidants (FRS, chelate, quench) + paradox

Apply it

• Oil industry: refine, modify, temper
• Baking: shortening, margarine, pastry
• Candy: chocolate form V, tempering
• Packaging: light barrier, low O₂, scavenger
• Functional: ω-3, phytosterols, CLA
• Low-cal: Salatrim, interesterification

Next chapters

• Ch.2 water activity → oxidation
• Ch.3 amylose-lipid complex
• Ch.5 protein-lipid oxidation cross-talk
• Ch.6 flavor (hexanal, 2,4-decadienal)
• Ch.7 lipase, LOX, SOD enzymes

🎮 Play minigames →

← → navigate　·　F fullscreen　·　🎮 6 minigames　·　中文版 →

Lipids

Six topics across 6 hours

Structure & Classification

Physical & Crystallization

Lipid Oxidation Mechanism

Prooxidants

Antioxidant Systems

Food Lipids & Health

Saturated FAs: straight, tightly packed, high melting

Double bonds: change geometry → change melting point

Essential FAs

99% of food lipids are TAG; sn position determines biology

Two tails, one head: natural emulsifiers

Sterols & waxes: small but critical

🐮 Sterols

🐝 Waxes

🍃 Sphingolipids

Food lipid fingerprints & purification

Refining (4 steps)

TAG vs Water: opposite in almost every way

Thermal

Why does chocolate melt sharply but butter slowly soften?

Food implications

Supercooling → Nucleation → Growth: 3 steps that decide everything

① Supercooling

② Nucleation

③ Crystal Growth

Food Applications

Same TAG, 3 crystal forms, different fates

α form (Hexagonal)

β' form (Orthorhombic)

β form (Triclinic)

Chocolate Tempering

Free fatty acids: the "sour" of dairy

Control

FFA in oil refining

First step of lipid oxidation: H abstraction → free radical

Oxidation's autocatalytic nature

② Propagation

③ Termination

Oxidation kinetics & lag phase

True rancid smell: low-MW aldehydes, ketones

Three classes of prooxidants, distinct mechanisms

🌟 Direct LOOH generation

⚡ Free radical generation

🔬 LOOH decomposition

Two "accelerators" with special mechanisms

🌞 Singlet O₂ (¹O₂)

🌱 Lipoxygenase (LOX)

Fe, Cu: strongest prooxidants

Chelators

Tocopherol, BHT etc.: "tame" high-energy radicals with low-energy ones

FRS types

1+1 > 2: three synergies + the antioxidant paradox

🤝 Three synergies

Natural vs Synthetic

⚠️ Antioxidant Paradox

The health shadow of partial hydrogenation

🔧 Hydrogenation

⚠️ Trans fat health effects

🔄 Alternatives

Lipids can be functional food ingredients

🐟 ω-3 Fatty Acids

🐄 CLA (Conjugated Linoleic)

🌱 Phytosterols

🥕 Carotenoids

🥄 Low-cal lipid mimetics

Five methods of lipid modification

Interesterification detail

From one fatty acid,to the fate of a chocolate bar

What you learned

Apply it

Next chapters

From one fatty acid,
to the fate of a chocolate bar