Lipids VIII Flashcards
What is the % of TG in milk fat?
96%
Why are sterols necessary in milk fat?
To maintain the fluidity of phospholipids
What are the main fatty acids in milk fat? (3)
- Oleic
- Stearic
- Palmitic
How much linoleic and linolenic does milk fat contain?
Very little
Which product contains butyrate? What is the chemical abbreviation?
Milk fat (C4:0)
In milk fat, long chain fatty acids are preferred in which positions?
- sn-1
- sn-2
In milk fat, short-chain fatty acids are preferred in which positions?
sn-3
What kind of TG are preferentially synthesized in milk fats?
TG with one short and two long-chain FA
How does the ratio of saturated to unsaturated FA vary in milk?
- Does not vary
- Due to their typical diet
TG are contained within ___________ that are surrounded by a _________
- fat globules
- membrane
_________ are synthesized by the microflora of the cow, and present health benefits
Conjugated linoleic acid (CLAs)
What are the components of the membrane that surround the fat globules in milk fats?
- Protein (41%)
- Phospholipids and glycolipids (30%)
- Cholesterol (2%)
- Neutral glycerides (14%)
- Water (13%)
How much cholesterol does milk, shrimp, and eggs contain?
- Milk: 27 mg
- Shrimp: 125 mg
- Eggs: 275 mg
What does the membrane that surrounds the fat globules in milk contain?
- Double layer of lipoproteins
- Enzymes, including lipase
What is the function of the membrane of the fat globule
Prevents lipolysis
What is the consequence of the disruption of the membrane of fat globules? In which situation could this happen?
- Homogenization of milk
- Allows lipase to bind to the fat globules and to hydrolyze TG at a high rate
- Milk becomes unpalatable
What must be done prior to homogenization? Why?
Lipases must be inactivated by pasteurization to avoid them hydrolyzing the TG
What is lactose degraded to during ripening? How?
Degraded to lactic acid by homofermentation
What does the type and extent of milk fat degradation depend on?
Depends on the microflora
What is a prerequisite for good aroma in cheese? What are the exceptions?
- As little lipolysis as possible
- Exceptions: stinky cheeses (ex: roquefort)
More/less free fatty acids are released in homogenized milk than untreated milk.
More
What do the different aromas of various types of cheeses arise from?
- From the different specificities of the lipases involved
- They exhibit specificity to hydrolyze certain substrates, which causes different aromas
Are the levels of saturated or unsaturated FA higher in red meat?
Unsaturated exceeds saturated
If the levels of unsaturated FA exceeds saturated FA in red meat, why are the lipid products solid?
Since they have more fully saturated fatty acids (GS3)
What is the % of total saturated lipids in red meat? Which fatty acids are the most present?
- Total: 46%
- Palmitic (16:0) > Stearic (18:0) > Myristic (14:0)
What is the % of total monounsaturated lipids in red meat? Which fatty acids are the most present?
- Total: 50%
- Oleic (18:1) > Palmitoleic (16:1)
What is the function of cholesterol in red meat? How much is found in 100 grams?
- Integral component of cellular membranes
- 70-90mg/100 grams
What is the main monounsaturated fatty acids found in skeletal muscles of red meat?
- Oleic acid (90% of MUFAs)
- 45% of total FA
What is the main polyunsaturated fatty acids found in skeletal muscles of red meat? What is the main source of saturated? What is the main source of unsaturated?
- Polyunsaturated: Linoleic acid
- Monounsaturated: Oleic acid
- Saturated: Palmitic and stearic acid (2:1 ratio)
What is the main saturated fatty acids found in skeletal muscles of red meat?
- Palmitic acid and stearic acid in a ratio of 2:1 (90%)
- 40% of total FA
How many eggs do hens produce per year?
225
What is the composition of the albumen of an egg?
10% protein, 0.03% lipids
What is the composition of the yolk of an egg?
16% protein, 35% lipids
What is the composition of the whole egg?
13% protein, 11% lipids
Why are eggs nutrient rich?
Complete protein, essential FAs, vitamin D
What is moderate egg consumption?
6 eggs/week does not increase coronary heart disease
What is the macronutrient composition of an egg yolk?
- Water: 48.7%
- Fat: 32.9%
- Protein: 16.4%
Are egg yolks water-soluble?
Yes, even if they behave as lipids, eggs are “soluble” and can readily disperse in water
Why can eggs readily “disperse” in water?
- High lipid content
- High proportion of phospholipids
- More than 90% of the lipids in the yolk are associated with lipoproteins
What is the ratio of LDL to HDL in egg yolks?
LDL: 68%
HDL: 14%
What does cholesterol provide in egg yolks?
Flexibility
How does the density of LDL and HDL compare?
LDL: 0.98
HDL: >1.0
How does the composition of LDL compare to HDL?
LDL: large amounts of lipids (85%); mostly TG (69%) and phospholipids (26%)
HDL: small amounts of lipids (20%); mostly phospholipids (60%) and TG (40%)
Where are LDL particles present in egg yolk? In what form?
In the form of tiny micelles suspended in the plasma fraction
Does LDL or HDL contain phosvitin? What is it?
- HDL
- Phosphorus-rich, lipid-free protein
Associate these words:
1) LDL
2) HDL
A) Lipovitellin
B) Lipovitellenin
LDL: Lipovitellenin
HDL: Lipovitellin
What influences the fatty acid composition of an egg yolk?
The breed and the diet
What is the lipid composition in egg yolks?
- TG (66%)
- Phospholipids (28%)
- Cholesterol (5%)
What is the fatty acid composition of egg yolks?
- Saturated FA: 30-35%
- MUFAs: 40-45%
- PUFAs: 20-25%
What happens when the dietary PUFA is elevated in egg yolk?
Linoleic acid increases and oleic acid decreases
What are the three main components of egg yolk phospholipids?
- Phosphatidylcholine/Lecithin (73%)
- Phosphatidylethanolamine/Cephalin (15%)
- Lysophosphatidylcholine (6%)
What is lysophosphatidylcholine?
- Derivative of phosphatidylcholine
- One of the FA has been replaced by a hydroxyl group
What are the deteriorative changes that occur in dried whole egg and egg yolk related to?
Maillard reaction
What leads to discoloration of dried whole egg and loss of palatability?
The reaction between cephalin and glucose (Maillard)
How is the development of off-flavour during storage eliminated in eggs?
- Elimination of glucose
- Addition of glucose oxidase followed by catalase
What are designer eggs?
- Enhance the image of eggs as healthy and nutritional
- Omega-3 fatty acids eggs (feeding hens flax or fish oil); darker yellow colour to the yolk
What is the fat content of fish depend on?
- Species of fish
- Maturity
- Season
- Food availability
- Feeding habit
Where does fat deposition occur in fish?
Muscle tissue, liver, intestines
Fish is an important contributor to what types of omega-3 fatty acids? What are the benefits and downsides?
- Omega-3-polyenic acids (5 or 6 double bonds)
- Nutritional value
- Preservation is difficult because of their easy peroxidation
What is the typical fatty acid profile of fish oil?
- Saturated (28%)
- Unsaturated (28%)
- Polyunsaturated (38%)
What is the % of TG in soybeans? What about phospholipids?
- TG (96%)
- Phospholipids (2%)
What is the fatty acid profile of soybean oil?
- Saturated FA (14%)
- Unsaturated FA (81%)
What is the main saturated FA in soybean oil? What are the main unsaturated FA in soybean oil?
- Palmitic acid (10%)
- Linoleic acid (51%)
- Oleic acid (23%)
When are lecithins removed in the processing of oil? Why?
- Removed from degumming
- To use their emulsifying power for other means
What are the unsaponifiables contained in soybean oil? When are they removed?
- Mostly tocopherol and sterols
- Partially removed in deodorization
When are free fatty acids and pigments removed from soybean oil?
Refining and bleaching
Why are soybean oils classified as semi-drying oils?
Due to their high linoleic and linolenic acid content
What is responsible for the stronger tendency of soybean oil to undergo oxidative phosphorylation?
Linolenic acid
