carbohydrates Flashcards
what is photosynthesis
is the process by which green plants use sunlight to make sugar from carbon dioxide and water
how does photosynthesis occur
-plant roots absorb water (H20) from the soil
-leaves take in carbon dioxide (CO2) from the air
-Chlorophyll in leaves absorb energy from the sun
what is the end result of photosynthesis
-glucose is formed
-oxygen is released into the air
what is the equation for photosynthesis
6CO2 + 6H2O → C6H12O6 + 6O2
what is the elemental composition of carbohydrates
carbon, hydrogen, oxygen
what are monosaccharides
one sugar molecule. it is the smallest unit of a carbohydrate
what is the chemical formula for monosaccharides
C6H12O6
give examples and sources of monosaccharides
glucose- fruit
fructose- fruit and honey
galactose- digested milk
what are disaccharides
two sugar molecules joined together
what is the chemical formula of disaccharides
C12 H22 O11
give examples and sources of disaccharides
maltose- barley
sucrose- table sugar
lactose- milk
what are polysaccharides
many sugar molecules joined together
what is the chemical formula for polysaccharides
(C6H1005)n
give examples and sources of polysaccharides
starch- cereals and potatoes
glycogen- meat
cellulose- skins of fruits and vegetables
what are the properties of sugars
solubility, sweetness, assist aeration, maillard reaction, caramelisation, crystallisation, hydrolysis and inversion
explain solubility as a property of sugar
sugar is a white crystalline compound. it is a soluble in water. a syrup is formed when a large amount of sugar is dissolved in a small amount of water, e.g. canned peaches
explain sweetness as a property of sugar
all sugars are sweet and give an appetising flavour to food. some sugars are much sweeter than others. this is measured on a point scale of sweetness, e.g. shortbread
explain assists aeration as a property of sugar
Aeration occurs when sugar is whisked with an egg, denatured egg protein unfolds, entraps air bubbles, and creates heat, causing the egg to coagulate and form a permanent foam, e.g. sponges
explain maillard reaction as a property of sugar
The maillard reaction is a non-enzymic browning process in food, resulting from the reaction between certain amino acids and sugars under dry heat. it produces an attractive brown colour and an appetising flavour, e.g. roast meat
explain caramelisation as a property of sugar
on heating, sugar melts and caramelises. this occurs over ten gradual stages between 104C and 177C. caramelisation normally occurs at 160C, resulting in an attractive brown colour and a sweet taste. if overheated caramel will carbonise or burn, e.g. crème caramel
explain crystallisation as a property of sugar
when a liquid has dissolved as much sugar as it can, it is saturated. if more sugar is added, crystals of sugar form in the solution and solidify when cooled, e.g. fudged
explain hydrolysis as a property of sugar
hydrolysis occurs during digestion. water and enzymes split disaccharides into two monosaccharides into glucose and galactose
explain inversion as a property of sugar
occurs when a liquid solution is heated in the presence of an acid or enzyme, causing the sucrose to split into glucose and fructose, e.g. jam-making
what are the properties of starch
solubility, flavour, hygroscopy, hydrolysis,
explain solubility as a property of starch
starch is a white non-crystalline powder. it is insoluble in cold water
explain flavour as a property of starch
starch is not sweet in flavour
explain hygroscopy as a property of starch
starch absorbs moisture from the air. this can cause uncovered foods, e.g. biscuits to soften and lose crunch
explain dextrinisation as a property of starch
when dry heat is added to starch-based foods, dextrins are formed. this causes a colour change on the surface of the food, resulting in an attractive brown appearance
explain gelatinisation as a property of starch
when starch is combined with liquid and heated to 55-70 the grains swell, burst and absorb the liquid around them, increasing the viscosity. as the temperature increases it becomes even more viscous and forms a sol. when the mixture cools, water molecules become trapped resulting in a gel, e.g. roux sauce
explain hydrolysis as a property of starch
hydrolysis occurs during digestion. water and enzymes split starch into the disaccharide maltose
what are the properties of non-starch polysaccharides
cellulose/dietary fibre, gums, pectin
explain cellulose as a property of non starch polysaccharides
cellulose is insoluble in water. it cant be digested by the body, but it absorbs water as it passes through the intestinal tract and helps stimulate peristalsis
explain gums as a property of non starch polysaccharides
gums are soluble in water. they can absorb large amounts of water to form a thick gel with a firm texture
explain pectin as a property of non starch polysaccharides
present in plants cells and cell walls of fruit and vegetable. its used as a setting agent, as it can absorb water to form a gel. its only present in ripe fruits, if underripe its in the form of protopectin and if its overripe it becomes pectic acid. for pectin to be absorbed it needs heat and acid, e.g. jam-making
what are the effects of dry heat on carbohydrates
-maillard reaction, e.g. roast beef
-caramelisation, e.g. crème caramel
-dextrinisation, e.g. toast
what are the effects of moist heat
-syrup formation, e.g. syrup in canned peaches
-gelatinisation, e.g. white sauce
-cellulose softens, e.g. potatoes
-pectin extractions, e.g. jam
what are the biological functions of carbohydrates
-supply the body with heat and energy. helps keep the body at 37C
-excess carbohydrates intake is converted to glycogen and stored in the liver and muscles as a long-term energy reserve
-cellulose/dietary fibre absorbs water as it passes through the intestinal tract and helps stimulate peristalsis. this is beneficial as it speeds up the passage of food and waste, preventing bowel disorders, e.g. constipation
