Influence of dehulling of rape seeds on chemical composition of meal

The aim of this work was to determine the effectiveness of dehulling of rape seeds with the objective of raising nutritive value of meal. udy was carried out on three Polish varieties of winter rape seeds and their fractions, size >2.0–2.5 mm (large) and 1.6–2.0 mm (small). Content of hull and chemical composition of seeds, hull and embryo were determined. Dehulling of rape seeds by definite deformation method and separation pneumatically was undertaken and the chemical composition of resultant fractions was determined. No significant differences (P≤0.05, n=6) in content of protein and crude fibre in seeds depending on variety were observed. The lowest content of hull (138 g kg−1) was from large seeds of the variety Polo. Large seeds show significantly higher (P≤0.05, n=18) mass of 1000 seeds (5.79 g) and contained more oil (2.5%), crude protein (2.6%), less hull (8.8%) and crude fibre (3.1%) but also more glucosinolates (by 10.4%). Significant differences (P≤0.01, n=9) in chemical composition (dry matter, oil, crude protein, crude fibre, tannic acid, condensed tannins, phytates, iron, copper and zinc) between hull and embryo were observed. The composition of hull and embryo was independent on size of seeds (at the 95.0% confidence level). Dehulling increased content of protein (to 439 g kg−1), glucosinolates (20.3 μM g−1), tannic acid (22.0 g kg−1), phytates (49.1 g kg−1) and zinc (63.3 mg kg−1) in meal and decreased content of crude fibre (67 g kg−1), condensed tannins (179 mg catechin × 10−2 g−1), iron (83.8 mg kg−1) and copper (5.7 mg kg−1). In the experimental conditions (n=6) dehulling of seeds reduced the meal fibre content from 124 to 72 g kg−1 (on oil-free dry matter basis) and increase of crude protein content from 388 to 437 g kg−1. The compositions of fraction overflow (dry matter, crude fibre, tannic acid) and underflow (crude protein, glucosinolates) depended on size of seeds (at the 95.0% confidence level).