《食品化学 Food Chemistry》课程教学课件（讲稿，英文版）Browning Reactions

Browning Reactions 9Maillard browning reducing sugar + amine brown pigments + flavors 9Caramelization sugar brown pigments + flavors high temps 9Enzymatic browning phenolics brown pigments + flavors polyphenoloxidase

Browning Reactions 9Maillard browning reducing sugar + amine brown pigments + flavors 9Caramelization sugar brown pigments + flavors high temps 9Enzymatic browning phenolics brown pigments + flavors polyphenoloxidase

Caramelization 9 At high temperatures, sugar reactions are accelerated – Isomerization – Water elimination – Oxidation no amines 9 Caramelization occurs at – High temperatures (~150˚C) – Low water content/high sugar Caramel flavors and pigments 9 Formation of – Enediols – Dicarbonyls

Caramelization 9 At high temperatures, sugar reactions are accelerated – Isomerization – Water elimination – Oxidation no amines 9 Caramelization occurs at – High temperatures (~150˚C) – Low water content/high sugar Caramel flavors and pigments 9 Formation of – Enediols – Dicarbonyls

Dehydration mechanism C C C C C C HO OH H 2OH OH OH H H H H - OH C C C C C C H 2O - OH H 2OH OH OH H H H H - O H H + + C C C C C C OH H 2OH - OH OH H H H H = O H 2O, H + 1. dehydration (elimination) 2. isomerization enediol C C C C C C - OH H 2OH H - H - - H H = O = O H - - OH dicarbonyl H new resonance, isomeriza￾tion

Dehydration mechanism C C C C C C HO OH H 2OH OH OH H H H H - OH C C C C C C H 2O - OH H 2OH OH OH H H H H - O H H + + C C C C C C OH H 2OH - OH OH H H H H = O H 2O, H + 1. dehydration (elimination) 2. isomerization enediol C C C C C C - OH H 2OH H - H - - H H = O = O H - - OH dicarbonyl H new resonance, isomeriza￾tion

Caramelization: Consequences 9 Leads to nice flavors and colors in many foods – Caramel aroma, coffee – Beverage colors, beer – Maltol one important flavor (produced by Maillard rxns also) 9 Can also lead to undesirable flavors and colors – “burnt-sugar” smell O OH CH 3 O

Caramelization: Consequences 9 Leads to nice flavors and colors in many foods – Caramel aroma, coffee – Beverage colors, beer – Maltol one important flavor (produced by Maillard rxns also) 9 Can also lead to undesirable flavors and colors – “burnt-sugar” smell O OH CH 3 O

Maillard Reaction

Maillard Reaction

Maillard Reaction 9Non-enzymatic browning 9Complex set of reactions between amines, usually from proteins, and carbonyl compounds, generally sugars. 9The consequences: – formation of many products, most of which have some impact on the flavor and appearance of the cooked food

Maillard Reaction 9Non-enzymatic browning 9Complex set of reactions between amines, usually from proteins, and carbonyl compounds, generally sugars. 9The consequences: – formation of many products, most of which have some impact on the flavor and appearance of the cooked food

Effects of Maillard Reaction 9 Desirable: – Color - bread crust, syrup, meat Flavor - coffee, cocoa, meats Antioxidants 9 Undesirable – Color - changes in color during storage Flavor - changes during processing and storage Nutritional loss - essential amino acids, Vitamins (vit c), palatability and digestibility Toxicity/mutagenicity

Effects of Maillard Reaction 9 Desirable: – Color - bread crust, syrup, meat Flavor - coffee, cocoa, meats Antioxidants 9 Undesirable – Color - changes in color during storage Flavor - changes during processing and storage Nutritional loss - essential amino acids, Vitamins (vit c), palatability and digestibility Toxicity/mutagenicity

Steps 9Condensation - amine/carbonyl 9Rearrangement - enolization 9Fragmentation 9Strecker degradation 9Polymerization - brown color

Steps 9Condensation - amine/carbonyl 9Rearrangement - enolization 9Fragmentation 9Strecker degradation 9Polymerization - brown color

Initial Step 9 Reaction between a reducing sugar and a primary amino acid. 9 Loss of water from this molecule produces an imine that is able to cyclise, resulting in the formation of an N glycoside (a sugar attached to an NR2 group)

Initial Step 9 Reaction between a reducing sugar and a primary amino acid. 9 Loss of water from this molecule produces an imine that is able to cyclise, resulting in the formation of an N glycoside (a sugar attached to an NR2 group)

N-Glycosylation

N-Glycosylation