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