Behaviour of a protein isolate from rapeseed (Brassica napus) and its main protein components — globulin and albumin — at air/solution and solid interfaces, and in emulsions

Oil-water interface and emulsion stabilising properties of rapeseed proteins napin and cruciferin studied by nonlinear surface rheology

HYPOTHESIS

Two major protein families are present in rapeseed, namely cruciferins and napins. The structural differences between the two protein families indicate that they might behave differently when their mixture stabilises oil-water interfaces. Therefore, this work focuses on elucidating the role of both proteins in interface and emulsion stabilisation.

EXPERIMENTS

Protein molecular properties were evaluated, using SEC, DSC, CD, and hydrophobicity analysis. The oil-water interface mechanical properties were studied using LAOS and LAOD. General stress decomposition (GSD) was used as a novel method to characterise the nonlinear response. Additionally, to evaluate the emulsifying properties of the rapeseed proteins, emulsions were prepared using pure napins or cruciferin and also their mixtures at 1:3, 1:1 and 3:1 (w:w) ratios.

FINDINGS

Cruciferins formed stiff viscoelastic solid-like interfacial layers (Gs' = 0.046 mN/m; Ed' = 30.1 mN/m), while napin formed weaker and more stretchable layers at the oil-water interface (Gs' = 0.010 mN/m; Ed' = 26.4 mN/m). As a result, cruciferin-formed oil droplets with much higher stability against coalescence (coalescence index, CI up to 10%) than napin-stabilised ones (CI up to 146%) during two months of storage. Both proteins have a different role in emulsions produced with napin-cruciferin mixtures, where cruciferin provides high coalescence stability, while napin induces flocculation. Our work showed the role of each rapeseed protein in liquid-liquid multiphase systems.

A Review of the Utilization of Canola Protein as an Emulsifier in the Development of Food Emulsions

Canola is the second-largest cultivated oilseed crop in the world and produces meal consisting of about 35-40% proteins. Despite this, less than 1% of the global plant-based protein market is taken up by canola protein. The reason behind such underutilization of canola protein and its rapeseed counterpart could be the harsh conditions of the industrial oil extraction process, the dark colour of the meal, the presence of various antinutrients, the variability in the protein composition based on the source, and the different properties of the two major protein components. Although academic research has shown immense potential for the use of canola protein and its rapeseed counterpart in emulsion development and stabilization, there is still a vast knowledge gap in efficiently utilizing canola proteins as an effective emulsifier in the development of various emulsion-based foods and beverages. In this context, this review paper summarizes the last 15 years of research on canola and rapeseed proteins as food emulsifiers. It discusses the protein extraction methods, modifications made to improve emulsification, emulsion composition, preparation protocols, and emulsion stability results. The need for further improvement in the scope of the research and reducing the knowledge gap is also highlighted, which could be useful for the food industry to rationally select canola proteins and optimize the processing parameters to obtain products with desirable attributes.

Physicochemical and functional properties of egg white peptide powders under different storage conditions

This study aims to evaluate the effects of different storage conditions (temperature and relative humidity) on the physicochemical and functional properties of egg white peptide powders (EWPPs). The samples (EWPPs) were stored for 28 d under four conditions (4 °C, 50% RH; 4 °C, 75% RH; 25 °C, 50% RH; 25 °C, 75% RH). Results showed that storage temperature and relative humidity had a significant effect on the physicochemical and functional properties of EWPPs. The contents of antioxidant amino acids such as histidine, tyrosine, tryptophan, and lysine were reduced significantly under different storage conditions, which resulted in the decrease of the antioxidant activity of EWPPs. Circular dichroism spectroscopy analysis indicated that the secondary structure of EWPPs changed from the regular structure to the irregular coiled structure during the storage. Additionally, the hydrophobic groups of the EWPPs originally embedded inside the molecules were exposed to the surface of the molecules during the storage, which led to an aggregation of EWPPs molecule and a decrease in solubility of EWPPs. The aggregation of EWPPs molecules resulted in a decrease in emulsification, emulsification stability, foaming ability and foaming stability of the EWPPs. Therefore, different storage conditions do have an impact on the physicochemical and functional properties of EWPPs. Lower temperature and humidity storing conditions were beneficial to retain the functional property of the EWPPs.

Comparative Composition Structure and Selected Techno-Functional Elucidation of Flaxseed Protein Fractions

This study aimed to comparatively elucidate the composition structure and techno-functionality of flaxseed protein isolate (FPI), globulin (FG), and albumin (FA) fractions. The results showed that FA possessed smaller particle dimensions and superior protein solubility compared to that of FG (p < 0.05) due to the lower molecular weight and hydrophobicity. FA and FG manifested lamellar structure and nearly spherical morphology, respectively, whereas FPI exhibited small lamellar strip structure packed by the blurring spheres. The Far-UV CD, FTIR spectrum, and intrinsic fluorescence confirmed more flexible conformation of FA than that of FG, followed by FPI. The preferential retention of free phenolic acids was observed for FA, leading to excellent antioxidant activities compared with that of FG in FPI (p < 0.05). FA contributed to the foaming properties of FPI, relying on the earlier interfacial adsorption and higher viscoelastic properties. FA displayed favorable emulsifying capacity but inferior stability due to the limited interfacial adsorption and deformation, as well as loose/porous interface. By comparison, an interlayer anchoring but no direct interface coating was observed for lipid droplets constructed by FG, thereby leading to preferable emulsion stability. However, FPI produced lipid droplets with dense interface owing to the effective migration of FA and FG from bulk phase, concomitant with the easy flocculation and coalescence. Thus, the techno-functionality of flaxseed protein could be tailed by modulating the retention of albumin fraction and specific phenolic acids.

Extraction, nutrition, functionality and commercial applications of canola proteins as an underutilized plant protein source for human nutrition

Concerns about sustainability and nutrition security have encouraged the food sector to replace animal proteins in food formulations with underutilized plant protein sources and their co-products. In this scenario, canola protein-rich materials produced after oil extraction, including canola cold-pressed cakes and meals, offer an excellent opportunity, considering their nutritional advantages such as a well-balanced amino acid composition and their potential bioactivity. However, radical differences among major proteins (i.e., cruciferin and napin) in terms of the physicochemical properties, and the presence of a wide array of antinutritional factors in canola, impede the production of a highly pure protein extract with a reasonable extraction yield. In this manuscript, principles regarding the extraction methods applicable for the production of canola protein concentrates and isolates are explored in detail. Alkaline and salt extraction methods are presented as the primary isolation methods, which result in cruciferin-rich and napin-rich isolates with different nutritional and functional properties. Since a harsh alkaline condition would result in an inferior functionality in protein isolates, strategies are recommended to reduce the required solvent alkalinity, including using a combination of salt and alkaline and employing membrane technologies, application of proteases and carbohydrases to facilitate the protein solubilization from biomass, and novel green physical methods, such as ultrasound and microwave treatments. In terms of the commercialization progress, several canola protein products have received a GRAS notification so far, which facilitates their incorporation in food formulations, such as bakery, beverages, salad dressings, meat products and meat analogues, and dairies.

The Effect of Precipitation pH on Protein Recovery Yield and Emulsifying Properties in the Extraction of Protein from Cold-Pressed Rapeseed Press Cake

Rapeseed is the second most cultivated oilseed after soybean and is mainly used to produce vegetable oil. The by-product rapeseed press cake is rich in high-quality proteins, thus having the possibility of becoming a new plant protein food source. This study aimed to investigate how the precipitation pH affects the protein yield, protein content, and emulsifying properties when industrially cold-pressed rapeseed press cake is used as the starting material. Proteins were extracted under alkaline conditions (pH 10.5) with an extraction coefficient of 52 ± 2% followed by precipitation at various pH (3.0–6.5). The most preferred condition in terms of process efficiency was pH 4.0, which is reflected in the zeta potential results, where the proteins’ net charge was 0 at pH 4.2. pH 4.0 also exhibited the highest protein recovery yield (33 ± 0%) and the highest protein concentration (64 ± 1%, dry basis). Proteins precipitated at pH 6.0–6.5 stabilized emulsions with the smallest initial droplet size, although emulsions stabilized by rapeseed protein precipitated at pH 5.0–6.0 showed the highest emulsion stability at 37 °C for 21 days, with a limited layer of free oil. Overall, emulsion stabilized by protein precipitated at pH 5.0 was the most stable formulation, with no layer of free oil after 21 days of incubation.

Surface tension of native and modified plant seed proteins

The present review, dedicated to Prof. Zbigniew Adamczyk on the occasion of his 70th anniversary, covers the literature data on surface tension and surface compression (dilational) rheology of the adsorbed layers of 21 plant seed proteins (10 leguminous and 11 non-leguminous plants). They are typically analyzed as protein concentrates or isolates, the latter usually obtained by isoelectric precipitation or diafiltration. Despite generally lower solubility, as compared to their animal counterparts (lactoglobulins, caseins, albumins, etc.), the plant seed proteins are also capable of lowering surface tension and forming viscoelastic adsorbed layers. Many seed proteins serve mostly as amino acids reservoirs for the future seedling (storage proteins), hence their instantaneous amphiphilicity is not always sufficient to induce strong adsorption at the aqueous-air interface. They can be, however, conveniently unfolded, hydrolyzed and/or chemically/enzymatically modified to expose more hydrophilic or hydrophobic patches. As shown in numerous contributions reviewed below, the resulting shift of the hydrophilic-lipophilic balance can boost their surface activity to the level comparable to that of many animal proteins or low molecular weight surfactants. An important advantage of the plant seed proteins over the animal ones is their much lower environmental cost and abundance in many plants (e.g. ~40% in sunflower or soybean seeds).

The Effect of pH and Storage Temperature on the Stability of Emulsions Stabilized by Rapeseed Proteins

Rapeseed press cake (RPC), the by-product of rapeseed oil production, contains proteins with emulsifying properties, which can be used in food applications. Proteins from industrially produced RPC were extracted at pH 10.5 and precipitated at pH 3 (RPP3) and 6.5 (RPP6.5). Emulsions were formulated at three different pHs (pH 3, 4.5, and 6) with soy lecithin as control, and were stored for six months at either 4 °C or 30 °C. Zeta potential and droplet size distribution were analyzed prior to incubation, and emulsion stability was assessed over time by a Turbiscan instrument. Soy lecithin had significantly larger zeta potential (−49 mV to 66 mV) than rapeseed protein (−19 mV to 20 mV). Rapeseed protein stabilized emulsions with smaller droplets at pH close to neutral, whereas soy lecithin was more efficient at lower pHs. Emulsions stabilized by rapeseed protein had higher stability during storage compared to emulsions prepared by soy lecithin. Precipitation pH during the protein extraction process had a strong impact on the emulsion stability. RPP3 stabilized emulsions with higher stability in pHs close to neutral, whereas the opposite was found for RPP6.5, which stabilized more stable emulsions in acidic conditions. Rapeseed proteins recovered from cold-pressed RPC could be a suitable natural emulsifier and precipitation pH can be used to monitor the stability in emulsions with different pHs.

Alternative Protein Sources as Technofunctional Food Ingredients

Proteins obtained from alternative sources such as plants, microorganisms, and insects have attracted considerable interest in the formulation of new food products that have a lower environmental footprint and offer means to feed a growing world population. In contrast to many established proteins, and protein fractions for which a substantial amount of knowledge has accumulated over the years, much less information is available on these emerging proteins. This article reviews the current state of knowledge on alternative proteins and their sources, highlighting gaps that currently pose obstacles to their more widespread application in the food industry. The compositional, structural, and functional properties of alternative proteins from various sources, including plants, algae, fungi, and insects, are critically reviewed. In particular, we focus on the factors associated with the creation of protein-rich functional ingredients from alternative sources. The various protein fractions in these sources are described as well as their behavior under different environmental conditions (e.g., pH, ionic strength, and temperature). The extraction approaches available to produce functional protein ingredients from these alternative sources are introduced as well as challenges associated with designing large-scale commercial processes. The key technofunctional properties of alternative proteins, such as solubility, interfacial activity, emulsification, foaming, and gelation properties, are introduced. In particular, we focus on the formation of isotropic and anisotropic structures suitablefor creating meat and dairy product analogs using various structuring techniques. Finally, selected studies on consumer acceptance and sustainability of alternative protein products are considered.

Adsorption of rapeseed proteins at oil/water interfaces. Janus-like napins dominate the interface

Plants offer a vast variety of protein extracts, typically containing multiple species of proteins that can serve as building blocks of soft materials, like emulsions. However, the role of each protein species concerning the formation of emulsions and interfaces with diverse rheological properties is still unknown. Therefore, deciphering the role of the individual proteins in an extract is highly relevant, since it determines the optimal level of purification, and hence the sustainability aspects of the extract. Here, we will show that when oil/water emulsions were prepared with a rapeseed protein extract containing napins and cruciferins (in a mass ratio of 1:1), only napins adsorbed at the interface exhibiting a soft solid-like rheological behavior. The dominance of napins at the interface was ascribed to their small size (radius r = 1.7 nm) and its unique Janus-like structure, as 45% of the amino acids are hydrophobic and primarily located at one side of the protein. Cruciferins with a bigger size (r = 4.4 nm) and a more homogeneous distribution of the hydrophobic domains couldn't reach the interface, but they appear to just weakly interact with the adsorbed layer of napins.

Statistically designed optimal process conditions for recuperation of protein from rapeseed meal

This work proposes the exploitation of under-utilized, non-expensive rapeseed press-cake as a source for producing high yield of protein, having superior whiteness and emulsion properties, and reduced level of residual phytate content. The chosen response parameters are relevant to food, pharmaceutical and cosmetic industries. Improvement in functional properties (emulsion properties) along with reduction in dark colour and toxic phytic acid level is expected to make rapeseed protein safer and commercially more viable for various applications. A multi-objective optimization technique based on Response surface methodology (RSM) has been presented. Using Derringer function, an optimum and feasible experimental condition was obtained with high composite desirability. The calculated regression model proved suitable for the evaluation of extraction process, whose adequacy was confirmed by Anderson-Darling Normality tests, Relative Standard Error of the Estimate (RSEE) and also by means of additional experiments performed at derived feasible experimental condition. The proposed simple alkaline protein extraction process, from defatted partially dephenolized rapeseed meal, under feasible optimal condition, was found to be suitable and potent for the recovery of high-quality vegetable protein.

Some characteristics and functional properties of rapeseed protein prepared by ultrasonication, ultrafiltration and isoelectric precipitation

BACKGROUND

The presence of complex protein constituents and difficulties in extracting protein from rapeseed meal limit the application of rapeseed protein in food processing. However, double-low rapeseed (low erucic acid, low glucosinolate) protein is a type of complete protein that is of potential use in the food industry. In this study the characteristics and functional properties of rapeseed protein prepared by ultrasonic-assisted extraction, ultrafiltration and isoelectric precipitation were analysed and compared with those of soybean protein.

RESULTS

The extraction efficiency with the ultrasonic-assisted method was significantly higher than that obtained with the traditional method. Ultrafiltration and isoelectric precipitation yielded three different proteins: ultrafiltered protein RPs and precipitated proteins RP5.8 and RP3.6. Chromatographic separation of RPs resulted in four fractions: RPsI, RPsII, RPsIII and RPsIV. The distribution of the isoelectric point of rapeseed protein was investigated by two-dimensional electrophoresis. The amino acid composition of RPs renders it suitable for human consumption. The hydrophobic/hydrophilic amino acid ratio of rapeseed protein was higher than that of soybean protein. The functional properties (oil adsorption ability, emulsifying capacity, foaming capacity and foam stability) of RPs, RP5.8 and RP3.6 were found to be better than those of soybean protein.

CONCLUSION

Ultrasonication and ultrafiltration were significantly better than the traditional method of rapeseed protein extraction. The ultrafiltered rapeseed protein RPs had superior functional properties. The results of this study provide useful indicators for rapeseed protein as a potential replacement for other proteins.

Characterisation and foaming properties of hydrolysates derived from rapeseed isolate

Two hydrolysis methods used to obtain rapeseed isolate derivates were compared: chemical hydrolysis performed under alkaline conditions and pepsic proteolysis performed under acidic conditions. The mean molecular weights obtained for the hydrolysates varied from 26 to 2.5 kDa, depending on the level of hydrolysis. Further characterisation showed that, at the same level of hydrolysis, the chemical hydrolysates differed by their charges and hydrophobicity from those derived from enzymatic digestion. Analysis of the foaming properties showed, for both cases, that a limited degree of hydrolysis, around 3%, was sufficient to optimise the foaming properties of the isolate despite the different physicochemical properties of the peptides generated. The study of foaming properties at basic, neutral and acidic pHs showed that the hydrolysate solutions yielded dense foams which drained slowly and which maintained a very stable volume under the three pH conditions tested.

The effects of denaturants on protein conformation and behavior at air/solution interface

In this study, we discuss the interfacial behavior of five proteins with different conformational character, and each is investigated in native and denatured states. The protein molecules are layered and spread onto the air/solution interfaces to form protein monolayer. The surface pressure-time (Pi(t)) and surface pressure-area per molecule (Pi-A) isotherms were measured by using the Langmuir-Blodgett (LB) balance consisted of a Nima trough system. The differences between monolayered protein's behaviors at air/solution interface indicate that denaturants, such as urea, guanidinium chloride and dithiothreitol, have different effects on conformational changes of proteins. Additionally, the interfacial behavior of the proteins in our study provides a fundamental profile about the protein structural stability and implies industrial applications in protein refolding process.

Adsorption Kinetics and Rheological Interfacial Properties of Plant Proteins at the Oil−Water Interface

Adsorption and rheological properties of plant proteins were determined by means of the dynamic pendant drop technique. The plant protein properties were compared with the interfacial properties of gelatin, which is well-known for its surface-active properties and is commonly used in food and health products. The results showed that alpha gliadins (wheat proteins) and pea globulins have the highest surface active properties at the oil-water interface, even higher than gelatin at the same concentration (weight/volume). After a short time of adsorption, alpha gliadin interfacial behavior is characterized by a pronounced viscoelasticity, which was confirmed with time whereas pea protein interfacial behavior became elastic after a long initial adsorption period. Finally, the behavior of gelatin is very close to the alpha gliadin behavior for the short initial adsorption period, whereas it looks like the behavior of legume seed proteins for longer times of the adsorption kinetics. This study emphasizes the importance of the choice of the proteins and the emulsification time in the encapsulation process, according to the interfacial behavior.

Comparison of protein chemical and physicochemical properties of rapeseed cruciferin with those of soybean glycinin

Rapeseeds contain cruciferin (11S globulin), napin (2S albumin), and oleosin (oil body protein) as major seed proteins. The effects of oil expression and drying conditions on the extraction of these proteins from rapeseed meal were examined. The conditions strongly affected the extraction of oleosin and only weakly affected the extraction of cruciferin and napin. The protein chemical and physicochemical properties of cruciferin, the major protein present, were compared with those of glycinin (soybean 11S globulin) under various conditions. In general, cruciferin exhibited higher surface hydrophobicity, lower thermal stability, and lower and higher solubility at mu= 0.5 and mu = 0.08, respectively, than did glycinin. At the pHs (6.0, 7.6, and 9.0) and ionic strengths (mu= 0.08 and 0.5) examined, the emulsifying ability of cruciferin was worse than that of glycinin, except at mu= 0.08 and pH 7.6. The emulsifying abilities of cruciferin and glycinin did not correlate with thermal stability and surface hydrophobicity. Higher protein concentration, higher heating temperature, higher pH, and lower ionic strength were observed to produce harder gels from cruciferin. Gel hardness partly correlated with the structural stability of cruciferin.