Abstract
Rapeseed meal is a by-product of the oil-producing industry with a currently underestimated application. Two protein isolates, PI2.5–8.5 or PI10.5–2.5, were obtained from industrial rapeseed meal after treatment with an aqueous ethanol solution. The alkaline-extracted proteins were sequentially precipitated by two different modes, from pH 10.5 to 2.5, and vice versa, from 2.5 to 8.5, with a step of 1 pH unit. The preparation approach influenced both the functional and antioxidant properties of the isolates. The PI10.5–2.5 exhibited higher water and oil absorption capacities than PI2.5–8.5, reaching 2.68 g H2O/g sample and 2.36 g oil/g sample, respectively. The emulsion stability of the PI2.5–8.5, evaluated after heating at 80 °C, was either 100% or close to 100% for all pH values studied (from 2 to 10), except for pH 6 where it reached 93.87%. For the PI10.5–2.5, decreases in the emulsion stability were observed at pH 8 (85.71%) and pH 10 (53.15%). In the entire concentration range, the PI10.5–2.5 exhibited a higher scavenging ability on 2,2-diphenyl-1-picryl hydrazyl (DPPH) and hydroxyl radicals than PI2.5–8.5 as evaluated by DPPH and 2-deoxyribose assays, respectively. At the highest concentration studied, 1.0%, the neutralization of DPPH radicals by PI10.5–2 reached half of that exhibited by synthetic antioxidant butylhydroxytoluene (82.65%). At the same concentration, the inhibition of hydroxyl radicals by PI10.5–2 (71.25%) was close to that achieved by mannitol (75.62%), which was used as a positive control. Established antioxidant capacities add value to the protein isolates that can thus be used as both emulsifiers and antioxidants.
Highlights
Rapeseed oil is a valuable commodity widely used in the food industry [1] or other industrial sectors to produce biofuel, paper, textile, plastics, lubricants, and surfactants [2,3]
The protein isolate PI10.5–2.5 was obtained by sequential precipitation of the proteins from the extract starting at pH 10.5 to 2.5 by lowering the pH by one unit
The authors speculated that the PI10.5–2.5, having a precipitation onset at pH 10.5, contained a higher amount of napin and less cruciferin than PI2.5–8.5, which explained the better solubility of the PI10.5–2.5 in the acidic pH region [21]
Summary
Rapeseed oil is a valuable commodity widely used in the food industry [1] or other industrial sectors to produce biofuel, paper, textile, plastics, lubricants, and surfactants [2,3]. It is used in agriculture for dust masking in swine barns [4] or as a biopesticide [5]. It is used as an inexpensive protein-rich ingredient in feed formulation [8,9]. The presence of substantial amounts of glucosinolates, tannins, and fibres limits the inclusion of the meal because of their negative effect on animal growth and physiology [10]
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