??Other carbon hydrogen nitrogen and sulfur
50-55% 6.7-7.3% 19-24% 13-19% 0-4% P, Fe, I, Mn, Zn
The only protein source of nitrogen in the body.
First, the physiological functions of proteins:
1, constitutes a tissue, cell components:
Human tissues, organs, and both contain protein. Is the most important
physiological functions. Maintain the child's growth and development,
adult tissue renewal.
2, constitute a variety of important physiological active substance
Such as the nuclear protein - constitute the nucleus and affect cell
function; enzymes - all the biochemical reactions in the body; help
food digestion, absorption and utilization;
Hormone - a variety of physiological processes regulating the immune
protein antibodies - to maintain immune function.
Maintain normal capillary osmotic pressure, to prevent edema;
transport functions; in coagulation process. Maintenance of body fluid
acid-base balance and maintain normal vision
3, the supply of energy
Deamination Pr ¡ú AA ¡ú ¡ú ¡ú ¦Á-keto acid oxidation and decomposition of
the citric acid cycle + release energy. 1 gram of protein can produce
4 kcal heat. Is a secondary function.
Second, amino acids and essential amino acids
(A) of the amino acids and peptides:
Amino acids (amino acid) is composed of basic units of proteins,
molecules with amino and carboxyl groups, and different amino acids
have a common basic structure.
Peptides: two or more amino acids connected by peptide bonds into
compounds called peptides (peptide).
By two or three amino acid peptide, called dipeptide (dipeptide) or
three peptides (tripeptide)
Usually composed of 10 AA peptide named the following oligopeptides
(0ligopeptide); 10 or more peptide composed of AA, said polypeptide
(B) of the essential amino acids (EAA)
Essential amino acids (essential amino acid): synthesis of the human
body can not synthesize or can not meet the body's need for speed, you
must supply food directly from the amino acid;
Non-essential amino acids (nonessential amino acid), synthesized in
vivo AA, not the body does not need, but can be synthesized in the
body, the lack of food anyway.
Essential amino acids:
Methionine Methionine (Met) tryptophan Tryptophan (Trp) Phe
Phenylalanine (Phe) Lys lysine (Lys)
Threonine Threonine (Thr) Leu leucine (Leu) isoleucine Isoleucine
(Ile) Val Valine (Val)
Histidine Histidine (His)
Non-essential amino acids (NEAA):
Aspartate Asparticacid (Asp) asparagine Asparagines (Asn) glutamate
Glutamine Glutamine (Glu) Glycine Glycine (Gly) Pro Praline (Pro)
Serine Serine (Ser)
Arginine arginine (Arg) alanine alanine (Ala) Cys Cystine (Cys-Cys)
Conditions essential amino acids:
Definition: EAA can reduce the body needs some AA.
Methionine cysteine ¡û
Phenylalanine Tyrosine ¡û
EAA composition of calculating food, often to methionine and cysteine,
phenylalanine and tyrosine together
(C), amino acid pattern and limiting amino acid
1, the amino acid pattern (amino acid Patten)
Refers to a variety of essential amino acids in a protein composition
That is based on protein content of essential amino acids to
tryptophan content of at least 1 to calculate the corresponding ratios
of other amino acids.
Quality protein: animal protein in the eggs, milk, meat, fish and soy
proteins with human proteins AAP AAP closer to EAA contained in the
body to a higher utilization rate.
Reference protein (reference protein).
Egg protein AA AA model and the human body model is most similar to
proteins in the nutritional value of food is often compared as a
2, the limiting amino acid (limiting amino acid)
Food proteins in one or more EAA was relatively low, leading to other
essential amino acids in the body can not be adequately reduced by
leaving the nutritional value of protein.
These relatively low levels of amino acids called the limiting amino
acid (1imiting amino acid). That, because of the lack of these amino
acids, limiting the use of other amino acids.
The lowest levels, said first limiting amino acid, while the remainder
and so on.
First limiting amino acid:
Rice, flour, soybean lysine --- --- --- tryptophan, methionine corn
3, the complementary role of the protein.
In order to improve the nutritional value of plant proteins, often of
two or more foods mixed food, through the complementary amino acids in
proteins, thereby enhancing the nutritional value of protein. This
protein contains amino acids through food between each other,
complementary roles, known as the complementary role of the protein.
Or products such as soy or meat + rice, flour can be added lysine
Third, the protein digestion and absorption and metabolism
1, protein digestion
Under normal circumstances, the Food and Pro peptide hydrolysis of AA
and the rear can be absorbed.
Starting from the stomach, but mainly in the small intestine.
(A) the stomach digestive
Acid before the protein denaturation.
¡ú pepsinogen pepsin (with activity); the role of pepsin optimum pH
value of 1.5-2.5,
(B) of the small intestine digestion and absorption
Small intestine is the main site of protein digestion.
Mainly depends on the pancreatic secretion of trypsin and
chymotrypsin, the hydrolysis of protein AA, the second peptide,
tripeptide absorption ¡ú liver and other tissues and organs used.
Note: the absorption of amino acids with similar structure, with
competition with each other, that certain amino acids by adding too
much will affect the absorption of other amino acids of the same type.
Intestinal digestion and absorption of protein, not only food protein,
but also off the cells and intestinal digestion of proteins
---- Exogenous protein food protein
---- Mainly from endogenous protein digestion and the shedding of
Also includes exogenous fecal nitrogen and endogenous nitrogen
nitrogen (fecal metabolic N)
Amino acid metabolism:
Amino acid pool: present in human tissues, organs and body fluids as
free amino acids in the amino acid pool.
Food Pr be absorbed by the digestive AA (exogenous AA) and Pr from the
decomposition of body tissue AA (endogenous amino acids) mixed,
distributed in the body, involved in metabolism, also known as amino
acid metabolism library.
--- Amino acid metabolites which urea, creatinine, uric acid, ammonia,
etc. may be out of the body in urine.
The urine contained more nitrogen, including nitrogen exogenous and
Reaction of nitrogen balance is the amount of protein intake and
metabolism with the loss of the relationship between the amount of
Nitrogen balance = nitrogen intake - (fecal N + urinary N + N others)
Zero nitrogen balance: nitrogen intake = nitrogen excreted
Positive nitrogen balance: nitrogen intake> excretion of nitrogen
Negative nitrogen balance: nitrogen intake <discharge of nitrogen
Fourth, the nutritional evaluation of food protein
"Quantity" and "quality"
Biological method: Determination by animal or human studies of food
protein digestibility and utilization in the body;
Chemical analysis: The amino acids in food analysis, and compared to
pre-evaluate the reference protein.
(A) of the protein content of food
Determination of total nitrogen in food protein conversion factor
multiplied by 6.25, that was protein content.
(B) digestibility of food protein
Food protein digestibility (digestibility): is absorbed in the
digestive tract of the protein percentage of total protein intake; is
to evaluate the nutritional value of food protein biological methods.
Apparent digestibility, true digestibility.
1, true digestibility of protein
True protein digestibility (%) = Food, N-(faecal N-metabolic fecal N)
Fecal nitrogen source:
Protein digestion and absorption of food is not;
Shedding of intestinal cells, digestive and intestinal bacteria
2, protein digestibility
Excluding that endogenous fecal protein digestibility of nitrogen.
Apparent digestibility of protein intake of N-dung (%)=( N)
Protein digestibility of factors: the nature of protein, dietary
fiber, polyphenols, enzyme reaction and processing methods.
(C) the utilization of food protein
Of food proteins are digested and absorbed to be used in the body
after the extent of nutritional assessment of food protein commonly
used biological methods.
Methods: The weight-based; to nitrogen retention in the body is based.
1, the biological value
Biological value (biological value, BV)
Is a reflection of protein digestion and absorption of food, the
degree of utilization is an indicator of the body; biological value of
the higher, indicating higher protein utilization by the body, the
higher the nutritive value of protein, the maximum value of 100.
2, protein efficiency ratio
Protein efficiency ratio (protein efficiency ratio, PER) is based on
animal weight gain as indicators; is the experimental period, average
intake of animal protein 1g weight gain when the number of grams.
Several common food protein PER:
3.92 whole eggs, milk 3.09, fish 4.55, beef 2.30, soy 2.32, 0.60 and
refined flour, rice 2.16.
V. Evaluation of protein malnutrition and nutritional status
First, dietary protein intake
Second, the body measurement
Weight, height, arm circumference, arm muscle circumference, chest
circumference, and growth index.
Third, the biochemical
(A) of the blood protein
Serum albumin :35-55g / L
Prealbumin :200-555mg / L
Serum transferrin :2-4 g / L
Fibronectin :200-280 mg / L
Pure retinol binding protein :40-47¦Ìg / L
Sixth, and food sources of protein supply
Adults: Protein intake should be 10-12% of the total heat
Children: 12-14% should be
Dietary Reference Intakes RNI
Light physical adult male 75g / day, women 65g / day
Adult males in the physical 80g / day, women 70g / day
Heavy physical adult male 90g / day, women 80g / day
Pregnant women: 1-3 months +5 g, 4-6 ÔÂ +15 g, 7-9 ÔÂ +20 g
Nurse: +20 g
Protein food sources:
Vegetable protein: grains, beans
Animal protein: milk, eggs, meat (poultry, livestock and fish muscle)
Quality protein accounted for 30-50% of total protein