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Enzymes are readily inactivated in harsh micro-environment due to changes in pH, temperature, and ionic strength. Developing suitable and feasible techniques for stabilizing enzymes in food sector is critical for preventing them from degradation. This review provides an overview on chitosan (CS)-based enzymes encapsulation techniques, enzyme release mechanisms, and their applications in food industry. The challenges and future prospects of CS-based enzymes encapsulation were also discussed. CS-based encapsulation techniques including ionotropic gelation, emulsification, spray drying, layer-by-layer self-assembly, hydrogels, and films have been studied to improve the encapsulation efficacy (EE), heat, acid and base stability of enzymes for their applications in food, agricultural, and medical industries. The smart delivery design, new delivery system development, and in vivo releasing mechanisms of enzymes using CS-based encapsulation techniques have also been evaluated in laboratory level studies. The CS-based encapsulation techniques in commercial products should be further improved for broadening their application fields. In conclusion, CS-based encapsulation techniques may provide a promising approach to improve EE and bioavailability of enzymes applied in food industry. Enzymes play a critical role in food industries but susceptible to inactivation. Chitosan-based materials could be used to maintain the enzyme activity. Releasing mechanisms of enzymes from encapsulators were outlined. Applications of encapsulated enzymes in food fields was discussed. [ABSTRACT FROM AUTHOR]

BACKGROUND: The method of emulsification/internal gelation is commonly used to prepare alginate microspheres for lactic acid bacteria (LAB). This paper focused on the influence of acidification parameters, i.e. acid/Ca molar ratio and acidification time, on the physical properties and cell protection efficiency of microspheres and their correlations. RESULTS: With increasing acid/Ca molar ratio and acidification time, the average diameter of microspheres decreased and their mechanical strength increased. Interestingly, wet alginatemicrospheres shrank in simulated gastric juice (SGJ) while they swelled in bile salts solution (BS). The shrinkage or swelling ratio decreased with increasing mechanical strength. Correlation analysis showed that the encapsulated cell survivals in both SGJ and BSwere positively correlatedwith the mechanical strength of microspheres but negatively with the shrinkage or swelling ratio. BacLight LIVE/DEAD assay suggested that the viability of encapsulated cells in fresh, SGJ-treated and BS-treated microspheres was closely related to cell membrane integrity. CONCLUSION: Acidification is a key step during microsphere preparation, which strongly affected the physical properties of alginate microspheres, resulting in different cell protection efficiency. The resulting well-protected LAB can be applied in probiotics foods. [ABSTRACT FROM AUTHOR]

Abstract: Gelation behavior of sodium alginate was investigated in an aqueous system at various CaCO3 doses using two alginate samples of different mannuronate (M)/guluronate (G) ratios but with comparable molecular masses. Macroscopic rheological properties of the polysaccharide were discussed during gelation in relation to microscopic supermolecular structures imaged by atomic force microscopy and Ca2+ binding. At fixed concentrations of the polysaccharide (0.5 w/v%) and glucono-δ-lactone (15mM) as an acidic material, the G-rich sample was higher in elasticity with rod-like molecular assemblies at the highest CaCO3 dose; 15mM, while the M-rich sample was higher in elasticity with network-like molecular assemblies at the lowest CaCO3 dose; 3.75mM. Gelation behavior near the sol-to-gel transition was generally described by the percolation model, except for the M-rich sample at the lowest CaCO3 dose. A critical CaCO3 dose corresponded to 7.5mM at which both alginate samples showed essentially the same gelation kinetics. In an equilibrium state, it was estimated that the G-rich sample was bound to larger amount of Ca2+ at the lowest CaCO3 dose, while the M-rich sample was bound to larger amount of Ca2+ at the highest CaCO3 dose. The amount of bound Ca2+ did not directly relate to elasticity of the system. Based on these results, dominant block structures are suggested for gelation. [Copyright &y& Elsevier]

Functions of low molecular-weight polyuronate fractions in the calcium binding and calcium-induced gelation of normal low-methoxyl pectin (LMP) were investigated. The fractions from pectin with two different degrees of esterification (DE) and also from alginate with two different mannuronate/guluronate (M/G) ratios were prepared within the weight average molecular-weight range from ca. 40–65 kg/mol. In the mixtures of LMP and each polyuronate fraction, changes in the relative viscosity ( η r ) of dilute solutions and in rheological properties of gels were examined in the presence of calcium. Different results were indicated between the pectin and the alginate fractions. The addition of the pectin fractions, regardless of its DE, increased η r of dilute solutions and increased dynamic storage modulus ( G ′) of gels with showing greater effects at the lower DE. On the contrary, the addition of the alginate fractions, regardless of its M/G ratio, increased the critical threshold concentration of calcium required for the increase in η r of dilute solutions and decreased G ′ of gels with showing greater effects at the lower M/G ratio (i.e. guluronate rich). Based on the results, molecular associations of the mixtures were presented schematically to compare the functions between the pectin and the alginate fractions. [ABSTRACT FROM AUTHOR]

The functions of low molecular-weight M w polyuronate on the calcium binding and calcium-induced gelation of normal sodium alginate (ALG) have been investigated. Mannuronate- and guluronate-rich fractions were prepared from ALG at two different M w for each. In the mixtures of ALG and each alginate fraction, changes in the relative viscosity of dilute solutions and rheological properties of the gels were examined after calcium addition. In dilute solutions, the mannuronate-rich fractions did not substantially alter the calcium binding behavior of ALG regardless of M w . On the contrary, the guluronate-rich fractions changed the calcium binding behavior of ALG, and more calcium was required for increase in the relative viscosity relating to the formation of egg-box dimers and subsequent aggregations. These results were more evident when M w of guluronate-rich fractions was lower. Gel rheology was also different between the mannuronate- and the guluronate-rich fractions. In the gels, both fractions decreased the storage modulus in the linear viscoelastic regime with increased yield strain, but these effects of the guluronate-rich fractions were greater than the mannuronate-rich fractions when compared at equivalent M w . These functions of the guluronate-rich fractions were quite different from those of low-methoxyl pectin fraction. By using well-characterized polyuronate samples, calcium-induced gelation for the mixture of ALG and each low M w polyuronate was compared on the molecular level. [ABSTRACT FROM AUTHOR]

Abstract: Emulsification/internal gelation is an effective encapsulation method to protect probiotics from adverse environment. In this paper, microcapsules of Lactobacillus acidophilus CGMCC1.2686 were prepared by emulsification and gelation of alginate solutions with slow release of Ca2+ ions from calcium carbonate (CaCO3) and calcium disodium ethylenediaminetetraacetate (Ca-EDTA). Physical characterization of the two types of microcapsules showed that alginate-Ca-EDTA microcapsule was more uniform in size than alginate-CaCO3, with a span factor of 0.96 and 1.20, respectively. Mechanical measurements demonstrated that alginate-CaCO3 microcapsule was more robust and elastic, which was supported by its denser structure as observed by electron scanning microscopy. Bacteria encapsulation yields in the two microcapsules were similar, 37.9% for alginate-CaCO3 and 36.9% for alginate-Ca-EDTA. However, alginate-CaCO3 microcapsule exhibited much higher cell survivals in both simulated gastric juice and bile salts solution (22.2% and 2.6*10−2%, respectively) than alginate-Ca-EDTA (7.1% and 0%, respectively), indicating a more effective protection of L. acidophilus CGMCC1.2686. The protection efficiency was discussed in relation to the mechanical properties of the microcapsules and the calcium sources used. [Copyright &y& Elsevier]

The Pueraria has been distributed in most countries of the world, but starch isolated from its root is only popular in China, Japan and other East Asian countries. Herein, we summarize the isolation, components, structure, properties, modifications and applications of kudzu starch. The coexistence of isoflavones with starch leads to the unique feature of kudzu starch. Similar to other common starches, kudzu starch molecules are composed of amylose and amylopectin. However, the fine structure of kudzu starch is different from other starches, influencing its transparency, solubility, swelling power, freeze-thaw stability, gelatinization, retrogradation, pasting and rheological properties, and even in vitro digestion. Kudzu starch has been modified by physical, chemical and enzymatical methods to improve its properties and then potentially broaden its applications. Although kudzu starch has been applied in food and non-food fields, its large-scale utility is limited as compared with other commercial starches. This review would provide useful information for the development and applications of kudzu starch. [Display omitted] • We comprehensively review on various aspects of kudzu starch. • Kudzu starch is compared with other common and commercial starches. • The composition, structure and properties of kudzu starch are described. • The modifications and applications of kudzu starch are discussed. [ABSTRACT FROM AUTHOR]

Alginate is an important natural biopolymer and has been widely used in the food, biomedical, and chemical industries. Ca2+-induced gelation is one of the most important functional properties of alginate. The gelation mechanism is well-known as egg-box model, which has been intensively studied in the last five decades. Alginate also forms gels with many other monovalent, divalent or trivalent cations, and their gelation can possess different mechanisms from that of Ca2+-induced gelation. The resulted gels also exhibit different properties that lead to various applications. This study is proposed to summarize the gelation mechanisms of alginate induced by different cations, mainly including H+, Ca2+, Ba2+, Cu2+, Sr2+, Zn2+, Fe2+, Mn2+, Al3+, and Fe3+. The mechanism of H+-induced gelation of alginate mainly depends on the protonation of carboxyl groups. Divalent ions-induced gelation of alginate show different selection towards G, M, and GM blocks. Trivalent ions can bind to carboxyl groups of uronates with no selection. The properties and applications of these ionotropic alginate gels are also discussed. The knowledge gained in this study would provide useful information for the practical applications of alginate. [Display omitted] • Ions-induced gelation of alginate has different mechanisms. • Egg-box model is a typical ion-dependent gelation mechanism of alginate. • Alginate gels formed through different ions show different characteristics. [ABSTRACT FROM AUTHOR]

One of the possible advantages of protein fibers in composites is that they can interact with the continuous gel matrix as active fillers at neutral pH. This study aimed to investigate the impacts of short (SAF) and long amyloid fibrils (LAF) and ionic strength (0–150 mM NaCl) on the whey protein isolate (WPI)-based fiber-hydrogel composites. The water holding capacity of the composite gels more depended on the gel coarseness rather than their elasticity. Significant differences were observed between the rheological data of the SAF-WPI and LAF-WPI composites, and the maximum elastic modulus (G′) was achieved at 100 mM NaCl where the LAF-WPI composites outperformed the SAF-WPI ones in enhancing G′ and hardness. Nevertheless, the elasticity and hardness of the composites dramatically dropped at 150 mM NaCl due to the change in the gel microstructure from fine strand to particulate, according to CLSM and SEM images. Interestingly, the trend in average particle size changed at 150 mM NaCl for the SAF- and LAF-WPI soluble aggregates compared to the WPI soluble aggregates. The effects of amyloid fibril and NaCl concentration on the protein aggregates as the initial building blocks of the gel were confirmed by size exclusion chromatography. These results indicated that the properties of composite gel were related to the balance between aggregate creation and the development of cross-links between them during gelation. The findings of the current study could be exploited to predict the functional behavior of globular protein gels containing amyloid fibrils with different lengths at various NaCl concentrations. [Display omitted] • The reinforcing effect of long fibril is better than short one, up to 100 mM NaCl. • Long fibrils develop inhomogeneous random aggregates at high NaCl concentrations. • WHC of the composites depends on the gel coarseness rather than the elasticity. • The mechanism of protein aggregation changes at 150 mM NaCl concentrations. [ABSTRACT FROM AUTHOR]

Abstract In this study, the influence of Persian gum (PG) on the properties of whey protein concentrate (WPC) emulsion gel prepared through cold set gelation method (incorporation of CaCl 2) was investigated. The mean droplet size of emulsions was analyzed prior to gelation and the emulsion gel samples were characterized by rheological studies, scanning electron microscopy (SEM) and water holding capacity (WHC) measurement. Results showed PG affected the droplet size of the initial emulsions and the matrix of gel systems. Emulsions containing 0.3% w/w PG revealed higher heat stability compared to the control. A viscoelastic behavior was observed for all emulsion gels with G′ being greater than G″ over the whole frequency range tested. Increasing the concentration of PG led to a change in the gel structure at pH 7. SEM images exhibited that PG at 0.3% w/w gave rise to an ordered honeycomb-like microstructure with an interconnected porous matrix of thin walls. In contrast, adding 0.6% w/w PG resulted in a non-uniform network with large pores of thick and rough walls and reduced the WHC. These findings suggest the viscoelastic properties and microstructure of WPC emulsion gel can be tailored by adjusting PG concentration for food formulations. Highlights • The structure-to-function properties of WPC emulsion gels containing PG were assessed. • The size of emulsion droplets and the structure of whey protein concentrate gel were influenced by Persian gum. • 0.3% w/w PG provided better WHC and ordered continuous microstructure in the system. • Microstructure and rheological properties of whey protein concentrate emulsion gels varied by Persian gum concentration. [ABSTRACT FROM AUTHOR]

Abstract Previous studies have demonstrated that oligoguluronate (guluronate block extracted from alginate, GB) was an efficient modulator of the gelation and gelling properties of macromolecular alginate in the presence of calcium. Here we report totally different modulatory effects of the oligomer when used to modify the gelation of low methoxyl pectin (LMP). GB was found to promote the gelation of LMP in the range of R ([Ca]/[guluronate + galacturonate]) < 0.25 and could make non-gelling systems gellable. This is significantly different from the case of alginate where no gelation could be induced at all. In the range of 0.25 < R < 0.60, the addition of GB was found to inhibit the gelation of LMP, whereas it had a negligible effect on the gelation of alginate as long as a fixed R was considered. In the range of R > 0.60, GB was found to promote the gelation of LMP again, which is similar to the case of alginate. The results were in consistence with microstructural observations by AFM. The different modulatory effects of GB were thought to arise from the different gelation mechanisms of LMP and alginate, that is, a progressive dotting growth of LMP dimers vs. a critical zippering growth of alginate dimers during Ca-induced crosslinking. The mechanism of GB modulating the gelation of LMP was proposed and compared to that for alginate. Graphic abstract Unlabelled Image Highlights • Oligoguluronate modulates efficiently the gelling properties of pectin/alginate. • Pectin and alginate behave quite differently in oligoguluronate modulation. • The difference is due to the presence of point-like cross-links in pectin gels. [ABSTRACT FROM AUTHOR]

Gelation of methylcellulose aqueous solution was investigated by a high-pressure viscosity measurement device which consisted of diamond anvil cell, microscope and CCD. And the temperature and pressure dependence of the viscosity of methylcellulose aqueous solution was measured utilizing a rolling-ball technique. The results showed that sol-gel thermal transition of methylcellulose solution occurred at the temperature of 53 °C under atmospheric pressure. Upon compression, it was indicated that the viscosity showed a dramatic change in the vicinity of the pressure of 500 MPa. Parabolic phase diagram of methylcellulose aqueous solution was constructed, and it showed that the melting point was an increasing function of pressure at the first stage and an decreasing function of pressure at the final stage. The mechanism of sol-gel transformation of methylcellulose aqueous solutions was also discussed, it might be assumed that both hydrogen and hydrophobic bonds were involved with the gel formation in the case of methylcellulose aqueous solution. [ABSTRACT FROM AUTHOR]

Sol-gel transition behavior of agarose aqueous solution was investigated by using rheology and fluorescence measurement. On heating, the storage modulus G′ decreased gradually, then deviated abruptly at the temperature of about 65 °C, and finally decreased slowly again. For fluorescence measurement, the phase transition point kept almost at the temperature of 65 °C, which was consistent with that in rheology measurement. Upon compression, it was indicated that the fluorescence lifetime for the probe in the agarose aqueous solution showed a dramatic change in the vicinity of the phase transition point. T vs. P phase diagram of agarose aqueous solution was constructed, which showed that the melting point was an increasing function of pressure. Based on the phase diagram, the agarose gels were prepared by cooling under atmospheric pressure and the pressure of 300 MPa, respectively. From the result of the recovered samples studied by optical rheometry, it was found that agarose gel prepared under high pressure had a higher elasticity and lower viscosity index, compared with that under atmospheric pressure. It could be speculated that such kinds of properties might be attributed to the smaller pore size during gelation under high pressure. [ABSTRACT FROM AUTHOR]

Calcium-chelating oligouronates can be employed to modulate calcium-dependent food hydrogels. However, very little attention has been paid to their role of structuring a real food system so far. In this study, alginate-derived oligoguluronate (GB) and pectin-derived oligogalacturonate (GaB) was shown to considerably modify the gelation process and the final gel characteristics of calcium-dependent Tofu. GB and GaB significantly accelerated the gelation process and enhanced the gel strength and water holding capacity of Tofu. The sensory properties were correspondingly altered and the addition of 15 mmol/L GB produced the most favorable smell, appearance and overall acceptance. Microstructure analysis demonstrated that GB and GaB can intensively increase the density and uniformity of Tofu gel, which potentially can be used to explain their implications on the gel and textural properties. Our findings provide an alternative strategy for modulating texture of calcium-dependent foods using dietary fiber-derived oligosaccharides with prebiotic potentials. • Oligoguluronate and oligogalacturonate can accelerate the gelation of Tofu. • Oligoguluronate and oligogalacturonate contributes to a dense and uniform Tofu gel. • Oligoguluronate and oligogalacturonate can improve the texture of Tofu. • Tofu with 15 mM oligoguluronate produced the most favorable sensory acceptance. [ABSTRACT FROM AUTHOR]

The gelation of β-lactoglobulin (BLG) and its fibrils was investigated in the presence of dithiothreitol (DTT) and transglutaminase (TGase). BLG fibrils were prepared by heating BLG at 80 °C and pH 2 for 10 h and then adjusting to pH 7. The structure of fibrils was observed by atomic force microscopy. The small and large amplitude oscillatory measurements were done to examine the gelation process and to get more insight into gel properties. It was shown that TGase alone could induce gelation for fibrillar BLG although it could not for non-fibrillar BLG. TGase could cross-link BLG fibrils to form a gel at very low protein concentration in comparison with other protein gels, and enhance the network formation of both non-fibrillar and fibrillar BLG in the presence of DTT. The scanning electron microscopic observation revealed that TGase increased the network density for non-fibrillar gels while it made network strands thicker for fibrillar gels. [ABSTRACT FROM AUTHOR]

[Display omitted] • Panda bean protein fibrils (PDPF) enhanced heat-induced pea protein isolate (PPI) gel. • The PPI-PDPF composite gel network possessed a small and uniform pore size. • Hydrogen bonds and hydrophobic interactions played important roles in PPI-PDPF gels. • The addition of PDPF affected the non-network proteins leach-out of PPI gel. The roles of panda bean protein amyloid fibrils (PDPF) in modifying the textural and rheological properties of heat-induced pea protein isolate (PPI) gels were investigated. It was found that the incorporation of PDPF significantly enhanced (p < 0.05) the strength of PPI gel. This effect was PDPF concentration-dependent and was predominantly attributable to the enhanced intermolecular interactions between PDPF and PPI through hydrogen bonds and hydrophobic interactions. Synchronously, the non-network proteins content in PPI-PDPF gels decreased from 23.6 % to 6.6 % when PDPF concentration increased from 0 to 1.50 % (w/w). Cryo-scanning electron microscopy proved that PDPF was filled in the PPI gel network leading to more compact and interconnected gel structure. However, the water holding capacity and secondary structures of PPI gel were not significantly affected. The findings of this study showed that PDPF was effective in improving the PPI gel functional quality, which provided scientific support for PDPF as a promising gel ingredient in food industrial applications. [ABSTRACT FROM AUTHOR]

The present work investigates the calcium-induced gelation behavior and gel properties of alginate samples of lithium-, sodium-, and potassium-forms. It was found that the effect of the alkali metal counterions varied greatly with the calcium concentration regime, namely, the molar ratio of calcium to guluronate (R = Ca/G). Four different regions were identified, including R < 0.25, 0.25 < R < 0.55, 0.55 < R < 1.0, and R > 1.0. The counterion dependence was interpreted by the relative interaction strength of the monovalent cations with COO− groups and their exchange reaction with Ca2+ ions. A mechanistic model depicting the role of counterions was proposed in relation to different steps of the binding and gelation of alginate with calcium. The knowledge gained in the study would further advance the understanding of the gelation mechanism of the industrially important alginate and guide its specific utilizations. [Display omitted] [ABSTRACT FROM AUTHOR]

The modulatory effect of oligoguluronate (GB) on the gelation of macromolecular alginate (ALG) was investigated by means of dynamic oscillatory rheology, fluorescence and AFM measurements. An inhibitory effect in the range of 0.25 < R (Ca/G) < 0.60 and a promotive effect in the range of R > 0.60, were quantified. The two effects are thought to be associated with the different molecular events that dominate the gelation of alginate, namely, egg-box dimerization and lateral aggregation. Quantitative analysis indicates a competitive binding rather than a screening binding during egg-box dimerization, which is responsible for the inhibitory effect in the lower Ca concentration regime. On the other hand, in the higher Ca concentration regime where alginate gelation is predominated by chain lateral aggregation, the dimers formed by GB could act as a binder to enhance the aggregation of alginate dimers, resulting in a promotive effect on alginate gelation. The results are consistent with the microstructures observed by AFM. [ABSTRACT FROM AUTHOR]

The goal of this study was to evaluate the impact of electrostatic complexation with three different β-lactoglobulin aggregates on the conformational transition and gelation of κ-carrageenan (κ-car). We prepared native granular β-lactoglobulin (NGBLG), nanoparticle β-lactoglobulin (NPBLG), and fibrillary β-lactoglobulin (FBLG), and then assessed their electrostatic complexation with κ-car and the resultant impact on κ-car conformational transition, gelation, and microstructural changes. A quantitative model based on the McGhee-Hippel theory was adopted as a means of describing the impact of electrostatic complexation on the κ-car conformational transition in the presence of these protein aggregates. FBLG resulted in the most significant inhibition of κ-car conformational transition and gelation, whereas NPBLG had the least significant impact on this process. This was attributed to the fact that NPBLG imposed the least steric hindrance of these three aggregates. Together, these data highlight promising approaches to regulating polysaccharide gelation, viscoelasticity, rheological behavior, and conformational transition for use in a range of industrial applications. [Display omitted] • Evaluated the gelation of κ-car complexation with three β-lactoglobulin aggregates. • Prepared native granular β-lactoglobulin and its aggregates NPBLG and FBLG. • FBLG resulted in the most significant inhibition of κ-car gelation. • A quantitative model was adopted to describe electrostatic complexation. [ABSTRACT FROM AUTHOR]

• Oligoguluronate (GB) modulated soy protein (SPI) gel by competitively binding Ca2+. • Ca-GB dimers contributed to the gel formation and modified the gel microstructure. • GB significantly reduced the strength, hardness and chewiness of SPI gels. • SPI gel containing 30 mM GB showed the highest water holding capacity. Naturally-sourced oligoguluronate (GB) has Ca-binding ability and can be employed to modulate Ca-dependent gels. Here soy protein isolate (SPI) gel was used as a model to investigate the influence of GB on the microstructure and properties of Ca-dependent food gels. The results showed that GB significantly decreased the storage modulus (G′), mechanical strength, elasticity, hardness and chewiness of SPI gels. Among all samples, the gel containing 30 mM GB showed the most compact network structure and thus the highest water holding capacity of 77.5 %. It should be noted that Ca-GB dimers were beneficial to the gel formation and can modify the gel properties but have no impact on the gelation kinetics. The findings gained in this study confirmed the great potential of GB in modulating the structure and properties of Ca-dependent gels, thereby obtaining food products with desired characteristics (e.g., soft and brittle tofu). [ABSTRACT FROM AUTHOR]

• Chemical structure affected the gelation of alginate and pectin in a different way • pH, temperature and co-solute can significantly influence the gelation process • Pectin showed a different gelation mechanism from alginate • Oligosaccharides potentially can control the gelation of alginate and pectin Alginate and pectin are emblematic natural polyuronates that have been widely used in food, cosmetics and medicine. Ca-dependent gelation is one of their most important functional properties. The gelation mechanisms of alginate and pectin, known as egg-box model, were believed to be basically the same, because their Ca-binding sites show a mirror symmetric conformation. However, studies have found that the formation and the structure of egg-box dimmers between alginate and pectin were different. Very few studies have reviewed those differences. Therefore, this study was proposed to first summarize the intrinsic and extrinsic factors that can influence the gelation of alginate and pectin. The differences in the effect of these factors on the gelation of alginate and pectin were then discussed. Meanwhile, the similarity and difference in their gelation mechanism was also summarized. The knowledge gained in this review would provide useful information for the practical applications of alginate and pectin. [ABSTRACT FROM AUTHOR]