Solubility, In Vitro Digestibility and Allergenicity of Brassica juncea, Brassica napus and Sinapis alba Proteins
Canola (Brassica napus, Brassica rapa and Brassica juncea) and mustard (Brassica juncea and Sinapis alba) are economically important Brassicaceae crops in Canada. Distribution of proteins and antinutritive compounds in the seed coat and cotyledons and the solubility properties of the seed proteins were evaluated in six varieties of Brassicaeae [(B. juncea (oriental, brown and canola-quality mustard), B. napus (canola) and S. alba (yellow mustard)]. In vitro digestibility and potential allergenicity, as determined by pepsin digestibility and bioinformatic analysis, respectively, were conducted for the major seed storage proteins. The major components in Brassicaceae oilseeds are oil and proteins. B. juncea and B. napus seed contain 40-42% oil; for S. alba seed the value is 30-32%. The seed coat percentage (by weight) of S. alba seed is higher than that of the other species; canola-quality B. juncea seed has a lower content of seed coat than B. napus. Glucosinolates, phytic acid and phenolic compounds are minor compounds present in Brassicaceae seed which may have negative effects on the nutritional value of seed meal. The contribution of non-protein nitrogen to total seed N ranged from 3.1-10.8% depending on the seed type. In Brassicaceae seeds, 11S cruciferin and 2S napin were the major storage proteins. The solubility of storage proteins from all Brassicaceae seeds was dependent on pH. Napin protein in all species showed high solubility between pH 3 and 4, and the minimum total protein solubility of seed was observed within this range. Both napin and cruciferin proteins were soluble in strongly alkaline and acidic pH ranges. In all varieties, Na+ and Ca2+ increased overall protein solubility; however, the extent of protein solubility changes in relation to ion type varied among species. The combination of salt and pH in the media can be manipulated to maximize the solubility of seed storage proteins. The in vitro digestibility values for the defatted meals were lower than those of the napin-free meals. Napin protein exhibited the lowest digestibility, and for the six seed types it was less than 10%. It was evident that the low digestibility of napin was related to the overall low protein digestibilities of the meals, and that low level of intestinal protease inhibitors, i.e., trypsin and chymotrypsin inhibitors, may have a negligible effect on protein digestibility. At a high pepsin concentration, cruciferin was quickly digested and would be expected to show no or weak resistance to proteolytic cleavage under simulated gastric conditions. However, napin was resistant to pepsin digestion, and a large fraction of this protein remained intact within the gastric and intestinal digestion period, indicating the potential to remain as a gastrointestinal allergen. The sequence homology assessment of napin from B. juncea, B. napus and S. alba revealed a high degree of homology among the napin protein of these species, and some isoforms exhibited almost 100% sequence identity to the known mustard allergens (Bra n 1, Bra j 1, Sin a 1) and a strong possibility of cross-reactivity among species. Cruciferin protein sequence alignment resulted in lower scores for other known allergens (from cashew, hazelnut, etc.). This implies that cruciferin protein has a lower possibility of cross-reactivity with these known seed allergens.
DegreeMaster of Science (M.Sc.)
DepartmentFood and Bioproduct Sciences
SupervisorWanasundara, Janitha; Shand, Phyllis
CommitteeReaney, Martin; Tabil, Lope
Copyright DateNovember 2011
Canola, protein, digestibility, allergenicity, solubility