Carbohydrates FDSC251 Flashcards
What group present on aldoses has strong reducing power?
Aldehyde
What can aldehydes do?
Reduce metal ions (converts aldehyde to a COOH)
Monosaccharides are also named
Reducing sugars
How to test for reducing sugars and what does it involve?
Fehling’s Test which involves the reduction of Cu(II) in the form of copper tartrate to Cu(i) oxide
Fehling’s agent only reacts with
Free aldehydes (only with the open-chain form)
When is the reducing power of a sugar lost?
When the OH at the anomeric carbon is bonded to another group because the ring can’t open.
Sucrose is a
Non reducing sugar
Dehydration
Water evaporates so dehydration and oxidative fission can take place which leads to the breakdown of the C chain into smaller units (flavor compounds)
How can water be eliminated?
1- Loss of water from two sugar molecules by reaction of their hydroxyl groups
2-Elimination of sugar within a sugar which forms highly unsaturated ring structures
What are the two categories of browning reaction?
Oxidative browning and non-oxidative browning
Oxidative browning
Not related to carbs
Browning of plant tissues by enzyme polyphenol oxidase
E.g. quinones
Caramelization
When concentrated sugar solution is heated
Non enzymatic/oxidative browning
Two types
Sugar sugar reactions (caramélisation)
Sugar amine reactions (Maillard)
Caramel flavours come from
Sucrose solution
Caramel colour comes from
Glucose syrup
What does Maillard reaction involve ?
Primary amines and proteins
What is Strecker Degradation? What does it involve?
Sub component of Maillard Reaction. Involves reaction of free aa with dicarbonyl intermediates produce by Maillard or caramelization
What is produced from Strecker Degradation?
CO2, ammonia, formaldehyde and pyrazines which are compounds that contribute to the characteristic of roasted foods
How are sugar alcohols produced?
By reducing the aldehyde group to a hydroxyl group by hydrogenation
Sweetening power is related to _______
Solubility
Sweetness __________ with increasing temperature
Decreases (due to changes in concentrations of alpha, beta and open chain forms)
Xylitol
Sweet sugar alcohol produced from xylan
Starch is made of D or L glucose
D-glucose
Starch is made of two fractions that are:
Amylose (linear polymer linked by alpha 1,4 glycosidic bond)
Amylopectin (branched polymer linked by alpha 1,4 glycosidic bonds and alpha 1,6 glycosidic bonds at its branch point)
Where is starch found?
In most plants sources as hard, water-insoluble granules
Gelatinization
Due to heating in the presence of moisture that breaks the H bonds
How does the process of gelatinization start?
Swelling of the granule due to absorption of water facilitated by heat. Increasing kinetic energy breaks H bonds and granule slowly hydrates as water molecules access the OH groups on the polymer.
What happens if we stir the solution of granules?
The granules will break up and disperse to from a colloidal solution
Does amylose have a high solubility?
No because it readily forms hydrogen bonds to neighbouring polymers to form large aggregates that precipitate out of solution. So on its own it is useless in food systems
How does amylopectin form a gel?
Because it is branched, it produces a net web in solution which creates a viscous solution.
What happens when amylose and amylopectin are combined to form a gel?
Amylose acts like a cross-linking agent, entrapping water which creates a three-dimensional gel. The gel forms when the kinetic energy of the system is reduced sufficiently to allow H bonds to reform.
What is an undesirable aspect of starch behaviour?
Retrogradation. When gels become firmer because H bonds form between starch molecules. Gels become more opaque
Sugars tend to retard gel formation and retrogradation. Why?
Because they compete for available water and interfere with starch-to-starch hydrogen bonding.
What is the effect of surface-active agents on retrogradation and gelation?
It inhibits retrogradation and gelation by forming complexes with starch
Effect of high pH on gel viscosity
Reduction
Does ionic strength have an effect on starches?
No (for the most part) because most starches have no ionizable groups
Pre-gelatinized starches
Heated below gelatinization temperatures which causes them to swell. They are them drum-dried. Disperssible in cold water
Oxidized starches
Starch is now charged = more susceptible to variations in pH and ionic strength
Acid-modified starches
Produced at lower temperatures in an acidic medium. They are then neutralized and dried. Used in candies
Cross-linked starches
Cross-linked so that granules do not break down. Lower viscosity but more resistant.
What are the modified starch?
Pre-gelatinized, acid-modified, cross-linked and derivatives
Starch derivatives
Adding hydroxypropyl or orthophosphate groups
What are the two types of starch conversions?
Dry pyroconversion to produce cold-water-soluble starches and acid hydrolysis to produce dextrines or as a first step in sugar production
Pyroconversion produces
White dextrins
Yellow dextrins
British Gums
Acid Hydrolysis
Old way to produce sugars and syrups
Starch is gelatinized in the presence of hydrochloric acid and pressurized steam. It’s also hydrolyzed by the acid
How is reducing sugar content expressed?
In terms of dextrose equivalents D.E= (Reducing Power/g of syrup)/(RP/g of dextrose)
If hydrolysis of starch is 100, them D.E = 100
How can we obtain syrups that have high D.E?
Enzymatic conversion by enzymes that hydrolyze starch. Can reach D.E higher than 90
What enzymes can carry enzymatic conversion?
alpha-amylase reduces molecular weight producing oligosaccharides
Beta-amylase produces maltose
Glucoamylase converts maltose to glucose
Pullulanase takes care of branch points
What is D glucose transformed into?
D fructose using glucose isomerase
Why is high-fructose syrup great?
It’s sweeter than glucose
It’s more soluble
It doesn’t cristallize
What is added to cellulose to make it more soluble and able to contribute to viscosity?
A carboxymethyl group
What is are pectin substances?
Polysaccharides associated with the middle lammella between plant cell walls. It’s a complex carb
What is the basic unit of pectin substances?
Galacturonic acid
What are the categories of pectin substances?
1- Pectic acids: no methyl groups
2- Pectinic acids: some methylation
3- Pectin: more than 50% of the carboxyl groups methylated
What is particularly used in the rehydration of dry powders in instant products?
Guar gum
What is used to produce smooth meltdown of ice cream and softer doughs?
Locus bean gum
What is used as a flavor carrier/dispersant?
Gum Arabic
What polysaccharides are extracted from seaweed?
Irish moss- carrageenan
Red algae- agar
Giant kelp- alginates
What’s carrageenan unique ability?
It forms a very light gel with milk proteins used in insoluble chocolate solide
Dextrans
Microbial gums. Polysaccharides that don’t form organized crystalline granules like starch
