Midterms [Carbohydrates] Flashcards
Food Chemistry definition
- the study of the composition of food, the interaction between these components, and changes that occur during harvesting, transportation, handling, storage, and packaging until the food gets to the table of the consumers
Macronutrients
- Require in large amounts for the body
- Carbohydrates, lipids, water, proteins
Micronutrients
- Require in small amounts for the body
- Vitamins and minerals
How many kcal/g in
- Carbohydrates
- Protein
- Lipids
- Alcohol
- 4 kcal/g
- 4 kcal/g
- 9 kcal/g
- 7 kcal/g
Carbon - hydrates
- hydrates of carbon
- carbon to which water has been added
General formula for carbohydrates
Cx(H2O)Y
Carbohydrates definition
- compounds that have carbon, hydrogen, and oxygen with hydrogen and oxygen in the same ratio as found in water (2:1)
- polyhydroxy aldehyde (CHO) or polyhydroxy ketones
Alkanal
- third carbon position of the carbonyl group
Alkanone
- second/middle carbon position of the carbonyl group
Group of Carbohydrates
- Monosaccharides
- Oligosaccharides
- Polysaccharides
Monosaccharides
- one sugar unit
Oligosaccharides
- 1 < x < 10
- Disaccharide, trisaccharide
Polysaccharide
- > 10
Nomenclature for carbohydrates
- according to the functional group
- according to the number of carbon atoms
Aldose
- CHO
- sugar with aldehyde
Ketose
- CH2OH
- sugar with ketones
Three carbon atom sugar
- triose
Four carbon atom sugar
- tetrose
Five carbon atom sugar
- pentose
Six carbon atom sugar
- hexose
Sucrose
- contains glucose and fructose
- table sugar
Maltose
- contains two molecules of glucose
- malt sugar
Lactose
- milk sugar
- one molecule of glucose and galactose
Monosaccharide (in-depth)
- simple sugars
- smallest units that make up any carbohydrate
- glucose, galactose
Sugar can be drawn into two forms
- Fischer projection
- Haworth projection
Fishcer projection
- line form
- Left = top
- Right = bottom
Haworth projection
- ring form
Furan
- Five membered ring cyclic
Pyran
- six membered ring cyclic
Configuration of sugar
- determined on the Fischer projection
- determined by the position of the carbonyl group
Penultimate
- carbon before the last (C5)
D-sugar
- hydroxy group (OH) is in the 5th on the right (Fischer projection)
L-sugar
- hydroxy group (OH) is in the 5th on the left (Fischer projection)
Conformation of sugar
- found at C1
Alpha (conformation)
- OH at the botton (at C1)
Beta (conformation)
- OH at the top (at C1)
Epimers
- sugar differ in one carbon atom
- Cx epimers (x = which carbon they differed)
Galactose epimer
C4 epimer of glucose
Mannose
- C2 epimer of glucose
Disaccharide
- sugars that contain 2 sugar units
Alpha 1-4 glycosidic bond
- bonds two glucose molecules
- C1 and C4 joins up
Condensation in disaccharide
- linking monosaccharides by removing water
Hydrolysis at disaccharide
- add water to split the disaccharide
Lactose
- milk sugar
- galactose and glucose
Sucrose
- glucose and fructose
- linked with alpha-1-glucose and beta-2-fructose bond
Fructose
- fruit sugar
- 5 membered ring
Isomers
- same chemical formula but different structure
Optical activity
- whether it can rotate plane polarized light
- have chiral center
Chiral center
- has four different atoms attached to it
Vant hoffs rule
- Number of chiral centers can estimate the number of possible isomers that such compound can have
- Isomers = 2n, n = chiral center
Disaccharide examples
- Maltose
- Lactose
- Sucrose
Oligosaccharides
- typically less than 10 monsaccharides linked together
- 2 < x < 10
Maltotriose
- maltose and glucose
- linked by alpha 1-4 glycosidic bond
Polysaccharide
- more than 10 monosaccharide combined
- more than 10 bonds
- glycans
Homopolysaccharides
- contains a single type of monosaccharide
- Storage form of monosaccharides
- Ex. only contains glucose
Heteropolysaccharides
- contains 2 or more different types of monosaccharide
- branched or unbranched
- Ex. contains fructose and glucose
Starch
- storage form of monosaccharides in plants
- main carbohydrate in human diet
- found in bread, cereal, and rice
- homopolysaccharide
Functions of carbohydrates
- Provides energy through oxidation
- Storage in the form of glycogen
- Supply carbons for synthesis of reactions
- Form part of the structural framework of DNA and RNA
- Structural components of cell membranes when linked to lipids
- Cell to cell and cell to molecule recoginition processes when linked to proteins
Solubility of sugars
- sugars are soluble
- highly branched polysaccharides like starches are not soluble
Viscosity and surface activity of sugar
- polysaccharides are viscous
- it thickens up when added water
Crystallinity of sugar
- have a wide range of crystallinity
- sucrose is readily crystallized
Hygroscopicity of sugar
- can absorb water easily even after drying
Stability of sugar
- fairly stable molecules
- reducing sugars are sensitive to oxidation
Optical properties of sugar
- absorb light in the UV and spectral regions
Hydrolysis of sugar
- sugars can be hydrolyzed
Oxidation/reduction of sugar
- highly oxidized; resistant to oxidation
Uronic acid
- COOH is at C6
Onic acid
- COOH at C1
Aric acid
- oxidation of both C1 and C6
Functional groups
- in addition to aldehydes and ketones, have primary and secondary hydroxy groups
Chelation and complexation
- display affinity towards various classes of iron ions
Reactions that can take place during processing
- Hydrolysis
- Enolization
- Dehydration
- Caramelization
Enolization
- changing from a keto- to an -enol form
- at higher temperatures, acyclic sugars undergo enolization
Dehydration
- in an acidic environment (pH < 3) enolization is followed by dehydration
- formation of unwanted 2-furaldehydes
Caramelization
- degradation reaction can also occur during melting of dry sugars and during heating of syrups above 100C
Caramelisation occurs during food processing
- heated strongly
- jams and certain fruit juices
- wine preparation
- traditional sucrose syrups
Caramelization involves 4 stages
- Enolisation
- Dehydration
- Fragmentation
- Polymerisation
Functional properties of sugar in foods
- can act as sweeteners
- can contribute to the viscosity
- food preservative (at high concentration)
Pectin
- located in the middle of lamella
- useful for fruit preserves
- gellling agents
Process of pectin
- As fruit ripen, hydrolysis of the glycosidic bonds by polygalacturonases and hydrolysis of their methoxyl groups by pectin methyl esterases leads to conversion of protopectin to pectinic acids (which are more soluble)
Formation of pectinic acids =
- softening and improvement in sensory quality
If continued, polygalacturonic acids forms, then turned to monomeric galacturonic acid
- fruit is too soft and susceptible to microbial spoilage
Starch
- present in cereals, root parts, tuberous plants, and legumes
- made up of amylose (linear) and amylopectin (branched)
Waxy starch
- contains little or no amylose
- waxy maize
Starch granule properties
- occurs in different sizes and shapes
- extract starch from different plants
Functions of starch
- Adhesion
- Binding
- Clouding
Gelatinization and pasting
- used to describe changes starch undergoes heating
- Powder + water = pasting
- Cools down = gelatinization
In the native form of starch
- not stable
- less application in the food industry
- must be modified to enhance their use
Cross-linking
- forms bond between the cross-linking agent and hydroxy group
- to strengthening the starch and make it more stable
Substitution
- substitute some functional groups to a new chemical agent
Acid hydrolysis and dextrinization
- acidification of starches under stringent control
- makes it dispersible without thickening
Dextrins formation
- starch are heated dry under agitation
- used in the coating of foods
Maltodextrin
- controlled enzymatic hydrolysis with amylase
Pregelatinization
- starches are gelatinized and then dehydrated to dry powder form
