Preparation and characterization of emulsion gels stabilized by adequately preprocessed insoluble soybean fiber from okara

Emulsion gels as soft materials were formulated by insoluble soybean fiber (ISF) assembled from okara in this study. Steam explosion on okara (ISFS) transformed the insoluble fiber in the original okara (ISFU) into soluble fiber. Enzymatic hydrolysis led to a lower protein content, smaller particle size and smaller contact angle of ISF. ISFE, which was obtained by enzymatic hydrolysis of ISFU, was not able to produce stable emulsion gels at 0.50 to 1.50 wt% ISF, whereas the ISF after a combined steam explosion-enzymatic hydrolysis treatment (giving rise to ISFSE) stabilized emulsion gels at varying oil volume fractions (phi) from 10 to 50%. The zeta-potential of emulsion gels was around -19 to -26 mV. The droplet size first decreased (from 43.8 mu m to 14.8 mu m when at phi = 0.3) with increasing ISF content (from 0.25 wt% to 1.25 wt%) and then remained constant, as also seen from the microstructure. The apparent viscosity and viscoelastic properties were strengthened upon increasing both the ISF concentration and oil volume fraction. The protein and soluble fiber contributed to the interfacial activity of ISF while the insoluble fiber played an important role in the gel-like structured network of emulsion gels, making them maintain physical stability during long term storage. These findings could provide novel information about soybean fiber to fabricate soft materials and the utilization of okara at an industrial-scale

Characteristics of insoluble soybean fiber (ISF) concentrated emulsions : effects of pretreatment on ISF and freeze–thaw stability of emulsions

The properties of emulsions could be affected by the interactions between the components and network stabilization effect, which are commonly adjusted by changes in pH, ionic strength and temperature. In this work, insoluble soybean fiber (ISF) obtained via homogenization after alkaline treatment was pretreated firstly and then resultant emulsions were freeze-thawed. Heating pretreatment reduced droplet size, enhanced viscosity and viscoelasticity as well as subsequent stability of ISF concentrated emulsions, while both acidic pretreatment and salinized pretreatment decreased the viscosity and weakened the stability. Furthermore, ISF emulsions exhibited a good freeze-thaw performance which was further improved by secondary emulsification. Heating promoted the swelling of ISF and strengthened the gel-like structure of emulsions while salinization and acidization weakened the electrostatic interactions and caused the destabilization. These results indicated that pretreatment of ISF significantly influenced the concentrated emulsion properties, providing guidance for the fabrication of concentrated emulsions and related food with designed characteristics

Effect of alkaline pH on the physicochemical properties of insoluble soybean fiber (ISF), formation and stability of ISF-emulsions

Cellulose derived from agricultural by-products as a promising stabilizer for novel food emulsions has been attracting numerous interests. In this work, defatted okara was used to extract insoluble soybean fiber (ISF) under alkaline pH (7.0-12.0). The physicochemical properties of ISF, as well as the formation and stability properties of O/W emulsions (10% w/w of oil) prepared by ISF, were characterized. The results exhibited a lower residual protein content (p < 0.05), as well as a stronger electronegativity and hydrophilicity of ISF, as indicated by -potential and water-in-air three-phase contact angles (theta(wa)) measurements, respectively, as the treating pH increased. ISF extracted at lower pH (<= 10.0) could quickly form O/W emulsions, whereas with little stability. For the emulsions with better stability prepared using ISF extracted at pH 12.0, the storage ability (30 d), and sensitivity regarding pH and NaCl were evaluated. The results revealed that the gel-like network, electrostatic repulsion, and steric hindrance played dominant roles in stabilizing ISF-emulsions. These results will contribute to the development of efficient ISF-based emulsifiers/stabilizers, which may greatly improve the valorisation of soybean by-products

Formation and characterization of oleogels derived from emulsions : evaluation of polysaccharide ratio and emulsification method

In the present work, highly oil-binding oleogels were fabricated by two polysaccharides (insoluble soybean fiber (ISF) and hydroxypropyl methylcellulose (HPMC)) using an emulsion-templated method. The polysaccharide -based network was developed by oven-drying ISF and HPMC co-stabilized emulsions to obtain the oleogels and two emulsification methods were compared. The aqueous polysaccharide mixtures displayed an increased hydrodynamic diameter but decreased viscosity with increasing proportions of ISF, leading to a reduced inter-facial tension. Increased HPMC reduced the droplet size of emulsions while it improved the apparent viscosity and loss modulus. Emulsions prepared by high-pressure homogenization displayed a smaller droplet size and lower viscosity while the oleogels exhibited abundant liquid oil. By contrast, emulsions prepared by high-speed shearing presented a larger droplet size while the oleogels exhibited well-structured semi-solid oil. The oleogels were endowed with stronger gel strength (increased to 184 g and 461 g, respectively) and hardness from increased HPMC, resulting in a decreased oil loss. Increasing the HPMC content contributed to a more compact structure of the oleogels and emulsions whereby emulsions with a too small droplet size were difficult to be fully converted into gel-like semi-solid oil. Results indicate that ISF and HPMC can be applied in structuring oleogels as substitutes for solid fats

Rheology and stability of concentrated emulsions fabricated by insoluble soybean fiber with few combined-proteins: Influences of homogenization intensity

Insoluble soybean fiber with few proteins, which is extracted from defatted okara by homogeneous combined with alkali treatment, was used to prepare concentrated emulsions. Firstly, insoluble soybean fiber extracted under pH12 was used to fabricate concentrated emulsions containing various particle concentrations and oil volume fractions and the optimized condition was obtained. Subsequently, insoluble soybean fiber extracted under pH12 followed by different homogeneous strengths were utilized. Concentrated emulsions stabilized by insoluble soybean fiber that was subjected to stronger homogenization presented lower absolute values of the zeta-potential about -47.7 mV and average droplet sizes of 37.0 mu m approximately. Moreover, these emulsions exhibited a higher viscosity and elastic modulus, thereby providing better stability and less pronounced environmental sensitivities towards either pH 5 or 100 mM NaCl. Overall, results revealed that insoluble soybean fiber with few protein, especially subjected to homogenization during fiber extraction, was well suited to fabricate concentrated emulsions

Effect of homogenization associated with alkaline treatment on the structural, physicochemical, and emulsifying properties of insoluble soybean fiber (ISF)

Comprehensive utilization of okara has received a growing interest from manufacturers and researchers in the food industry. In this work, ISF was extracted from defatted okara in the sequence of "homogenization followed by pH12 treatment" and "pH12 treatment followed by homogenization", which are indicated as HA-ISF and AH-ISF, respectively; Subsequently, the basic properties and initial structure of these ISFs, as well as their emulsification performance were systematically characterized. The results indicated that as the homogenization intensity was enhanced, more negatively charged, smaller particle as well as porous structures were detected in the extracted ISF. The size of oil droplets in ISF-emulsions decreased and then increased, the absolute value of the zeta-potential and the loss angle (tan delta) were reduced, the apparent viscosity and elastic modulus (G') increased, and the flocculated structure in the ISF-emulsions was promoted as the homogenization intensity was increased. Creaming in the ISF-emulsions was effectively inhibited by homogenization via adsorption of ISF onto the interface and network stabilization. More obvious aforementioned changes were observed in AH-ISF than HA-ISF, as well as in the corresponding emulsions. These results provided valuable information for the exploitation of ISF as emulsifier, which is a promising approach to enhance the added-value of okara

Evaluation of the Hydrolysis Specificity of an Aminopeptidase from <i>Bacillus licheniformis</i> SWJS33 Using Synthetic Peptides and Soybean Protein Isolate

The substrate specificity of aminopeptidases has often been determined against aminoacyl-<i>p</i>-nitroanilide; thus, its specificity toward synthetic peptides and complex substrates remained unclear. The hydrolysis specificity of an aminopeptidase from <i>Bacillus licheniformis</i> SWJS33 (BLAM) was evaluated using a series of synthetic peptides and soybean protein isolate. The aminopeptidase showed high specificity for dipeptides with Leu, Val, Ala, Gly, and Phe at the N-terminus, and the specificity was significantly affected by the nature of the penultimate residue. In the hydrolysis of soy protein isolate, BLAM preferred peptides with Leu, Glu, Gly, and Ala at the N-terminus by free amino acid analysis and preferred peptides with Leu, Ala, Ser, Trp, and Tyr at the N-terminus by UPLC-MS/MS. The introduction of complex substrates provides a deeper understanding of the aminopeptidase’s specificity, which can instruct the application of the enzyme in protein hydrolysis