Effects of pressing technology of oil separation and heat treatment on the protein value of low-glucosinolate rapeseed cake for non-ruminants

The effects o f two pressing methods vs solvent extraction, and o f different heat treatment o f the press cake on the nutr i t ional value o f rapeseed protein were studied. Rapeseed cake contained more fat (9-12 vs 4-5% D M ) and less protein (31-33 vs 36% D M ) than solvent extracted meal while digestibility and biological value o f cake and meal protein for rats d id not differ significantly (80.9 vs 79.2 and 86.1 vs 83.5, respectively). The incubation o f seeds pr ior to pressing aiming at activation o f endogenous enzymes had variable effects. The first batch o f the pre-incubated cake had lower lysine content (4.91 vs 5.76g /16g N ) , ileal digestibility o f lysine in pigs (57.8 vs 72.3%) and biological value o f protein for rats (78.8 vs 86.8) as compared wi th solvent meal. The second batch evaluated in rats had lower biological value o f protein (81.9 vs 86.1) only as compared w i t h cake f rom nonincubated seeds. Heat treatment o f the cake on pi lot scale (autoclaving or toasting and heat moisture treatment at 120 and 140°C) reduced glucosinolate content f rom 22.9 to 9.1 /rni/g fat-free D M and tended to decrease protein digestibility (from 80.4 to 76.6) but not its biological value. Each step o f the industrial technology o f pressing (pre-pressing, full pressing, toasting, heating) resulted in lower glucosinolate content (decrease from 13.7 to 5.8 /rni/g fat-free D M ) and thyro id * Some results were presented on } t h International Rapeseed Congress, Cambridge ( U K ) , 4-7 July 1995 236 NYSTROM R. ET A L . weight o f rats (from 20 to 11 mg/100 g B W ) while growth performance o f animals and nut r i t ional value o f the cake protein were not affected. I t was concluded that properly heated rapeseed press cake may have similar protein value for non-ruminants as solvent extracted meal. K E Y W O R D S : rapeseed cake, pressing, heating, protein digestibility, rats, pigs I N T R O D U C T I O N The most commonly used technology for oil separation from rapeseed involves prepressing of flaked and cooked seeds followed by solvent extraction and desolventizing toasting of the meal. This process is both labour and equipment intensive; therefore more cost effective, pollution free and safe operations are searched for (Loutas, 1991). Some procedures alternative to solvent extraction have been proposed and tested on experimental scale such as expression of oil with single or twin-screw expellers (Isobe et al., 1991), pressing after pre-treatment of seeds with enzymes to enhance oil recovery (Sosulski and Sosulski, 1991), or aqueous enzymatic process (Jensen et al., 1991). The most extensively evaluated parameters were the yield and quality of oil while less attention was paid to the effects of pressing technology on the nutritional value of expeller cake and on the need of post pressing heat treatment. Moderate heat treatment of rapeseed meal or cake is necessary to inactivate myrosinase and to remove the degradation products of glucosinolates still present in double-low rapeseed. Negative effects of glucosinolates on feed intake, growth rate and thyroid functions were observed in many animal species (for review see Mawson et al., 1994 a, b). It is also well known that overheating may decrease total and available lysine content and impair protein utilization (Anderson-Hafermann et al., 1993; Grala et al., 1994; Jensen et al., 1994). Thus heating parameters such as temperature, duration and moisture should be carefully chosen to ensure the high protein value of processed rapeseed feeds. The study was set up as a part of an investigation on the choice of the proper technology of pressing rapeseed oil without solvent extraction in a Finnish oil mill. The objective was to estimate the effects of different pressing methods (as compared with solvent extraction), and heat moisture treatments on the nutritional value of protein of the cake produced on experimental (pilot) scale. The nutritional value of the cake issued from the consecutive steps of industrial pressing in the oil mill was verified. The main criteria of the nutritional value of rapeseed products was protein, fat and glucosinolate contents, protein utilization (digestibility and biological value) and growth performance estimated with rats. Ileal and total digestibility of PROCESSED RAPE SEED PROTEIN VALUE FOR NON-RUMINANTS 237 protein and amino acids was determined in pigs to compare the effects of the two methods of oil separation. MATERIAL AND METHODS Technological treatments Methods of oil separation Three methods of oil separation from rapeseed (Finnish 00 type) were compared: standard procedure of solvent extraction which final product was rapeseed oil meal (RSM), and two experimental procedures of pressing which final product were rapeseed cakes (RC). RSM was produced in the oil mill equipped with desolventizer toaster working both with live and indirect steam. At the end of the process meal was treated with pressurized heat-moisture for a short time. The cakes were produced in a pilot plant using two procedures: 1. rape seeds were incubated 4 h in 50°C at 30% moisture to activate endogenous enzymes, flaked, heated to 80°C and pressed on a Reinartz continous screw press, type Ap V I I (the cake was designated as RC e n z), 2. nonincubated seeds were heated and pressed as in procedure 1 (the cake was designated as RC). Two batches of RSM (RSM 1 and RSM 2), two RC e n z (RC e n z l and RC e n z2) and one RC were evaluated. Heat moisture treatment of the cake The cake produced according to procedure 2 (nonincubated) was further submitted in a pilot plant to different heat-moisture treatments. The cakes treated as follows were evaluated: non treated (RC 0), control, autoclaved during 15 min to 120°C at 18% moisture (RC a u t), toasted during 45 min in 100°C at 18% moisture and nextly heat-pressure treated at 120°C (RC t l 2 0 ), as above, but heat-pressure treated at 140°C (RC t l 4 0 ) . Industrial processing in the oil mill The flow chart of the industrial process based on pressing the oil without solvent extraction is shown in Figure 1. The samples of cake were taken after pre-pressing (RC p p), full pressing (RC p), full pressing and toasting during 45 min 238 NYSTRÔM R. ET A L .