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Oligosaccharides

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Oligosaccharide-Introduction

Oligo--Greek, few Definition: 2-20 monosaccharide units More than 20 monosaccharide units is a

polysaccharide Poly--Greek, many

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Oligosaccharides

In the disaccharides, the aglycon is a monosaccharide unit

Higher order oligosaccharides are named tri-, tetra-, penta-, etc.

Structures may be predominately linearor branched

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Overall structures

Linear

Branched

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Structural features

Linear– Features a head-to-tail linkage– 1 reducing end– 1 non-reducing end

Branched– 1 reducing end– Several to many non-reducing ends

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Acid catalyzed reversionMaltose

2 Glucose

-1,4-linkage

-1,4-linkage

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Reversion

If this reaction continues, the oligomers produced will tend to be highly branched and contain a variety of anomers and linkages

Readily occurs under water-limiting conditions (nearly dry)

A good commercial example of this is the bulking agent Polydextrose

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Polydextrose

Polydextrose is produced by the reversion reaction between D-glucose, sorbitol, and citric acid

This mixture is heated to produce the oligomer Polydextrose

The degree of polymerization (DP) is fairly low

Sold commercially as Litesse (and under other names as well)

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Polydextrose

O

OOH

OHHO

CH2ORO

OH

OHHO

CH2OR

O O

O

O

O

OO

O

OCH2

OHHO

O

OH

HOCH

CH2OH

HO

OCH2

HOOH

OH

O

OH

OH

CH2

O

CH2

OHHO

OHOCH2

HOOH

O

O

OH

OH

HOCH2

OH

OHHO

HOCH2

OH

OHHO

O

CH2

O

OR

R = H, D-glucose, sorbitol, citric acid, or polydextrose moieties

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Maltose

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Maltose

Obtained from starch by the action of -amylase (from Bacillus bacteria)

Yield = 80%

-amylaseNon-reducingend

Maltose Maltose Maltose

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Maltose

Maltose may also be prepared by the action of debranching enzyme and then -amylase on amylopectin

Maltose crystallizes from aqueous solution as -maltose.H2O

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Maltose uses

A mild sweetener in foods and pharmaceuticals

A parenteral injectable for slow release of D-glucose

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Maltose

Proper name: 4-O-(-D-glucopyranosyl)-D-glucopyranose

Exists as and -anomers Reducing sugar It’s glycosidic linkage is acid labile

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Acid hydrolysis of glycosides

Acid Hydrolysis of a Glucoside

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Lactose

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Lactose

Milk sugar– [lactose] in nature: 2.0-8.5%– Cow/goat: 4.5-4.8%– Human: 7.0%

Provides 40% of the energy obtained during nursing

To utilize, lactose must be broken down to D-glucose and D-galactose

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Lactose production

Cow’s milk

Coagulated casein

Curd

Whey

Crystalline lactose

Adjust to IEP;heat or rennin ultrafiltration

Ion exchange

Concentration

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Lactose production

Crystallizes as -lactose monohydrate Potential lactose from whey is 23 billion

pounds per year So far its potential production has far

outstripped its commercial use

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Lactose characteristics

Name: 4-O-(-D-galactopyranosyl)-D-glucopyranose

Reducing sugar Hydrolyzable Multiple anomeric forms

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Lactose uses

Food– Toppings– Icings– Pie fillings– Confections– Ice creams

In food, lactose contributes body but little (20% of sucrose) sweetness

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Pharmaceutical uses

Provides bulk and rapid dissolution– Present in 20% of prescription drugs– Present in 6% of over the counter (OTC)

drugs

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Natural occurrence

Lactose is relatively high in milk and milk products but lower in fermented dairy products such as yogurt and some cheeses

During fermentation some lactose is converted to L-lactate

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Lactate production in food

Lactose D-Glucose + D-Galactose

-galactosidaseof bacteria

Fermentation bybacteria

CH3

OH H

O O-

L-lactate

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Lactose digestion

Digestion in gut mediated by lactase, a -galactosidase that occurs in brush border epithelial cells

The monosaccharides so produced are rapidly absorbed and enter the blood stream

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Lactose intolerance

If lactose is not completely hydrolyzed and absorbed in the small intestine, it will proceed into the large intestine

Here anerobic bacteria ferment the lactose to lactic acid and other short chain acids, in addition to CO2, H2, and methane

This causes the symptoms of lactose intolerance

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Lactose intolerance

Abdominal distention Flatulence Cramping Diarrhea

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Lactose intolerance

Usually not seen in children until 6 years of age

After 6 years of age, the percent of lactose intolerant people increases with increasing age, with the greatest incidence among the elderly

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Genetic control

Lactose intolerance tends to be high among African Americans, Native Americans, Asian Americans, and Mexican Americans

Relatively lower in Western European Americans

Suggests that production of lactase is under genetic control

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Dealing with lactose intolerance

Reduce/remove lactose by fermentation– Yogurt, buttermilk

Add lactase to food (or consume lactase) just before consuming lactose containing food– This may increase the sweetness of the food

slightly when the extent of hydrolysis reaches 80%

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Other incompletely digested oligosaccharides Mostly from legumes, especially beans

– Raffinose, a trisaccharide– Stachyose, tetrasaccharide

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Lactose chemistry

Lactose can be reduced to lactitol with hydrogen gas and Raney nickel

Lactitol is not absorbed from the small intestine

It is fermented in the large intestine to lactic and acetic acid

Due to the water attracting properties of these acids, they soften stools and facilitate bowel function

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Lactose chemistry

Lactose can be isomerized in alkali to the keto sugar lactulose

Lactulose is similar in its physiological effect to lactitol, that is it facilitates bowel function

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Sucrose

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Sucrose

One of the principal sugars in fruits and honey

Isolated from sugar cane Produced in China during the 1st century

B.C. In ancient days it was very expensive

and, thus, reserved for the nobility

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Sucrose utilization

Per person per day disappearance data: 160 grams

Per person per day consumption data: 55 grams

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Sucrose structure

Odd as it is a “head-to-head” type structure (anomeric carbon to anomeric carbon)

Non-reducing The glycosidic bond is high energy, thus

unstable– Easily hydrolyzed in dilute acid or enzymes

(sucrase or invertase)

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Invert sugar

Glucose---Fructose Glucose Fructose+H+

Invert sugar[]D +66.5o

[]D -33.3o

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Sucrase and invertase

Human sucrase(-glucosidase)

Yeast and bacterialinvertase(-fructofuranosidase)

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Sucrose synthesis

Synthesized mainly in plants leaves, then transported throughout the plant

Stored in root or tuber structures

Sucrose phosphate

Sucrose

UDPGlucose +Fructose-6-phosphate

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Sucrose from sugar cane

Isolation involves processing 12-18 month old sugar cane through a series of steps that involve crushing, treating with lime, heating, filtration, and crystallization

This produces raw sugar and blackstrap molasses

The raw sugar is further cleaned up by treating with lime and phosphate, decolorizing, and crystallizing

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Sucrose from sugar beet Utilizes countercurrent

extraction of sugar beet slices (called cosettes)

The extracting solution (12% sugar) is then treated with lime, carbon dioxide, filtered, decolorized with SO2, and concentrated to crystallize the sugar

Impurities: raffinose and stachyose

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Raffinose and stachyose

Galp(16)Galp(16)Glcp(12)βFrufSucrose

Raffinose

Stachyose

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Other sugar products Brown sugar

– Incompletely purified table sugar or (more commonly) made by adding back cane sugar molasses to table sugar to get desired brownness and taste

– Industry refers to this as soft sugar

Powdered sugar– Pulverized table sugar +

3% corn starch as an anti-caking agent

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Other sugar products (cont.) Fondant sugar

– Very fine sucrose crystals surrounded with a saturated solution of invert sugar, corn syrup, or maltodextrin

– Used in icings and confections

Transformed sugar– Agglomerated sucrose

crystals– Low density, rapid

dissolving Liquid sugar

– Refined aqueous solution of sucrose

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Sucrose crystal and solution properties Sucrose can form highly concentrated

solutions– Syrups– Honey

Uses– Sweetener– Preservative– Humectant

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Cryoprotectant function

In a solution of sucrose, as freezable water freezes, the [sucrose] increases

Thus, freezing point decreases As [sucrose] increases, viscosity increases Eventually the liquid phase solidifies as a

glass– This explains how some carbohydrates can

protect against dehydration (via crystallization) that destroys structure and texture on freezing

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Sucrose solution structure

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OO

OH

OHHOH2C

O

OH

OH

H

OH

OH

In solution andcrystal state

In crystal stateonly

6’

1’

2

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Derivatives of sucrose Sucrose esters

– Low derivatization (1, 2, 3 fatty acids) Surfactants

(emulsifiers)– Octaacetate

Very bitter Used to denature

ethanol– Longer fatty acids

6-8 fatty acids (stearic, palmitic, oleic)

Olestra (frying oil fat substitute from Proctor and Gamble)Not metabolized or absorbed

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Sucralose

OCl

OH

OH

O OH

OH

O

OH

Cl

Cl

O

Sucralose 650x sweeter than sucrose Good taste quality and

intensity Adequate water solubility Not hydrolyzed in small

intestine 60 times more stable to acid

than sucrose Approved for use in the US

on 4/1/98

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Sucralose uses

Tabletop sweetener (Splenda) Beverages Baked goods Chewing gum Dry mixes Fruits spreads Frozen desserts

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Isomaltulose

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OHOH

OHHOH2C

O

OHOH

OH

CH2OH

OIsomaltulose

50% as sweetas sucrose

-D-Glucopyranosyl-(16)-D-fructofuranose

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Isomaltulose preparation

Prepared enzymatically from sucrose Enzyme is from Protaminobacter rubrum Transfers glucose in sucrose from O-2’ to

O-6’

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Isomaltulose

Uses (in Europe)– Non-cariogenic candies– Speciality chocolate– Chewing gum– Cookies

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Palatinit

Hydrogenation of isomaltulose with hydrogen and a catalyst produces Palatinit

About 45% as sweet as sucrose Crystalline

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Palatinit (GPM and GPS)

O

OHOH

OHHOH2C

O OH

OH

OH

OH

OH

GPS

O

OHOH

OHHOH2C

O

OH

OH

OH

OHOH

GPM

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Palatinit uses

Chocolate Marzipan Chewing gum

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Effect of palatinit on blood glucose

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Leucrose

O

OHOH

OHHOH2C

O

O

OHOH

OH

OH

-D-Glucopyranosyl-(15)-D-fructopyranose

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Leucrose

Derived from sucrose by treatment with Leuconostoc mesenteroides

50% of the sweetness of sucrose

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Kestose and neosugar

Kestose (GF2) Nystose (GF3)Fructofuranosyl nystose (GF4)

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Neosugar preparation

A concentrated solution of sucrose is treated with invertase or a fungal transferase

This causes the transfer of D-fructosyl units onto sucrose, thus producing kestose and the other neosugars

50% as sweet as sucrose Non-cariogenic Approved for use in Japan

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Trehalose

Naturally occurring Non-reducing Structure

Shorthand:αGlcp(1↔1)αGlcp

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Trehalose

Occurs widely in nature– Mushrooms– Honey– Lobster– Shrimp– Certain seaweeds– Foods produced using yeast

Commercially produced by enzyme catalyzed reaction

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Trehalose

Properties– Stabilizes proteins against freezing and

drying– Maintains texture, flavor and color in frozen

and dehydrated foods, especially in Japan– Reduces retrogradation of starch– Preserves cell structure– Low hygroscopicity– RS 0.45

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Trehalose

Properties– No reactivity in Maillard reaction– Provokes less insulin response– Used in some sports drink and nutrition bars

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Oligosaccharides from starch and other sources Starch depolymerization (Chap 6)

– Maltodexrins Guar gum hydrolysis (Chap 8, 16) Galactopyranosyl units with glucose at

the reducing end– Treat lactose with galactosidase– Product contains 1→4 and 1→6 linkages– Some prebiotic activity (Chap 16)