Lecture 4-starch Flashcards
- Describe in general terms the structure of amylose and amylopectin
Amylose is a linear polymer of glucose with alpha-1,4 linkages and has no branches. The alpha 1,4 bonding allows for axial-equiatorial coupling forming a straight helix conformation with hydroxyl groups facing outwards
Amylopectin is branched molecule that has alpha 1,4 linkages on the main chain and then alpha 1,6 linkage at the branching points which occurs every 24 to 30 glucose residues. The central chain is the C chain and has the reducing end and the A and B are attached to C, The B chain will have branches but the A one has no branches. Each chain is in helical conformation.
- Describe the process of gelatinization
it is a process occuring in water with starch molecules being heated. The heat will cause the starch granules to expand/swell since more hydrogen bonds are being water and more water is involved. The water will be absorbed gradually in the granules ultimetly leading to them bursting, causing the irreversable dissolvment of the starch granule in water. This forms a thick liquid or gel
Explain why amylose and amylopectin form complexes of different colors with iodine.
Because they differ in structure, the complex that forms is based on the 1,4 glucan chains since the helical with hydrophohobic cavity and the outer surface rich in OHs can fit the idodine molecules perfectly. In amylose it is a straight chain of this so the iodine fits nicely and forms a blue complex. Amylopectin on the other hand is branched so the idodine reacts differently to the structure and forms a red-violet complex.
- Describe the effects of polar lipids on starch pasting,starch pastes and bread staling.
Bread Staling: Bread staling occurs from retrogradtion of both amylose which hapens once it reaches room temp and amylopectin that is slow, over days. But polar lipids will inhibit retogradtion which will delay staling. Polar lipids properties disrupt amylose and amylopectin from coming back together by disrupting hydrogen bonds.
Starch Pasting: can delay the gelitinzation since they form a protective barrier around starch granules, denying acess of water. Starch Pastes: can influence texture by influencing the interactions between starch and water molecules. and increases the stability as it inhibits retrogradtion
- Describe the process of starch synthesis
- chain elogongation: glucose 1 phosphate is converted to ADP-glucose with the help of ADP glucose phosphorylase and after that starch synthase will transfer the glucose residue to the OH position at carbon 4 to start creating the chain
- branching and debranching: branches are created when the chain is cleaved at the alpha 1-4 bond and the branching enzyme makes a link with another chain creating an alpha 1,6 bond. During this process the debranching enzyme will also cleave branches.
- How does the presence of damage granules effect gelatinzation?
Speeds up the process since starch granules are already broken down
- What is resistant starch?
Starch not digested in small intestine. Instead passes into Colin which then can be used by gut microflora. Known as dietary fibre.
Define retrogradation
Is the recrystalization process opposite of gelatinzation. What happens during this process is amylose and amylopectin in a gelatinized starches reassocaite forming ordered structures. In cooling this happens as water comes out
- define pasting
is the phenomenon that follows gelatinization when the granules have swelled to their maximum and begin to release molecules into the solution, leading to an increase in viscosity.
- Describe the composition and properties of starch hydrolysis products
starch→ dextrin→ maltodextrin →corn syrup→maltose→glucose/dextrose
as hydrolysis increases the number of reducing ends increase so DE increases and degree of polymirzation decreases starch has a DP greater than 600 and a DE lower than 1, and glucose/dextrose will have a DP of one and a DE of 100
- Describe the process and uses of starch in encapsulation applications.
process: mixing ingrediants with starch to protect bioactive materials
use: Applications include encapsulating flavors, vitamins, nutraceuticals, and pharmaceuticals to improve their stability, control their release, or mask unpleasant tastes
- Describe physical processes used to modify starch granule proper
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Pre-gelatinization: A process where starch is cooked and then dried, making it water-soluble and instant-thickening upon addition to cold water.
- Hydro-thermal treatments: Involves heating humidified starch to change its crystallinity and reduce its digestion rate, altering the properties of the starch granules depending on the type of starch and conditions used.
- Heating of dry starch: Applying heat at high temperatures and low humidity to increase the stability of starch in acidic conditions, modify paste viscosity, and adjust cooking temperature.
- what are resistant starch?
it is starch that is not digested in the small intestine and will enter the colon where it will be used by the gut microflora
- what is the general principle of pre-gelatinized straches and what is the use?
forms a dry past by preventing molecules from reassociating it is purpose is for products that are prepared by consumers like instant puddings, sauces,dry soups etc.
- what are cold thickening starches and what are their uses
is starch in its granular form that is gelatinized but not retrograded that is used for gel based applications is basically instant starch as it has the properties of starch without being cooked
