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.

-Protein rich meal is a valuable co-product of canola/rapeseed oil extraction. Seed storage proteins that include cruciferin (11S) and napin (2S) dominate the protein complement of canola while oleosins, lipid transfer proteins and other minor proteins of non-storage nature are also found. Although oil-free canola meal contains 36-40% protein on a dry weight basis, non-protein components including fibre, polymeric phenolics, phytates and sinapine, etc. of the seed coat and cellular components make protein less suitable for food use. Separation of canola protein from non-protein components is a technical challenge but necessary to obtain full nutritional and functional potential of protein. Process conditions of raw material and protein preparation are critical of nutritional and functional value of the final protein product. The storage proteins of canola can satisfy many nutritional and functional requirements for food applications. Protein macromolecules of canola also provide functionalities required in applications beyond edible uses; there exists substantial potential as a source of plant protein and a renewable biopolymer. Available information at present is mostly based on the protein products that can be obtained as mixtures of storage protein types and other chemical constituents of the seed; therefore, full potential of canola storage proteins is yet to be revealed.Keywords: Canola / rapeseed storage proteins / cruciferin / napin / protein digestibility / functional properties Résumé -Protéines de canola et de colza : fonctionnalités et nutrition. Les tourteaux riches en protéines repré-sentent un coproduit de valeur de l'extraction de l'huile de canola/colza. Dans la graine, les protéines de stockage, notamment la cruciférine (11S) et la napine (2S), dominent la fraction protéique du canola, mais des oléosines, des protéines de transfert de lipides et d'autres protéines mineures non dédiées au stockage sont également présentes. Bien que le tourteau de canola déshuilé contienne 36-40 % de protéines sur poids sec, la présence de composants non protéiques, dont les fibres, les polymères phénoliques, les phytates, la sinapine, etc. issus de l'enveloppe de la graine et des composants cellulaires rendent les protéines moins appropriées à une utilisation en alimentation humaine. Cette revue présente les connaissances actuelles en termes de valeur nutritionnelle et fonctionnelle des protéines issues des graines de canola. La séparation des protéines de canola des composants non protéiques représente un défi technique mais nécessaire pour libérer totalement le potentiel nutritionnel et fonctionnel de la protéine. Les protéines de stockage de canola peuvent satisfaire un grand nombre d'exigences nutritionnelles et fonctionnelles pour des applications alimentaires. Les macromolécules protéiques de canola offrent également des fonctionnalités requises dans les applications dépassant les seules utilisations alimentaires ; un potentiel important existe en tant que source de protéines végétales et de biopol...

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Seeds of six commercially produced Brassica juncea, Brassica napus and Sinapis alba varieties representing high-glucosinolate condiment-type and lowglucosinolate canola-type were studied for solubility characteristics of the predominant seed storage proteins (SSPs). The non-protein nitrogen components such as glucosinolates, nucleic acids, betaine, choline and sinapine contributed 3.1-5.2% and 7.9-10.8% for the total N content of low-and high-glucosinolate meals, respectively. The cruciferin and napin which are the predominant SSPs of crucifers were purified from these seeds and used to confirm soluble protein types under the conditions provided. The napins were soluble between pH 2 and 4 but not the cruciferins. Strong alkaline pH brought both cruciferin and napin into solution. In general, the SSP solubility was increased due to the presence of NaCl or CaCl 2 salts in the medium. The effect of CaCl 2 on solubility was more positive than NaCl for all the seed types except S. alba at neutral and alkaline pH. Presence of salts indeed reduced solubility of S. alba SSPs at alkaline pH. The medium pH and salt ions and their ionic strength can be manipulated to achieve selective solubility of napin and cruciferin of Brassicaceae seed meals.

Defatted meals and protein concentrates from six accessions of Sinapis alba and one accession of Brassica juncea mustard seeds were analysed for their polypeptide profile and functional properties. Two types of protein concentrates were prepared using acid-induced and calcium-induced protein precipitations. Meals from the S alba seeds had similar polypeptide composition, which was different from that of the B juncea meal. Non-reducing sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that two of the major polypeptides (50 and 55 kDa) in S alba seeds were susceptible to acid-induced precipitation but resistant to calcium-induced precipitation. The B juncea meal proteins were significantly (p ≤ 0.05) more susceptible to heat coagulation than the S alba meal proteins. Emulsifying activity index was significantly higher (p ≤ 0.05) in the B juncea meal and protein concentrates when compared with similar products from S alba. It was concluded that the presence of a high-molecular-weight (135 kDa) disulfide-bonded polypeptide could have contributed to the lower emulsifying power of the S alba products when compared with the B juncea proteins that do not have this polypeptide.