Starch

Question 1

what is starch

Answer 1

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

Question 2

outline the structure of starch

Answer 2

vary in size and shape based on their origin

contain two polysaccharides: amylose and amylopectin

Question 3

what is amylose

Answer 3

makes up 15-30% of the granule
dense, long and largely unbranched
long chain of d-glucose connected by alpha 1-4 linkages

Question 4

what is amylopectin

Answer 4

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

Question 5

how can starch granules be identified under the microscope

Answer 5

Maltese cross

Question 6

outline the process of the gelatinisation of starch

Answer 6

• 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

Question 7

outline the process of making a roux (from a food scientists point of view)

Answer 7

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

Question 8

what is dextrinisation

Answer 8

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

Question 9

name 3 natural sources of starch

Answer 9

corn starch
- cooks to a clear, translucent gel

rice starch
- soft, translucent gel

potato starch
- stringy transluscent solution

Question 10

outline the function of starch in pasta

Answer 10

reduces water access
proteins compete with starch for limited water
limited granule expansion

Question 11

outline the function of starch in mash

Answer 11

granules swell

bulging cells separate

Question 12

outline the function of starch in chips

Answer 12

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

Question 13

what are naturally occurring functional starches

Answer 13

• starches that have not been chemically processed
• have a desirable functionality
• e.g. maize starch

Question 14

what is unprocessed functional starch

Answer 14

waxy maize, rice, tapioca

Question 15

what is pregelatinised starch

Answer 15

instant, preheated with water to gelatinise to a specific point then rapidly dried to make a powder

Question 16

what is the advantage of modified starch

Answer 16

they produce a consistent product

Question 17

what is the role of amylase

Answer 17

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

Question 18

a lack of what enzyme may be the cause of food intolerances

Answer 18

disaccharide enzymes

Question 19

what are the components of modified starch

Answer 19

acid modified
cross linked
stabilised

Question 20

what is cross linked starch

Answer 20

• 25% of all food starch
• strengthens structre
• resistant to pH and shear
• slow to gelatinise
• e.g. canned fruit pie fillings

Question 21

what is cellulose

Answer 21

found in plant cell walls, component of dietary fibre, chains bound via hydrogen bonding, provide strength

Question 22

what is aliginate

Answer 22

brown seaweed, thickener

Question 23

what is pectin

Answer 23

thickener found in fruit, used in jam

Question 24

are carbohydrates considered an essential nutrient

Answer 24

no-only energy and protein

Question 25

how are sugars taken up by the cell

Answer 25

gut lumen- cell- blood

enter via enterocytes

Question 26

what causes absorption

Answer 26

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

Question 27

what is stabilised starch

Answer 27

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