Characterization of biopolymers and soy protein isolate-high-methoxyl pectin complex

Effect of γ-polyglutamic acid on the physicochemical properties of soybean protein isolate-stabilized O/W emulsion

An increased interest has been observed in the application of soybean protein isolate (SPI) into O/W emulsion because of the amphipathic characteristics of SPI. However, at pH around 4.5, SPI was almost lost its hydrophilic characteristic, thus greatly limiting its application in emulsion under an acidic environment. Therefore, this drawback of SPI needs to be urgently solved. This study aims to investigate the effect of γ-polyglutamic acid (γ-PGA) on physicochemical properties of SPI-stabilized O/W emulsion. The results suggested that the interaction between γ-PGA and SPI improved the SPI solubility in solution, and increased emulsifying properties of SPI in the pH range of 4.0-5.0 via electrostatic interaction. Meanwhile, the charge neutralisation between SPI emulsions with γ-PGA was confirmed via ζ-potentiometry. With the presence of γ-PGA in emulsion at pH 4.0 and 5.0, the electrostatic complexation between SPI and anionic γ-PGA exhibited decreased the viscosity of SPI emulsion, which might be related to the phenomenon as indicated by the confocal laser scanning microscope measurements. Therefore, the electrostatic complexation between SPI and γ-PGA suggested that the promising potential of γ-PGA to be used in SPI-stabilized O/W emulsion under an acidic environment.

Optimization of Soybean Protein Extraction with Ammonium Hydroxide (NH4OH) Using Response Surface Methodology

Plants have been recognized as renewable and sustainable sources of proteins. However, plant protein extraction is challenged by the plant's recalcitrant cell wall. The conventional extraction methods make use of non-reusable strong alkali chemicals in protein-denaturing extraction conditions. In this study, soy protein was extracted using NH4OH, a weak, recoverable, and reusable alkali. The extraction conditions were optimized using response surface methodology (RSM). A central composite design (CCD) with four independent variables: temperature (25, 40, 55, 70, and 85 °C); NH4OH concentration (0.5, 1, and 1.5%); extraction time (6, 12, 18, and 24 h) and solvent ratio (1:5, 1:10, 1:15 and 1:20 w/v) were used to study the response variables (protein yield and amine concentration). Amine concentration indicates the extent of protein hydrolysis. The RSM model equation for the independent and response variables was computed and used to create the contour plots. A predicted yield of 64.89% protein and 0.19 mM amine revealed a multiple R-squared value of 0.83 and 0.78, respectively. The optimum conditions to obtain the maximum protein yield (65.66%) with the least amine concentration (0.14 Mm) were obtained with 0.5% NH4OH concentration, 12 h extraction time, and a 1:10 (w/v) solvent ratio at 52.5 °C. The findings suggest that NH4OH is suitable to extract soybean protein with little or no impact on protein denaturation.

RuBisCO as a protein source for potential food applications: a review

RuBisCO is a complete protein, widely abundant and recognized as ideal for human consumption. Further, its biochemical composition, organoleptic and physical features mean RuBisCO has potential as a nutritionally beneficial food additive. Nonetheless, despite growing plant-based market trends, there is a lack of information about the applications of this protein. Here, we explored the biochemical features of RuBisCO as a potential food additive and compared it with other plant protein sources currently available. We describe potential advantages, including nutritional content, digestibility, non-allergenicity and, potential bioactivities. Despite the lack of industrial procedures for RuBisCO purification, a growing number of novel methods are emerging, justifying discussion of their feasibilities. Overall, this information can help both researchers and industry to review the use RuBisCO as a sustainable source of protein for plant-based food products or formulation of novel functional foods.

In Vitro Digestion and Storage Stability of β-Carotene-Loaded Nanoemulsion Stabilized by Soy Protein Isolate (SPI)-Citrus Pectin (CP) Complex/Conjugate Prepared with Ultrasound

In this study, we employed the ultrasound-prepared electrostatic complex and covalent conjugate of soy protein isolate (SPI) and citrus pectin (CP) to prepare β-carotene-loaded nanoemulsions. The in vitro digestion and storage stability of nanoemulsions stabilized by different types of emulsifiers were investigated and compared. Nanoemulsions stabilized by ultrasound-treated complex/conjugate showed the highest encapsulation efficiency; during gastric digestion, these nanoemulsions also demonstrated the smallest droplet sizes and the highest absolute values of zeta potential, indicating that both electrostatic complexation/covalent conjugation and ultrasound treatment could significantly improve the stability of the resulting nanoemulsions. In comparison, complexes were more beneficial for the controlled release of β-carotene; however, the conjugate-stabilized nanoemulsion showed an overall higher bioaccessibility. The results were also confirmed by optical micrographs. Furthermore, nanoemulsions stabilized by ultrasound-prepared complexes/conjugates exhibited the highest stability during 14-day storage at 25 °C. The results suggested that ultrasound-prepared SPI–CP complexes and conjugates had great application potential for the delivery of hydrophobic nutrients.

Effect of high-intensity ultrasound on the physicochemical properties, microstructure, and stability of soy protein isolate-pectin emulsion

In this study, an emulsion stabilized by soy protein isolate (SPI)-pectin (PC) complexes was prepared to investigate the effects of high-intensity ultrasound (HIU) treatment (150-600 W) on the physicochemical properties, microstructure, and stability of emulsions. The results found that the emulsion treated at 450 W showed the best emulsion stability index (ESI) (25.18 ± 1.24 min), the lowest particle size (559.82 ± 3.17 nm), the largest ζ-potential absolute value (16.39 ± 0.18 mV), and the highest adsorbed protein content (27.31%). Confocal laser scanning microscopy (CLSM) and atomic force microscopy (AFM) revealed that the emulsion aggregation was significantly improved by ultrasound treatment, and the average roughness value (Rq) was the smallest (10.3 nm) at 450 W. Additionally, HIU treatment reduced the interfacial tension and apparent viscosity of the emulsion. Thermal stability was best when the emulsion was treated at 450 W, D43 was minimal (907.95 ± 31.72 nm), and emulsion separation also improved. Consequently, the creaming index (CI) was significantly decreased compared to the untreated sample, indicating that the storage stability of the emulsion was enhanced.

Effect of high intensity ultrasound on the structure and solubility of soy protein isolate-pectin complex

In this study, a soy protein isolate (SPI)-pectin (PC) complex was prepared, and the effects of different high intensity ultrasound (HIU) powers on the structure and solubility of the complex were studied. Fourier transform infrared (FTIR) spectroscopy analysis exhibited that with increasing HIU power, the α-helix content of the SPI in the complex was significantly reduced, and the random coil content increased; however, an opposite trend appeared after higher power treatments. Fluorescence spectra showed that HIU treatment increased the fluorescence intensity of the complex, and the surface hydrophobicity was increased. The trend of the protein structure studied by Raman spectroscopy was similar to that of FTIR and fluorescence spectroscopy. When the HIU treatment was performed for 15 min and at 450 W power, the particle size of the complex was 451.85 ± 2.17 nm, and the solubility was 89.04 ± 0.19 %, indicating that the HIU treatment caused the spatial conformation of the protein to loosen and improved the functional properties of the complex. Confocal laser scanning microscopy (CLSM) revealed that the complex after HIU treatment exhibited improved dispersibility in water and smaller particle size. Gel electrophoresis results indicated that HIU treatment did not affect the protein subunits of the complex. Therefore, the selection of a suitable HIU treatment power can effectively improve the structural properties and solubility of SPI in the complex, and promote the application of the SPI-PC complex in food processing and industries.

Comparative Analysis of the Chemical Composition and Physicochemical Properties of the Mucilage Extracted from Fresh and Dehydrated Opuntia ficus indica Cladodes

The development of sustainable extraction methods to obtain natural products constitutes a challenge for the food industry. The aim of this work was to compare yield, separation efficiency, chemical composition, and physicochemical properties of the mucilage extracted from fresh cladodes (FNM) and mucilage extracted from dehydrated cladodes (DNM) of O. ficus indica. Suspensions of fresh and dehydrated cladodes (4% w/w) were prepared for mucilage extraction by using a mechanical separation process. Subsequently, the separated mucilage was precipitated with ethyl alcohol (1:2 v/v) then, yield and separation efficiency were determined. The mucilage was characterized by measuring Z potential, viscosity, color, and texture attributes. Additionally, chemical proximate analysis, scanning electron microscopy, and thermogravimetric analysis (TGA) were conducted. No significant differences (p < 0.05) were detected in the yield and separation efficiencies between samples. Nevertheless, the dehydration process of cladodes prior to mucilage extraction increased protein, ashes, nitrogen free extract, and calcium content. The viscosity was higher in DNM than in FNM. The TGA revealed a different thermal behavior between samples. In addition, the DNM showed lower L (darkness/lightness), cohesiveness, adhesiveness, and springiness values than those of FNM. These results support that differences found between the chemical and physicochemical properties of DNM and those of FNM will determine the applications of the mucilage obtained from the O. ficus indica cladodes in the food, pharmaceutical, and cosmetic industries.

Spirulina platensis Protein as Sustainable Ingredient for Nutritional Food Products Development

Spirulina platensis, microalgae, is emerging as a sustainable source for highly nutritional food ingredient production to cover the food demands of the global population. This study aimed to characterize food prototypes supplemented with microalgae protein isolate to develop health-promoting food products. The nutritional composition (proximate composition, fatty acids, and mineral content) of the spirulina biomass, the structural characterization of spirulina platensis protein (SPP) isolates, and the physicochemical properties of SPP- developed food products were evaluated. High protein (47%), ϒ-Linolenic acid (24.45 g/100 g of fat), iron (16.27 mg/100 g), calcium (207 mg/100 g), and potassium (1675 mg/100 g) content in the spirulina biomass was found. SPP (76% of purity) with sodium alginate produced stable emulsions (>90%) during storage (14 days). Amaranth + SPP pasta resulted in good appearance, texture, color, and high nutritional value in protein (above 30%) and minerals, mainly iron (9–10 mg/100 g) and magnesium (300 mg/100 g), meeting the daily intake recommendations. In addition, the amino acid profile of the pasta was in line with the amino acid pattern requirements for adults. SPP can be considered as potential additive for emulsions stability and provided nutritional and physicochemical desired in the elaborated pasta.

Whey Protein Isolate Microgel Properties Tuned by Crosslinking with Organic Acids to Achieve Stabilization of Pickering Emulsions

Whey protein isolate (WPI) can be used effectively to produce food-grade particles for stabilizing Pickering emulsions. In the present study, crosslinking of WPI microgels using organic acids (tannic and citric acids) is proposed to improve their functionality in emulsions containing roasted coffee oil. It was demonstrated that crosslinking of WPI by organic acids reduces the microgels’ size from ≈1850 nm to 185 nm and increases their contact angle compared to conventional WPI microgels, achieving values as high as 60°. This led to the higher physical stability of Pickering emulsions: the higher contact angle and smaller particle size of acid-crosslinked microgels contribute to the formation of a thinner layer of particles on the oil/water (O/W) interface that is located mostly in the water phase, thus forming an effective barrier against droplet coalescence. Particularly, emulsions stabilized by tannic acid-crosslinked WPI microgels presented neither creaming nor sedimentation up to 7 days of storage. The present work demonstrates that the functionality of these crosslinked WPI microgels can be tweaked considerably, which is an asset compared to other food-grade particles that mostly need to be used as such to comply with the clean-label policy. In addition, the applications of these particles for an emulsion are much more diverse as of the starting material.

Rheological and Solubility Properties of Soy Protein Isolate

Soy protein isolate (SPI) powders often have poor water solubility, particularly at pH values close to neutral, which is an attribute that is an issue for its incorporation into complex nutritional systems. Therefore, the objective of this study was to improve SPI solubility while maintaining low viscosity. Thus, the intention was to examine the solubility and rheological properties of a commercial SPI powder at pH values of 2.0, 6.9, and 9.0, and determine if heat treatment at acidic or alkaline conditions might positively influence protein solubility, once re-adjusted back to pH 6.9. Adjusting the pH of SPI dispersions from pH 6.9 to 2.0 or 9.0 led to an increase in protein solubility with a concomitant increase in viscosity at 20 °C. Meanwhile, heat treatment at 90 °C significantly improved the solubility at all pH values and resulted in a decrease in viscosity in samples heated at pH 9.0. All SPI dispersions measured under low-amplitude rheological conditions showed elastic-like behaviour (i.e., G′ > G″), indicating a weak “gel-like” structure at frequencies less than 10 Hz. In summary, the physical properties of SPI can be manipulated through heat treatment under acidic or alkaline conditions when the protein subunits are dissociated, before re-adjusting to pH 6.9.

Complex coacervate formation between hemp protein isolate and gum Arabic: Formulation and characterization

In this study, intermolecular interactions and structure formation between hemp protein isolate (HPI) and gum Arabic (GA) were investigated to unravel their complexation mechanisms. For this purpose, structural transition as a function of pH (2.0-7.0) and protein to polysaccharide ratio (HPI:GA, R = 0.5:1-13:1 w/w) was evaluated via turbidimetric analysis, ζ-potentiometry, state diagram construction and coacervate yield. It was proved that critical phase transition pH shifted to higher values with R increase, until reaching a plateau at ratio 10:1, with complexes to be formed even at pH region where both biopolymers were negatively charged. The shift of pH value, where maximum turbidity was noticed (pH_opt), was well in accordance with net charge neutrality of HPI-GA mixtures found by electrophoretic mobility measurements. Maximum coacervation, occurred at ratio R = 2:1 and pH_opt = 3.5, was depicted by the highest yield (92%), while morphological characteristics of liquid as well as freeze-dried HPI-GA coacervates, obtained through optical and scanning electron microscope measurements, gave a further perception of the associative processes during complex coacervation. Additionally, the molecular interactions between HPI and GA were confirmed by Fourier transform infrared spectroscopy (FTIR) revealing primarily electrostatic interactions with secondary stabilization of hydrogen bonds. Therefore, these findings could provide useful information for the development of HPI - GA coacervates as a potential bioactive encapsulation means.

Modulation of volatile release and antimicrobial properties of pink pepper essential oil by microencapsulation in single- and double-layer structured matrices

The bioactivity of essential oils applied in foods to act as natural preservatives can be reduced due to interactions with other components of the food matrix. Microencapsulation can help to increase the functionality of these compounds. In addition, the electrostatic interaction between proteins and polysaccharides can result in double-layered encapsulating structures, ensuring greater protection to essential oils than using only protein as surface active agent. In this work, pink pepper essential oil was microencapsulated by spray drying of single-layer emulsions, stabilized by soy protein isolate (SPI), and of double-layer emulsions, stabilized by soy protein isolate/high methoxyl pectin (SPI/HMP). Pink pepper essential oil showed predominance of α-pinene, β-pinene, β-mircene, δ-3-carene, d-limonene, and germacrene D. Compared to SPI microcapsules, SPI/HMP microcapsules better preserved the total volatile content identified in pure oil, showed less water adsorption during storage at relative humidity ≥75% and improved antimicrobial properties. When stored for 20 days (25 °C/RH = 52.8%), both microcapsules allowed more gradual release of volatiles compared with non-encapsulated oil. Microencapsulation by spray drying did not have negative effects on the antioxidant activity of the encapsulated oil, as the microcapsules showed similar results to the non-encapsulated oil, around 11 μg Trolox/mg of oil. After storage, however, the non-encapsulated oil showed greater losses of its antioxidant activity due to higher rates of volatile release. In the in vitro antimicrobial activity assay, both microcapsules inhibited growth of Staphylococcus aureus, Bacillus subtilis, Listeria monocytogenes and Listeria innocua, although no inhibition was observed against Gram-negative bacteria. When added in milk, both microcapsules reduced bacterial growth, whereas non-encapsulated oil showed no satisfactory inhibition. Faster reduction of microbial growth in milk was observed for SPI/HMP microcapsules. Inhibition results were better for skim milk than for whole milk, suggesting that the interaction of essential oil with other lipids present in milk decreased its bioactivity. Microencapsulation positively affected the functionality of pink pepper essential oil, highlighting its potential for application as a natural preservative in food products.