A B S T R A C TKey words: Rapeseed detoxification, seed flour, functional properties, foaming capacity, water absorption, cooking loss, amino acid composition.
INTRODUCTIONThe increased interest in rapeseed as a source of edible oil and protein (Appelquist and Ohlson 1972;Bunting 1986) Few investigations of the functional properties of the resulting rapeseed flours or protein concentrates have been published and in these an acceptable or good functionality has been reported. However, one has to draw attention to the deteriorating effect of heat treatment on the functional properties of rapeseed protein products reported by Hermanson et a1 (1974) and Ohlson and Anjou (1979). A chemical or enzymic modification of such a protein concentrate was necessary to obtain a product with acceptable functionality (Hermanson et a1 1974). Moreover, heat treatment of intact rapeseeds or rapeseed meals not only causes aggregation and denaturation of proteins but also favours undesirable interactions between proteins and non-protein compounds.The present paper is concerned with a procedure for the preparation of detoxified and high-functional rapeseed flours which consists of the first stage of a lowtemperature soaking of intact seed under mild acidic or alkaline conditions.
EXPERIMENTAL
MaterialsThe rapeseed flours were prepared from a low-erucic acid variety 'Marinus' of Brassica napus (harvested 1986). Ammonium carbamate (Merck, Darmstadt, FRG), citric acid (Chemapol, Prague, CSSR) and Reinecke salt (Fluka AG, Buchs, Switzerland) were analytical reagent grade.Preparation of rapeseed flours (Fig 1) Ammonium carbarnate variant Rapeseed (1 kg) was soaked overnight with 1 litre of 50g litre-' ammonium carbamate solution at room temperature (pH 7-9). The procedure was repeated after draining the swollen seeds by suction. The seeds were then dried on filter paper at room temperature and finally kept for 2 h at 60°C in an oven. The dried seeds (900g) were crushed in a roll crusher. The dehulling was performed using air classification after screening the raw meal through a 2-mm sieve. Then the meal was defatted by diethyl ether extraction in a Soxhlet apparatus. The defatted material was finely ground and screened. The fraction with particle diameter < 160 pm was used for the final dehulling step. The latter consisted of flotation of the small hull fraction still remaining in the meal using hexane according to Sosulski and Zadernowski (1981); 160 g of a light creamcoloured flour was obtained (sample 1).
Citric acid variantRapeseeds (1 kg) were soaked for 3 h with 1 litre l o g litre-' citric acid monohydrate and filtered under suction. The pH of the filtrate was 4.0. The procedure was repeated three times. The pH of the last filtrate was 3.5. After drying, defatting and dehulling as in the foregoing procedure, 150g of a light cream coloured flour with a particle diameter < 160 pm was obtained (sample 2).
Alcohollammonia treatmentTen grams each of samples 1 and 2 above were stirred with 80 ml of a mixture of methanol/ammonia (85 vol m...
