Carbohydrates Flashcards
Importance of carbohydrates
Major energy source Sweet taste Provide structure and texture in food Lower aw and affect crystallization (ice cream) Fat substitute (modified starch) Impart flavors and colors (Maillard browning) Energy source in fermentation (yogurt) Health benefits (dietary fiber)
Monosaccharides
Glucose
Fructose
Galactose
Disaccharides
Lactose
Maltose
Sucrose
Oligosaccharides
a few monosaccharides linked together
Polysaccharides
Many monosaccharides linked together
Inulin
polysaccharide
extracted from chicory root, used to replace sugar, fat, and flour
Pectin
polysaccharide
in cell walls of plants, used as gelling agent, thickening agent, stabilizer
Sugar alcohols
C=O (carbonyl) replaced with –OH
Small amounts in fruit
Synthesized industrially
Non-metabolized sweeteners
Caramelization
Series of non-enzymatic reactions when sugar heated above 150°C
No proteins involved
Sucrose inverts to glucose and fructose; isomers, fragments, and polymers form; dehydration and condensation occur
Flavor compounds and brown pigments arise
In ring form
Have free radicals: molecules that do not have enough atoms to fill all of the bonding requirements
Part of reason why caramels are sticky
Maillard reaction
Amino acid, sugar, usually heat reaction
Toast
Beer
Steak sear
Starch
Produced by plants from CO2 and H2O through photosynthesis
Their major food and nutrient reserve
Hundreds or thousands of glucose molecules chained together
Bonds between glucoses easily broken, used as energy source by plants and those eating them
Classified by three-dimensional structure
Sources:
From arrowroot, corn, tapioca, wheat
Comprises 85% of corn flour, 70% of wheat flour
Different properties depending on amylopectin-amylose ratio
Amylose
Starch
Helical, little branching
Tight packing
Amylopectin
Starch
Branched, fold into sheets
More soluble
Around ¾ of starches in plants
Gelatinization
Starch heated in water, goes from practically insoluble semi-crystalline product to soluble amorphous substance
Produces viscous solutions which set to a semisolid elastic mass (jelly or gel) after cooling
Onset characterized by loss of granular structure, promotes swelling
Gelatinization point partly depends on granule size: smaller granules more resistant to swelling
Retrogradation
Thickening of cooked, unmodified starch when cooled for long enough time
Starch molecules gradually aggregate to form gel, rearranging to more crystalline structure
Molecular associations occur between amylose and amylopectin
Tightly packed organization of small granule starches causes retrogradation to occurs much more slowly
Ex: staling of bread
Modified starch
Tailored for specific applications
Pre-gelatinized: cooked with water to gelatinize and dehydrated, swells to desirable thickness with addition of water, no heat needed
Thin-boiling: treated with acid, many amylopectin branches cleaved off, starch can be delivered through pipes in plant, forms strong gels
Cross-linked: produced under alkaline conditions, used as thickening agents, limited retrogradation
Soluble fiber
gum, dissolves in water, attracts and binds water, limited calories
Alginic acids: from seaweed, thickener and stabilizer, includes agar and carrageenan
Pectin: from fruit skin, gelling agent in jams and jellies
Psyllium: from plantains, digestion aid
Raffinose: in beans and cruciferous vegetables
Insoluble fiber
absorbs water without dissolving in it, provides bulk
Cellulose, hemicellulose, lignin, resistant starch
Hemicellulose: heteropolymer, random structure, little strength
Lignin: cross-linked, in cell walls
Resistant starch: not digested in small intestine, high levels in beans and lentils
Carboxymethyl Cellulose (CMC)
Very viscous, used as thickener
Also used in laxatives, toothpaste, water-based paint
Stabilizes emulsions in ice cream
Water-soluble, combines with other gums, imparts body and chewiness
Only 0.1-0.2% needed
Eliminates need for high level of churning and very low temperatures
Absorbs 15-20 times its weight in water
Fibers make texture plumper and fatlike without adding calories
Also imparts glossy appearance
Used in Swiss Miss Hot Cocoa Mix, Wish-Bone Chunky Blue Cheese Dressing, Kraft Macaroni and Cheese
Artificial sweeteners
6 types approved by FDA: Acesulfame-K (Sweet One) Aspartame (Equal, Nutrasweet) Neotame Saccharin Stevia (Truvia) Sucralose (Splenda)