Professor Dr. Jin BangquanDeparment. of Food Science &

NutritionNJNU

Review: Protein Metabolism

Review: Protein Chemical Function

氨基酸缩合

肽链延长 蛋白质

亚基形成

§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 proteinα-AA chain Peptide can carry onthe protein function

Classification 1According to α-AA chain -NH3

+, -COO-

AlkaliNeutral

Suppl.

Acid

Classification 2According 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 Special for Growing

Ideal Ratio: Lys: Met: Thr = 100: 60: 40 in Ration

Amino Acid Pattern ： Compared with different 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 Arg Asp

Asn Glu Gln

Gly Pro Ser Conditional EAA Cys TyrWhen 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 foodstuffsSuch 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 Corn Flour Soya Account

（ % ） 21 31 48 100

Lys/Met Lys Lys Met Lys Met

BV(%) 60 67 64 70

Kinds Flour Millet Soya Beef Account

（ % ） 39 13 22 26 100

BV(%) 67 57 64 69 89

Balanced Diet

Nitrogen Balance

Suppl.

§4Nitrogen Balance & Balanced Diet

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 Definition: N-intake is equal to N-ejection every day keeping weight for adults Index NB= N-intake - N-ejection (Urine + Feces + Skin)

1. Zero Nitrogen Balance ： N-intake = N-ejection2. Positive Nitrogen Balance ： N-intake > N-ejection3. 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 Digestibility1 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 Absorptivity :

Percentage of Nutrients in Gut Biological Value (BV)*

BV=Food N-(FN+UN)/ Food N-FN100% Net Protein Utilization (NPU)

NPU= Digestibility BV= UN-EnN/Food N100

Nutritional Evaluation for Foods2

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, SoybeanSuppl. Ratio in diet ： 40-50%Protein in Energy ： 15-20%

Malnutrition P17-18

Low-protein in blood (albumin 35-50g/L)

Dropsy

Marasmus

Examplesin 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

Question1 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 ？