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Carbohydrates FDSC251 Flashcards

1
Q

What group present on aldoses has strong reducing power?

A

Aldehyde

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2
Q

What can aldehydes do?

A

Reduce metal ions (converts aldehyde to a COOH)

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3
Q

Monosaccharides are also named

A

Reducing sugars

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4
Q

How to test for reducing sugars and what does it involve?

A

Fehling’s Test which involves the reduction of Cu(II) in the form of copper tartrate to Cu(i) oxide

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5
Q

Fehling’s agent only reacts with

A

Free aldehydes (only with the open-chain form)

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6
Q

When is the reducing power of a sugar lost?

A

When the OH at the anomeric carbon is bonded to another group because the ring can’t open.

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7
Q

Sucrose is a

A

Non reducing sugar

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8
Q

Dehydration

A

Water evaporates so dehydration and oxidative fission can take place which leads to the breakdown of the C chain into smaller units (flavor compounds)

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9
Q
A
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9
Q

How can water be eliminated?

A

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

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10
Q

What are the two categories of browning reaction?

A

Oxidative browning and non-oxidative browning

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11
Q

Oxidative browning

A

Not related to carbs
Browning of plant tissues by enzyme polyphenol oxidase
E.g. quinones

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12
Q

Caramelization

A

When concentrated sugar solution is heated

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13
Q

Non enzymatic/oxidative browning

A

Two types
Sugar sugar reactions (caramélisation)
Sugar amine reactions (Maillard)

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14
Q

Caramel flavours come from

A

Sucrose solution

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15
Q

Caramel colour comes from

A

Glucose syrup

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16
Q

What does Maillard reaction involve ?

A

Primary amines and proteins

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17
Q

What is Strecker Degradation? What does it involve?

A

Sub component of Maillard Reaction. Involves reaction of free aa with dicarbonyl intermediates produce by Maillard or caramelization

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18
Q

What is produced from Strecker Degradation?

A

CO2, ammonia, formaldehyde and pyrazines which are compounds that contribute to the characteristic of roasted foods

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19
Q

How are sugar alcohols produced?

A

By reducing the aldehyde group to a hydroxyl group by hydrogenation

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19
Q

Sweetening power is related to _______

A

Solubility

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20
Q

Sweetness __________ with increasing temperature

A

Decreases (due to changes in concentrations of alpha, beta and open chain forms)

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21
Q

Xylitol

A

Sweet sugar alcohol produced from xylan

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22
Q

Starch is made of D or L glucose

A

D-glucose

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23
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)
24
Where is starch found?
In most plants sources as hard, water-insoluble granules
25
Gelatinization
Due to heating in the presence of moisture that breaks the H bonds
26
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.
27
What happens if we stir the solution of granules?
The granules will break up and disperse to from a colloidal solution
28
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
29
How does amylopectin form a gel?
Because it is branched, it produces a net web in solution which creates a viscous solution.
30
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.
31
What is an undesirable aspect of starch behaviour?
Retrogradation. When gels become firmer because H bonds form between starch molecules. Gels become more opaque
32
Sugars tend to retard gel formation and retrogradation. Why?
Because they compete for available water and interfere with starch-to-starch hydrogen bonding.
33
What is the effect of surface-active agents on retrogradation and gelation?
It inhibits retrogradation and gelation by forming complexes with starch
34
Effect of high pH on gel viscosity
Reduction
35
Does ionic strength have an effect on starches?
No (for the most part) because most starches have no ionizable groups
36
Pre-gelatinized starches
Heated below gelatinization temperatures which causes them to swell. They are them drum-dried. Disperssible in cold water
37
Oxidized starches
Starch is now charged = more susceptible to variations in pH and ionic strength
37
Acid-modified starches
Produced at lower temperatures in an acidic medium. They are then neutralized and dried. Used in candies
38
Cross-linked starches
Cross-linked so that granules do not break down. Lower viscosity but more resistant.
39
What are the modified starch?
Pre-gelatinized, acid-modified, cross-linked and derivatives
40
Starch derivatives
Adding hydroxypropyl or orthophosphate groups
41
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
42
Pyroconversion produces
White dextrins Yellow dextrins British Gums
43
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
44
How is reducing sugar content expressed?
In terms of dextrose equivalents D.E= [(Reducing Power/g of syrup)/(RP/g of dextrose)](100) If hydrolysis of starch is 100, them D.E = 100
45
How can we obtain syrups that have high D.E?
Enzymatic conversion by enzymes that hydrolyze starch. Can reach D.E higher than 90
46
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
47
What is D glucose transformed into?
D fructose using glucose isomerase
48
Why is high-fructose syrup great?
It’s sweeter than glucose It’s more soluble It doesn’t cristallize
49
What is added to cellulose to make it more soluble and able to contribute to viscosity?
A carboxymethyl group
50
What is are pectin substances?
Polysaccharides associated with the middle lammella between plant cell walls. It’s a complex carb
51
What is the basic unit of pectin substances?
Galacturonic acid
52
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
53
What is particularly used in the rehydration of dry powders in instant products?
Guar gum
54
What is used to produce smooth meltdown of ice cream and softer doughs?
Locus bean gum
55
What is used as a flavor carrier/dispersant?
Gum Arabic
56
What polysaccharides are extracted from seaweed?
Irish moss- carrageenan Red algae- agar Giant kelp- alginates
57
What’s carrageenan unique ability?
It forms a very light gel with milk proteins used in insoluble chocolate solide
58
Dextrans
Microbial gums. Polysaccharides that don’t form organized crystalline granules like starch
59

Carbohydrates (2 decks)

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