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Carbohydrates > Carbohydrates FDSC251 > Flashcards

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
Q

Starch is made of two fractions that are:

A

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
Q

Where is starch found?

A

In most plants sources as hard, water-insoluble granules

25
Q

Gelatinization

A

Due to heating in the presence of moisture that breaks the H bonds

26
Q

How does the process of gelatinization start?

A

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
Q

What happens if we stir the solution of granules?

A

The granules will break up and disperse to from a colloidal solution

28
Q

Does amylose have a high solubility?

A

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
Q

How does amylopectin form a gel?

A

Because it is branched, it produces a net web in solution which creates a viscous solution.

30
Q

What happens when amylose and amylopectin are combined to form a gel?

A

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
Q

What is an undesirable aspect of starch behaviour?

A

Retrogradation. When gels become firmer because H bonds form between starch molecules. Gels become more opaque

32
Q

Sugars tend to retard gel formation and retrogradation. Why?

A

Because they compete for available water and interfere with starch-to-starch hydrogen bonding.

33
Q

What is the effect of surface-active agents on retrogradation and gelation?

A

It inhibits retrogradation and gelation by forming complexes with starch

34
Q

Effect of high pH on gel viscosity

A

Reduction

35
Q

Does ionic strength have an effect on starches?

A

No (for the most part) because most starches have no ionizable groups

36
Q

Pre-gelatinized starches

A

Heated below gelatinization temperatures which causes them to swell. They are them drum-dried. Disperssible in cold water

37
Q

Oxidized starches

A

Starch is now charged = more susceptible to variations in pH and ionic strength

37
Q

Acid-modified starches

A

Produced at lower temperatures in an acidic medium. They are then neutralized and dried. Used in candies

38
Q

Cross-linked starches

A

Cross-linked so that granules do not break down. Lower viscosity but more resistant.

39
Q

What are the modified starch?

A

Pre-gelatinized, acid-modified, cross-linked and derivatives

40
Q

Starch derivatives

A

Adding hydroxypropyl or orthophosphate groups

41
Q

What are the two types of starch conversions?

A

Dry pyroconversion to produce cold-water-soluble starches and acid hydrolysis to produce dextrines or as a first step in sugar production

42
Q

Pyroconversion produces

A

White dextrins
Yellow dextrins
British Gums

43
Q

Acid Hydrolysis

A

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
Q

How is reducing sugar content expressed?

A

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

45
Q

How can we obtain syrups that have high D.E?

A

Enzymatic conversion by enzymes that hydrolyze starch. Can reach D.E higher than 90

46
Q

What enzymes can carry enzymatic conversion?

A

alpha-amylase reduces molecular weight producing oligosaccharides
Beta-amylase produces maltose
Glucoamylase converts maltose to glucose
Pullulanase takes care of branch points

47
Q

What is D glucose transformed into?

A

D fructose using glucose isomerase

48
Q

Why is high-fructose syrup great?

A

It’s sweeter than glucose
It’s more soluble
It doesn’t cristallize

49
Q

What is added to cellulose to make it more soluble and able to contribute to viscosity?

A

A carboxymethyl group

50
Q

What is are pectin substances?

A

Polysaccharides associated with the middle lammella between plant cell walls. It’s a complex carb

51
Q

What is the basic unit of pectin substances?

A

Galacturonic acid

52
Q

What are the categories of pectin substances?

A

1- Pectic acids: no methyl groups
2- Pectinic acids: some methylation
3- Pectin: more than 50% of the carboxyl groups methylated

53
Q

What is particularly used in the rehydration of dry powders in instant products?

A

Guar gum

54
Q

What is used to produce smooth meltdown of ice cream and softer doughs?

A

Locus bean gum

55
Q

What is used as a flavor carrier/dispersant?

A

Gum Arabic

56
Q

What polysaccharides are extracted from seaweed?

A

Irish moss- carrageenan
Red algae- agar
Giant kelp- alginates

57
Q

What’s carrageenan unique ability?

A

It forms a very light gel with milk proteins used in insoluble chocolate solide

58
Q

Dextrans

A

Microbial gums. Polysaccharides that don’t form organized crystalline granules like starch

59
Q
A

Carbohydrates (2 decks)

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