《食品化学与分析 Food Chemistry and Analysis》课程PPT教学课件（英文版）Protein

PROTEINS Polymer of amino acids linked by amide linkage. Functions: 1. Nutritional: growth, digestion, metabolism (enzymes). 2. Physical structure: cheese, bread, foaming agent, gel￾forming

PROTEINS Polymer of amino acids linked by amide linkage. Functions: 1. Nutritional: growth, digestion, metabolism (enzymes). 2. Physical structure: cheese, bread, foaming agent, gel￾forming

Amino Acids C H HO C H CH 2OH O O C OH NH2 C H CH 3 L -Glyceraldehyde L - Alanine Zwitterion O C OH NH 2 C H CH 3 O C O - NH 3 + C H CH 3

Amino Acids C H HO C H CH 2OH O O C OH NH2 C H CH 3 L -Glyceraldehyde L - Alanine Zwitterion O C OH NH 2 C H CH 3 O C O - NH 3 + C H CH 3

Evidence of Zwitterion in Amino Acids at Neutral pH N H3 + CH2 C O￾O CH3COOH CH3CH2N H2 CH3 C O￾CH3 CH2 NH3 + O 1. At Neutral pH CH3CH2COOH CH3 CH CH3 NH2 CH3 CH C O - NH3 + O Melting Point -101 C 295 C 22 C 2

Evidence of Zwitterion in Amino Acids at Neutral pH N H3 + CH2 C O￾O CH3COOH CH3CH2N H2 CH3 C O￾CH3 CH2 NH3 + O 1. At Neutral pH CH3CH2COOH CH3 CH CH3 NH2 CH3 CH C O - NH3 + O Melting Point -101 C 295 C 22 C 2

L is naturally-occurring form for amino acids. Ionizable groups Zwitterion pKa for pKb for What form do we get at pH = 1? pH = 3.5? pH = 7.5? pH =9.5? and pH = 11.5? C OH O NH2 C OH O = 2.2 NH 2 = 9.5

L is naturally-occurring form for amino acids. Ionizable groups Zwitterion pKa for pKb for What form do we get at pH = 1? pH = 3.5? pH = 7.5? pH =9.5? and pH = 11.5? C OH O NH2 C OH O = 2.2 NH 2 = 9.5

DISSOCIATION OF THE CARBOXYL GROUP (pKa) R C COO￾NH3 + H H NH3 + R C COOH + H+ H + K1 = H NH3 + R C COO￾R C COOH NH3 + H H + = K1 H NH3 + R C COOH R C COO￾NH3 + H pH = pK1 Log H NH3 + R C COO￾R C COOH NH3 + H [ ] +

DISSOCIATION OF THE CARBOXYL GROUP (pKa) R C COO￾NH3 + H H NH3 + R C COOH + H+ H + K1 = H NH3 + R C COO￾R C COOH NH3 + H H + = K1 H NH3 + R C COOH R C COO￾NH3 + H pH = pK1 Log H NH3 + R C COO￾R C COOH NH3 + H [ ] +

DISSOCIATION OF THE AMINO GROUP (pKb) R C COO￾NH2 H H + H NH3 + R C COO- + H + K2 = H NH2 R C COO￾R C COO￾NH3 + H H + = K2 H NH2 R C COO￾R C COO￾NH3 + H pH = pK2 Log H NH2 R C COO￾R C COO￾NH3 + H [ ] [ ] +

DISSOCIATION OF THE AMINO GROUP (pKb) R C COO￾NH2 H H + H NH3 + R C COO- + H + K2 = H NH2 R C COO￾R C COO￾NH3 + H H + = K2 H NH2 R C COO￾R C COO￾NH3 + H pH = pK2 Log H NH2 R C COO￾R C COO￾NH3 + H [ ] [ ] +

[A-] pH = pK + Log [AH] [COO-] [NH2] pH - pK = Log or Log [COOH] [NH3+] RELATIONSHPI BETWEEN DISSOCIATION OF THE AMINO GROUP (pKb) AND pH

[A-] pH = pK + Log [AH] [COO-] [NH2] pH - pK = Log or Log [COOH] [NH3+] RELATIONSHPI BETWEEN DISSOCIATION OF THE AMINO GROUP (pKb) AND pH

pH 1 -1.2 -8.5 pH 2.2 0 -7.3 pH 3.5 1.3 -6 pH 5.5 3.3 -3.3 pH 7.5 5.3 -3 pH 9.5 7.3 0 pKa = 2.2 Log pKb = 9.5 Log pH 11.5 9.3 2 [COOH] [COO-] [NH3+] [NH2] Effects of pH on the Concentration of Different Groups

pH 1 -1.2 -8.5 pH 2.2 0 -7.3 pH 3.5 1.3 -6 pH 5.5 3.3 -3.3 pH 7.5 5.3 -3 pH 9.5 7.3 0 pKa = 2.2 Log pKb = 9.5 Log pH 11.5 9.3 2 [COOH] [COO-] [NH3+] [NH2] Effects of pH on the Concentration of Different Groups

pK' AND pI VALUES OF CERTAIN AMINO ACIDS pK'1 a - COO￾pK'2 a - NH3+ pK'R R Group pI Glycine 2.34 9.78 6.06 Alanine 2.35 9.69 6.02 Isoleucine 2.36 9.69 6.02 Serine 2.21 9.15 5.68 Aspartic Acid 2.09 9.82 3.86 2.97 Asparagine 2.02 8.80 5.41 Glutamic Acid 2.19 9.67 4.25 3.22 Glutamine 2.17 9.13 5.65 Histidine 1.82 9.17 6.00 7.58 Cysteine 1.71 10.78 8.33 5.02 Tyrosine 2.20 9.11 10.07 5.65 Arginine 2.17 9.04 12.48 10.76 Lysine 2.18 8.95 10.53 9.74

pK' AND pI VALUES OF CERTAIN AMINO ACIDS pK'1 a - COO￾pK'2 a - NH3+ pK'R R Group pI Glycine 2.34 9.78 6.06 Alanine 2.35 9.69 6.02 Isoleucine 2.36 9.69 6.02 Serine 2.21 9.15 5.68 Aspartic Acid 2.09 9.82 3.86 2.97 Asparagine 2.02 8.80 5.41 Glutamic Acid 2.19 9.67 4.25 3.22 Glutamine 2.17 9.13 5.65 Histidine 1.82 9.17 6.00 7.58 Cysteine 1.71 10.78 8.33 5.02 Tyrosine 2.20 9.11 10.07 5.65 Arginine 2.17 9.04 12.48 10.76 Lysine 2.18 8.95 10.53 9.74

GROUPS OF AMINO ACIDS 1. Aliphatic amino acids 2. Hydroxy amino acids 3. Acidic amino acids 4. Amide amino acids 5. Basic amino acids 6. Sulfur-containing amino acids 7. Aromatic amino acids 8. Secondary amino acids

GROUPS OF AMINO ACIDS 1. Aliphatic amino acids 2. Hydroxy amino acids 3. Acidic amino acids 4. Amide amino acids 5. Basic amino acids 6. Sulfur-containing amino acids 7. Aromatic amino acids 8. Secondary amino acids