PROTEINS File

Comments

Transcription

PROTEINS File
PROTEINS
Proteins have a role in both living organisms and in food
products
Primary food sources
Eggs, dairy products, meats, poultry, and fish
Grain sources
Legumes (beans, soybeans, peas, chickpeas, lentils)
PROTEIN STRUCTURE
Chemically, Proteins are macromolecules, made of individual
“building block” units called amino acids (AAs) that are linked
together
There are 20 AAs in the human body, and about 150 others
found in plants and animals.
Proteins contain four basic elements, carbon, hydrogen,
oxygen and nitrogen. Amino acids are organic
compounds, so called because they contain a carboxyl
group (COOH), with ACID properties, and an AMINO
group (-NH2), having basic properties.
BASIC STRUCTURE OF AN AMINO ACID
Central carbon atom (alpha carbon [Cα]) linked to
Amino group (positive)
Carboxylic acid group (negative)
Hydrogen
Distinctive side chain (R)
Makes each AA different
AMINO ACIDS ARE BRIKS THAT BUILD A PROTEIN
PEPTIDE BOND:
two amino acids are linked together by
expelling a water molecule
THE MOLECULE RESULTING FROM THE
COMBINATION OF TWO AMINO ACIDS IS
CALLED DIPEPTIDE.
A chain of AAs is called a peptide.
Long peptides are proteins or polypeptides.
The order of the AAs allows different proteins to have different functions.
R GROUPS FOR SOME AMINO ACIDS
Glycine
HCH3H3C
Alanine
HO-CH2CH3-CH-
Serine
Threonine
OH
CH-
Valine
H3C
CH2-
H3C
SH
CH-CH2-
Cysteine
Leucine
CH2-CH2-
H3C
Methionine
S-CH3
CH2
CH2
CHCH3
Isoleucine
-OOC-CH 2
Aspartic acid
ESSENTIAL AMINO ACIDS
Amino acids can be classified into two groups: ESSENTIAL and nonessential (body cannot make them on its own)
Leucine
Tryptophan
Methionine
Isoleucine
Threonine
Lysine
Valine
Histidine
Phenylalanine
Other 11 amino acids are NOT ESSENTIAL (NEAA)
–Can be made from other amino acids in the diet
Some NEAAs can become EAAs under certain conditions
–Infants have different needs for growth
–Defects in amino acid metabolism
• Tyrosine can become essential in individuals with phenylketonuria (PKU), an
inborn error of phenylalanine metabolism
6
Protein-rich foods, or the sweetener aspartame (as it contains
phenylalanine), can act like poisons to people with Phenylketonuria (PKU).
Classical PKU is caused by a deficiency of an enzyme called
phenylalanine hydroxylase (PAH). The role of this enzyme is to break
down excess phenylalanine from food. Phenylalanine is a necessary part
of the human diet. However, if there is not enough of the PAH enzyme,
then excess phenylalanine from the protein in foods builds up in the
blood, affecting brain development and function.
Untreated PKU can lead to intellectual disability, seizures, and other
serious medical problems. The best proven treatment for classical PKU
patients is a phenylalanine-restricted diet supplemented by a medical
formula containing amino acids and other nutrients.
The diet requires severely restricting or
eliminating foods high in Phe, such
as meat, chicken, fish, eggs, nuts, legumes,
cheese, milk and other dairy products.
PROTEIN STRUCTURE
Primary Structure
sequence of amino acids
Secondary Structure
Helical coil (α-helice)
β-strand
PROTEIN STRUCTURE
Tertiary Structure
folding of coil
3-dimensional structure
Determined by AA sequence
Specificity of a protein’s function
Diversity of protein functions
proteins typically contain a few hundred AAs
infinite combinations of amino acids
tremendous diversity of protein types
PROTEINS
Polypeptide
PROTEIN SYNTHESIS
Sequencing errors
PROTEINS
Amino acid sequences can vary
resulting in almost an endless number of
combinations.
Each protein’s sequence is determined
by the DNA
As each amino acid has unique
chemical characteristics and electrical
charges, the resulting shapes can be very
complex.
PROTEIN
SHAPE
AND
FUNCTION
HEMOGLOBIN
FIBROUS and GLOBULAR
PROTEIN
• Proteins can be
classified in two
classes:
Fibrous
protein
Globular protein
Globular Protein
• Water soluble
• Almost spherical
• Many biological functions
They are:
• Enzymes
• Hormones
• Carrier Proteins
• Storage Proteins
Fibrous Protein
• Animal origin
• Water insoluble
• Structural roles
They are divided into three categories:
keratins
collagen
silks
Forming protective tissues
Forming connective tissues
As the cocoons of silkworms
BIOLOGICAL FUNCTIONS OF PROTEINS
Enzymes
All biological enzymes are made of protein
• For example, the digestive enzymes trypsin and amylase
Hormones (some)
Insulin and glucagon
Not all hormones are proteins (e.g. Testosterone is a steroid)
Structural
Actin & myosin (muscle)
Collagen (skin), Keratin (hair)
BIOLOGICAL FUNCTIONS OF PROTEINS
IMMUNOLOGIC
–All antibodies (antibodies are giant proteins that bind up specific
invaders like viruses or antigens)
TRANSPORT AND STORAGE
–Carriers of fatty acids, oxygen (hemoglobin), iron, vitamin A,
copper, and other nutrients
–Cholesterol and triglycerides carried by lipoproteins
ENERGY SOURCE
–When carbohydrates are limited (gluconeogenesis = The brain
and nervous system must have glucose. Once the amino group is
removed from the protein, the remaining carbon molecules can
be used to create energy - 4 Kcal per gram or stored as fat)
DENATURATION AND COAGULATION OF
PROTEINS
Denaturation is when the actual nature of the protein is changed.
This usually occurs during food preparation when a protein is
heated, agitated, or when chemicals are added to it
The molecules unravel themselves and lose their coiled structure.
In the case of moderate heating, denaturation may be reversible.
When a protein is heated, coagulation occurs.
Coagulation is when proteins form clots
Examples include curdling milk to form cheese or cooking an egg.
When a protein is agitated, disrupts the protein structures and causes them
to form new positions with other molecules.
When chemicals, such as acids, are added to a proteins, it causes curdling.
DENATURATION AND COAGULATION OF
PROTEINS
Both of these processes are used to make new
foods (e.g. milk to cheese) or to prepare
foods (e.g. cooking an egg)
It is important to remember that denaturation can
be over done (over coagulation), which can cause
a change in taste and texture of food. It also can
ruin a recipe (e.g. over agitation of a meringue
will cause clots to form)
FUNCTION OF PROTEINS
Proteins are used in the preparation of foods in
many ways:
Gelling agents
o Gelatin protein can be heated in water and then cooled; or
eggs, milk and sugar can be heated to make a custard
Gelatin provides several benefits:
o Structure and support
o Stabilizer
o Thickening agent
o Controls ice crystal growth in frozen foods
FUNCTION OF PROTEINS
Texturize
Proteins can be texturized through denaturation
This process is used to make soybeans into meat
substitutes, or to create processed cheeses
Emulsifiers
An emulsion is a stable mixture of a fat and a water based
liquid
An emulsifier is a molecule that has a polar end and a
non polar end and require heat or mechanical action to
denature and form the emulsion
Egg yolks are an excellent emulsifier
Food products such as ice cream and mayonnaise
require emulsifiers to stay together
FUNCTION OF PROTEINS
Foams
Foam is gas suspended in a liquid or semi solid
Foams can be made using proteins such as eggs or
dairy by incorporating air, mechanical agitation or by
a sudden release in pressure (aerosol can)
Examples of foams are: Merinques, marshmallows,
whipped cream
Gluten
Gluten is an elastic protein formed when wheat flour is
combined with moisture and stirred
It coagulates when baked and forms an airy texture,
such as bread
A gluten-free diet is a diet that excludes gluten, a protein composite
found in wheat and related grains, including barley and rye. Gluten
causes health problems in sufferers of celiac disease (CD) and some
cases of wheat allergy. For those diagnosed with celiac disease, a
strict gluten-free diet constitutes the only effective treatment to date.
Some people believe that there are health benefits to glutenfree eating for the general population, but there is no
published experimental evidence to support such claims.
Some proteins contain chemical groups
other than amino acids
Many enzymes contain only amino acids and no other chemical group →
SIMPLE PROTEIN
Other proteins contain, in addition to amino acids, functional chemical
groups permanently associated → CONIUGATED PROTEIN. The nonamino acid part is defined prosthetic group.
PROTEIN DIGESTION
Gastric phase (stomach)
Hydrochloric acid (HCl) from cells in stomach unfolds protein
Pepsinogen (chief cells)
Pepsin digests proteins
HCl
Pepsin (enzyme)
Large peptide fragments
Small intestine phase
Cholecystokinin (hormone released in upper small intestine)
triggers pancreas to secrete digestive enzymes once digestion
products leave the stomach
Digestive enzymes are activated and continue to break down
peptides into di-/tripeptides and free amino acids, which are
taken up by intestinal cells
29
PROTEIN ABSORPTION
Carriers - cells of the villi of the
SI have gates through which
carrier substances transport the
amino acids.
Capillaries, which are the
smallest branches of the
circulatory system carry the
free amino acids from the villi
throughout the body.
FAST VERSUS SLOW DIGESTION OF PROTEINS
Proteins are digested at different rates
–Similar to glycemic index concept for carbohydrates
Whey versus casein
–Whey is rapidly digested and results in quick rise in plasma AAs (fast protein)
–Casein forms a curd and takes longer to empty from the stomach (slow protein)
• Less dramatic, but more sustained rise in plasma AAs after consumption
Soy protein
–Digested faster than whole milk protein, which contains both whey + casein
• Overall, more like a fast protein, but slower than whey
PROTEIN TURNOVER
There is a constant flux between making new muscle protein and
breaking down old muscle protein, known as “protein turnover”
Goal for increasing muscle size is for muscle protein synthesis to
exceed breakdown
Muscle
protein
Muscle
breakdown
Muscle
synthesis
Amino
acids
Blood
Amino acids
FAST- VERSUS SLOW-DIGESTED PROTEINS IN PROTEIN TURNOVER
In general, milk proteins are superior to soy for stimulating
protein synthesis
– Whey (fast protein) stimulates protein synthesis to a greater
extent than casein (slow protein) and soy (moderate-fast
protein)
– Casein reduces muscle protein breakdown better
than whey protein
Mixed protein sources provide benefits of all
COMPLETE AND INCOMPLETE PROTEIN
Foods that contain all eight essential AA’s are
called complete proteins
Most of these sources come from animal products,
with the soybean plant also added to the list
Foods that are short of one or more of the
essential AA’s are called incomplete proteins
Most of these are found in grains and vegetables
Combining these will create a complete
protein
Complementary Proteins
Combinations of incomplete proteins that, when added
together, result in a complete protein
Legumes: methionine,
lysine
Grains:
methionine, lysine
Combining complementary proteins at each meal for
vegetarians is not necessary
What matters is total intake of complementary proteins
spread over the course of the day
PROTEIN QUALITY
Vegetarian Diets
Is there a protein problem?
Plant proteins are “Incomplete proteins”
Complementary Proteins
Example: Mexican Food
Tortilla: low lysine, high methionine
Beans: low methionine, high lysine
PROTEIN AND NUTRITION
Daily protein needs
Quantity of protein
Quality of protein
Protein Quality
How well a protein meets the body’s need for health,
growth, etc…
Digestibility
Amino acid composition
Essential Amino Acids composition
PROTEIN QUALITY
Reference protein
Complementary proteins
PROTEIN QUALITY
Measures of protein quality
Biological Value (BV)
Measures body retention of food protein
BV=100 => 100% of food protein retained
Protein Efficiency Ratio (PER)
Measures ability of protein to support growth
g growth/g protein fed
PER=3 => 3g growth per g or protein fed
Biological value (BV)
It takes into account the reused % of amino acids absorbed
in order to produce human proteins
BV = AAs used
× 100
AAs absorbed
For example: a protein introduced by food produces 950 AA
during digestion. After their absorption, only 585 AAs will
become part of human proteins newly synthesized, the rest will
have to be wasted. What is the BV of the protein?
BV = ( 585/950) × 100 = 61.6
PROTEIN QUALITY: BV
100
80
60
40
20
0
Egg
Milk
Beef
Soy
Peas
Rice
Wheat
Lentils
PROTEIN QUALITY: PER
4
3,5
3
2,5
2
1,5
1
0,5
0
Egg
Milk
Beef
Soy
Peas
Rice
Wheat
Lentils
PROTEIN REQUIREMENTS
Current RDA for protein is 0.8 g/kg body weight per day
– ~65 g/day for a 180-lb (82-kg) individual
– ~47 g/day for a 130-lb (59-kg) individual
The RDA for protein is set to prevent deficiency (ie, maintain
protein balance) in healthy adults.
Does not consider potential benefits that might be obtained from
amounts beyond RDA
– For example, the optimal protein intake for muscle function and
athletic performance
USDA National Agricultural Library Food and Nutrition Information Center. Available at:
http://fnic.nal.usda.gov/nal_display/index.php?info_center=4&tax_level=3&tax_subject=256&topic_id=1342&level3_id=5140.
PROTEIN INTAKE RECOMMENDATIONS
American College of Sports Medicine (ACSM) /
American Dietetic Association (ADA)
–Endurance athletes, 1.2 to 1.4 g/kg per day
•Accounts for greater use of protein as fuel for
energy
–Strength athletes, 1.2 to 1.7 g/kg per day
•To support muscle growth, particularly during early
training phase when gains are greatest and protein
utilization is less efficient
HOW MUCH PROTEIN ARE ATHLETES EATING?
Many athletes may already meet or exceed protein
recommendations
Strength athletes in particular may believe that much higher protein
intakes are needed for muscle building
– Intakes at 4- to 6-g/kg range are not uncommon
– Unlikely to provide benefit beyond 2.0 g/kg
– It is possible that this much protein intake could adversely
affect the nutrient quality of the overall diet
Protein intake below 2 g/kg per day is safe in healthy individuals
Protein intake above 2 g/kg per day is not recommended due to
lack of proven benefit and potential for adverse health effects
POTENTIAL DOWNSIDE TO “HIGH-PROTEIN” DIETS
Hydration status
– Nitrogen that is obtained from consuming protein must be excreted in
the urine as urea
– Increased urinary output due to high protein load may increase chances
of dehydration
Diets very high in protein may lack appropriate amounts of
carbohydrate, fiber, and some vitamins/minerals
– Could impair exercise performance
– Could increase long-term risk of diseases such as colon cancer (possibly
due to lack of fiber or increased intake of red meat)
Excessively fatty protein sources could increase risk of cardiovascular
disease
– Choose mostly lean protein sources (salmon instead of ribeye steak)
POTENTIAL DOWNSIDE TO “HIGH-PROTEIN” DIETS
Kidney disease
– Protein-rich diets are high in phosphorus, which can be harmful
to individuals with kidney disease
– A high protein diet increases the load on the kidneys, which in
Chinese medicine means degenerative changes will take place
earlier.
• Primarily a concern with elderly or sick individuals, as opposed to healthy
athletes
Bone health
– Higher protein diets may increase calcium loss in urine
– Elevated protein diets appear to have either no or a slightly
beneficial effect on skeletal health
WHAT ABOUT AMINO ACID SUPPLEMENTS?
As long as the complete protein requirements are met, the
individual AA requirements will be met as well
No need for additional AA supplements to prevent
deficiency
Because vegetarians eat few complete sources of protein, they
should be cognizant of complementary protein sources
throughout the day to prevent deficiency of particular AAs
Branched chain amino acids are popular as a supplement
among athletes
–Claims mainly center on decreasing muscle soreness and
improving either performance or recovery from exercise
–Doses can range from 2 to 7 g/day to more than 20 g/day
BRANCHED CHAIN AMINO ACIDS (BCAAS)
BCAAs are
H3C
CH2
H
COO-
CH-CH2- C
H3C
NH3
+
Leucine
H
H
CH2
CH- C
CH3
NH3
COO+
Isoleucine
H3C
H3C
CH- C
COO-
NH3+
Valine
BCAA supplementation, for people with low dietary protein intake,
can promote muscle protein synthesis and increase muscle growth
over time.
Leucine is also unique among AAs in its ability to stimulate synthesis
of new muscle proteins.
Taurine is an amino acid that's found in large
amounts in the heart and brain. It's also found in
food sources—the best ones being meat and fish,
though it's also included in energy drinks and
some supplements used to support athletic activity.
VEGETARIAN DIETS:
WHY BECOME A VEGETARIAN?
Health benefits
Environmental concerns about meat based diets
Animal welfare/ethical considerations
Economic reasons
World hunger issues
Religious beliefs
VEGETARIAN DIETS:
POTENTIAL HEALTH BENEFITS
Obesity
% of obesity lower in vegetarian populations
Cardiovascular Disease
Risk of CHD 31% lower in vegetarian men and 20% lower in
vegetarian women
Lower LDL-C, lower HDL-C
Hypertension
42% non-veg with hpt, 13% vegetarians
Also lower prevalence for
Diabetes
Cancer
VEGETARIAN DIETS: TYPES
Non-red meat vegetarian
poultry, fish, dairy, eggs OK
Nutritional Benefits
Less fat, saturated fat, cholesterol
Nutritional Concerns
no special nutritional problems
Lacto-ovo vegetarian
Milk & eggs OK
Nutritional Benefits
Like non-meat vegetarians
Nutritional Concerns
No special nutritional problems
May be high in fats, saturated fats (cheese & eggs)
VEGETARIAN DIETS: TYPES
Strict Vegetarian: Vegan
no animal foods
Nutritional Benefits
Low fats, high fiber, plant-based
Nutritional Concerns
protein quality
probably OK, quantity may be an issue
calcium
no dairy, plant sources (leafy greens, soy), fortified foods (soy, rice milk)
iron
no meat, plant sources (leafy greens), cereals
vitamin B12
probably OK, cereals & supplements
VEGETARIAN DIET PLANNING
Protein is almost always adequate unless too much
sugar and fat are used.
Good sources include beans, tempeh, tofu, quinoa
and low fat dairy or soy milk products. TVP may
be used occasionally.
Vegans must use the equivalent of 1-1/2 cups of
beans daily.
Textured or texturized vegetable protein (TVP), also k
nown as textured soyprotein (TSP), soy meat, or soya
chunks is a defatted soy flour product, a byproduct of extracting soybean oil.

Similar documents