Carbohydrates (1. LF UK, NT)

Classification

According to the number of sugar units

• Monosaccharides
• Oligosaccharides (2–10 monosaccharide units)
• Polysaccharides ( more than 10 monosaccharide units)
• Complex (conjugated) carbohydrates

By attachment:

• loosely
• bound
  • homoglycosides
  • heteroglycosides
  • aglycone (non-sugar component)

Monosaccharides

• polyhydroxyalkyl substituted aldehydes and ketones, derived compounds
• main nutrients, biologically and sensorially active substances
• characteristic: sweet taste

Structure and classification

According to the type of carbonyl group

• aldos
• ketosis

By number of carbon atoms (3–8), (multiples of CH2O (formaldehyde))

• trios
  • D-(+)-glyceraldehyde (D-glycero-triose)
  • L-(-)-glyceraldehyde
  • 1,3-dihydroxyacetone (1,3-dihydroxypropan-2-on)
• tetros
• pentoses
• hexoses
  • D-glukose (D-gluko-hexose) = dextrose, grape sugar
  • D-fructose (D-arabino-hex-2-ulose) = levulose, fruit sugar

According to the arrangement of the string

• with a direct chain
• with a branched chain

According to the type of lactol

• furanoses
• pyranoses

Mutarotation

• anomers, anomeric C, anomeric OH

Conformation

• furanoses (envelope E, crossed T)
• pyranoses (chairs ⁴C₁, ¹C₄)
• acyclic forms (conformation cik-cak)

Occurrence

• component of almost all foods
• atypical monosaccharides
  • D-apiosa (branched sugar), root vegetables
  • L-sorbose (L-series sugar), rowan berries
  • D-manno-hept-2-ulose (ketoheptose), avocado

(abbreviations: glucose Glc, furanose f, fructose Fru, pyranose p, mannose Man, acid A, apiose Api, sorbose Sor, β-D-glucopyranose β-D-Glcp)

Derivates of monosaccharides

chemical reactions of their formation:

• oxidation (rearrangement) – sugar acids, ketoaldoses, diketoses
• reduction – sugar alcohols, deoxysugars
• dehydration – anhydrosugars
• reaction with other compounds – glycosides, ethers, esters

Sugar acids

• aldonic (glykonic) – (glucose oxidase, Ca-gluconan (medicine), δ-lactone (fermented salami, 0.1%)
• alduronic (glycuronic) – polysaccharides: D-GlcA6 (glycoproteins), D-GalA6 (pectins), D-ManA6 and L-GulA6 (alginates)
• aldaric (glycaric), e.g. tartaric and malic acid
• content in chicory and malt

Ketoaldoses, diketoses

• key products of the Maillard reaction and oxidation
  • 3-deoxyglykosulose, 1-deoxyglykodiulose, 4-deoxyglykodiulose

Sugas alcohols

• alditols, glycitols (glycerol derivatives)
• reduction of hemiacetal hydroxyl of mono- and oligosaccharides

• natural food ingredients
  • ribitol – riboflavin
  • arabinitol – mushrooms
  • xylitol – mushrooms
  • D-glucitol – plums, rowanberries, pears
  • D-mannitol – mushrooms, rowan berries, celery, green coffee
  • galaktitol – mushrooms, fermented milk products
• synthetic (reduction of H2/cat., NaHgx, substitute sweeteners)
  • xylitol, D-glucitol

• cyclitols - content
• cyklohexane-1,2,3,4,5,6-hexols (inositols, cykloses)
  • myo-inositol (meso-inositol)

widespread, phospholipids, phytates, pseudo-oligosaccharides (legumes)

Deoxysugars

• reduction of primary / secondary hydroxyl - natural, Maillard reaction

2-deoxysugars

• 2-deoxy-D-ribose (thyminose), deoxyribonucleic acid

6-deoxysugars (6-deoxyhexosis = methylpentosis)

Anhydrosugars

sugar anhydrides, glycosans, elimination of water, mainly hemiacetal and other OH

• natural polysaccharide components CH2O
  • 3,6-anhydro-α-D-galaktopyranose ( carrageenans )
  • 3,6-anhydro-α-L-galaktopyranose (agar)
• products of thermal reactions
  • 1,6-anhydro-β-D-glukopyranose (β-glucosan, levoglucosan) (caramel)

Glycosides, ethers, esters and other derivates

• O-glycosides – very widespread
• ethers: 4-O-methyl-D-GlcpA (hemicelluloses), 2-O-methyl-D-Xylp (pectins)
• esters – natural (phosphates, acetates, benzoates, etc.), synthetic (fatty acids, emulsifiers)
• S-glycosides – glucosinolates
• N-glycosides - natural (ATP, NADH), Maillard reaction (glycosylamines)
• aminodeoxysugars – natural (chitosamine), Maillard reaction (Amadori products)
• C-glycosides

Oligosaccharides

• homoglycosides
• pentoses, hexoses, sugar acids, etc. derivatives
• furanoses, pyranoses

Classification

By number of monosaccharides (monos, 2-10)

• disaccharides (bioses) – decasaccharides (decaoses)

According to the presence of hemiacetal OH

• reducing (glycosides)
• non-reducing (glycosylglycosides)

According to the predominant monosaccharide

• glucooligosaccharides
  • maltose, maltooligosacharides
• fructooligosaccharides
  • sucrose
• galactooligosaccharides
  • lactose, α-galactosides

According to digestibility

• digestible
• indigestible

According to biological effects

• prebiotic effects (stimulate growth and metabolism of desirable microflora)
• probiotic effects (with fiber they influence and regulate peristalsis)
• synbiotic effects (both prebiotic and probiotic)

Nomenclature

• maltose
  • α-D-glukopyranosyl-(1→4)-D-glukopyranose,
  • 4-O-α-D-glukopyranosyl-D-glukopyranose
  • α-D-Glcp-(1→4)-D-Glcp
• α,α-trehalose
  • α-D-glukopyranosyl-α-D-glukopyranoside
  • α-D-Glcp-(1↔1)-α-D-Glcp

Gluco-oligosaccharides

maltose = α-D-Glcp-(1→4)-D-Glcp (malt sugar )

Occurrence

• starch hydrolysis product, glucose reversion
• malt, bread (1.7-4.3%), honey (2.7-16%)

Production

• maltose (85%), glucose syrups (acids, enzymes)
• maltose
• isomerization to maltulose, α-D-Glcp-(1→4)-D-Fruf
• reduction to maltitol, α-D-Glcp-(1→4)-D-glucitol

Frukto-oligosaccharides

sacharóza = α-D-Glcp-(1↔2)-β-D-Fruf (beet sugar)

Occurence

fruit	to 8 %	.
vegetables	0,1–12 %	.
green coffee	6–7 % (0,2 %)	.
beet sugar	15–20 %	beet sugar
cane sugar	12–26 %	cane sugar
sugar maple (juice)	5 %	maple sirup
dates	81 %	date sugar

Production (from sugar beet)

• cuttings extraction (diffusion)
• purification (epuration) of raw juice, clarification of Ca(OH)2
• CO2 saturation
• filtration, light juice
• thickening - heavy juice (61-67% sucrose, 68-72% solids)
• raw (brown) sugar - 96% sucrose, 2-3% non-sugars, 1-2% water (1.0-1.2% organic, 0.8-1.0% inorganic)
• affinade
• refining – molasses (feed, substrate for fermentation processes), production of invert sugar, other products

Galakto-oligosaccharides

laktosis = β-D-Galp-(1→4)-D-Glcp (milk sugar)

Occurrence

• cow's milk 4-5%
• human milk 5.5-7%

Production (from whey)

• by ultrafiltration
• after thickening by crystallization – production of galactose, galactitol, lactulose, lactitol

other β-galactooligosaccharides of milk

α-galaktooligosacharides of legumes

content

Reactions of saccharides

• complex enzymatic and non-enzymatic reactions
• carbonyl, anomeric OH, primary OH, secondary OH

Non-enzymatic browning reaction

• reactions of the carbohydrates themselves
• Maillard reaction (reaction with proteins, amino compounds)
• caramelization

Reaction of carbohydrates

• Reactants
  • reducing mono- and oligosaccharides
  • non-reducing oligo- and polysaccharides after hydrolysis

Main reactions of monosaccharides (reactions catalyzed by acid-base)

• in an acidic environment (other factors: temperature, time)
  • formation (hydrolysis) of glycosides, dehydration, formation of reductones
• in an alkaline environment
  • mutarotation, isomerization, rearrangements, fragmentation, oxidation

Formation and hydrolysis of glycosides

• reaction of hemiacetal OH

Hydrolysis (inversion)

• production of starch syrups
• invert sugar
• galaktose

Formation (reversion, Fischer reaction)

• inversion by-products (starch syrups: 5-6%)
• byproducts of caramelization
• low energy products
• counterfeit indicators

Dehydratation

• reaction of hemiacetal OH and other OH
• hemiacetal OH / other OH → anhydrosugars (glycosans)
• another OH / another OH → deoxysugars

Anhydrosugars

• β-D-Glcp → 1,6-anhydro-β-D-Glcp (β-glukosan)
• inversion by-products (glucose < 1%)
• byproducts of caramelization (more)

Deoxysugars

• 1,2-enolisation (series of isomerisations and dehydrations)
• 2,3-enolisation (caramel aroma)

Formation of reductones

• antioxidants
  • reduction of organic substances, metal ions
  • pH < 6 (similar to enediolates) monoanionts
  • pH > 6 dianionts

Isomeration

• aldose → ketose
• aldose → aldose ( epimerization) .

Isomerization of disaccharides

• laktosis – β-D-Galp-(1→4)-D-Glcp
• laktulosis – β-D-Galp-(1→4)-D-Fruf
• epilaktosis – β-D-Galp-(1→4)-D-Manp

Changes to acids

• 1-ene-1,2-diol, Cannizzaro reaction, benzyl rearrangement

Fragmentation

• formation of very reactive compounds
  • retroaldolization
  • by oxidation (after isomerization, dehydration)

Malliard reaction

non-enzymatic browning reaction

Reactants

• sugars (carbonyl compounds)
  • monosaccharides and reducing oligosaccharides
  • (non-reducing oligosaccharides, polysaccharides, glycosides)
    • triosa > …. > pentose > hexose (acyclic form)
    • aldose > ketose
    • α-dicarbonyls > aldehydes > ketones > carbohydrates
• proteins (amino compounds)
  • ε-NH2 Lys, N-terminal NH2, guanidyl Arg, SH Cys
  • free amino acids, amines, ammonia
  • ε-NH2 > …. > β-NH2 > α-NH2
  • NH3 > R-NH2 > amino acid

Reaction conditions

• water activity (aw 0.3–0.7)
• pH (9–10)
• other (temperature, reaction time, other components)

Consequences positive, negative

• formation of aromatic substances
• formation of yellow, brown, black melanoidin pigments
• reduction of nutritional value
• potentially toxic products
• in vivo reaction (glycosylation of proteins)

Reaction mechanisms – 3 reaction phases

• initial phase
  • formation of glycosylamine (Amadori rearrangement) and aminodeoxysugar (Amadori product)
• middle phase
  • breakdown of carbohydrates, glycosylamines, aminodeoxysugars (dehydration, fragmentation)
  • breakdown of amino acids (Strecker degradation)
• final stage
  • reaction of products and decomposition products, formation of aromatic, taste and colored substances (melanoidins)

Glykosylamines and aminodeoxysugars

• ketoses → ketosylamine → aldosamine (2-amino-2-deoxyaldose), Heyns' p.

• mechanisms (reactions of acyclic forms)

Decomposition of aminodeoxysugars

• 1,2-enolization, acidic environment
• 2,3-enolization, neutral and alkaline environment
  • the formation of glycosulos and glycodiulos (aldoketos and diketos)

Analogy with the reactions of sugars themselves

• lower activation energy
• products contain N and S
• qualitatively and quantitatively more products

parallel breakdown of the sugars and amino acids themselves

Important heterocyclic products

Malliard reaction in major commodities

• positive and negative consequences, desirable and undesirable reactions

technology (aroma, taste, color, nutritional value)

• roasting
• cooking, baking, frying
• drying
• extrusion, microwave heating
• milk, dairy products - Lys: 10-30% traditional drying, 3% spray drying
• cereals, cereal products - Lys: 70% bread crust, 10% total
• meat, meat products – mutagens
• fruit vegetables
• coffee, cocoa, nuts

Reaction during milk processing unusable (blocked) Lys

• isomerization of lactose → lactulose + epilactose
• lysinoalanine

Maillard reaction inhibition

• creating unfavorable conditions
  • water content (activity), temperature reduction, pH adjustment
• removal of one of the partners
• use of inhibitors

Caramelization

• sugars (sucrose, glucose, fructose, starch syrups, invert sugar)
• temperature 150–190 °C (240 °C)
• reaction time 5-10 hours
• catalyst

• caramel – a solid product
• cooler - solution

class		name of cooler	another substances	usage
I	CP	caustic	Na2C03, K2CO3, NaOH. KOH, H2S04, acetic acid, citric acid	spirits (high alcohol content)
II	CCS	caustic sulfite	S02, H2S04, Na2S03, K2S03, NaOH, KOH	vinegar, beer, spirits, flavored wines, mead
III	AC	ammoniacal	NH3, (NH4)2S04, Na2C03, H2S04, NaOH, KOH	beer etc. alcoholic beverages, acidic foods
IV	SAC	ammonia-sulphite	NH3, S02, (NH4)2S03, Na2S03, K2S03, Na2C03, K2C03, NaOH, KOH, H2S04	acidic foods, soft drinks

Source

• DAVÍDEK, Jiří. 5. CARBOHYDRATES [online]. [cit. 2012-03-12]. <https://el.lf1.cuni.cz/p46134582/>