Carbohydrates.2007

Following co2 production co chemical reactions

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Unformatted text preview: Temperature and aw (0.6 to 0.7) favor the reaction Desirable Attributes Color & flavor of baked, roasted and dried foods Undesirable Attributes Off-flavor Texture - unintentional in products such as dried milk Texture and mashed potatoes and Chemical reactions Chemical MAILLARD BROWNING General stages First reaction Carbonyl carbon of the reducing sugar is reacted to the nitrogen Carbonyl of an amino acid (nucleophilic attack – electron of the N attack C) of A glycosamine (a.k.a. glycosylamine) is formed Reversible reaction Not favorable at low pH Chemical reactions Chemical MAILLARD BROWNING The glycosamine undergoes Amadori rearrangement to The produce a 1-amino-2-keto sugar (1-amino-2-ketose) produce Amadori compound MAILLARD BROWNING Degradation of Amadori compound 2 pathways Melanoidin pigments Brown N-polymers Flavor and color of cola, bread, etc. HMF Astringent bitter flavor Unacceptable Good odor Can form melanoidins Can also form via dehydration Reductones Strong odor/flavor Can also form melanoidins - Favored by less acid pH (>5) Favored by low pH (<5) Chemical reactions Chemical MAILLARD BROWNING Strecker degradation Reaction of an amino acid with dicarbonyl compounds formed in the Reaction Maillard reaction sequence Maillard The amino acid is converted to an aldehyde Aldehydes formed that contribute to the aroma of bread, peanuts, Aldehydes cocoa, maple syrup, chocolate… cocoa, CO2 produced Produces pyrazines Very powerful aroma compounds Corny, nutty, bready, crackery aromas Also produces pyrroles Strong aroma and flavor compounds Favored at high temperature and pressure Chemical reactions Chemical MAILLARD BROWNING Examples of volatiles that form via Maillard browning 50:50 amino acid + D-glucose Glycine caramel aroma Glycine Valine rye bread aroma Valine Glutamine chocolate Glutamine Sulfur containing a.a. produce different aromas than other a.a. Methionine + glucose potato aroma Methionine Cysteine + glucose meaty aroma Cysteine Cystine + glucose “burnt turkey skin”! Cystine Amino acid type matters Chemical reactions Chemical MAILLARD BROWNING Examples of volatiles that form via Maillard browning (cont.) Aroma compounds can vary with temperature Valine at 100°C rye bread aroma Valine at 180°C chocolate aroma Proline at 100°C burnt protein Proline at 180°C pleasant bakery aroma Histidine at 100°C no aroma Histidine at 180°C cornbread, buttery, burnt sugar aroma Chemical reactions Chemical MAILLARD BROWNING Factors which affect browning Water activity Max at aw 0.6-0.7 Neutral and alkaline pH is favored Acid pH slows down or inhibits browning Acid pH Amino group on amino acid is protonated and glucosamine production Amino prevented prevented Metals Copper and iron catalyze browning Catalyze oxidation/reduction type reactions Chemical reactions Chemical MAILLARD BROWNING Factors which affect browning (cont.) Temperature Higher temperatures catalyzes Linear up to 90°C then more rapid increase Carbohydrate structure Pentoses (most reactive) > Hexoses > Disaccharides > Pentoses Oligosaccharides > Sucrose (least reactive) Oligosaccharides Fructose (ketose) is far less reactive than glucose (aldose) Concentration of open form Pigment formation is directly proportional to the amount of open chain Pigment form form Chemical reactions Chemical MAILLARD BROWNING Inhibition/control of browning Lower pH and T Control a w Use non-reducing sugar Remove substrate E.g. drying of egg whites Use sulfiting agents (most common chemicals used) Add enzyme (D-glucose oxidase) prior to drying to oxidize glucose to Add glucono-δ -lactone glucono- React with carbonyls to prevent polymerization and thus pigment React formation formation Problems Degrade thiamine, riboflavin and oxidize methionine Can cause severe allergies Chemical reactions Chemical MAILLARD BROWNING Undesirable consequences of browning 1) Aesthetically and sensorially undesirable Dark colors, strong odors and flavors 2) Formation of mutagenic compounds Data shows that some products from the reaction of D-glucose or Dfructose with L-lysine or L-glutamic acid may demonstrate fructose mutagenicity mutagenicity 3) Leads to anti-nutritional effects Loss of essential amino acids Primarily lysine; may be critical in lysine limited foods (cereals, grain Primarily products) products) Chemical reactions Chemical MAILLARD BROWNING Undesirable consequences of browning (cont.) Due to its highly reactive and basic amino group lysine is most Due susceptible to Maillard browning reactions susceptible Extent of lysine degradation in milk products Milk Fresh Condensed Non-fat dry Non-fat dry ºC 100 --150 150 Time Few minutes --Few minutes 3 hours Degradation (%) 5 20 40 80...
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