Structural studies on native and chemically modified storage proteins from rapeseed (Brassica napus L.) and related plant proteins

Destructuration of Canola Protein Gels during In Situ Gastrointestinal Digestion Studied by X-ray Scattering

We are studying the destructuration of canola protein gels, as a solid food model, during in situ gastrointestinal digestion using synchrotron small-angle X-ray scattering (SAXS). Digestion of two gels, prepared by heating pH 8 and pH 11 solutions, was carried out by diffusion of enzymatic juices into the gel from the top of the capillary and monitored for several tens of hours. Very similar time evolutions of SAXS curves occur at different positions of the gel in the capillary, with a delay determined by the distance from the surface initially in contact with the digestive juice. The main phenomena observed are (i) at the scale of the protein conformation (1-5 nm). The scattering curve is a power law, the exponent of which measures the compactness (related to the degree of unfolding). It can be plotted as a function of the characteristic size of proteins/and interprotein distances and as a function of the scattering intensity. Such diagrams clearly show successive digestion processes. For the pH 11 gel, in which proteins are initially hardly unfolded, the digestive processes are unfolding (1st step), recompaction-aggregation phenomena (2nd step) due to gastrointestinal pH conditions and enzymatic cleavage, further unfolding-disaggregation (3rd step), and final protein cleavage (4th step) down to small peptides. For the pH 8 gel, proteins are initially unfolded, and only the last three steps are observed, showing the influence of easier access for the enzymes. (ii) At the scale of large aggregates (10-50 nm), we observe for both gels a decrease in the size and/or number of these aggregates during digestion and alteration of their interfaces. (iii) At the scale of the secondary protein structure, wide-angle X-ray scattering is very useful for detecting the degradation of the secondary protein structure at different steps of digestion.

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.

Structural Properties of Cruciferin and Napin of Brassica napus (Canola) Show Distinct Responses to Changes in pH and Temperature

The two major storage proteins identified in Brassica napus (canola) were isolated and studied for their molecular composition, structural characteristics and the responses of structural features to the changes in pH and temperature. Cruciferin, a complex of six monomers, has a predominantly β-sheet-containing secondary structure. This protein showed low pH unstable tertiary structure, and distinctly different solubility behaviour with pH when intact in the seed cellular matrix. Cruciferin structure unfolds at pH 3 even at ambient temperature. Temperature-induced structure unfolding was observed above the maximum denaturation temperature of cruciferin. Napin was soluble in a wider pH range than cruciferin and has α-helices dominating secondary structure. Structural features of napin showed less sensitivity to the changes in medium pH and temperature. The surface hydrophobicity (S₀) and intrinsic fluorescence of tryptophan residue appear to be good indicators of cruciferin unfolding, however they were not the best to demonstrate structural changes of napin. These two storage proteins of B. napus have distinct molecular characteristics, therefore properties and functionalities they provide are contrasting rather than complementary.

Studies on Brassica carinata seed. 1. Protein molecular structure in relation to protein nutritive values and metabolic characteristics

The objectives of this study were to investigate (1) the protein chemical profile, (2) the protein subfractions partitioned by the Cornell Net Carbohydrate and Protein System (CNCPS), (3) the rumen crude protein (CP) degradation kinetics, (4) the protein supply predicted by the DVE/OEB system, (5) the protein structural features using a Fourier transform infrared (FTIR) spectroscopic technique with attenuated total reflectance (ATR), and (6) the correlations between protein intrinsic structural features and nutritional profiles in three strains of Brassica carinata in yellow and brown seed coats, with comparison to canola seed as a reference. The results showed that carinata seed strains were different in both nutritional values and IR absorbance within the protein spectral region (ca. 1720-1482 cm(-1)). The comparison between yellow and brown B. carinata seeds indicated that the former was lower in acid detergent insoluble crude protein (ADICP; P = 0.002) and undegradable protein fraction (PC; P = 0.002) and greater in the degradable (D) fraction (P = 0.004) and true absorbed protein in the small intestine (DVE; P = 0.02) as well as feed milk value (FMV; P = 0.02) than the latter. The brown canola seed (Brassica napus L.) was also not in full accordance with B. carinata seed on these parameters. The FTIR studies showed significant differences in protein amide II peak height, amide I peak area, and β-sheet height among different B. carinata strains. However, multivariate spectral analyses indicated a similarity in protein structural makeup in these four kinds of oilseed. The not very strong correlations shown in this study implied that the limited sample size and narrow range in biological and spectral variation might be responses for the weak relationships between chemical profile and mid-IR spectral data. Further studies using sufficient samples with wide and diverse range in nutritional properties are needed to illustrate the actual relationship between spectroscopic data and nutritional profiles in oilseeds.

Explore protein molecular structure in endosperm tissues in newly developed black and yellow type canola seeds by using synchrotron-based Fourier transform infrared microspectroscopy

This study was conducted to characterize the protein molecular structure in endosperm tissues in newly developed black and yellow-type canola seeds by using synchrotron-based Fourier transform infrared microspectroscopy. The results showed that the yellow canola seeds contained relatively lower (P<0.05) percentage of β-sheet and amide I and amide II area compared to the black-type canola seed. This might be an indication that the protein value of the yellow canola seeds as food or feed is different from that of the black canola seeds. The multivariate molecular spectral analyses (AHCA, PCA) showed that there were not significant molecular structural differences in the protein amide I and amide II fingerprint region (ca. 1720-1480 cm(-1)) between the yellow and the black-type of canola seed. It can be concluded that both the yellow and the black-seeded canola contain the same proteins but in different ratios.

Canola proteins for human consumption: extraction, profile, and functional properties

Canola protein isolate has been suggested as an alternative to other proteins for human food use due to a balanced amino acid profile and potential functional properties such as emulsifying, foaming, and gelling abilities. This is, therefore, a review of the studies on the utilization of canola protein in human food, comprising the extraction processes for protein isolates and fractions, the molecular character of the extracted proteins, as well as their food functional properties. A majority of studies were based on proteins extracted from the meal using alkaline solution, presumably due to its high nitrogen yield, followed by those utilizing salt extraction combined with ultrafiltration. Characteristics of canola and its predecessor rapeseed protein fractions such as nitrogen yield, molecular weight profile, isoelectric point, solubility, and thermal properties have been reported and were found to be largely related to the extraction methods. However, very little research has been carried out on the hydrophobicity and structure profiles of the protein extracts that are highly relevant to a proper understanding of food functional properties. Alkaline extracts were generally not very suitable as functional ingredients and contradictory results about many of the measured properties of canola proteins, especially their emulsification tendencies, have also been documented. Further research into improved extraction methods is recommended, as is a more systematic approach to the measurement of desired food functional properties for valid comparison between studies.

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.

Behaviors of bovine serum albumin and rapeseed proteins at the air/water interface after grafting aliphatic or aromatic chains

The influence of grafting aliphatic or aromatic groups on the behaviors of bovine serum albumin (BSA) and rapeseed proteins (napin and cruciferin) at the air/water interface is studied. From compression isotherms, it is shown that the chemical modification induces an increase in the interfacial molecular areas of the three proteins. The more hydrophobic the groups grafted, the more important this increase is. The dilatational modulus clearly emphasized that the grafting of hydrophobic groups also leads to an increase of the collapse pressure, demonstrating a higher cohesiveness and resistance to pressure of the interfacial films. These results are discussed on the basis of the physicochemical changes due to these chemical modifications, especially the conformation, the surface hydrophobicity, and the flexibility of the modified proteins. The improvement of surface properties obtained by grafting aliphatic or aromatic chains onto these proteins looks very promising in regard to emulsifying and foaming properties.