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Unformatted text preview: e at alkaline conditions Starch and Sucrose Chemical reactions Chemical
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
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
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
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.
- Spring '08