lecture 7-cell wall/cellulose Flashcards
- what do cell walls do in plant cells?
- provide sturcture
- provide tensile strength
- protect against mechanical and osmotic stress
- allows for trugor pressure to develop which is what lets water from soil come up into the plant tissues
- what is the structure of cell walls?
is made of three main compnents cellulose, liginin and hemicellulose.
- describe the parts of the cell wall: liginin, cellulose and hemicellulose
cellulose: the main component and is a polysachride made up of D-glucose units (B-1,4)
hemicellulose: is made up of different sugars with xylose and arabinose being the main ones ligin: is not a carbohydrate techinically but because of its close association with dietary fiber component it affects physiological effects and is therefore classified as a dietary fiber. It is a organic polymer of phenol sub units
- what does liginin do?
it acts as a binder of cellulose fibers to add strength and stiffness to the plant cell and will inhbit the cell wall digestion of polysachrides.
- whats special about the cell walls of cereals
have beta-D-glucans
- whats the function in food of cell walls?
- provide a barrier to cellular contents meaning there is a slow penetaration of water and therefore swelling of starch granules
- cell wall fragments absorb water and oil allowing food to be moist
- in whole grain bread the bran will disrupt gluten network making a more coarse product
- describe the role of cellulolytic microganisms.
These microgoranisms from bacteria and fungal produce enzymes which can degraded cellulose by hydrolysis either through aerobic degradtion which will produce cellobiase and glucose or by anaerobic degradation which will make glucose and cellodextrins. The fate of both of these products will be to go into fermantion. From aerobic conditions carbon dioxide, hydrogen and organic acids will be produced and from anaerobic conditions methane and carbon dioxide will be produced.
- explain how comerical cellulose is prepared
- hot sodium hydroxide an alkali treatment is used to extract cellulose from wood pulp
- further treatment is done to remover other polysachride s and liginin
- further purification is done by sodium hypochlorite
- how is the quality of cellulose measured?
by the amount of alpha cellulose which is insoluble in alkali solution, alpha is the purest form and you want more of it
- how is powdered cellulose obtained
purified cellulose is miled to reduce the size.
- what is the use of powdered celulose
large particles are used for providing bulk as they absorb more water and they are non-caloric
small particles are used for producing products with a smoother texture often added to cheese that is grated or shredded to prevent caking
- how is microcrystalinine cellulose made
it is made by partially depolymerizing cellulose through partial hydrolysis. Which will then be grinded to reduce paritcle size and purified.
- what are the functions of microcrystaline cellulose
- natural source of dietary fiber
- non-caloric bulking agent
- anti-caking agent
- emulsifer
- fat substitute
- what do both MCC and powdered cellulose have in common?
insoluble in water and does not gel
- what are the three substuations that can occur on modified cellulose?
- carboxymethylcellulose
- methylcellulose
- hydroxypropcellulose
- what is the theoritical range for degree of substituation and why
0-3 because there are only 3 available hydroxyl groups per monomer at position 2,3 and 6
- How do you calculate substitutions?
of substitutions over number of glucose units
- what is an ether molecule and are they in pectin or cellulose
ether is R-O-R which is in modified cellulose and pectin has esters
- what do the properties of cellulose derivatives depend on?
- degree of substituation so the amount of esterfication
- what the substituent group
- the average molecular weight of the derivatized cellulose molecules
- distrubtion of substieunt groups on 2,3 or 6th position
- distrubtion of the substient groups on the cellulose chain like if they are clustered or random
- describe the carboxymethyl cellulose (CMC)
It is produced by reacting cellulose with chloroacetic acid, introducing carboxymethyl groups into the cellulose chain. This modification significantly alters the properties of cellulose, making CMC soluble in both hot and cold water it has a DS of 0.7-0.8.
- The presence of carboxylate groups in CMC makes it anionic, which contributes to its effectiveness in stabilizing and thickening by repulsion between negatively charged groups along the polymer chain.
- describe what increases water solubility of CMC
decreased DP and increased carboxymethyl substitution
- describe the viscosity of CMC
is increased with increased DP and increased concentrations. It has thixotropic behaviour.
- how are the rheological propertiers of CMC affected by pH
at a pH between 3 adn 4 repulsion beyween the molecules will decrease because the hydrogen will remove the negative charge which caused repulsions which will allow for more assocations to be made and increase the viscosity
below 3 though percepitation of aggeration will hapen above 11 hydrolysis will happen and viscosity will decrease over time
- what are the functions of CMC
- thickeners
- protien stabilizer
- how are methylcellylose and hydroxypropylcellulose made and what is the result ?
methyl: by treating with methyl chloride creating methyl ether groups with a DS of 1.1-1.2
hydroxy: by treating with propylene oxide and methyl chlodride creating bulky hydrophobic side chains with a DS of 0.02-0.3
- Give the probable explanation for thermal gelation of HPMC (Hydroxypropyl methylcellulose) solutions
HPMC has hydrophobic (C-C-C) and hydrophilic regions (cellulose from OH). At lower tempertures the hydrophilic interactions dominate so it can dissolve in water but at certain temperature there are suffienct hydrophobic interactions that allow for crosslinks to form and a gel to form . Cooling will cause the reverse to happen and it will go back to liquid form
- describe the properties of MC and HPMC aka MC and how they are useful
- they disperse easily in cold water because they are fully soluble as the hydrophobic bulky sidechains prevent intermolecular associations which is useful for food products that are heated to prevent oil from entering deep fried layer. so they protect
- they are surfactants as they reduce the surface tensions bewteen two phases as either an emsulifer between oil and water and liquid and gas as a foaming agent.
- what are MCs used for?
- in bakery products because of film formation
- in deep fried foods to prevent oil absorbtion
- salad dressings as an emuslifer and stabilzer
- whipped toppings asa foam stabilzer
- what are emulsions
fine dispersion of minute droplets of one liquid which is not soluble in another
- how do substances like MC stabilze emuslifcation
- by thickening and therefore increasing the viscosity they will create kinetic stabilzation by slowing down the rate of collisions between droplets preventing coalescene
- by inhibiting coalescene by creating a protective coating on droplets
- what are foams
basically emulsions but it is an air bubble instead of an oil droplet that needs stabilzation
