Residual Waste After Protein Isolation From Ethanol-Treated Rapeseed Meal has Physico-Chemical Properties for Functional Food Systems Formulation

Rapeseed meal is a by-product of the oil-producing industry which is currently underutilized. The study was focused on biochemical and functional characterization of deproteinized rapeseed meal residue (DRM) which remained after protein extraction from ethanol-treated rapeseed meal as a waste. The influence of pH (3–10), NaCl concentrations (0.03 and 0.25 M) and temperature (20–90 °C) on water absorption capacity (WAC) of the DRM were evaluated. The new product mainly consisted of proteins (16.79%) and dietary fibers (67.59%). Cellulose (29.16/100 g) and lignin (20.48/100 g) prevailed in the alcohol-insoluble fraction of the DRM. The DRM was rich in micronutrients with iron being in the highest amount (94.19 mg/kg) followed by zinc (63.96 mg/kg) and manganese (45.31 mg/kg). Thermogravimetric and differential scanning calorimetry analyses demonstrated that thermal degradation of the material began after 160 °C. Up to this temperature, the sample weight was reduced by 10.1% which was due to the release of water. DRM exhibited pH-dependent WAC which varied from 3.80 (g H2O/g sample) to 5.00 (g H2O/g sample) under all conditions studied. The highest WAC was observed at alkaline pH (8, 9 and 10), while the lowest values were obtained in highly acidic pH (3 and 4) regardless of NaCl supplementation level. Significant influence of the NaCl addition was observed in alkaline media (pH 9 and 10) but not in the acidic pH range. Temperature elevation slightly increased the WAS of the DRM which, however, did not exceed one unit (1 g H2O/g sample) in a difference. The DRM exhibited relatively high WAC which implied its potential utilization as a value-added product in the food industry.