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Professor Dr. Jin Bangquan
Deparment. of Food Science & Nutrition
NJNU
Review: Protein Metabolism
Review: Protein Chemical Function
氨基酸缩合
肽链延长
亚基形成
蛋白质
§1 Concept

Definition:
Protein is the life base
Complex of 20 Amino Acids (AA) in body

Named:
1836 Chemist Muldgr (柏采里.乌斯 Sweden) found
1888 Berzelius named
1852-1919 Emil Fischer (Germany) ，建立有机结构
化学和蛋白质分析法，1902年获诺贝尔化学奖, 1907
年合成18个AA的肽链。
Composition

Main Elements: C, H, O, N

Fewer Others: S, Fe, Cu----

Content in Body: 16-19%

Renew: 3% in a day (20g Prot. or 3.2g N)

Exchange : 1/4 in total
Surviving 30-50d when starving
Analysis Method (GB)


kjeldehl
CP% = N×6.25
§2 Protein function & classification
1 Function

Composition in Body: Muscle,
Blood plasma

Physiological Actives: Enzyme
keeping osmosis

Supplying Energy: 1g = 4kcal/g
= 16.7kJ/g
2 Classification

按EAA： 完全蛋白
半完全蛋白
不完全蛋白

按结构和溶解度：
简单蛋白
硬蛋白
结合蛋白
*Protein classification in Nutrition
N: 根据食物蛋白质所含氨基酸的种类和数量
将食物蛋白质分三类：
1. 完全蛋白质 这是一类优质蛋白质。它们所含的必需氨基酸
种类齐全，数量充足，彼此比例适当。这一类蛋白质不但可以
维持人体健康，还可以促进生长发育。奶、蛋、鱼、肉中的蛋
白质都属于完全蛋白质。
2. 半完全蛋白质 这类蛋白质所含氨基酸虽然种类齐全，但其
中某些氨基酸的数量不能满足人体的需要。它们可以维持生命，
但不能促进生长发育。例如，小麦中的麦胶蛋白便是半完全蛋
白质，含赖氨酸很少。食物中所含与人体所需相比有差距的某
一种或某几种氨基酸叫做限制氨基酸。谷类蛋白质中赖氨酸含
量多半较少，所以，它们的限制氨基酸是赖氨酸。
3. 不完全蛋白质 这类蛋白质不能提供人体所需的全部必需氨
基酸，单纯靠它们既不能促进生长发育，也不能维持生命。例
如，肉皮中的胶原蛋白便是不完全蛋白质。
4 Reference Protein
Egg
Human milk
These AA pattern are similar to human AAP
§3 Amino Acid (AA) & Peptide
Definition
 AA is the basic unit
for synthesizing protein
α-AA chain
 Peptide can carry on
the protein function
Classification 1
According to α-AA chain -NH3+, -COONeutral
Alkali
Acid
Suppl.
Classification 2
According to Nutritional important

Essential Amino Acid (EAA)

Limiting Amino Acid (LAA)

Non-Essential Amino Acid (NEAA)
Essential Amino Acid (EAA):(8+1)
Leucine (Leu, 1st 1810) Isoleucine (Ile)
Lysine (Lys)
Methionine (Met)
Phenylalanine (Phe)
Threonine (Thr, last 1935)
Trypotophane (Try)
Valine (Val)
Histidine (His for Infant)
Known as 1983
We need them from Food, but not made in ourselves
Limiting Amino Acid (LAA)

Three: Lys, Met, Thr

Ideal Ratio: Lys: Met: Thr = 100: 60: 40 in Ration

Amino Acid Pattern：Compared with different
Special for Growing
kinds, ratio & content between human body and food
supplement
Trp as 1

High quality of protein:
Nonessential Amino Acid (NEAA)
NEAA can be synthesized from others in body
Ala
Asn
Arg
Glu
Asp
Gln
Gly
Pro
Ser
Conditional EAA
Cys
Tyr
When Cys and Tyr were enough in body the requirement
of Met and Phe was decreased by 30% and 50% .
Amino Acid Pattern (AAP)
Complementary Action of Protein/Amino Acids
can be access to body protein pattern
from various foodstuffs
Such as : beef/ Pork + Corn/ Rice
Bio-value
Lys
Met + Cys
1The amino acid values for the pattern are expressed on a per-gram-of-nitrogen basis
2The amino acid patterns and the total nitrogen content were used to calculate the
levels of individual amino acids per 100 g of food
Examples:
Kinds
（%）
Lys/Met
BV(%)
Corn
21
Flour
31
Lys
Lys Met
60
67
Soya
48
Account
100
Lys Met
64
70
Kinds Flour Millet Soya Beef Account
（%） 39
13
22
26
100
BV(%) 67
57
64
69
89
§4Nitrogen Balance & Balanced Diet

Balanced Diet

Nitrogen Balance
Suppl.
1 Balanced Diet



Hypothesis of Ideal Protein
The number of EAA is enough
The ratio of AA is suitable from foodstuffs
Various food sources
A set of values that serve as the pattern for calculating
the amino acid profile of other similar foods
2 Nitrogen Balance


1.
2.
3.
Definition: N-intake is equal to N-ejection
every day keeping weight for adults
Index NB= N-intake - N-ejection (Urine + Feces + Skin)
Zero Nitrogen Balance：
N-intake = N-ejection
Positive Nitrogen Balance： N-intake > N-ejection
Negative Nitrogen Balance：N-intake < N-ejection
Notes: ONL≈3.2g/d (×6.25)
Protein Loss≈20g/d (= 16%×N)
Obligatory Nitrogen Loss/ ONL/必要的氮损失
§5 Nutritional Evaluation for Foods1


CP or AA content (Ratio of EAA : CP)
CP Digestibility
1 Apparent Digestibility:
(Protein in food - Protein in feces ) ÷ Protein in food × 100%
2 True Digestibility*:
(Protein in food - Protein in Control) ÷ Protein in food × 100%
P14-16
Nutritional Evaluation for Foods2

Nutritional Absorptivity :
Percentage of Nutrients in Gut

Biological Value (BV)*
BV=Food N-(FN+UN)/ Food N-FN100%

Net Protein Utilization (NPU)
NPU= Digestibility BV= UN-EnN/Food
N100
Protein Availability or Efficiency

Percentage of change and synthesis into
new tissue
Body Weight Gain÷ Protein in food × 100%
Body Weight Gain÷ a kind of food × 100%
Data tested from animal , no human
P16 top
§5 P-requirement & Supplement1




Basic requirement: 30g CP/d for adult
Safety Supplement: 0.8g/kg.d (48-56g/d)
Recommendation: 1.16g/kg.d (70-90g/d)
RDA: 72g/d
CP in Energy: 10-12% (P: E) for adult
12-14% for child
range: 10-20% (15-20)
P18
P-Supplement 2
From foods at all
Food Protein Source
1 Protein content >15%
eg: meat, egg, soybean

2 Better Protein Source
eg: as above
Sources and Content in foods

Grain： 8-14%

Beans：Soybean 35-40%
Other bean 12-25%

Meat, Egg, Fish, Poultry：10-20%

Milk：3-5%
High quality protein: Meat, Egg, Fish Poultry, Milk, Soybean
Suppl. Ratio in diet：40-50%
Protein in Energy：15-20%
Malnutrition

P17-18
Low-protein in blood
(albumin 35-50g/L)

Dropsy

Marasmus
Examples
in Nutritional Evaluation & Anthropometry
P197-205
Deficiency or Surplus

Deficiency： Dropsy & Marasmus

Surplus：Over acid in body
Accumulating NH4 + , Cr
Overload of liver & kidney
Protein Evaluation for Human

Arm Circle

Albumin in serum

Urine、Cr、BUN
Question
1 What is protein？
2 Water is referent protein?
3 Which food is the source of better protein？
4 What and how many are EAA ？
5 What is LAA？Why？
6 What is AA pattern？
7 How to increase bio-value of food protein？
8 What is N-balance Hypothesis？
9 Which effects are on protein utilization？
10 What is protein support problem？