Do not duplicate

Introduction to Carbohydrates: Oligosaccharides

Dr. Yuan Yao Whistler Center for Carbohydrate Research Short Course October 3, 2017 Basic Concepts 2 Do not duplicate • “Oligo-” is the prefix from Greek language “few”; Poly- “many” • Oligosaccharides: Products of glycosidic linkages of 2-20 monosaccharide units (most commonly 2-9). Polysaccharides: More than 20 units • In the disaccharides: the aglycone is a monosaccharide unit; higher order oligosaccharides are named “tri-”, “tetra-”, “penta-”, etc. • There can be α-/β-(1→2), (1→3), (1→4) or (1→6) glycosidic linkages, with different stabilities & digestibilities (as for human body) • The structures of oligosaccharides could be linear or branched.

Linear: head-to-tail linkage, 1 reducing end, 1 non-reducing end

Branched: 1 reducing end, multiple non-reducing ends Common Disaccharides 3 Do not duplicate • Disaccharides are the simplest oligosaccharides that are only composed of two monosaccharide units

o Highly abundant in nature; or the products of incomplete hydrolysis of higher oligosaccharides or polysaccharides

o Water-soluble, with sweet taste

• Most Common: Sucrose, Maltose, Lactose, & Trehalose

o Naturally occurring

o As the main product of photosynthesis, sucrose is ubiquitous in all plants, with high abundance in sugar cane and beet, as well as fruits

o Commonly known as table sugar, sucrose usually serves as a “standard” of sweetness for other sweeteners Common Disaccharides 4 Do not duplicate Sucrose

• A disaccharide of one glucose and one fructose unit, connected via β-(1,2)-glycosidic linkage • The “head-to-head” linkage is unstable due to high strain, and is therefore easily hydrolyzed (acid-catalyzed, or enzymatic) • Sucrose is a non-reducing sugar

α-D-glucopyranosyl-(1→2)-β-D-fructofuranoside 5 Common Disaccharides Inverted sugarDo (syrup) not duplicate

• Sucrose could be readily hydrolyzed. In industry, the mixture of produced glucose and fructose is known as inverted sugar

• Industrially, enzyme (sucrase or invertase) or acid (lemon juice or cream of tartar) is added to facilitate the reaction

• Extent of conversion can be measured using a polarimeter, due to inversion of optical rotation (from +66.5°of sucrose to −39° of glucose/fructose mixture when fully hydrolyzed)

• Inverted sugar is of higher sweetness, more hygroscopic and less prone to crystallization compared to sucrose, and is favored in bakery

Boiling sucrose solution - http://www.chefeddy.com/2009/11/invert-sugar/ Inverted sugar - http://alifelesssweet.blogspot.com/2009/05/because-you-askedinvert-sugar.html Common Disaccharides 6 Do not duplicate Inverted sugar • Schematic showing the mechanism of optical rotation; “+” indicating polarized light rotated clockwise

+

Boiling sucrose solution - http://www.chefeddy.com/2009/11/invert-sugar/ Inverted sugar - http://alifelesssweet.blogspot.com/2009/05/because-you-askedinvert-sugar.html Common Disaccharides 7 Do not duplicate Sucrose as cryoprotectant agent

• Sucrose can form highly concentrated solutions, used as sweetener, preservative, and humectant

• In a solution of sucrose, freezing point decreases when sucrose concentration increases

Derivatives of sucrose

• Sucrose esters: Low derivatization (1, 2, 3 fatty acids), as surfactants or emulsifiers

• Fat replacer: sucrose attached with 6-8 fatty acids (stearic, palmitic, oleic), e.g. Olestra (frying oil substitute from P&G) is not metabolized or absorbed Common Disaccharides 8 Do not duplicate Derivatives of sucrose: Sucralose

• Sucralose (also known as trichlorosucrose) is a partially chlorinated derivative of sucrose

• Discovered and patented by 1976

• Brand name “Splenda” in the US

Sucrose Sucralose 9 Common Disaccharides

Do not Maltoseduplicate • Another common disaccharide from plant source

• Two glucosyl units connect via an α- (1,4)-glycosidic linkage α-Maltose α-D-glucopyranosyl-(1→4)- • First discovered in malt (germinated, α-D-glucopyranoside dried cereal grain that contains partially digested starch by activated enzymes)

• Digestible for human by maltase (α- glucosidase)

• Unlike sucrose, maltose has a free β-Maltose reducing end, and is therefore a α-D-glucopyranosyl-(1→4)- β-D-glucopyranoside reducing sugar Common Disaccharides 10 Do not duplicate Maltose

Used as a mild sweetener and energy source, ~1/3 sweetness compared to sucrose Maltose production • Through enzymatic hydrolysis of starch (amylose, amylopectin) • Digestion of amylose by β-amylase, or of amylopectin by debranching enzyme + β-amylase

Amylose Amylopectin Common Disaccharides 11 Do not duplicate Lactose • The main form of carbohydrate in milk of all mammals • Disaccharide of one galactose and one glucose unit, connected via a β-(1,4)-glycosidic linkage • Provides ~40% of energy when nursing (the other coming from dairy fat and proteins). Lactose need to be broken down to D- glucose and D-galactose • Accounts for the slight sweetness of fresh milk (~1/6 sweetness of sucrose)

α-lactose β-D-galactopyranosyl-(1→4)- α-D-glucopyranoside

β-lactose β-D-galactopyranosyl-(1→4)- β-D-glucopyranoside Common Disaccharides 12 Do not duplicate Lactose • Like maltose, lactose retains an reducing end (anomeric center on glucose unit), and is therefore a reducing sugar, undergoes anomerization (mutarotation) • Isolated from whey, a by-product of cheese manufacturing, the liquid after milk is curdled and strained o For cheese production, rennet (an enzyme) or an edible acid (citric or tartaric acid) is added to milk, making it curdle o Whey is remained when coagulated casein (the primary milk protein) is removed o Whey undergoes centrifugation to remove fat, ultrafiltration to separate whey protein, ion exchange to remove salt, and crystallization to isolate lactose

https://www.oregondairy.org/wp-content/uploads/2017/04/1b-derrick.pdf Common Disaccharides 13 Do not duplicate Lactose intolerance

• In human body, lactose is digested by lactase (β-D-galactosidase), the monosaccharides produced are absorbed • Lactase is most abundant in GI tract of infants, who rely on milk as the only energy source; its activity plummets after weaning (young children may lose ~90% lactase activity by the age of 4) • If lactose is not completely hydrolyzed in the small intestine, it will enter the large intestine • When lactose enters large intestine, it is fermented by anaerobic gas-generating microorganisms, producing short-chain fatty acids,

CO2, H2, CH4, etc., which results in bloating, flatulence, abdominal cramping, diarrhea, etc. • This causes the symptoms of lactose intolerance Common Disaccharides 14 Do not duplicate Strategies to overcome lactose intolerance

• Avoid ingestion of (excessive) lactose

o Drink soy milk; use soy products as a substitute of protein and calcium source

o Consume yogurt instead of milk (lactose greatly reduced and converted to lactic acid)

o Choose lactose-free milk & milk products

• Use supplementary lactase

o Available as pills (taken before diary consumption) or liquids (added to diary before service)

Soy Milk – http://jpnfood.com/archives/2985 Lactose-Free Milk - http://www.bestgrocerydelivery.net/Great-Value-Lactose-Free-Whole-Milk--12-Gallon_p_10048.html Supplementary Lactase - http://www.healthpost.co.nz/solgar-lactase-3500-sglac.html Common Disaccharides 15 Do not duplicate Trehalose • Naturally occurring non-reducing disaccharide • Occurs widely in nature: mushrooms, honey, lobster, shrimp, certain seaweeds, foods produced using yeast • Properties o Stabilizes proteins against freezing and drying o Maintains texture, flavor and color in frozen and dehydrated foods o Reduces retrogradation of starch o Preserves cell structure o Reduces hygroscopicity o No reactivity in Maillard reaction o Provokes less insulin response Trehalose o Broadly used in bakery Glc(α1↔1)Glc Functional Oligosaccharides 16 Do not duplicate “Novel” oligosaccharides drawing interest of food scientists, due to their potential benefits for human health as food additives or dietary supplements; collectively referred to as “functional oligosaccharides”.

• Raffinose (a trisaccharide)

• Stachyose (a tetrasaccharide)

• Raffinose and stachyose are both components of “soybean oligosaccharides”

• Isomaltooligosaccharides (IMO, a mixture of isomaltose, isomaltotri/tetrasaccharide, etc.)

• Fructooligosaccharides (FOS, Glu-Frun, n=1-5)

• Galactooligosaccharides (GOS, Glu-Galn, n=1-7)

• Xylooligosaccharides (XOS, Xyln, n=2-7). Functional Oligosaccharides 17 Do not duplicate • Primary benefit of functional oligosaccharides is to be “prebiotics” • Prebiotics: Substances that enhance the growth and/or activities of probiotics (microorganisms that provide health benefits to their hosts, especially those residing in GI tract) • Most common GI tract probiotics: Lactobacillus, Lactococcus, Bifidobacterium, etc. • Major benefits of probiotics: o Adjustment of GI function: alleviation of constipation or diarrhea, prevention of inflammatory bowel diseases or cancer o Enhancement of immune system o Weight control; prevention of metabolic syndrome; lowering of LDL o Prevention or alleviation of oral or dental diseases o Producing supplementary vitamins or other nutrients Functional Oligosaccharides 18 Do not duplicate Raffinose and stachyose

gal(α1→6)gal(α1→6)glc(α1↔2β)fru Sucrose

Raffinose

Stachyose Functional Oligosaccharides 19 Do not duplicate Raffinose A trisaccharide of galactose, glucose, and fructose • Rich in legumes, especially in soybean: one component of “soybean oligosaccharides” • 20-30% of sweetness and 33% of calorie compared to sucrose • Non-digestible for human due to lack of α-galactosidase • Fermented by Bifidobacterium, as well as lower intestine gas- generating bacteria to produce carbon dioxide, methane, hydrogen gas, etc. (flatulence associated with legume consumption)

gal(α1→6)glc(α1↔2β)fru 20 Functional Oligosaccharides

StachyoseDo not duplicate A tetrasaccharide of two galactose units, one glucose and one fructose • Naturally occurring in legumes and other plants like raffinose, and of similar structure; one of “raffinose family of oligosaccharides” (RFOs) • 22-28% of sweetness and 30-50% of calories compared to sucrose • Not fully digestible for human, yet a great substrate for Lactobacillus and Bifidobacterium • Gas-generating but to less extent compared to raffinose

gal(α1→6)gal(α1→6)glc(α1↔2β)fru 21 Functional Oligosaccharides

IsomaltooligosaccharidesDo not duplicate (IMO) A mixture of a group of glucose oligomers with mainly α-(1,6)-linkages • Occur naturally or manufactured through enzymatic conversion of starch. Also found in some fermented foods • Unlike α-(1,4)-linkage in maltose, α-(1,6)-linkage of glucose are not easily digested in human GIT • Fermented by probiotic microorganisms to generate short-chain fatty acids that keep colon acidic, inhibiting pathogen growth

Isomaltose Panose Isomaltotriose glc(α1→6)glc glc(α1→6)glc (α1→4)glc glc(α1→6)glc (α1→6)glc 22 Functional Oligosaccharides

FructooligosaccharidesDo not (FOS)duplicate

Derivatives of sucrose

• Concentrated solution of sucrose treated with invertase or a fungal transferase

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

• 50% as sweet as sucrose, non- cariogenic Kestose Nystose Fructofuranosyl (GF2) (GF3) nystose (GF4) Functional Oligosaccharides 23 Do not duplicate Galactooligosaccharides (GOS)

A series of galactose oligomers with mainly β-(1,4)-linkages.

• Produced through enzymatic conversion of lactose

• Composition of GOS relying on a variety of factors (e.g. enzyme type, quantity, medium composition)

• Facilitating absorption of minerals (especially calcium)

gal(β1→[4)gal(β 1→]p4)glc