MODIFIED STARCH-Applications | Focus
THE APPLICATION OF MODIFIED STARCH
The basic structure of starch is a polymer polysaccharide formed by glucose units connected by α-1,4-glycosidic bonds (amylose) and α-1,6-glycosidic bonds (amylopectin). Its molecules contain a large amount of hydroxyl groups. Modified starch is a starch derivative obtained after the modification of natural starch through the comprehensive application of physical, chemical and biological enzymatic methods. Compared with raw starch, its physicochemical properties, such as solubility, viscosity, stability, film-forming, etc.), are significantly optimized, so as to meet more complex industrial or food needs. Physical modification of starch refers to the modification of starch by physical means such as heat, mechanical force, and physical field, to destroy the crystal structure, amorphous region, molecular arrangement or intermolecular hydrogen bonds of starch particles, and achieve structural remodeling. The main means include hydrothermal fluid, microwave, ionizing radiation, ultrasound, ball milling, extrusion, etc. Microwave treatment is widely used in the food industry to prepare starch grafted copolymer superabsorbent resin with strong water absorption and water retention.
HEAT TREATMENT MODIFICATION
By controlling temperature, moisture, and time, the gelatinization, regeneration, or molecular rearrangement of starch particles are regulated, and common methods include pre-gelatinization, annealing, and moist heat treatment.
(1) Pregelatinized Starch
Process: The starch is dispersed in cold or hot water, heated to a gelatinization temperature (usually 60-90°C) to make the particles completely gelatinized, and then dehydrated and dried to obtain a non-granular, cold-water-soluble starch product.
Mechanism: Heating makes the starch particles absorb water and expand, the crystal structure is destroyed, the molecular chains unfold and intertwine to form a three-dimensional network, and the network structure is "fixed" after drying, and the water is quickly rehydrated to form a paste when used.
Characteristic changes: high solubility in cold water, gelatinization temperature close to room temperature, medium transparency of paste, but lower viscosity and gel strength than raw starch.
Application: Convenience food (such as instant noodle seasoning packs, instant soup ingredients), paper sizing agents, textile sizing agents (simplified process).
(2) Annealing
Process: Starch is kept warm in warm water higher than the glass transition temperature but lower than the gelatinization temperature for several hours to tens of hours, and the moisture content (30%-50%) is controlled.
Mechanism: In the subgelatinized state, amylose molecules migrate from the amorphous region to the crystallization zone, promoting short-range orderly rearrangement and enhancing the stability of the crystallization zone.
Characteristic changes: the starting temperature of gelatinization increases, the thermal stability of the paste increases, and the hardness of the gel increases, but the solubility decreases slightly.
Applications: Foods that require high-temperature processing (e.g., aseptic packaged foods) or products that require increased gel strength (jelly, meat products).
(3) Hydrothermal Treatment (Ht)
Process: Adjust the dried starch to more than 30% moisture content, then heat it to 80-120°C, keep warm for a few hours and then dry.
Mechanism: Under high moisture, the starch particles absorb water and expand, partially destroy the crystal structure, and then the molecular chains are rearranged during drying to form denser amorphous regions or new crystalline structures, while inhibiting the exposure of enzymatic hydrolysis sites.
Characteristic changes: gelatinization temperature increases, paste viscosity decreases, digestibility enhances (more resistant starch RS3 is generated), and solubility depends on treatment intensity (moderate treatment increases solubility, excessive treatment decreases).
Applications: Low GI foods (e.g., resistant starch bread, breakfast cereals), feed (improve nutrient utilization), bioethanol fermentation (reduce energy consumption for enzymatic hydrolysis).
MECHANICAL TREATMENT MODIFICATION
Through mechanical shearing, extrusion or grinding, the starch particle structure is destroyed and the molecular chain is refined, and common methods include extrusion and extrusion, ball milling and grinding, and ultrasound-assisted mechanical treatment.
(1) Extrusion Modification
Process: After the starch is mixed with a small amount of moisture (10%-30%) and possible additives, it is treated by a screw extruder at high temperature (120-200°C), high pressure (5-20 MPa) and high shear force, and the material is sprayed from the die to reduce pressure and expand to form a porous structure.
Mechanism: High-pressure shear force destroys the crystallization and amorphous regions of starch particles, the molecular chain breaks and reorients, and the high temperature promotes the breakage of intermolecular hydrogen bonds, forming a loose porous network structure.
Characteristic changes: the expansion rate can reach 5-20 times, the solubility is greatly increased, the solubility of cold water is reduced, the gelatinization temperature is reduced, the thermal stability is improved, and the porous structure buffers thermal decomposition, but the molecular weight decreases.
Application: Puffed food (such as corn on the cob, rice crackers), pet food, biodegradable materials (porous starch adsorbent).
(2) Ball Milling
Process: The starch and grinding balls are ground at low speed in the ball mill for several hours to tens of small sizes), and the refinement is achieved through the collision and friction between the balls and starch particles.
Mechanism: Mechanical forces break starch particles into nano/micron-scale fragments, the crystal structure is completely destroyed, and the molecular chain breaks and more hydroxyl groups are exposed.
Characteristic changes: particle size decreases, specific surface area increases, solubility is extremely high (nanoscale starch can form hyaglocolloid), gelatinization rate is accelerated, but gel strength decreases.
Applications: Nanocomposites, such as starch/polymer nanoparticles, drug carriers, high specific surface area adsorption drugs, degradable plastic fillers.
(3) Ultrasound-Assisted Mechanical Treatment
Process: The starch suspension is placed in an ultrasonic generator, and the cavitation effect of ultrasound assists mechanical shear to destroy the particle structure.
Mechanism: The local high pressure and shear force generated by the rupture of cavitation bubbles accelerate the depolymerization of starch particles and molecular chain breakage, while the thermal effect of ultrasound promotes molecular movement.
Characteristic changes: shortening of gelatinization time (cavitation effect destroying the crystallization area), improvement of paste stability (shorter molecular chain, not easy to regenerate), and increase solubility.
Applications: Rapid gelatinization of starch (e.g., instant labeling adhesive), biodiesel production (improving the efficiency of starch conversion to glucose).
PHYSICS PROCESSING MODIFICATION
Using electromagnetic waves, radiation and other physical field energies to induce changes in the structure of starch molecules, common methods include microwave treatment and irradiation treatment (γ rays, electron beams).
(1) Microwave Treatment
Process: Mix starch with water (moisture 20%-50%), heat it in the microwave oven for several minutes to tens of minutes, and gelatinize the starch and reshape the structure through the internal heating effect of the microwave.
Mechanism: Microwave penetrates starch particles, causing polar molecules (water, hydroxyl groups) to vibrate and generate heat at high frequency, and the rapid internal heating leads to instant expansion of particles, destruction of crystal structure, and breakage of molecular chains.
Characteristic changes: very short gelatinization time (minutes vs. tens of minutes of conventional heating), low viscosity of paste (molecular chain breaking), and improved thermal stability (uniform microwave heating reduces local superheat degradation).
Application: Industrial rapid pregelatinized starch production, sewage treatment (microwave modified starch adsorption of heavy metal ions).
(2) Irradiation Treatment
Process: Dry starch is irradiated under γ rays or electron beams to break molecular bonds through ionizing radiation.
Mechanism: Radiation energy excites electrons in starch molecules and produces free radicals (such as · OH、· H), which initiates molecular chain breaks (glycosidic bonds, C-C bonds) and hydroxyl oxidation, while inhibiting microbial growth.
Characteristic changes: reduced molecular weight (reduced gelatinization temperature), increased solubility, increased clarity of paste, low dose irradiation can delay regeneration (extend food shelf life), high dose leads to excessive degradation.
Applications: Food preservation (irradiated modified starch as a coating, inhibiting water migration), medical dressing (irradiated starch film, antibacterial and degradable).
CHEMICAL MODIFICATION OF STARCH
The Chemical Modification Of Starch Includes Acid Hydrolysis, Oxidation, Etherification, Esterification And Cross-Linking, Which Is The Most Widely Used Method Of Starch Modification.
ACID HYDROLYSIS STARCH
In The Process Of Acid Hydrolysis, the gelatinization temperature decreases at the initial stage, the hydrolysis temperature increases at the peak of hydrolysis and the final stage, and the endothermic value increases first and then decreases with acid hydrolysis, and the swelling force and solubility increase. Chemical modification of starch by acid hydrolysis is the process of degrading high molecular weight starch into low molecular weight products (such as dextrin, oligosaccharides or monosaccharides) by breaking the glycosidic bonds of starch molecules by acids. By reducing the molecular weight and polymerization of starch, its physicochemical properties are significantly changed, so as to obtain specific functions (e.g., low viscosity, high solubility, good transparency, etc.).
REACTION MECHANISM OF ACID HYDROLYSIS MODIFICATION
Starch is a polymer polysaccharide formed by glucose units connected by α-1,4-glycosidic bonds (amylose backbone) and α-1,6-glycosidic bonds (amylopectin branch points), and the core of acid hydrolysis is the catalytic breaking of glycosidic bonds by acids, the specific process is as follows:
Protonation: The acid provides H⁺, which binds to the oxygen atoms in the starch molecule (oxygen or hydroxyoxygen with glycosidic bonds), protonating it and weakening the stability of the glycosidic bonds.
Glycosidic bond breakage: The protonated glycosidic bond is hetero-cleaved to form an oxygallium ion intermediate, which is subsequently hydrolyzed into low molecular weight dextrin, maltose, or glucose.
Hydrolysis differences of amylopectin: The bond energy of α-1,6-glycosidic bonds is higher than that of α-1,4-glycosidic bonds, so the branching points of amylopectin break more slowly during acid hydrolysis, and the final product may retain some short branched chain structures.
CHANGES IN THE PROPERTIES OF ACID-HYDROLYZED STARCH
Compared with raw starch, the physical and chemical properties of acid hydrolyzed starch are significantly changed due to the decrease of molecular weight, mainly manifested as:
Reduced molecular weight and polymerization
Glycosidic bond breakage caused starch molecules to change from long to short chains, reducing the degree of polymerization by 50%-90%.
Viscosity drops significantly
The molecular chains became shorter, the intermolecular winding and hydrogen bonding were weakened, the initial viscosity of the paste was significantly reduced, and the viscosity stability was improved at high temperature
Improved solubility
The low molecular weight products reduce intermolecular aggregation, increase the solubility of cold water, and improve the clarity of the paste.
The gelatinization temperature is reduced
The crystalline structure of starch particles is destroyed by acid (especially the ordered structure of amylose starch), and the energy required for gelatinization is reduced, and the gelatinization temperature is reduced
(The gelatinization temperature of raw corn starch is 62-72 °C, and it can be reduced to 55-65 °C after hydrolysis).
Film formation and adhesion adjustment
Lightly hydrolyzed starch still retains a certain degree of cohesion, which is suitable for papermaking sizing or textile sizing; Deep hydrolysis reduces adhesion but forms a more uniform film(e.g. for food coating).
Improved digestion
With a decrease in molecular weight, acid-hydrolyzed starch is more easily hydrolyzed by amylase and has an increased digestion rate (e.g., as used as a source of easily digestible carbohydrates in baby food)
ETHERIFICATION STARCH
1. Starch Hydroxypropylation is a form of starch etherification, hydroxypropylated starch can reduce the degradation of starch, change the gelatinization temperature, viscosity and other characteristics of starch. After the hydroxypropyl modification of starch, the free expansion ability and molar substitution degree of starch were improved, and the turbidity, dehydration shrinkage percentage and degradation rate were reduced. Starch hydroxypropylation is the process of introducing hydroxypropyl (-O-CH₂-CHOH-CH₃) into starch molecules through etherification reaction, which is a nonionic etherification modification. The modification changed the intermolecular forces and hydrophilic balance of starch by introducing hydrophilic ether bonds, significantly improving its solubility, stability and functional diversity. Hydroxypropylated starch is widely used in food, medicine, papermaking and other fields due to its high safety and excellent performance.
Reaction Mechanism Of Hydroxypropylation：
Under alkaline conditions (e.g., NaOH), starch hydroxy deprotons form alkoxy anions (-O⁻), enhancing nucleophilicity. Alkoxy anions attack the carbon atoms of propylene oxide, causing the epoxy ring to rupture, forming intermediate products. After hydrolysis, starch hydroxypropyl ether is finally formed
Changes in the properties of hydroxypropylated starch：
Compared with nonionic etherification (such as methylation), the hydrophilic steric hindrance effect of hydroxypropyl groups confers unique properties to starch, with the following core changes:
Solubility And Gelatinization Properties
The solubility of cold water is significantly improved: the ether bond (-O-) of hydroxypropyl group forms hydrogen bonds with water molecules, and the hydrogen bond between starch molecules is weakened by steric hindrance, so that starch is rapidly dispersed and dissolved in cold water.
Gelatinization temperature reduction: hydroxypropyl destroys the crystallization structure of starch particles and reduces gelatinization resistance
(The gelatinization temperature of the original starch is 60-80°C, and it is reduced to 50-70°C after hydroxypropylation).
Paste Stability And Anti-Regeneration
Excellent freeze-thaw stability: the steric hindrance of hydroxypropyl prevents starch molecules from rearranging and crystallizing during freezing-thawing, and the paste remains clear after 3-5 freeze-thaw cycles (-20°C/25°C), without water separation (better than raw starch and acetate starch).
Low regeneration tendency: hydroxypropyl groups hinder the spiral aggregation between amylose molecules, and the viscosity of the paste decreases slowly during storage
(suitable for long-term storage of food or coatings).
Low initial viscosity: hydroxypropyl reduces the intermolecular force, and the initial viscosity of the paste is lower than that of the original starch, but the viscosity stability is improved at high temperature (it is not easy to reduce viscosity due to shear or heating).
Good film-forming flexibility: The hydrophilicity of hydroxypropyl makes the film not easy to break after absorbing water, and the film is transparent and resistant to folding (used for packaging film or textile sizing).
2. Cationic Starch is a quaternary ammonium group (-NR₄⁺) with a positive charge on the hydroxyl group (-OH) of starch molecules through quaternization reaction to form cationic starch ether, which gives the starch a positive charge, so that it can electrostatically attract with negatively charged substances, and significantly improve its flocculation, enhancement and retention properties. Cationic starch has become a core additive in papermaking, sewage treatment, oil drilling and other industries due to its high efficiency, easy degradation and low cost.
The reaction mechanism of cationization
The starch hydroxyl group (-OH) reacts with an alkylation reagent containing a quaternary ammonium group to form a covalently bonded quaternary ammonium ether
Paper industry: wet additives to improve fiber/filler retention and enhance paper dry/wet strength, surface sizing agents
Sewage treatment: sludge dehydration flocculant: remove anionic pollutants: adsorption dyes, heavy metal complexes
Oil drilling: filtration loss reduction agent, cationic starch adsorbs the clay of the well wall and reduces filtrate intrusion
Leak plugging material: compounded with calcium carbonate to seal microcracks
Textiles & Daily Chemicals: Shampoo thickener: Cationic properties adsorb the surface of the hair, giving it a feeling of softness (instead of quaternary ammonium cationic surfactant)
OXIDIZED STARCH
The hydroxyl group in primary starch is the main site of oxidation reaction. Oxidative modification attacks the hydroxyl or glycosidic bonds of starch molecules through oxidants, triggering two types of reactions:
Hydroxyl oxidation: The hydroxyl group is oxidized to carbonyl (aldehyde, ketone) or carboxyl (-COOH), which reduces the intermolecular hydrogen bonding and improves the solubility and reactivity of starch.
Glycosidic bond breaking: The oxidant attacks the glycosidic bonds, causing the molecular chain of starch to break, resulting in low molecular weight products such as dextrins, which reduce the molecular weight and viscosity of the starch.
Compared With The Original Starch, The Physicochemical Properties Of Oxidized Starch Are Significantly Changed:
Improved solubility: hydroxyl groups are oxidized to carboxyl/carbonyl groups, weakening intermolecular hydrogen bonds, and increasing solubility in cold water (especially amylopectin).
Reduced gelatinization temperature: Molecular chain breakage and hydroxyl group reduction reduce the crystallinity and expansion resistance of starch particles, making gelatinization easier.
Enhanced paste stability: Low molecular weight products reduce regeneration (aging), and the paste is clearer and less prone to delamination
(If used in food sauces, the shelf life can be extended)
Reduced viscosity: The molecular weight decreases due to the breakage of glycosidic bonds, and the initial viscosity of the paste decreases, but the viscosity stability is improved at high temperatures (suitable for paper sizing).
Improved film formation: The presence of carboxyl groups enhances intermolecular forces, resulting in more uniform and flexible film formation (for packaging or textile sizing).
CROSS-LINKING STARCH
Cross-linking is often used to modify natural starch, especially for the production of low-water sensitive materials. esterification imparts hydrophobicity to starch products through hydroxyl substitution, crosslinking is to increase intramolecular and intermolecular connections at random positions in starch particles, and crosslinking can also be used to limit water absorption due to the ability to increase the density of crosslinking in the starch structure.
Crosslinking modification is the formation of covalent bonds ("molecular bridges") between the hydroxyl (-OH) groups of starch molecules through bifunctional or multifunctional crosslinkers, linking multiple starch molecules into a three-dimensional reticule. The core goal is to enhance the structural stability of starch particles, inhibit particle rupture during gelatinization, and improve the shear resistance, temperature resistance, acid and alkali resistance of the paste.
Reaction mechanism
Starch molecules contain a large amount of hydroxyl (-OH), and the crosslinker reacts with the hydroxyl group in two ways to form a bridge bond:
Single crosslinking: the two active groups of the crosslinker react with the hydroxyl groups of the two starch molecules (e.g., phosphate binding to the two hydroxyl groups at the C6 position);
Double crosslinking: Multiple active groups of the crosslinker react with different hydroxyl groups of the same starch molecule
(e.g., epichlorohydrin binds to hydroxyl groups at the C2 and C3 positions of the same molecule, or reacts with hydroxyl groups of two different starch molecules (forming intermolecular bridges)
·
Typical reaction examples (sodium trimetaphosphate crosslinking):
The starch hydroxyl group (-OH) deprotonates under alkaline conditions to form an alkoxy negative ion (-O⁻), attacks the phosphorus atom of sodium trimetaphosphate ((NaPO₃)₃), and forms a phosphate ester bond (-O-PO₂⁻-O-) after deprotonation under alkaline conditions, connecting the two starch molecules.
Significantly improved shear resistance: the paste maintains a high viscosity
(textile sizing to avoid slurry loss)
Thermal stability enhanced: The gelatinization temperature increased
(60-80°C for raw starch, 70-95°C after cross-linking), and the paste was not easy to decompose at high temperature(Suitable for canned food sterilization at high temperature)
Good acid and alkali resistance: the paste is stable in the pH range of 2-12
(Different from raw starch, which is easy to reduce viscosity in strong acids/alkalis), and can be used in acidic beverages(juice) or alkaline detergent additives
Particle morphology retention: Some intact particles are still retained after gelatinization, and the transparency of the paste is high
(Used for papermaking coatings to improve paper smoothness)
ESTERIFICATION MODIFICATION STARCH
Esterification modification involves the reaction of acid/acid anhydride/acyl chloride with starch hydroxyl groups to introduce ester groups (-COOR, -PO₃R₂, etc.) into starch molecules to change their hydrophilicity, hydrophobicity, charge and reactivity. Acetylation modification of starch is to introduce an acetyl group (-COCH₃) to the hydroxyl group (-OH) of the starch molecule through an esterification reaction to form starch acetate. This is a typical non-ionic esterification modification that regulates the hydrophilicity, hydrophobicity, charge and intermolecular force of starch through the introduction of acetyl groups, thereby significantly improving its functional properties (such as emulsification, stability, and anti-aging properties). Acetylated starch is widely used in food, papermaking, textile and other fields due to its high safety and excellent performance. The glucose unit in the starch molecule is rich in hydroxyl groups (-OH). The essence of the acetylation reaction is the esterification reaction of acid anhydride and alcohol.
The Introduction Of Ester Groups Gives Starch a Unique Hydrophobic Balance And Functionality
Acetate starch: lowers the gelatinization temperature (original starch 60-80°C, 50-70°C after acetate esterification), high transparency of the paste; strong aging resistance (inhibits amylose retrogradation), used in ice cream and quick-frozen dumplings to prevent storage from hardening; good emulsification, can be used as an emulsifier to stabilize food emulsions (such as juice drinks). Acetylated starch increases hardness without significantly affecting cohesion value, and it can partially replace low-protein wheat flour used in the production of instant noodles, reducing fat intake.
Phosphate starch: Strongly hydrophilic (phosphate groups form hydrogen bonds with water molecules), paste viscosity is high and stable, used in papermaking coatings (to improve pigment retention), anionic properties (phosphates are negatively charged), can be used in conjunction with cationic additives (such as quaternary ammonium salts), and can be used as flocculants in sewage treatment. Food-grade phosphate starch is non-toxic and can be used as a thickener for baby food (such as rice flour, fruit puree)
Starch stearate: The hydrophobicity is significantly improved and can be used to prepare degradable hydrophobic films (such as packaging materials) or sustained-release drug carriers (drugs are wrapped inside starch granules and released slowly)
Octenyl Succinic Anhydride Modified Starch Sodium Salt (OSA starch for short) is a non-ionic surface-active modified starch produced by introducing octenyl succinic anhydride (OSA) groups into starch through an esterification reaction. Its core is that under alkaline conditions, the starch hydroxyl group reacts with the anhydride group of OSA to form starch octenyl succinate, which is then neutralized into a sodium salt. Interfacial activity and emulsification Low critical micelle concentration (CMC),
High emulsifying ability: (salad dressing, coffee mate, emulsion stability).
Resistant to electrolytes (NaCl ≤ 5%) and freeze-thaw cycles (-20℃/25℃ three times without demulsification).
Hydrophobic-hydrophilic balance (HLB value adjustable) suitable for O/W emulsification (such as milk, flavored milk)
Double bond oxidative cross-linking: After hydrogen peroxide treatment, the double bonds form epoxy groups and the gel strength is improved (used for imitation cream coating).
In food: emulsified flavors, beverage emulsions, infant formula, baked goods.
In cosmetics: cream emulsifier, drug [capsule] carrier
Textile printing, emulsifier in industrial crude oil
ENZYMATIC TREATMENT OF STARCH
Biomodification is enzymatic treatment of starch, such as cyclodextrin, maltodextrin, amylose, etc., which are all modified starches obtained by enzymatic treatment.
Enzymatic modification of starch uses the catalytic effect of biological enzymes to accurately cut or reconstruct the glycosidic bonds of starch molecules through reactions such as hydrolysis, transglycosylation or debranching, thereby changing its molecular structure (such as molecular weight, degree of branching, number of reducing ends, etc.), and ultimately regulating its physical and chemical properties (such as solubility, gelatinization characteristics, digestibility, viscosity, etc.). Compared with traditional chemical modification, enzyme treatment has the advantages of mild conditions (normal temperature and pressure, neutral pH), high specificity, few by-products, and green and environmental protection. It is an important direction in the current deep processing of starch.
1. Solubility and gelatinization properties
Low molecular dextrin: Soluble in cold water, the gelatinization temperature is lowered (the molecular chain is short and it is easy to absorb water and swell).
Amylose: medium solubility (amylose is easy to aggregate), gelatinization temperature increases (linear intermolecular hydrogen bonds are stronger).
Resistant starch RS2 (non-gelatinized enzyme treatment): For example, after partial debranching by pullulanase, high amylose starch forms a crystal structure, is insoluble in cold water, and still maintains digestion resistance after gelatinization.
2. Viscosity and thermal stability
Maltodextrin (limited hydrolysis by alpha-amylase and glucoamylase): low initial viscosity (small molecular weight), stable viscosity at high temperatures (no long-chain molecular entanglement).
High maltose syrup (beta-amylase treatment): medium viscosity, good thermal stability (the force between maltose molecules is weak and not easy to decompose).
Resistant starch (transglucosidase cyclization): low viscosity after gelatinization (the ring structure is not easy to absorb water and swell), and still maintains low viscosity after cooling.
3. Digestive and physiological functions
Rapidly digestible starch (RDS, complete hydrolysis by glucoamylase): high glucose content, fast digestion
(used in glucose syrup, sports drinks).
Slowly digested starch (SDS, limited hydrolysis by β-amylase): mainly maltose and limit dextrin, slow digestion
(used in low GI foods to delay the rise of blood sugar)
Resistant starch (RS, enzymatic debranching and annealing): If debranched by pullulanase and treated with moist heat, it forms a crystal structure and is not hydrolyzed by small intestinal enzymes.
(Function of dietary fiber, regulating intestinal flora)
4. Functional application features
Film-forming properties: High amylose starch (after debranching) has good film-forming properties and is used for degradable packaging films.
Flavor stability: Low reducing end dextrin (α-amylase treatment) is not prone to Maillard reaction and can be used to maintain color in baked goods.
