Dispersion stability of non-refined turnip rapeseed (Brassica rapa) protein concentrate: Impact of thermal, mechanical and enzymatic treatments

Abstract

Aqueous dispersion properties of a protein concentrate obtained from turnip rapeseed (Brassica rapa) press cake were investigated. Protein content of the press cake was enriched from 35.9% to 45.8% by sequential supercritical-CO2 extraction, milling and air classification. The protein denaturation degree and the solubility in the prepared protein concentrate were compared with a commercial canola protein isolate. Partial loss of the protein native structure was observed in the protein concentrate. The ζ-potential in the soluble fraction of the protein concentrate dispersion was ca. 20mV lower (more negative) compared with the commercial isolate at pHs 4–10, which was attributed to the presence of charged carbohydrates such as pectin in the protein concentrate. To improve the dispersion stability of the protein concentrate, enzymatic crosslinking with transglutaminase and microfluidization at 1850 bars were applied. Microfluidization resulted in the formation of rod-like aggregates formed mainly of the insoluble cell wall polysaccharides glued together with proteins as imaged by confocal laser scanning microscopy. Improvement in colloidal stability was observed in all samples upon microfluidization. Pre-treatment with transglutaminase resulted in different distributions of the components in the rods and further improved dispersion stability against sedimentation. Heat treatment caused compaction of the structures.