Sugars tend to retard gel formation and retrogradation
How do sugars retard gel formationa and retrogradation?
They compete for available water and interfere with starch-starch hydrogen bonding
How do surface active agents affect gel formation?
Surface active agents tend to inhibit retrogradation and gelation
How do molecular inclusions affect gelation?
It has been suggested that molecular inclusions similar to iodine within the polymer helix are formed with surfactants and that this affects the ability of amylose to associate with its comanio macromolecules
What is the pH of most foods?
The pH of most foods lie in the range of 4-7
Why does pH have only minor effects on starches?
pH has only minor effects on starches as they are uncharged polymers
What happens to highly acidic foods when heated or storef dor etensive periods of time?
In highly acidic foods, particulary when heated or stored for extensive periods of time there can be reduction in viscosity due to acid hydrolysis of starch
How does thermal processing affect the final viscosity?
Thermal processing can affect the final viscosity (hydrolysis) by magnifying the effects of pH
Why does ionic strength have only a minor effect on gelation?
Like pH, ionic strength has only minor effects as most starch have no ionizable groups
How do proteins affect gelation?
Proteins are capable of dramatically changing how a starch behaves in terms of gelation and viscosity
What reaction involving proteins and starch is well known?
The interaction of starch with milk proteins is well known, producing a smooth gel known as pudding
Which properties of starch can be significantly changed in the presence of protein?
The viscometric behavior of starch and end product texture and organoleptic properties can be changed significantly in the presence of proteins
Why is the specific behavior of starch in food systems hard to predict?
The specific beavior of starch is hard to predicvt in complex food systems as it depends on many factors- usually determined out by product formulation testing
At which temperature do most starches gelatinize?
Most starch gelatinize around 60°-70°C
At which temperatures do high amylose starches (>55%) gelatinize?
High amylose starchses may take temperatures of 100-110°C to gelatinize
What is a desirable property of high amylose starches?
Such starches have good film forming properties and can be used to prodeuce biodegradable packaging materials or packages which are readily water soluble
Where is most of our starch in North America drived from?
In North America most of our starch is derived from corn (some wheat, little pea)
Why are starches modified?
Starches can be modified to provide very specific properties which provide unique functionalities that food processor require
What are preglatinized starches?
Starch granules are heated just below their gelatinization temperature causing them to swell- they are then drum dried
What does pregelatinization of starches cause?
Cuases some disorganization of the starch granule
Makes it cold water dispersible
Allows the developement of viscosity without requiring as much heating or time
What is the downside of pregelatinized starches
One requries more pregelatinized starch than regular sarch to attains imilar viscosity effects
What is one application of pregelatinized starches?
Instant gravy mix
What is another term for acid modified starches?
Commonly termed 'thin boiling starches'
How is acid modified starch formed?
Holding starch just below its gelatinization temperature in an acidic medium
What is the acid used for in acid modified starches?
Acid is used to partially and randomly hydrolysed the glycosidic linkages within the starch granule without destroying the integrity of the granule per se- neutralize and dry
Where are thin boiling starches used?
Thin boiling starches are used in candy manugfacture- are easy to handle, low viscosity fluids which set into a firm gel upon cooling (starch gum candies- turkish delight, jujubes)
What do cross-linked starches result in?
Maximym viscosity is normally reached when the starch granules are swollen extensively but still intact-- however, normally they rbeak down with subsequent shear
How are starch granules held together?
One can hold starch granules together by crosslinking starch chemically so that the swollen granule retains its integrity rather than disintegrating into a colloidal solution
What are typically used as crosslinking agents?
Acetic, citric or adipic anhydrides
What is the net result of crosslinking starches?
The net result is a starch granule which will swell somewhat less, but will mainain its structural integrity
What are crosslinked starches less susceptible to?
Cross-linked starches are less susceptible to acid hydrolysis as the crosslinks make up for some of the bonds broken by the action of acid
What are starch derivatives used to control?
Improve freeze/thaw stability
Reduce textural and opacity changes
What is the overall objective of starch derivatives?
To reduce inter polymer hydrogen bonding via introduction of charged groups or by bulky groups to cause steric hinderance
How are orthophosphate groups used to creat starch derivatives?
These are charged and will repel like charged polymers as long as the pH is not too close to the polymer isoelectric point
What are some common derivatizations?
What is etherification?
Introduction of hydroxylpropyl groups into the starch granule
How does steric hinderance effect starch derivatives?
Steric hindernce prevents the polymers from associating as readily as in natural starch
What is an examply of a specialty derivative of starch?
Starch can have substantive hydrophobic side chains (C16-C18) introduced to enable them to be used as emulsifiers and/or emulsion stabilizers
How are starches oxidized?
Can use sodium hypochlorite (NaOCl) to oxidize a portion of the hydroxyl groups into carboxyl groups
Some aldehyde and ketone groups may also be introduced
What happens when starches are oxidized?
Starch becomesx a charged molecule and its solubility is pH dependent like phosphorylated starches
What happens when COOH is introduced onto a starch molecule?
COOH introduction stabilizes the molecule to retrogradatio but it now becomes susceptible ot pHa nd ionic variations in food products
What are the 2 basic starch conversion categories?
Dry starch pyroconversio- roasting
Wet starch conversion- acid and enzymativ hydorlysis of starch
What is dry starch pyroconversion?
For the proeduction of cold water soluble starchs- also known as 'roasted' starches
What is wet starch conersion?
Acid and enzymatic hydrolysis of starh
Wet conversion for the production of dextrins or as a perliminary step to the production of sweeteners from starch
What is the general concept of pyroconversion?
Starch granules are sprayed with dilute HCl and subjected to a relatively high temperatures
What are the key reactions in pyroconversion?
Random hydrolysis of the alpha 1,4 and 1,6 linkages
Repolymerization- any free sugars produced can repolymerize
Caramellization reactions can take place with free sugars formed with color development ensuing
What is transglucosidation?
The breaking of alpha 1,4 and the reformation of other linkages, generally random in nature ix. 1,3 or 1,5 etc
What are the three general types of roasted starch products?
How are white dextrins produced?
Produced under conditions of high moisture, high acid and relatively low temperature- hydrolysis reaction predominates
What is the main property of white dextrins?
Cold water soluble
How are yellow dextrins produced?
The conditions are lower mositure, moderate levels of acid and higher temperatures
How does the yellow color in yellow dextrins develop?
Yellow color develops due to non-enzymatic browning (caramellization) as a result of free sugars released and reacting at higher temperatures
How are british gums produced?
Low moisture- little or no acid used with higher temperatures
Why are british gums dark in color?
Acid is a catalyst and high temperatures promote extensive more caramellization- gums are dark in color with little hydrolysis and much more transglucosidation (crosslinking)
When are british gums used an why?
Used extensively in candy manufacutre- this type of product is much more viscous and capable of forming a stiff gel
What is starch an indirect source of?
How is wet starch conversion done?
The starting point gelatinizing the starch, followed by hydrolysis using a combination of high pressure steam and hydrochloric acid
Under these conditions hydrolysis is extensive and random producing both dextrins and sugars
What is gained from controlling wet starch conversions?
By controlling this process, the extent of hydrolysis can be manipulated to produce syrups having a range of viscosities and sweetnesses (inversely proportional to each other)
Why are there limitations on the degree of starch conversion?
Acid hydrolysis can come to equilibrium and there are limits on the degree of starch conversion attainable and hence a limit to the sweetness attainable
How can the degree of starch breakdown be followed?
The degree of starch breakdown can be followed by measuring the reducing sugar content of the hydrolysate (Fehling's test)
How is reducing sugar content expressed?
Reducing sugar content is expressed in terms of dextrose equivalents or DE
What makes reducing sugar content increase?
Reducing sugar content increases with hydrolysis as mono, di and oligosaccharides are produced
What is dextrose equivalents?
The DE is the ratio of the reducing power (RP) per gram of the converted syrup relative to an equivalent weight of pure dextrose
DE = [(RP/g of syrup)/(RP/g Dextrose)]*(100)
What does a DE of 100 mean?
The hydrolysis of starch is 100% complete
Why can acid hydrolysis generally not reach beyond a DE of 50?
Acid hydrolysis generally cannot yield dfextrose equivalents much beyond DE=50 as equilibrium is reached, leading to re-polymerization
How does one attain syrups with a DE>50?
To obtain syrups which are >50% glucose, enzymatic conversion is required
Why does gelatinization precede any enzymatic conversion?
Starch gelatinization precedes any enzymatic conversion process to facilitate enzymativ access to the substrate
Which enzymes are capable of hydrolyzing starch?
The enzymes which are capable of hydrolyzing starch are commonly termed 'amylases' and these enzymes are found in most living systems
How do we attain amylases commercially?
Commercially we now tend to obtain these enzymes from microorganisms
What is alpha-amylase?
An endoenzyme- can attack alpha-1,4 glycosidic linkages anywhere within the starch molecule but not the alpha-1,6 branch point
What is alpha-amylase also known as?
alpha-amylase is also known as a liquifying enzyme- characteristically adding this emzyme causes a rapid loss in viscosity in a gelatinized starcch solution
Why does alpha-amylase result in a rapid loss in viscosity in a gelatinized starch solution?
This is due to the random internal bond breakage rapidly reducing the overall molecular weight of starch
What is the end product after adding alpha-amylase to a gelatinized starch solution?
End products- largely oligosaccharides, some glucose, maltose and pannose (a trisaccharide contain the alpha 1.6 branching linkage)
What is beta-amylase?
Exoenzyme which attacks the non-reducing end of the starch chain knocking off 2 glucose units at a time
What does beta-amylase produce?
Produces maltose by hydrolysing the alpha-1,4 glycosidic bond every two glcose units over
What is beta-emylase commonly known as?
Commonly knwon as saccarifying enzyme as its use only develops sweetness rapidly, but viscosity does not change significantly
What are glucoamylases?
Can remove single glucose units from the non-reducing end of starch as weel as split maltose into two glucose units
What is the end product of glucoamylases?
Produces glucose, which is much sweeter than maltose
What is the result of the combined action of alpha and beta amylase as well as glucoamylase?
Combined action of alpha and beta amylase as well as glucoamylase leaves mainly 'limit dextrins'- largely made up of the trisaccharide- pannose
What is pullulanase?
This enzyme specifically hydrolysise alpha-1,6 glycosidic linkages
How does pullulanase work?
Attacks the branch points so that the trisaccharide pannose can be broken down to glucose plus maltose
What is the combination of the 4 basic enyzmes used for? (alpha-amylase, beta-amylase, glucoamylase, pullulanase)
The combination of these four basic enzyme provides a means of converting starch to predominantly D-glucose (dextrose)
What is the net result of using all four enzymes?
Net result one can produce syrups which have a DE>90 (predominantly glucose)
What is a benefit of obtaining a DE>90?
At DE>90, glucose can be crystallized out of solution and obtained in pure form in a manner very similar to sucrose refining