Carbohydrates.2007

0026 63 chemical reactions chemical hydrolysis

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Unformatted text preview: e at alkaline conditions Starch and Sucrose Chemical reactions Chemical REDUCTION Reducing sugars Monosaccharides Non-reducing Monosaccharides Glucose Fructose All others Maltose Lactose None Sucrose Raffinose Stacchyose Di and oligosaccharides Di and oligosaccharides s Chemical reactions Chemical REDUCTION Hydrogenation to the double bond between the oxygen Hydrogenation and the carbon group of an aldose or ketose and oxidation H+ reduction What about fructose? Chemical reactions Chemical ENOLIZATION/ISOMERIZATION Aldose & ketose sugars are Aldose enolized in the presence of enolized alkali solutions solutions Thus glucose, mannose & Thus glucose mannose fructose can be in equilibrium fructose with each other through a 1,2with Endiol Therefore, you can get Therefore, isomerization (transfer of 1 sugar type to another type) of varying yield yield Can happen during storage and Can heating heating Glucose in dilute alkali after 21 days -66% Glucose -29% Fructose -1% Mannose Chemical reactions Chemical ENOLIZATION/ ISOMERIZATION Lactulose used in infant nutrition as a bifidus factor promotes friendly bacteria in breast milk Not hydrolyzed by digestion - strong laxative - prevents constipation Chemical reactions Chemical DEHYDRATION Favored at acid pH Occurs when you heat sugar solids or syrups with a Occurs dilute acid solution dilute Leads to dehydration of sugars with the b-elimination of Leads water water Leads to furan end products HEXOSE - 3 H O + HMF (Hydroxymethyl furfural) 2 Flowery odor, bitter/astringent flavor PENTOSE - 3 H2O + Furfural PENTOSE Chemical reactions Chemical DEHYDRATION REACTIONS -Detrimental to thermally processed fruit juices -Indicator of thermal abused products CHO HOH 2C O HCO H C OH D - Glucose H H C OH H C OH HO C H HOH 1,2-Endiol HCO CO HCH 3-D eoxy-Dgluco sulose HOH HOH CH O CH O HOH 2C O OH O Furfural 5-H ydroxyme thyl furfur al Chemical reactions Chemical H2 C OH CO HO C H D-Fructose DEHYDRATION REACTIONS Both contribute to flavor of baked bread H H2 C OH CO HOH HCH HO C H CH3 CO OC C OH HC CH2OH HO H3CO HO O CH2 HOH H3CO HOH O HO H3C HOH C OH OC C OH C OH 1-Deoxy-D-Erythro 2,3-hexodiulose HO O Isomaltol Maltol O Chemical reactions Chemical DEHYDRATION REACTIONS 1 CARMELIZATION Brown pigment & caramel aroma Formed by melting sugar or syrups in acid or alkaline catalysts Dehydration, degradation and polymerization 3 2 4 5 PIGMENT Chemical reactions Chemical MAILLARD BROWNING Browning in foods happen via: 1) Oxidative reactions 2) Non-oxidative reactions Oxidative reactions involve enzymes and oxygen Polyphenol oxidase browning in pears, apples, bananas, Polyphenol shrimp etc. (covered later) shrimp No carbohydrates directly involved Non-oxidative reactions are non-enzymatic browning Non-oxidative reactions reactions Maillard browning Chemical reactions Chemical MAILLARD BROWNING Not well defined and not all pathways known However, the following must be there for Maillard However, browning to occur: browning 1) 2) 3) A compound with an amino group (typically an amino acid or compound amino protein – most commonly lysine) protein A reducing sugar (most commonly glucose) reducing Water Can follow the reaction by observing color formation Can (420 or 490 nm in a spectrophotometer) or by following CO2 production CO Chemical reactions Chemical MAILLARD BROWNING General effects Flavor, color, odor Decline in protein quality Usually a decline in digestibility as well as lysine availability...
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This note was uploaded on 03/03/2011 for the course FOS 4311 taught by Professor Kristinsson during the Spring '08 term at University of Florida.

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