Major components of grains Flashcards
What is starch? what polymers is starch comprised of?
A digestible polysaccharide composed of glucose molecules linked by α-glycosidic bonds
- amylose (linear) and amylopectin (branched) units
What is the significance of starch?
- Major source of energy in plant-based foods
- Used as a thickening, gelling, and stabilizing agent in food processing
List major sources of starch. where is starch stored in grains?
- Cereal grains (wheat, corn, rice, barley, oats)
- Legumes (peas, lentils, beans)
- Tubers & Roots (potatoes, cassava, yams)
-stored in the endosperm
In which part of the grain is starch stored for legumes and pulses?
The cotyledon
explain how the structure of grains impacts the access to starch.
the starch in grain is embedded in a complex matrix, with protein surrounding the starch
-this limits access of enzymes to breakdown starch
-heating + grinding exposes starch, imrpoving the ability for starch to be hydrolyzed
List food sources with high starch content.
- Corn (68-72%)
- Cassava (75-80%)
- Potato (75-78)
What type of carbohydrate is starch classified as?
A homopolysaccharide
-polysachharide of alpha-glucose units
what is an example of a hetero polysaccharide starch?
Gums
What are the major components of starch granules? what are some characteristics of each? (stability, gel texture, structure)
Major:
* Amylose (~20-30%)
-linear (alpha 1-4), unstable, hard gel texture (tighter packing)
* Amylopectin (~70-80%)
-branched (alpha 1-4/1-6) , stable, soft gel texture
What is the effect of higher amylose content in starch? what properties would this grain have? provide an example of rice that is high in amylose.
Long grain/fluffy rice (Indica)
-non-sticky texture
-retrodegradation leads to resistant starch = lower GI
What is the effect of higher amylopectin content in starch? what properties would this grain have? provide an example of rice that is high in amylose.
Short grain/sticky rice (japonica)
It provides a sticky texture.
-slow retrodegradation -> lower amounts of resistant starch -> higher GI
What are the types of starch based on amylose content? how much amylose does each contain?
- Waxy Starch (<10%)
- Regular Starch (18-25%)
- High-Amylose Starch (>40%)
What is a functional difference of waxy starches?
Good for thickening and stability in frozen foods
-form high viscous products
How does more branching in starch affect its functionality?
Increases viscosity & stability.
What is the impact of more linearity in starch on its properties?
Leads to stronger gels & lower glycemic index.
What is the process by which starch absorbs water and swells upon heating?
Starch gelatinization
This process is crucial for cooking and food preparation.
What are the two types of starch granules based on their structure?
A-type (cereal starch)
-larger, lentical shape
B-type (tuber starch) granules
-smaller, spherical
A-type granules are compact, while B-type granules are more open.
Explain the cluster model and the structure of amylopectin
amylopectin contains:
1) crystalline regions: high molecular order regions formed by double helices of amylopectin chains
2) amorphous regions: low molecular order regions of amylose and amylopectin chains
what bond stabilizes the ultra-structure of starch granules?
intermolecular H-bonds
What is the hierarchical structure of starch granules?
Granules, growth rings, clusters of semi-crystalline nano-blocklets, blocklets
This structure affects digestibility and functionality.
What part of teh starch granule is classified as resistant starch 2? what characteristic does this exhibit?
the highly packed crystalline regions
-they resist enzyme hydrolysis
-enzymes penetrate amorphous region first
what 3 forms is amylose found in?
1) free amylose (in amorphous region)
2) bound to lipids (amylose-lipid complex)
3) crystalized w amylopectin (co-crystalized regions)
-highly resistant to hydrolyzation
co-crystalized regions higher in higher amylose containing pulse, corn and barley starches
-> digested slowly
how is amylose content determined?
breaking down amylose into free amylose coils and using iodine to determine [amylose]
-free amylose binds to iodine forming a complex, which is measured by the intensity of blue colour
What are V-amylose crystals? what are they also classified as?
lipid-amylose complexes taht form crystalline structures
-classified as a resistant starch type 5 (RS5)
-highly resistant to amylase enzymes
These crystals are classified as Resistant Starch Type 5.
How does the amylose-lipid complex affect starch texture?
It changes conformation from linear to helical, reducing re-association and tight packing after baking
-production of amylose-lipid complex creates helical structure which results in a softer texture in foods
Is native starch soluble in water? why or why not?
It is not typically soluble in water due to tight packing of molecules
It is soluble in water if a lot of water and heat is provided
Heat is required to disrupt the granule for solubility.
What is Starch Gelation? what T does this occur?
A two-phase process involving gelatinization and retrogradation
Most starch gelatinizes below 90 oC
Gelatinization is heat-induced swelling and thickening, while retrogradation involves cooling and molecular re-association.
What 3 things occur during the gelatinization phase of starch?
1) granule swelling; water penetrates structure
2) Crystal / helix melting; expansion of water exerts presure on crystalline region, pulling it apart
3) amylose leaching
Amylose begins to leach out from granules.
What are the important functional properties of gelatinization?
Increases thickness and digestibility of starch
Important for sauces, gravies, and custards.
What happens during the retrogradation phase of starch?
Molecular reassociations occur (amylopectin/amylose) increasing firmness and causing syneresis
-after storage/cooling water is pushed out and interactions are stronger
Leads to formation of resistant starch (RS3).
Why are amorphous regions important in starch gelatinization?
They allow water to penetrate and hydrate starch molecules
-separates H-bonds
Water acts as a plasticizer, reducing intermolecular forces.
What is the significance of temperature in starch gelatinization?
Higher temperatures break crystalline structure completely; partial gelatinization occurs at lower temperatures (~65 degrees) and crystalline regions remain present
Different textures result from varying degrees of gelatinization.
What is Amylolysis?
Amylolysis refers to the enzymatic breakdown of starch into smaller carbohydrate molecules (dextrins, maltose, glucose)
This process is critical for digestion and industrial food applications, such as corn syrup production.
What are the 4 primary enzymes involved in starch hydrolysis? where do they work?
- Alpha-Amylase
-cleave 1-4 bonds within the molecule - Beta-Amylase
-cleaves 1-4 bonds from the end - Amyloglucosidase
-cleaves 1-4 and 1-6 from the end - Pullulanase
-cleaves 1-6
Each enzyme has a specific function in breaking down starch.
How does the structure of amylose affect its hydrolysis? how does this compare to amylopectin?
Amylose has a linear structure, making it easier to hydrolyze
In contrast, amylopectin is highly branched and harder to break down.
Where does amylase have a preference to hydrolyze? how does hydrolyzation of a native starch differ?
amylase preferentially hydrolyses the loosely packed amorphous regions
native starches take longer to hydrolyze due to tighter crystalline regions
-crystalline regions must be melted
What are the major sugars in corn syrup? how is it made?
Corn syrup is produced by hydrolyzing starch into glucose and maltose
It is used as a sweetener and thickener in processed foods.
What are the steps in the corn syrup production process?
- Liquefaction: Starch is gelatinized and partially hydrolyzed by alpha-amylase to make dextrins
- Saccharification: Dextrins are further hydrolyzed by glucoamylase, producing glucose, maltose, and maltotriose.
-breaking down complex sugars into simple sugars
Used in soft drinks and baked goods.
What is high-fructose corn syrup (HFCS)?
HFCS is produced by further processing corn syrup with glucose isomerase to convert glucose into fructose
Fructose is sweeter than glucose, allowing for less product use.
Why is liquefaction necessary in starch processing?
It prevents excessive swelling of starch making a thick slurry, keeping it fluid
This is important in industrial food production.
What role does starch play in food applications?
1) retorting of soups
-high T sterilization
2) sauces / salad dressings
-adds texture / stability
3) starch based desserts
- prevents synerisis
What is the function of pre-gelatinized starches in microwavable pies?
To create a stable structure and prevent moisture migration when heated
-starch coats it to protect migration of liquid
How does starch help in breaded food products?
It binds breadcrumbs to food surfaces and improves adhesion so it doesnt fall off during transport
What are microencapsulated flavors used for?
To protect sensitive flavors from degradation and spoilage
What are 5 functional properties of food starch?
1) Thermal stability
2) shear stability
3) freeze-thaw & gel stability (prevention of synerisis)
4) acid stability
5) cold solubility
what are 2 common chemical modifications of starch? why are they done?
cross linking: creation of covalent bonds between starch molecule to increase stability under heat, shear and acidic conditions
substitution: addition of chemical groups to alter starch properties, creating a more flexible / adaptable structure
-alters freeze/thaw stability, cold water solubility and texture
What is resistant starch?
Starch that resists digestion in the small intestine and ferments in the colon
-acts like fiber
How is rapidly digestible, slowly digestible, very slow digestible, and resistant starch distinct? what is classified by?
RD: < 20 min
SD: 20min - 2hr
VS: 2-16hr
RS: >16hr
digetsibility classification is based on how fast the sugar is released from the starch
What is RS1? where is it found? how does it work?
Physically trapped starch
-native starch or minimally processed grains, seeds, and legumes
-slowly, but fully digested
-limited acessibility by enzymes
What is RS2? Where is RS2 commonly present? how does it act?
Amylopectin in crystals are slowly but fully digested in native and retrograded starch
-found in minimally cooked food
-can be melted by heat
What is RS3? Where is RS3 commonly present? how does it act?
Amylose crystalline regions are tightly packed and are indigestible in retrograded starch
-enzymes can’t access glycosidic bonds
-considered insoluble dietary fiber (fermented in the colon)
What is RS4? Where is RS4 commonly present? how does it act?
Chemically (cross link / substitution) and enzymatically modified starch
-modified starches
-considered soluble dietary fiber
where does fermentation occur for resistant starch?
the colon (large intestine)
What are the health benefits of resistant starch?
- Produces short-chain fatty acids (SCFAs)
- Improves gut health
- Lowers cholesterol
- May act as a prebiotic.
What are low-glycemic ingredients derived from starch?
- Polydextrose
- Isomaltose
- Isomaltooligosaccharides (IMO).
