Effects of inulins with various molecular weights and added concentrations on the structural properties and thermal stability of heat-induced gliadin and glutenin gels

Effects of thermal treatment and Glucono-δ-lactone on the quality of alkaline dough and steamed buns

In the present study, the effects of glucono-δ-lactone (GDL) as an acid reagent during thermal treatment on the quality of alkaline dough and steamed buns were examined. During the heating process, GDL improved the viscoelasticity and fluidity of the alkaline dough and enhanced intermolecular hydrogen bonding. The hardness of steamed buns was reduced by 61.04 %, whereas the specific volume was increased by 10.4 % with 0.8 g of GDL. The color and taste were also improved to a certain extent. Scanning electron microscopy revealed that excessive GDL caused the dissolution of the gluten network and reduced the formation of gluten protein aggregates. During the heating process, GDL is beneficial to the aggregation of the gluten network. During the process of heating from 25 °C to 60 °C, GDL reduced the -SH content and zeta potential in gluten proteins, enhanced thermal stability, and formed a more ordered gluten network. Excessive GDL reduces the pH of the system by approximately 50 %, causing gluten network dissolution and the reduced formation of gluten protein aggregates. When the temperature increased from 60 °C to 95 °C, a stable gluten network system was formed inside the alkaline dough, and GDL changed the pH of the dough by reacting with sodium bicarbonate, resulting in greater elasticity and lower hardness of the dough. These results provide a theoretical basis for using GDL as an acid reactant for chemical fermentation.

Composite gel based on κ-carrageenan-soybean isolate protein/soy protein fibrils: Focus on structural differences and gel properties

The effects of different concentrations of κ-carrageenan (κC) on the structure and gel properties of soybean protein isolate (SPI) and soybean protein fibrils (SPF) were investigated in this work. The interaction between κC and SPI/SPF was explored by SDS-PAGE, FTIR, fluorescence spectroscopy, surface hydrophobicity (H0). Results indicated that the binding of κC to SPI and SPF is mainly hydrogen bonding and hydrophobic interactions. With the increase of κC concentration, the fluorescence intensity and H0 of SPI/SPF-κC decrease. When κC was 8 mg/mL, the H0 of SPI/SPF-κC decreased by 53.56 % and 57.23 % respectively. The addition of κC increased the particle size and turbidity of SPI, while the opposite results for SPF. The gel properties of SPI/SPF-κC were evaluated by texture, rheology and LF-NMR. The results showed that the gel properties of SPF were better than those of SPI, and the addition of κC significantly increased the G', apparent viscosity and resistance to denaturation of the gel. When κC concentration was 8 mg/mL, the hardness of SPI/SPF-κC was 127.2 ± 5.82 g and 134.23 ± 5.89 g, respectively. In conclusion, the fibrillation of proteins and κC can effectively improve the gel properties of SPI gels, which provides a theoretical basis for expanding the high-value utilization of SPI and SPF.

Soluble fibres modulate dough rheology and gluten structure via hydrogen bond density and Flory-Huggins water interaction parameter

Soluble fibres are gaining increasing interest for functional food applications like bread, but their interaction with gluten and effects on dough rheology are not fully elucidated. This study hypothesized that soluble fibres influence gluten structure and dough rheology by acting as plasticizers and humectants. Plasticizing properties depend on the effective number of hydrogen bonding sites available in the fibre molecule (N OH,s ). Humectant properties are related to the water interaction parameter derived from analysis of the sorption behaviour. Oligo-fructoses, inulins, polydextrose and a glucose syrup were added individually and in mixtures to wheat dough to test the hypothesis. PCA and multi-linear regressions showed that the G' from temperature sweeps increased with an increase in the effective volume fraction of hydrogen bonding sites (Φ w , e f f ) in the solvent and in the water interaction parameter (χ eff ). The enhanced G' corresponded to a reduction in tan(δ), indicating an increased elastic behaviour. The parametersΦ w , e f f and χ eff also explained the changes in phase transitions during heating, i.e. Tonset and Tpeak of starch gelatinization (R2 > 0.9). Image analysis of the gluten network revealed that fibre structure and physico-chemical properties influenced the gluten network by altering branching rate, lacunarity, and protein strand width. Comparing inulins and polydextrose of similar molecular weights (Mw) indicated that interactions with gluten were influenced more by N OH,s than Mw. High Mw inulins, with a linear structure, promoted junctions in the gluten network through hydrogen bonds, and possibly phase separation in gluten-rich and inulin-rich phases. In contrast, the more hydrophilic, branched polydextrose reduced junction formation in the gluten network due to fewer N OH,s . This study provides new insights into the physico-chemical properties of soluble fibres and their role in wheat dough functionality.

Comparison of the effects of pectin with different esterification degrees on the thermal aggregation of wheat glutenin and gliadin

Our previous study found that pectin with different degrees of esterification (DE) could affect the thermal aggregation of gluten, but the mechanism was not clear. Analyzing the thermal aggregation of glutenin and gliadin supplemented with pectin can clarify this mechanism. With the increase of temperature, the particle size, disulfide bonds and β-sheet of glutenins increased, the surface hydrophobicity (H0) and fluorescence intensity decreased, and the network gradually aggregated, but the change trend of gliadins was opposite. These results suggested that the thermal aggregation of gluten mainly depended on glutenin. Glutenin and gliadin supplemented with low ester pectin (LEP) were in an aggregated state. At 95 °C, LEP (DE = 37 %) increased the particle size of glutenin and gliadin (141.83 μm and 19.91 μm), promoted the conversion of thiol to disulfide bonds, increased β-sheet (34.01 % and 31.13 %), decreased fluorescence intensity (2186.33 and 5165.33) and H0 (49.65 and 369.26). Scanning electron microscope (SEM) indicated that glutenin and gliadin supplemented with LEP retained a dense network structure, especially glutenin. This study elucidated the specific mechanism of how pectin affected the thermal aggregation of gluten. These results provide a more comprehensive theoretical support and scientific basis for understanding how pectin regulates the final quality of gluten-based products.

Enhanced Gelation Properties and Saltiness Perception of Low-Salt Surimi Gel with Psyllium Husk Powder

Reducing salt intake is an effective strategy for preventing and managing hypertension and cardiovascular diseases. In this study, psyllium husk powder (PHP) was incorporated into surimi to address the challenges of diminished saltiness and texture in low-salt surimi products. PHP promoted the conversion of α-helix structures into β-sheet and strengthening intermolecular interactions, such as ionic bonds, hydrogen bonds, hydrophobic interactions, and disulfide bonds. The addition of PHP enhanced the connectivity and uniformity of the surimi gel network, resulting in an increase in gel strength from 11.35 to 13.88 N and a reduction in cooking loss from 6.33% to 2.27%. Additionally, the more compact gel network structure improved the fluidity of immobile water within the low-salt surimi gel. The surimi gel containing 1.5% PHP accelerated a 30% higher Na+ release rate compared to the low-salt surimi gel, enhancing the saltiness perception to levels comparable with high-salt surimi gel, as measured by an electronic tongue. These findings present a promising approach to improving the texture and saltiness perception of surimi gel products while reducing salt content.

Limited enzymatically hydrolyzed pea protein-inulin interactions in gel systems

Gelation of protein-polysaccharide mixtures can help create a variety of distinctive gel systems as compared to single polysaccharide or protein gels. The properties of these functional gels are heavily reliant upon the nature of protein-polysaccharides interactions, their gelling compatibility, and mechanism. Pea protein isolate dispersions (7.5%) were subjected to limited enzymatic hydrolysis using the enzyme Alcalase® at three hydrolysis times (0, 3, and 6 min). Inulin was added according to three ratios (0, 1:4, and 2:4) with pea protein. Viscoelastic properties of the gels formed were measured using amplitude sweep and frequency sweep. Storage modulus (G') measurements from the amplitude sweep indicated that samples hydrolyzed for 3 min with 1:4 ratio of inulin to pea protein had maximum gel strength, exhibiting G' values of ∼307 Pa. G' values for samples hydrolyzed for 0 and 6 min with different inulin ratios averaged ∼13 and ∼144 Pa, respectively. Confocal laser scanning microscopy showed that gels developed by samples hydrolyzed for 3 min showed a dense network as compared to an open network in gels formed by samples hydrolyzed for 6 min, whereas large random aggregates were observed in gels formed by samples hydrolyzed for 0 min. The study confirmed that inulin promotes noncovalent bond formation in samples hydrolyzed for 3 min with a 1:4 inulin ratio, shown by an ∼18% increased protein solubility in urea. Additionally, collaboration between noncovalent bonds and disulfide linkages stabilized the gel structure, as indicated by further increase in solubility in combination of urea and Dithiothreitol. PRACTICAL APPLICATION: Plant proteins are gaining attention as alternatives to animal proteins. However, they have inferior functionality, which affects their applicability in food products. This investigation aimed to evaluate enzymatic hydrolysis to enhance the structural and functional properties of pea proteins, thus increasing their applicability in the food industry. Inulin is an oligosaccharide and soluble fiber, which promotes gut health. Thus, gels combining hydrolyzed pea protein and inulin can serve as a model mixed food system of interest to both the industry and consumers.

Effects of inulin with different polymerization degrees on the structural and gelation properties of potato protein

This study investigated the effect of inulin with different polymerization degrees (DP), including L-inulin (DP 2-6), M-inulin (DP 10-23) and H-inulin (DP 23-46), on the structural and gelation properties of potato protein isolate (PPI). Results revealed that textural properties (hardness, cohesiveness, springiness and chewiness) and water-holding capacity (WHC) of PPI-inulin composite gels were positively correlated with the inulin DP and addition content at 0-1.5% (w/v), but deteriorated at 2% due to phase separation. The addition of 1.5% H-inulin showed the most significant increment effects on the WHC (18.65%) and hardness (2.84 N) of PPI gel. Furthermore, M-/H-inulin were more effective in increasing the whiteness and surface hydrophobicity, as well as in strengthening hydrogen bonds and hydrophobic interactions than L-inulin. Fourier transform infrared spectroscopy analysis and microstructural observation indicated that inulin with higher DP promoted more generation of β-sheet structures, and leading to the formation of stronger and finer network structures.

Rheological, thermal, and structural properties of heat-induced gluten gel: Effects of starch with varying degrees of debranching

This study evaluated the effects of starch with varying degree of debranching on the rheological, thermal, and structural properties of heat-induced gluten gel. As the duration of starch debranching treatment increased from 0 to 8 h, the viscoelasticity of the gel containing debranched starch (DBS) improved. Compared with the gluten gel (G), the gel strength of the G + DBS (8 h) sample increased by 65.2 %. The degradation temperature of gluten was minimally affected by DBS, while the weight loss rate increased by 4.4 %. Furthermore, the α-helical structure of gluten decreased, concomitant with an increase in β-sheet content. Notably, DBS treated for 8 h exhibited more hydrogen bonds with the tyrosine of gluten and triggered disulfide bridge conformation to transition from g-g-g to t-g-g, thereby reducing the stability of the molecular conformation of gluten proteins, as evidenced by the decreased height and width of the molecular chains observed in atomic force microscopy images. Overall, the composite gel structure induced by DBS exhibited a more continuous and homogeneous owing to the improved compatibility between DBS and gluten proteins, favoring the formation of a robust gel. These findings provide valuable insights for utilizing DBS to enhance gluten gel properties.

Soybean isolate protein complexes with different concentrations of inulin by ultrasound treatment: Structural and functional properties

The effects of ultrasound and different inulin (INU) concentrations (0, 10, 20, 30, and 40 mg/mL) on the structural and functional properties of soybean isolate protein (SPI)-INU complexes were hereby investigated. Fourier transform infrared spectroscopy showed that SPI was bound to INU via hydrogen bonding. All samples showed a decreasing and then increasing trend of α-helix content with increasing INU concentration. SPI-INU complexes by ultrasound with an INU concentration of 20 mg/mL (U-2) had the lowest content of α-helix, the highest content of random coils and the greatest flexibility, indicating the proteins were most tightly bound to INU in U-2. Both UV spectroscopy and intrinsic fluorescence spectroscopy indicated that it was hydrophobic interactions between INU and SPI. The addition of INU prevented the exposure of tryptophan and tyrosine residues to form a more compact tertiary structure compared to SPI alone, and ultrasound caused further unfolding of the structure of SPI. This indicated that the combined effect of ultrasound and INU concentration significantly altered the tertiary structure of SPI. SDS-PAGE and Native-PAGE displayed the formation of complexes through non-covalent interactions between SPI and INU. The ζ-potential and particle size of U-2 were minimized to as low as -34.94 mV and 110 nm, respectively. Additionally, the flexibility, free sulfhydryl groups, solubility, emulsifying and foaming properties of the samples were improved, with the best results for U-2, respectively 0.25, 3.51 μmoL/g, 55.51 %, 269.91 %, 25.90 %, 137.66 % and 136.33 %. Overall, this work provides a theoretical basis for improving the functional properties of plant proteins.

Entanglement between Water Un-Extractable Arabinoxylan and Gliadin or Glutenins Induced a More Fragile and Soft Gluten Network Structure

This study aimed to investigate the effects of water-unextractable arabinoxylan (WUAX) on the gluten network structure, especially on gliadins and glutenins. The results indicated that the free sulfhydryl (free SH) of gliadins increased by 25.5% with 100 g/kg WUAX, whereas that of glutenins increased by 65.2%, which inhibited the formation of covalent bonds. Furthermore, β-sheets content decreased 5.63% and 4.75% for gliadins and glutenins with 100 g/kg WUAX, respectively, compared with the control. WUAX increased β-turns prevalence for gliadins, while the content of α-helixes and random coils had less fluctuation. In glutenins, the contents of α-helixes and β-sheets decreased and β-turns increased. Moreover, compared with the control, the weight loss rate for gliadins and glutenins increased by 2.49% and 2.04%, respectively, with 60 g/kg WUAX. The dynamic rheological analysis manifested that WUAX impaired the viscoelasticity property of gliadin and glutenin. Overall, WUAX weakened the structure of the gliadins and glutenins, leading to quality deterioration of gluten.

Functional and structural properties of gliadin as influenced by pH, extraction protocols, and wheat cultivars

Gliadin, owing to its low cost, ease to extract, high foaming capacity, easily available and high surface hydrophobicity, has found a wide range of applications both in the food and pharmaceutical sectors. The functional and structural characteristics of gliadin extracted with four extraction protocols from six wheat cultivars were investigated in this study. The surface-active properties of gliadin protein as a function of pH, extraction protocols, and wheat cultivars were compared, including solubility, zeta-potential, foaming properties, emulsion properties, surface hydrophobicity and secondary structure. Overall gliadin extracted using different extraction protocols and from different wheat cultivars was found to be higher in β-turns (24.88-37.91 %), followed by β-sheet (12.81-22.37 %), α-helix (15.13-20.70 %) and lower in random coil (6.53-9.08 %). Varied pH ranges, wheat cultivars, and different extraction protocols were found to have a substantial impact on solubility, zeta potential, foaming stability, emulsion capacity and surface hydrophobicity. The foaming capacity was observed to be more influenced by extraction protocols than wheat cultivars. Emulsion stability showed statistically significant (p ≤ 0.05) influence between the wheat cultivars, and a non-significant (p ≥ 0.05) difference among extraction protocols. The functional properties of freeze-dried gliadin extracted using different protocols were found to be pH-dependent. A comprehensive understanding of how the structural, surface active and functional properties of gliadin are influenced by the extraction protocols and wheat cultivars will enable us to understand the gliadin better and broaden its use for both food and non-food applications.

Konjac glucomannan improves the gel properties of low salt myofibrillar protein through modifying protein conformation

Improving the characteristics of low salt proteins is the key to the gel properties of low-salt meat products which are demanded by people nowadays. The present study focused on the effects of KGM concentrations on the changes in structure and gelling properties of low-salt myofibrillar protein (MP). KGM addition (≤0.75 %) irrespective of salt concentration modified secondary and tertiary structures of MPs, enhanced the binding capacity of Troponin-T and Tropomyosin, augmented the gelling behavior of proteins, and remarkably improved the storage modulus (G') and gel strength of heat-induced MP gels. Interestingly, KGM addition in low salt condition showed the transformation of the all-gauche SS conformation into gauche-gauche-trans and trans-gauche-trans, and the partial transformation of α-helices into β-sheets. overall, KGM modified the structure of low salt MPs and thus improved the gel properties of low salt MPs. Therefore, KGM is recommended for low-salt meat processing to enhance the MP gelling potential.