Synthesis and evaluation of physicochemical properties of cross‐linked Phaseolus aconitifolius starch

Highly substituted moth bean starch (MBS) phosphate ester was synthesized using POCl₃ as cross‐linking reagent. Titrimetric and FT‐IR spectral analysis was used to characterize the substitution. The physicochemical properties of cross‐linked moth bean starch (CLMBS) were done by using X‐ray powder diffractometer (XRD), thermogravimetric analysis (TGA) and swelling study at various temperatures. The change in starch morphology was done using scanning electron micrograph (SEM), and found that it lost its crystallinity after cross‐linking. The results revealed that crystalline nature of native MBS was transformed into amorphous after cross‐linking. TGA report exhibited higher thermal stability, which make it suitable for various industrial applications. Swelling behavior showed high swelling at low temperatures (30 and 60°C) as compared to at high temperature (90°C).     

Effects of cross‐linking on the rheological and thermal properties of sweet potato starch

Sweet potato starches were modified with three different concentrations of phosphorus oxychloride (POCl₃) (0.01, 0.02, and 0.03%, based on dry weight of starch) as a cross‐linking agent. The effects of crosslinking on rheological and thermal properties of sweet potato starch (SPS) pastes were evaluated. Cross‐linking considerably reduced the swelling power, consistency index (K), apparent viscosity (η_a), and yield stress (σ_oc) values of SPS, which significantly decreased with increase in POCl₃ concentration. The gelatinization temperature (T_p) and enthalpy (ΔH) values of the cross‐linked SPS, which were determined using differential scanning calorimetry, were higher than those of native SPS. Storage modulus (G′), loss modulus (G″), and complex viscosity (η*) of the cross‐linked SPS pastes determined using small deformation oscillatory rheometry, were higher than native starch, and they also decreased with increase in POCl₃ concentration from 0.01 to 0.03%. The tan δ (ratio of G″/G′) values (0.15–0.19) of the cross‐linked SPS samples were much lower than that (0.37) of the native SPS, indicating that the elastic properties of the SPS pastes were strongly influenced by modifications from cross‐linking. Finally, Cox–Merz plots showed that η* was much higher than η_a for the cross‐linked SPS pastes.     

Effect of cross‐linking on some properties of potato (Solanum tuberosum L.) starches

Starches separated from different potato cultivars were modified using two different cross‐linking agents: epichlorohydrin (EPI) and phosphoryl chloride (POCl₃) at different concentrations (1.0 and 2.0 g kg^?1 POCl₃; 2.5, 5.0 and 10 g kg^?1 EPI). Differential scanning calorimetry, rheological and retrogradation measurements were performed to characterise the influence of cross‐linking on the properties of potato starches. Cross‐linking considerably reduced swelling power, solubility, water‐binding capacity and paste clarity. The decrease became greater as the reagent concentration increased. The starches treated with 1.0 g kg^?1 POCl₃ exhibited exceptionally higher swelling power than their counterpart native starches. Neither cross‐linking agent caused any change in morphology of the starch granules. Studies on the phase transitions associated with the gelatinisation showed significantly higher values for the onset temperature (T_o), peak temperature (T_p), conclusion temperature (T_c) and enthalpy of gelatinisation (ΔH_gel) for the cross‐linked starches than the native starches. Starches treated with both the reagents showed lower peak storage modulus (G′) and loss modulus (G″) than their native counterparts. The tendency of the starch pastes towards retrogradation increased considerably with increases in storage duration. However, the starches treated with 1 g kg^?1 POCl₃ exhibited much lower syneresis than the other cross‐linked starches. Copyright © 2006 Society of Chemical Industry     

Effect of miniemulsion cross‐linking and ultrasonication on properties of banana starch

Miniemulsion technique has been widely used to prepare cross‐linked starch microsphere for food application. The objective of this study was to examine the effect of miniemulsion and ultrasonic treatment on the morphological, physicochemical and thermal properties of banana starch. Results showed that the miniemulsion cross‐linked banana starch (MCBS) exhibited lower swelling power (SP) and solubility (S) but higher gelatinisation enthalpy (ΔH_gel) than native banana starch. Ultrasonic treatment conditions (amplitude and time) did not show any significant difference in SP and ΔH_gel of MCBS. Ultrasonicated MCBS showed rough surfaces and slight fragmentations without any change in particle size. At gelatinisation temperature (80 °C), the SP and S of MCBS were higher than those at 29 °C. Moreover, MCBS with ultrasonic treatment showed a lower range in the gelatinisation temperature (ΔT) than untreated. The FT‐IR spectrums revealed that MCBS were fully cross‐linked and had high extent of hydrogen bonding.     

Physicochemical Properties of Non‐thermally Cross‐linked Corn Starch with Phosphorus Oxychloride using Ultra High Pressure (UHP)

Corn starch (20%, w/w) was non‐thermally and conventionally cross‐linked with phosphorus oxychloride (POCl₃; 0.01, 0.05, or 0.1%, based on dry weight of starch) at 400 MPa for 5, 15 and 30 min and at 45°C for 2 h, respectively. Swelling power and solubility of both non‐thermally and conventionally cross‐linked corn starches were relatively lower than those of native corn starch. The pressure holding time did not affect the solubility and swelling power of non‐thermally cross‐linked corn starches. X‐ray diffraction patterns and relative crystallinity were not significantly altered by both conventional and non‐thermal cross‐linking. DSC thermal characteristics of both non‐thermally and conventionally cross‐linked corn starches were not significantly changed indicating that the double helical structure of amylopectin was not influenced by both conventional and non‐thermal cross‐linking reactions. Both non‐thermal and conventional cross‐linking greatly affected the Rapid Visco Analyser (RVA) pasting properties, such as increase in pasting temperature and decrease in peak viscosity compared to native starch. This result suggests that in case of cross‐linking using POCl₃, both non‐thermal and conventional methods result in similar physicochemical properties and non‐thermal cross‐linking with POCl₃ can reduce the reaction time from 2 h to 15 min. This work shows the potential and possibility of non‐thermal starch modification and provides the basic and scientific information on the physicochemical properties of non‐thermally cross‐linked corn starches with phosphorus oxychloride using UHP.     

Effects of Granule Sizes on Physicochemical Properties of Cross‐linked and Acetylated Wheat Starches

Large and small wheat starch granules were used for cross‐linking and acetylation to determine effects of granule sizes on physicochemical properties of the modified starches. The native and cross‐linked starches from the small granules showed higher phosphorus contents than did those from the large granules. However, the level of phosphate substituents in the modified starches was not significantly different between the large and small granules under the same conditions. In contrast, the large granules had a higher reactivity with acetic anhydride than did the small granules. The phosphate group cross‐linked starch (CS), acetylated starch (AS) and acetylated cross‐linked starch (ACS) from the large granules had lower gelatinization temperatures and higher enthalpies than those from the small granules. The paste viscosities of the CSs from the large granules decreased rapidly, whereas those of the AS or ACS increased significantly as compared with those from the small granules. The pastes of cross‐linked starches from the small granules were more stable than those from the large granules, whereas the pastes of AS and ACS from the large and small granules had similar resistance to freeze‐thaw treatment. Scanning electron microscopy (SEM) also showed that the small granules were less damaged after modification than the large ones. Thus, the different granule sizes resulted in different physicochemical properties of starch after modification.     

Enhanced thermal and antibacterial properties of cross‐linked waxy maize starch granules by chitosan via dry heat treatment

Cross‐linked starch was synthesised using chitosan as cross‐linking agent via a dry heating method. Thermal properties measured by DSC showed transition temperatures increased as compared with that of native starch (P < 0.001), which might indicate the starch and chitosan molecules interacted with each other. XRD demonstrated that the crystalline pattern of the starch remained the same, but there was slight change in the crystallinity degree after the cross‐links. The significant reduction of solubility, swelling power and transparency (P < 0.001) indicated that the cross‐links restricted the starch granules swelling and molecules leaching. Agar diffusion test showed that chitosan‐cross‐linked starch had excellent bacterial growth inhibition, and its antibacterial activity was stronger against Gram‐negative bacteria than against Gram‐positive bacteria. Its antibacterial activity was further confirmed using liquid broth method. Thus, the cross‐linked starch may be directly used in the food formula for protecting food as a natural antimicrobial ingredient.     

Effect of Cross‐linking with Epichlorohydrin on the Properties of Cassava (Manihot esculenta Crantz) Starch

Cassava starch was cross‐linked with epichlorohydrin (EPI) at 45°C for 2 h in three different media which include water, water in the presence of a phase transfer catalyst (PTC) and N,N‐dimethylformamide (DMF). The products were characterized by determining their physicochemical, thermal and retrogradation properties. In aqueous medium, the use of a PTC, tetrabutylammonium bromide (TBAB) produced derivatives with higher degree of cross‐linking than those prepared without the use of the catalyst. The degree of cross‐linking was found to be higher using the same concentration of EPI when the reaction was carried out in DMF. At low levels of cross‐linking, the peak viscosity of the cross‐linked starches increased in comparison to that of the native starch. With increasing degree of cross‐linking, the peak viscosity showed a significant reduction. The swelling volume, solubility and light transmittance of the starch pastes were lower for the modified starches. The cross‐linked starches showed slightly reduced values for the gelatinization temperatures, T_onset, T_peak and T_end. The enthalpy of gelatinization of the modified starches increased with increase in the degree of cross‐linking. The modified starches exhibited higher water‐binding capacities (WBC) than the native starch; but with increase in the degree of cross‐linking, there was a gradual decrease in WBC. The in vitro alpha amylase digestibility of the modified starches decreased gradually with increase in the level of cross‐linking.     

Combined effect of autoclaving‐cooling and cross‐linking treatments of normal corn starch on the resistant starch formation and physicochemical properties

Normal corn starch (NCS) was treated by both autoclaving‐cooling and cross‐linking to produce resistant starch (RS). The RS yield, crystalline structure, as well as other physicochemical properties of the modified starch were investigated. The yield of RS was 12.2% by four autoclaving‐cooling cycles, and it could be further increased up to 31.0% by the subsequent cross‐linking using sodium trimetaphosphate/sodium tripolyphosphate. The scanning electron microscopy images clearly illustrated that the granular structure of native starch was disrupted and a continuous network with irregular shape was formed after autoclaving‐cooling cycles. The subsequent chemical cross‐linking appeared to make the network structure more compact and dense. X‐ray diffraction patterns showed that B‐ and V‐types coexisted in all the modified corn starches, and all these modified starches exhibited very low viscosity which remained almost constant regardless of temperature changes.     

Optimisation of cross‐linking β‐cyclodextrin and its recycling efficiency for cholesterol removal in milk and cream

This study was carried out to investigate the optimum conditions of cross‐linking β‐cyclodextrin (β‐CD) and recycling for cholesterol removal in milk and cream. The cross‐linked β‐CD was prepared with a 15% adipic acid solution, and the water solubility of the β‐CD was measured for the optimum conditions based on mixing temperature, mixing time, cross‐linking temperature, cross‐linking reaction time and cooling time. In the results of this study, optimum conditions were 80 °C mixing temperature, 2 h mixing time, 60 °C cross‐linking temperature, 24 h cross‐linking reaction time and 48 h cooling time. After determining the optimum conditions, the recyclable yields of the cross‐linked β‐CD ranged from 90.01% to 55.17% in six recyclings and the percentage of cholesterol removal by 15% cross‐linked β‐CD was over 90% until eighth recycling. On the basis of the results, this study suggests that 15% adipic acid‐added cross‐linked β‐CD maximised recyclable yield and that cholesterol removal was improved during recycling.     

Influence of the Cross‐linking Agent on the Gel Structure of Starch Derivatives

Hydrogels were synthesized through cross‐linking of carboxymethyl starch (CMS; Degree of Substitution DS = 0.45) using polyfunctional carboxylic acids (malic, tartaric, citric, malonic, succinic, glutaric and adipic acid). The syntheses used a cross‐linking agent ratio (ratio of the number of cross‐linking agent molecules to the number of monomer units constituting the polymer) of F_Z = 0.05. After cross‐linking the gels were dried, ground and then hydrogels of a polymer concentration of 4 mass‐% were produced. These CMS‐hydrogels were then rheologically characterized using dynamic oscillatory measurements. From measurements of the plateau region storage modulus G'_P, the network parameters molar mass between two entanglement points M_e (M_e ranging from 9.318 (citric acid) to 281.397 g/mol (tartaric acid)), the cross‐link density ν_e and the distance between two entanglement points ξ were calculated. Using carboxylic acids without other functional groups, a maximum in gel sturdiness is found at a spacer length of two CH₂‐groups. The evaluation of the loss factor tan δ for the CMS‐hydrogels showed that values of tan δ = 0.2 varied only slightly with the frequency ω. Flow curves showed a pseudopIastic flow behavior for all CMS‐hydrogels (the shear viscosity η declining over five decades in the range of the shear rate γ of 10⁻³ to 10³ s⁻¹) The different polyfunctional carboxylic acids have a strong influence on the sturdiness of the synthesized CMS‐hydrogels.     

Improved microstructure and properties of the gelatin film produced through prior cross‐linking induced by horseradish peroxidase,glucose oxidase and glucose

The effects of prior enzymatic cross‐linking of bovine gelatin via horseradish peroxidase, glucose oxidase and glucose on microstructure and properties of the target film (cross‐linked gelatin film) were assessed. The cross‐linked gelatin film exhibited similar film thickness and moisture content, lower water solubility and higher opacity than the gelatin film directly prepared with bovine gelatin. The cross‐linked gelatin film also demonstrated improved thermal stability and mechanical properties, characterised by higher melting point and glass transition temperature, enhanced tensile strength and elongation at break and greater storage modulus. Prior gelatin cross‐linking resulted in 30.2% and 68.6% reductions in water vapour and CO₂ permeability of the cross‐linked gelatin film, respectively, but did not affect oil permeability. Furthermore, the cross‐linked gelatin film possessed smaller cross‐sectional voids (diameter 100?360 nm vs. 200?595 nm) than the bovine gelatin film. This study shows that cross‐linking can efficiently improve film microstructure and properties of the gelatin‐like products.     

The effects of annealing and acid hydrolysis on resistant starch level and the properties of cross‐linked RS4 rice starch

The effects of ANN prior to cross‐linking of non‐wx rice starches on a RS level and granular shape were investigated to apply them for a fat replacer with RS in a liquid food system. Acid hydrolysis and sonication were also evaluated to improve RS quality. The RS level was also compared with AOAC and P/G methods. The RS levels of CRS analyzed with the AOAC method were higher than those analyzed with the P/G method, but the differences in the RS level of CRS affected an ANN condition and starch content during cross‐linking. When ANN was conducted at 50°C for 12 h using the AOAC method, and starch content (40%) used in cross‐linking was at 45°C for 3 h, the highest RS level of CRS treated with ANN was 69.4% compared to 38.3% RS level of CRS without ANN. The 1 h acid hydrolysis (pH 4.0) of CRS treated ANN increased 114.5% of the RS level (79.4% compared to 69.4% in CRS treated ANN), regardless of which analytical methods were used. CRS granules remained the same as native ones with a polygonal shape and A type crystallinity even after being treated with ANN, and acid hydrolysis. The sonication before cross‐linking reaction increased the RS level and prevented increase in size from aggregating CRS granules.     

Gelatinization and Thermal Properties of Modified Cassava Starches

The thermal properties of seven commercial modified cassava starches, including oxidized, acetylated, cross‐linked, and combined acetylated and cross‐linked starches were studied by differential scanning calorimetry (DSC) in the glassy and rubbery states. Increase in gel hardness in the rubbery state during storage was also monitored, as well as gelatinization behavior. The modified starches were prepared from granular starch and had a degree of substitution in the range 0–0.053. The glass transition temperatures (T_g) of the modified starches were 3–6°C significantly lower than that of the non‐modified starch. The physical aging peak temperatures were also significantly reduced by 2–3°C, compared to the non‐modified starch, while aging enthalpies increased. Starch modifications did not decrease amylopectin retrogradation significantly. During storage, the oxidized starch gel became significantly harder than the non‐modified starch gel, while the hardness of the acetylated and/or cross‐linked starch gels was significantly reduced, which confirmed that acetylation or cross‐linking can decrease hardness, even when the extent of modification is limited. Different modifications controlled different properties of the starch system, with cross‐linking and acetylation influencing the gelatinization behavior and the changes in starch gel texture during storage, respectively.     

Physicochemical and Functional Properties of Cross‐linked Banana Resistant Starch. Effect of Pressure Cooking

A resistant starch (RS)‐rich powder was prepared from phosphate cross‐linked banana starch. Serial autoclaving and cooling treatments of this cross‐linked material were also made. The powders were evaluated for chemical composition, resistant starch content, thermal characteristics, as well as for swelling and solubility properties. The parental cross‐linked starch had similar lipid and protein contents than its autoclaved counterpart, but the ash content decreased after autoclaving, a pattern that is in agreement with the low phosphorus index and degree of substitution recorded in the autoclaved preparation. Although the RS content in the autoclaved cross‐linked product was lower than in the non‐autoclaved starch, the autoclaved product still exhibited a remarkable indigestibility. The peak temperatures of gelatinization were 86.6 and 68.5ºC for cross‐linked and autoclaved cross‐linked starch, respectively. At low temperatures the autoclaved modified starch exhibited greater swelling values than its cross‐linked counterpart. The pattern of solubility values resembled the swelling behavior of both samples. The autoclaved cross‐linked banana starch appears suitable for the formulation of foods requiring none or moderate further heat treatment.     

Rheological,gelling and emulsifying properties of a glycosylated and cross‐linked caseinate generated by transglutaminase

The impacts of oligochitosan glycosylation and cross‐linking on some properties of a commercial caseinate were investigated in this study. The glycosylated and cross‐linked caseinate with glucosamine content of 4.74 g kg^?1 protein was generated by transglutaminase (TGase) and oligochitosan at pH 7.5 and 37 °C, with fixed substrate molar ratio of 1:3 (acyl donor to glucosamine acceptor), caseinate content of 50 g L^?1, TGase of 10 kU kg^?1 protein and reaction time of 3 h, respectively. In comparison with the caseinate, the glycosylated and cross‐linked caseinate had decreased reactable amino groups (0.58 vs. 0.51 mol kg^?1 protein), higher apparent viscosity, decreased emulsifying activity index (about 14.5%) and statistically unchanged emulsion stability index (92.6 vs. 90.5%). Based on the mechanical spectra of the acid‐induced gels, the glycosylated and cross‐linked caseinate showed shorter gelation time (95 vs. 200 or 220 min) than the caseinate or cross‐linked caseinate. The gels prepared from the glycosylated and cross‐linked caseinate also had enhanced hardness, springiness and cohesiveness. The results indicated that TGase‐mediated oligochitosan glycosylation and cross‐linking has the potential to obtain new protein ingredients.     

Improving gel formation of rice starch added with cross‐linked resistant starch prepared from rice starch

The gel formation properties of non‐waxy rice starch with cross‐linked resistant starch with phosphate (RS4, 10, 20, and 30% based on rice starch) prepared from three rice varieties with different amylose (AM) content were investigated to increase dietary fiber content, improve gel structure, and reduce the glycemic index of rice products. The AM contents of rice starches were 1.71% in Hanganchal1, 22.47% in Nampyeong, and 33.39% in Goamy. All RS4 showed A‐type crystallinity and their RS levels were 46.91, 54.54, and 66.01%, respectively. The initial pasting temperatures of RS4 added rice starches increased as RS4 contents increased, but peak and breakdown viscosities and enthalpy change (△H) reduced. The RS4 addition improved gel shape and texture properties including hardness, cohesiveness, and gumminess, except the 30% Goamy RS4 added gel. The 20% RS4 addition was appropriate to form rice starch gels. The network structure of RS4 added gel formed more regular and firmer than that of control, because RS4 granules were entrapped within the gel matrix like observed by light microscope and scanning electron microscopy. It is suggested that RS4 not only assist in forming a rigid network structure but also increasing a dietary fiber content.

     

Synthesis and Characterization of Cross‐linked Carboxymethyl Potato Starch Ether Gels

Hydrogels were synthesized by cross‐linking of potato starch (PS) with dichloroacetic acid (DCA) in the presence of monochloroacetic acid (MCA) to form etherified carboxymethyl starch (CMS) gels, to be used for ultrasonic medical examinations. By etherification cross‐linked CMS‐hydrogels can be produced, that are stable in contrast to the in the long‐term unstable esterified gels, that were presented in the last paper. The rheological benchmarks for the CMS‐hydrogels were set in comparison with synthetic ultrasonic gels. Gels with potato starch contents in the reaction batch ranging from 12.5% to 20% showed the best compliance with the benchmark parameters. The DS values of these CMS‐hydrogels vary from 0.42 to 0.49, increasing with decreasing amount of starch in the reaction mixture. The free swelling capacities (FSC) vary between 77 g/g for the 12.5% PS‐gel and 34 g/g for 20% PS‐gel, the turbidities of the samples being in the range from 14.5 NTU (Nephelometric Turbidity Units) (12.5% PS) up to 20.5 NTU (20% PS). The variation of the PS fraction in the reaction mixture showed that with an increased amount of PS in the reaction batch the number of cross‐links of the CMS‐gels increases, too. At a higher number of cross‐links the swelling capacity is reduced and the concentration needed to form stable hydrogels is greatly increased. Thus a hydrogel of a polymer concentration of 5 mass‐% from a 12.5% PS batch was produced, that showed the best accordance with the rheological benchmark parameters such as gelatinization time, visco‐elastic and pseudoplastic properties and long‐term stability. The ultrasonic pictures taken with this CMS‐gel were not different from those taken with the synthetic gels. This hydrogel was then subjected to long‐term‐stability measurements performed over one year and to rheological temperature cycle tests. The tests showed that the long‐term stability of the gels is sufficient for their use as ultrasonic gel.     

Zinc‐loaded whey protein nanoparticles prepared by enzymatic cross‐linking and desolvation

Zinc‐loaded whey protein nanoparticles were prepared by enzymatic cross‐linking whey protein followed by ethanol desolvation. Whey protein isolate (WPI) was denatured by heating (80 °C for 15 min) at pH 7.0 and then cross‐linked by transglutaminase at 50 °C for 4 h while stirring. Transglutaminase was inactivated by heating at 90 °C for 10 min, and then, ZnSO₄·7H₂O (1–10 mm ) was added. Zinc‐loaded whey protein nanoparticles were formed by adding ethanol at one to five times the volume of the protein solution at pH 9.0. The desolvated solutions were diluted by adding distilled water at ratio of 1:100 (w/v) immediately after desolvation. Dynamic light scattering (DLS) data showed that the particle size of zinc‐loaded whey protein nanoparticles increased with the amount of zinc and the volume of ethanol. Scanning electron microscopy micrographs revealed an almost spherical morphology for zinc‐loaded whey protein nanoparticles. The zinc loading efficiency was determined ranging from 76.7% to 99.2%. In vitro test data showed that the zinc release rate was low in simulated gastric fluid but high in simulated intestinal fluid. The results indicated that enzymatic cross‐linked whey protein nanoparticles may be used as a good vehicle to deliver zinc as a supplement.     

Dual Modification of Banana Starch: Partial Characterization

Banana starch was double modified by cross‐linking and substitution, using two different cross‐linking agents, i.e. phosphorus oxychloride (POCl₃) and a mixture of sodium trimetaphosphate/sodium tripolyphosphate. The morphological and physicochemical properties and the absorption capacity for heavy metals of the modified starches were assessed. Double modified starch granules (cross‐linked carboxymethyl starches CCSA and CCSB) presented changes in the surfaces. These starches had a bigger average particle size than unmodified starch due to the swelling of the granules during the chemical modification, also aggregates were formed. The double modified banana starches presented an A‐type X‐ray diffraction pattern with slightly decreased crystallinity compared with the unmodified counterparts. The double modification of banana starch decreases the temperature and enthalpy of gelatinization and the decomposition temperature. These results are related to partial disorganization during the chemical treatment. The double modified banana starch possess sorption capacity for heavy metal ions in the order Cd²⁺ >Pb²⁺>Cu²⁺>Hg²⁺. Due to their physicochemical characteristics and absorption capacity, the double modified banana starches can be used in diverse applications.