Nitrogen extraction from defatted rapeseed, with particular reference to United Kingdom commercial rapeseed meal

Nitrogen extraction profiles of rapeseed (RS), post‐press cake (PP) and commercial rapeseed meal (RSM), drawn from the same batch, were evaluated; the RS and PP being defatted in the laboratory prior to extraction. The RSM exhibited lower nitrogen extractability, with the profiles less sharply defined, at different conditions of pH and ionic environment than for RS or PP. This was attributed to the heat treatment received at the end of the process during the toasting‐desolventisation. The nitrogen extractability of RSM was further investigated using double extraction techniques with different solvents (NaCl, CaCl 2 and water), over a wide range of pH. None of the extraction regimes studied suggested improved practical possibilities for meal protein extraction, compared with single aqueous extraction at high pH. Meal protein extracts however, were found to be comparatively high in crude protein when expressed on a solids basis, a fact which suggests the possibility for additional concentration by ultrafiltration.