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Browning Reactions FDSC400 Important Types of Browning • Enzymatic (polyphenoloxidase). Fresh cut vegetables, non-toxic, no flavor • Caramelization. Sugars at very high temperatures. • Lipid Browning. Polymerization of frying oils • Vitamin C Browning. Similar to Maillard • THE MAILLARD REACTION Maillard Browning • “the sequence of events that begins with reaction of the amino group of amino acids with a glycosidic hydroxyl group of sugars; the sequence terminates with the formation of brown nitrogenous polymers or melanoidins” – John deMan The Maillard Reaction • Occurs between reducing sugars and amines at high temperatures – Produces flavor – Produces color – Produces antioxidant products – Produces toxic products – Destroys nutrients (lysine) Addition of an amine to an aldose The Amadori Rearrangement DH – A Crucial Intermediate Amines Strecker aldehydes Polymerize Pyrolytic products Sugar Pyrolytic Products O OH OH O O O maltol CH3 CH3 isomaltol Strecker Degradation O O -H2O R O H2N -H2O COOH H N H amine dicarbonyl O -H2O ine N H H OH R COOH NH3 CO2 Stecker O R -H2O R COOH O R -H2O O -H2O COOH O OH NH3 CO2 H Stecker aldehyde Rich nutty, meaty flavors Mutagens from the Maillard Reaction Asparagine O H2N Strecker aldehyde CH2 O C H O H2N CH C H2 Acrylamide Control Steps • Rapidly accelerated by temperature • Significant acceleration at intermediate water activities • Sugar type – Pentose>hexose>disaccharide>>polysaccharide • protein concentration (free amines) • Inhibited by acid – amines are protonated – and used up, pH drops • Sulfur dioxide Inhibition by Sulfite SO3- DH DSH