Starch Flashcards
what is starch
the predominant food reserve in plants
provides dietary calories to humans
used in foods for thickening, binding and gelling
sources include cereal grains and roots
outline the structure of starch
vary in size and shape based on their origin
contain two polysaccharides: amylose and amylopectin
what is amylose
makes up 15-30% of the granule
dense, long and largely unbranched
long chain of d-glucose connected by alpha 1-4 linkages
what is amylopectin
makes up 70-85% of the granule
d-glucose residues with an alpha 1-4 linkage
branched with alpha 1-6 linkages
chains form helices through hydrogen bonding which clump to form crystallites which line up to form crystalline (structured) and amorphous regions (unstructured) giving the appearance of growth rings
easily digested
how can starch granules be identified under the microscope
Maltese cross
outline the process of the gelatinisation of starch
- must be heated in excess water which leads to irreversible changes in the ordered structure of the starch granule, it swells causing a loss of biofringence
- the crystalline melts causing the helixes to unwind
- amylose leaches out leading to starch solubilisation which increases viscosity
- the amylose gels on cooling
outline the process of making a roux (from a food scientists point of view)
heating flour coats granules which separates them
starch swells gradually
boiling disintegrates granules
retrogradation upon calling allows amylose to assemble into a network
dextrinisation shortens chains giving a thinner sauce
what is dextrinisation
Dextrinization is the process involving the browning of starch foods when subjected to dry heat. It is defined as the breakdown of starch into dextrins (disaccharides) and it is a non-enzymatic browning and chemical change which is easily digested as partial breakdown is complete
name 3 natural sources of starch
corn starch
- cooks to a clear, translucent gel
rice starch
- soft, translucent gel
potato starch
- stringy transluscent solution
outline the function of starch in pasta
reduces water access
proteins compete with starch for limited water
limited granule expansion
outline the function of starch in mash
granules swell
bulging cells separate
outline the function of starch in chips
water evaporates and fat enters when cooked at high temperatures
dextrinisation occurs and forms a crust, colour, texture, flavour
starch granules do not swell due to lack of water
what are naturally occurring functional starches
- starches that have not been chemically processed
- have a desirable functionality
- e.g. maize starch
what is unprocessed functional starch
waxy maize, rice, tapioca
what is pregelatinised starch
instant, preheated with water to gelatinise to a specific point then rapidly dried to make a powder
what is the advantage of modified starch
they produce a consistent product
what is the role of amylase
it is an enzyme in salvia that breaks down food in the mouth
stomach pH and more amylase (which is released during pancreatic stimulation) further break down glucans in the small intestine
a lack of what enzyme may be the cause of food intolerances
disaccharide enzymes
what are the components of modified starch
acid modified
cross linked
stabilised
what is cross linked starch
- 25% of all food starch
- strengthens structre
- resistant to pH and shear
- slow to gelatinise
- e.g. canned fruit pie fillings
what is cellulose
found in plant cell walls, component of dietary fibre, chains bound via hydrogen bonding, provide strength
what is aliginate
brown seaweed, thickener
what is pectin
thickener found in fruit, used in jam
are carbohydrates considered an essential nutrient
no-only energy and protein
how are sugars taken up by the cell
gut lumen- cell- blood
enter via enterocytes
what causes absorption
IN
- sodium glucose linked transporter-
moves sodium and glucose into the cell
driven by the concentration gradient of sodium
- glut 5 -
moves fructose via facilitated diffusion resulting in higher levels o glucose in the gut vs the cell
IN/OUT
- sodium potassium pump-
sodium out, potassium in
alters electrolyte composition of cells
OUT
- glut 2-
moves glucose, galactose, fructose out of the cell and into the blood
what is stabilised starch
react with: acetic anhydride propylene oxide phosphorous oxychloride ocetenyl succinylcholine ester
acetyl/ hydroxypropylester stabilised produces freeze-thaw resistant gels
phosphate stabilised has a high paste viscosity
succinate stabilised is used as an emulsifier
