Retrogradation inhibition of starches in staple foods with maltotetraose-forming amylase.

To effectively inhibit the retrogradation of staple foods, the effects of maltotetraose-forming amylase(G4-amylase) on the short and long-term retrogradation of different staple starches such as rice starch (RS), wheat starch (WS), potato starch (PS) were studied. The results indicated that G4-amylase decreased the content of amylose. Amylose contents (21.09%) of WSG4 were higher than that (14.82%) of RSG4 and (13.13%) of PSG4. WS had the most obvious change in the chain length distribution of amylopectin. A chains decreased by 18.99% and the B1 chains decreased by 12.08% after G4-amylase treatment. Compared to RS (662 cP) and WS (693 cP), the setback viscosity of RSG4 (338 cP) and WSG4 (385 cP) decreased. Compared to RS (0.41), WS (0.45), and PS (0.51), the long-term retrogradation rate of RSG4 (0.33), WSG4 (0.31), and PSG4 (0.38) significantly reduced. It indicated that G4-amylase significantly inhibited the long-term retrogradation of WS, followed by RS and PS.

Adsorption properties of corn starch modified by malt amylases and crosslinking agents: A comparison between sodium trimetaphosphate and organic acids.

In order to investigate the effects of different crosslinking agents on physicochemical properties and adsorption properties of porous starch. Native corn starch was hydrolyzed by maltase and crosslinked with different crosslinking agents. Sodium trimetaphosphate crosslinked porous starch (STMP-MPS), malic acid cross-linked porous starch (MA-MPS) and citric acid cross-linked porous starch (CA-MPS) were prepared. After crosslinking, MA-MPS and CA-MPS showed a new CO stretching absorption peak at 1738 cm-1, and the crosslinking degree was much higher than that of STMP-MPS. The surface area of MA-MPS was 36 % higher than that of STMP-MPS. Compared with the average pore size of 12.43 nm of STMP-MPS, CA-MPS (14.02 nm) and MA-MPS (14.79 nm) were increased more significantly. The degradation temperature of MA-MPS and CA-MPS was increased by the introduction of ester bond, which indicates that the organic acid cross-linking strengthens the starch granules and hence more energy is required for disruption. Compared with STMP-MPS, the water absorption of MA-MPS and CA-MPS increased by 64 % and 32 %, respectively. Furthermore, the adsorption capacity of MA-MPS to essential oil was the strongest, about 4 times that of STMP-MPS. Overall, it is feasible to modify porous starch by crosslinking reaction to improve its heat resistance and adsorption properties.

Effects of polyols with different hydroxyl numbers on the structure and properties of starch straws.

To study the relationship between the number of hydroxyl groups of polyols and the plasticizing effect, the effects of different polyols including ethylene glycol, glycerol, erythritol, xylitol and sorbitol on the structure and properties of corn starch straws were analyzed and compared. The results showed that the addition of plasticizer significantly improved the performance of starch straws, which greatly improved the mechanical properties, water absorption rate (WAR) and thermal stability. However, there was no linear relationship between the plasticizing effect on starch straws and the number of hydroxyl groups in plasticizers. Fourier transform infrared (FTIR) results showed that erythritol formed the strongest intermolecular interaction with starch. Starch straws with erythritol (S-ERY) had the highest bending force (Fb = 25.78 N) and the lowest WAR. Starch straws with glycerol (S-GLY) showed the lowest relative crystallinity (RC = 12.87 %) and the highest temperature of the maximum degradation (Tdmax = 302.1 °C). In addition, after storing for 180 days, S-GLY showed higher modulus of elasticity in bending (Eb = 4.26 N/cm) and a uniform surface.

Effects of different ratios of mannitol to sorbitol on the functional properties of sweet potato starch films.

Sorbitol as a plasticizer is easily crystallized from starch film, resulting in the reduction in plasticizing effect. To improve the plasticizing performance of sorbitol in starch films, mannitol, an acyclic hexahydroxy sugar alcohol, was used to cooperate with sorbitol. The effects of different ratios of mannitol (M) to sorbitol (S) as a plasticizer on mechanical properties, thermal properties, water resistance and surface roughness of sweet potato starch films were investigated. The results showed that the surface roughness of starch film with M:S (60:40) was the smallest. The number of hydrogen bonds between plasticizer and starch molecule was proportional to the mannitol content starch film. With the decrease of mannitol contents, the tensile strength of starch films gradually decreased except for M:S (60:40). Moreover, the transverse relaxation time value of starch film with M:S (100:0) was the lowest, indicating that it had the lowest degree of freedom of water molecules. Starch film with M:S (60:40) is the most effective in delaying the retrogradation of starch film. This study offered a new theoretical basis that different ratios of mannitol to sorbitol improve different performances of starch films.

Effects of primary, secondary and tertiary structures on functional properties of thermoplastic starch biopolymer blend films.

To better understand the correlation between structure and properties in thermoplastic starch biopolymer blend films, the effects of amylose content, chain length distribution of amylopectin and molecular orientation of thermoplastic sweet potato starch (TSPS) and thermoplastic pea starch (TPES) on microstructure and functional properties of thermoplastic starch biopolymer blend films were studied. After thermoplastic extrusion, the amylose contents of TSPS and TPES decreased by 16.10 % and 13.13 %, respectively. The proportion of the chains with the degree of polymerization between 9 and 24 of amylopectin in TSPS and TPES increased from 67.61 % to 69.50 %, and from 69.51 % to 71.06 %, respectively. As a result, the degree of crystallinity and molecular orientation of TSPS and TPES films increased as compared to sweet potato starch and pea starch films. The thermoplastic starch biopolymer blend films possessed a more homogeneous and compacter network. The tensile strength and water resistance of thermoplastic starch biopolymer blend films increased significantly, whereas thickness and elongation at break of thermoplastic starch biopolymer blend films decreased significantly.

Intermolecular interactions between starch and polyvinyl alcohol for improving mechanical properties of starch-based straws.

Starch/polyvinyl alcohol (PVA) degradable straws with different PVA contents were prepared by the twin-screw extrusion method. The results showed that the starch/PVA straws with 40 % PVA (PS4) had the highest dispersion uniformity of starch and PVA to achieve the best compatibility, and the compatibility size was below the micron level. Molecular interactions between starch and 40 % polyvinyl alcohol reached the highest due to the highest strength of hydrogen bonds, hence resulting in the highest texture densities. Consequently, the largest compatibility and molecular interactions significantly improved the mechanical properties and water resistance of PS4. Compared to the starch/PVA straw with 0 % PVA (PS0), swelling volume of PS4 decreased by 45.5 % (4 °C) and 65.2 % (70 °C), respectively. After soaking, the diameter strength increased by 540.1 % (4 °C, 1 h) and 638.7 % (70 °C, 15 min), respectively. Water absorption decreased by 45.3 % (4 °C, 30 min) and 27.6 % (70 °C, 30 min).

Self-healing properties of retrograded starch films with enzyme-treated waxy maize starch as healing agent.

Waxy maize starch (WMS) was modified using sequential α-amylase and transglucosidase to create enzyme-treated waxy maize starch (EWMS) with higher branching degree and lower viscosity as an ideal healing agent. Self-healing properties of retrograded starch films with microcapsules containing WMS (WMC) and EWMS (EWMC) were investigated. The results indicated that EWMS-16 had the maximum branching degree of 21.88 % after transglucosidase treatment time of 16 h, and A chain of 12.89 %, B1 chain of 60.76 %, B2 chain of 18.82 % and B3 chain of 7.52 %. The particle sizes of EWMC ranged from 2.754 to 5.754 µm. The embedding rate of EWMC was 50.08 %. Compared to retrograded starch films with WMC, water vapor transmission coefficients of retrograded starch films with EWMC were lower, while tensile strength and elongation at break values of retrograded starch films were almost similar. Retrograded starch films with EWMC had higher healing efficiency of 58.33 % as compared to that Retrograded starch films retrograded starch films with WMC was 44.65 %.

Effects of different rapid cooling temperatures and annealing on functional properties of starch straws after thermoplastic extrusion.

To improve the performance of starch straws in rapidly cooling and annealing procedure of thermoplastic extrusion, control straw was prepared through slowly cooling at 25 °C, and starch straw was prepared through regulating different rapid cooling temperatures including 20 °C, 5 °C, -10 °C and -20 °C. The results indicated that control straw exhibited a homogeneous state, while starch straws treated by rapid cooling displayed like a wash-board structure. Compared to control straw, the ratio of the absorption peak intensity of 1047 and 1022 cm-1 increased from 1.050 to 1.455 as cooling temperatures decreased from 25 °C to -20 °C, indicating short-range order of the double helix structure significantly enhanced. The relative crystallinities of starch straws increased from 12.01 % to 16.58 %. The maximum bending force value (60.92 N) of starch straws cooled at -20 °C was significantly higher than that (46.14 N) of control straw. Conversely, the modulus of elasticity in bending values (4.21-16.43 N/cm) of rapid cooling-treated straws were significantly lower than that (48.42 N/cm) of control straw. Water absorption of rapid cooling-treated straws were lower than that of control straw, indicating the hydrophobicity property of starch straws significantly improved.

Effect of octenyl succinic anhydride modified starch on soy protein-polyphenol binary covalently linked complexes.

The present study aimed to investigate the effects of octenyl succinic anhydride modified starch (OSAS) on soy protein (SP)-(-)-epigallocatechin-3-gallate (EGCG) binary covalently linked complexes. Mean diameters of OSAS-SP-EGCG complexes decreased from 379.6 ± 54.9 nm to 272.7 ± 47.7 nm as the OSAS-to-SP-EGCG ratio changed from 1:2 to 4:1, while ζ-potential decreased from -19.1 ± 0.8 mV to -13.7 ± 1.2 mV. Fourier transform infrared spectroscopy results revealed that the characteristic peaks at 1725 cm-1 and 1569 cm-1 for OSAS disappeared in the OSAS-SP-EGCG complexes, indicating an interaction between OSAS and SP-EGCG complexes. X-ray diffraction analysis showed that with the increase of OSAS content, the diffraction peak at approximately 8.0° decreased from 8.22° to 7.74°, implying that the structures of OSAS and SP-EGCG complexes were rearranged after forming into OSAS-SP-EGCG complexes. The contact angle of the OSAS-SP-EGCG complexes significantly increased from 59.1° to 72.1° with the addition of OSAS increased, revealing that the addition of OSAS improved hydrophobicity of the SP-EGCG complexes. Transmission electron microscopy images revealed that the individual OSAS-SP-EGCG complexes became smaller but stuck together to form large fragments, which was different from the morphology of OSAS and SP-EGCG complexes. Thus, the OSAS-SP-EGCG complexes developed in this study may be effective emulsifiers for improving the stability of emulsion systems in the food industry.

The relationship between molecular structure and film-forming properties of thermoplastic starches from different botanical sources.

To illustrate the correlations between molecular structures and the film-forming properties of thermoplastic starch from various botanical sources, starches from cereal, tuber and legume were modified by thermoplastic extrusion and the corresponding thermoplastic starch films were prepared including thermoplastic corn starch (TCS), thermoplastic rice starch (TRS), thermoplastic sweet potato starch (TSPS), thermoplastic cassava starch (TCAS) and thermoplastic pea starch (TPES) films. TPES film displayed a higher tensile strength (6.28 MPa) and stronger water resistance, such as lower water solubility (15.70 %), water absorption (42.35 %), and water vapor permeability (0.285 g·mm·h-1·m-2·kPa-1) due to higher contents of amylose and B1 chains. TCAS showed a smoother and more amorphous film due to higher amylopectin content, resulting higher elongation at break and larger opacity. TCS film was the most transparent due to a compacter network and more ordered crystallinity structure, which was suit for the packaging of fresh vegetables and aquatic products, whereas TCAS film was the opaquest, which protected package foods from light such as meat products, etc. The outcome would provide an innovative theory to regulate accurately the functional properties of thermoplastic starch films for different food needs.

Comparison of structural and functional properties of maize starch produced with commercial or endogenous enzymes.

To explore an effective and economic method to prepare higher contents of resistant starch (RS), different enzyme treatments including single pullulanase (PUL), commercial α-amylase (AA) or/and ß-amylase (BA) with PUL, and malt endogenous amylase (MA) with PUL were used and the structural, physicochemical properties and digestibility of all modified starches (MS) were compared. All the enzyme-treated starches displayed a mixture of B and V-type diffraction patterns. The MA/PUL-MS showed higher V-type diffraction peak intensity as compared to other modified starches. Compared to the combination of commercial enzyme treatment, the combination of malt enzyme treatment led to higher apparent amylose contents (45.56%), RS content (53.93%) and thermal stability (302 °C), whereas it possessed lower solubility indices and predicted glycaemic index. The apparent viscosity and shear resistance of MA/PUL-MS were lower than that of AA/PUL-MS, whereas that of MA/PUL-MS was higher than that of BA/PUL-MS and BA/AA/PUL-MS. These findings would provide a theoretical and applicative basis to produce foods with lower GI in industrial production.

The relationship between linear chain length distributions of amylopectin and the functional properties of the debranched starch-based films.

The relationship between linear chain length distributions and the functional properties of the starch-based films after pullulanase debranching treatment of corn (CS), rice (RS) and wheat (WS) were investigated. The results indicated that the film thickness was negatively correlated with A chains content (r = -0.939) and apparent amylose content (r = -0.926), and was positively correlated with B3 chains content (r = 0.847). The tensile strength of the debranched starch-based films were positively correlated with apparent amylose content (r = 0.813), and the elongation at break were inversely proportional to B3 chains content (r = -0.817). The hydrophobicity of the starch-based films was positively and negatively correlated with the proportions of linear chains with DP 6-12 (r = 0.892) and DP 25-36 (r = -0.863), respectively. On the contrary, no significant correlation was noticed between chain length distribution of amylopectin and transparency and thermal stability.

Structural, physicochemical and long-term retrogradation properties of wheat starch treated using transglucosidase.

To reduce the wheat-flour-based food texture and flavor deterioration caused by starch retrogradation, herein wheat starch, the most ingredient in wheat flour, was modified by transglucosidase to delay long-term retrogradation of wheat starch. The study proposed promising data of transglucosidase-treated starch about structure, crystallinity and retrogradation kinetics. Structural properties showed that transglucosidase treatment shortened the average chain length from 19.49 to 16.10 and induced the dominance of amorphous state. Moreover, branching degree increased from 14.11% to 17.97% after transglucosidase treatment, resulting in higher water mobility. Amylose content increased from 25.33% to 59.00% due to the hydrolysis ability of transglucosidase. Relative crystallinity of the retrograded starches decreased from 24.33% to 14.50%. Furthermore, the Avrami parameters demonstrated that transglucosidase treatment significantly retarded the retrogradation rate of wheat starch due to the decrease of re-crystalline rate. The outcoming would supply a solid theory foundation for exploring the wheat staple foods with higher qualities.

Corn starch modification during endogenous malt amylases: The impact of synergistic hydrolysis time of α-amylase and ß-amylase and limit dextrinase.

To expand the utility of barley malts and decrease the cost of enzyme-modified starch production, the structural and physicochemical characteristics of corn starch modified with fresh barley malts at different hydrolysis time were investigated. The results indicated that compared to native starch, A chain (DP 6-12) of the enzyme-treated starches increased at hydrolysis time (≤12 h), but it decreased at hydrolysis time (>12 h). Inversely, B chains (DP > 13) decreased at hydrolysis time (≤12 h) and they generally increased at hydrolysis time (>12 h). The relative crystallinity decreased from 25.63% to 21.38% and 1047 cm-1/1022 cm-1 reduced from 1.042 to 0.942 after endogenous malt amylases at hydrolysis time from 0 to 72 h, and the thermal degradation temperatures decreased from 323.19 to 295.94 °C, whereas the gelatinization temperatures slightly increased. The gel strength decreased at hydrolysis time less than 12 h, but it increased at hydrolysis time more than 12 h. The outcomings would provide a theoretical and applicative basis about how endogenous malt amylases with lower price modify starches to obtain desirable starch derivatives and industrial production.

Effects of ultrasonication on the properties of maize starch/stearic acid/ sodium carboxymethyl cellulose composite film.

Ultrasonic treatment can improve the compatibility between a hydrophobic material and a hydrophilic polymer. The light transmittance, crystalline structure, microstructure, surface morphology, moisture barrier, and mechanical properties of a composite film with or without ultrasonication were investigated. Ultrasound increases the film's light transmittance, resulting in a film that has good transparency. Ultrasonication did not change the crystalline structure of the polymer film, but promoted V-type complex formation. The surface of the film became smooth and homogeneous after the film-form suspension underwent ultrasonic treatment. Compared to the control film, after ultrasonication at 70% amplitude with a duration of 30 min, the average roughness and maximum roughness declined from 212 nm to 17.6 nm and from 768.7 nm to 86.5 nm, respectively. The composite film with ultrasonication exhibited better tensile and moisture barrier properties than the nonsonicated film. However, long-term and strong ultrasonication will destroy the polymer structure to some extent.

Structural and functional modification of kudzu starch using α-amylase and transglucosidase.

The large agglomeration of starch paste in hot water, and fast retrogradation tendency and low transparency of starch gel restrict widespread application of kudzu starch. To improve the above defects, kudzu starch was modified with sequentially α-amylase (AA) and transglucosidase (TG), the latter for varying times. The results indicated that, compared to kudzu starch, amylose content and molecular weight of AA/TG-treated starches reduced by 20.07% and 69.50%, respectively. The proportion of A chain increased by 68.68%, whereas B1, B2 and B3 chains decreased by 14.28%, 48.29% and 23.44%, respectively. The degree of branching dramatically increased by 128.3%. After AA→TG treatment, the changes of starch structure enhanced the functional properties of kudzu starch. The solubility, paste clarity and gelatinization temperature increased, whereas the relative crystallinity, viscosity, storage and loss moduli decreased. Overall, the AA→TG modification would be desirable to improve the functional properties of kudzu starch to expand more large-scale application.

The functionality of laccase- or peroxidase-treated potato flour: Role of interactions between protein and protein/starch.

Potato flour is used in bakery products, extruded products and snacks. However, it displays weaker gel strengths and thus the wholesome utility is curtailed significantly. To improve viscoelastic properties and stability of potato gels, herein potato flour was treated with laccase and peroxidase to create a protein network structure leading to stable gels. The results revealed that the secondary structure of potato proteins altered upon the enzyme treatment. The gels of peroxidase-treated potato flour (PPF) and laccase-treated potato flour (LPF) displayed larger anti-shear ability, thermal stability and stronger three-dimensional network structure compared to the native potato gel. The PPF and LPF gels exhibited stronger viscoelastic properties and structural stability compared to peroxidase-treated potato protein and laccase-treated potato protein gels. The outcome serves as a theoretical basis to improve the properties of potato gels and to promote the designing and the development of novel potato flour based functional food.

Synergistic effects of branching enzyme and transglucosidase on the modification of potato starch granules.

Potato starch displayed high viscosity, low hydroscopicity and dispersity, and acid susceptibility leading to the limited application of potato starch. To expand the potato starch utility with appropriate processing characteristics, potato starch granules were modified with branching enzyme (BE) and transglucosidase (TG). The results indicated that the susceptibility of potato starch granules to TG was higher than BE. Moreover, the two enzymes showed the synergistic effect in enzymatic modification of potato starch granules. They cooperatively attacked the external and interior of potato starch granules. The crystal forms of potato starch changed from B to C-type after double enzyme treatments, and enzyme-treated starches exhibited homogeneous crystal distribution. Compared to BE or TG alone, the combined action of BE and TG increased significantly the ratio of α-1,6-glycosidic linkage and the amounts of short chains of potato starch, which led to the significant reduction in degree of crystallinity, viscosity, gelatinization temperature and enthalpy, and a remarkable increase in solubility. Especially, the physicochemical characteristics of modified starch largely depended on the treatment time of TG. Thus, through the combination of BE and TG, the appropriate treatment time of TG may be chosen to improve the physicochemical properties of potato starch in processed starch-based products.

Electrochemical synthesis of poly(3-aminophenylboronic acid) in ethylene glycol without exogenous protons.

A non-aqueous solution of tetra-n-butylammonium fluoride (TBAF) in ethylene glycol has been tried for the first time as a supporting electrolyte for the electropolymerization of 3-aminophenylboronic acid (APBA). Unlike the traditional acidic aqueous solution, the present medium needs no exogenous protons; moreover, the presence of CF3COOH is found to be unfavorable for the polymerization. The protons are in situ generated by the reaction between the boronic acid group on APBA and 1,2-dihydroxyl on ethylene glycol. So, ethylene glycol serves as not only the solvent but also the proton source. As a part of the supporting electrolyte, F(-) is found to be involved in the electrochemical synthesis of poly(3-aminophenylboronic acid) (PAPBA), but it is not indispensable. Studies on the electropolymerization process indicate that the size of the ions in the electrolyte affects the rate of the doping/dedoping process. The smaller the cation, the easier the doping/dedoping process, and the better the stability of the grown film. As demonstrated by Fourier transform infrared spectra, UV-vis spectra, and scanning electron microscopy, the obtained PAPBA is a cross-linked nanoporous polymer membrane that has a good adherence to the glassy carbon electrode.

Gold nanoparticles tune the activity of laccase in anionic reverse micelles.

The interfacial property of reverse micelles is an important factor affecting the catalytic activity of enzymes hosted in the micelles. In this article, the effect of gold nanoparticles (GNPs) on the catalytic activity of laccase (non-surface-active enzyme) and the related mechanism are reported. It was found that laccase activity was dependent on the size of the particle and its concentration as well as on the water content and the concentration of AOT. It was shown that there existed several types of micelles in the present reverse micellar system in the presence of GNPs. The population of the various micelles depended on the concentrations of both GNPs and AOT. Fluorescence and circular dichroism spectra of laccase at different water contents and GNP concentrations indicated that the conformation of laccase and its activity were tuned by GNPs via changing the structure of the reverse micelles. Analysis showed that changes in the thickness of the water layer (Lw) and in the apparent occupied area of individual AOT molecules (AAOT) caused by GNPs were the main parameters affecting the activity of laccase. The present work extends and deepens the understanding of the tuning mechanism of GNPs on enzymatic performance in reverse micelles and provides guidance for rational design of the optimal microenvironment of laccase.