NUTRITIVE VALUE OF ENZYME-TREATED CANOLA MEAL

Bogdan A. Slominski, Malgorzata Cyran,

 Wilhelm Guenter and Lloyd D. Campbell

Department of Animal Science, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2; e-mail address: B_Slominski@UManitoba.ca

ABSTRACT

In vitro incubation studies were carried out to determine if various enzyme preparations contained appropriate activities to target specific substrates (ie., cell wall polysaccharides, phytate, oligosaccharides, protein) in canola meal.  The preparations evaluated included some new cellulase-like enzymes  in addition to enzymes already investigated in our earlier research (ie., "-galactosidase, phytase, pectinase).  Seven commercial cellulase preparations were evaluated. Following enzyme evaluation studies, a large quantity of canola meal was subjected to enzyme treatment.  In addition to partial depolymerization of the cell wall polysaccharides, which was demonstrated by the decrease in total non-starch polysaccharide (NSP) content and an increase in soluble NSP, complete hydrolysis of oligosacharides was accomplished and the reduction in phytate content exceeded 30%.  The enzyme-treated meal was incorporated into a semi-purified diet at a level of 30% and was fed to growing rats for four weeks.  As a consequence of no response to enzyme-treated canola meal in weeks 1 and 2 of the experiment, the performance of growing rats determined for the entire trial showed only a tendency toward improved weight gain (4%) and feed efficiency (3%).  As compared to control diet, a significant enhancement in total NSP (1.4 vs 9.8%), soluble NSP (19.8 vs 28.0%), oligosaccharides (61.3 vs 100%) and phytate (31.1 vs 97.7%) digestibilities was observed for the enzyme-treated canola meal.

KEYWORDS: Canola meal, carbohydrase, cellulase, phytase, rats

INTRODUCTION

            Canola meal contains high quality protein but its use in diets of monogastric animals, particularly poultry, has been limited by the relatively high level of fibre, resulting in low energy yield and less than optimum protein utilization.  The fibre components of canola meal include lignin with associated polyphenols (8%), cellulose (4-6%) and non-cellulosic polysaccharides (13-16%) which consist predominantly of pectic substances (Slominski and Campbell, 1990).  Other important components include oligosaccharides (2.5%), glycoprotein (5%; ie. arabinogalactan-protein, cell wall protein), phytate (3.3%), minerals associated with the fiber fraction (1%) and gums (4%)(Slominski and Campbell, 1991).  These components total 35-40% of the meal and undergo a limited conversion to substrates available for absorption as demonstrated by less  than optimum digestibility values for the various constituents: protein (70-75%) (Bell and Keith, 1987; Sauer et al., 1991), dietary fibre (3-8%) (Slominski and Campbell, 1990); oligosaccharides (60%)(Chibowska et al., 1997); phytate (47%)(Nernberg et al., 1997); gums (60%).  It is believed, however, that these components could be degraded by exogenous enzymes of microbial or fungal origin, thereby, improving the nutritive worth of canola meal.

            Recent results from this laboratory have shown improved utilization of canola meal following supplementation of poultry diets with a combination of carbohydrase, protease and phytase enzymes (Slominski et al., 1992, Simbaya et al., 1996).  In the course of enzyme research, however, the most difficult task experienced was to match the substrate with the proper enzyme preparation. The major limitations encountered when evaluating the commercially available enzyme preparations included:

• Lack of a multi-activity complex suitable for effective canola fibre depolymerization,

• Optimum pH often lower than that reflecting the physiological conditions of the small intestine,

• Activity inhibited by acidic environment of the upper gut and dietary ingredients (ie., Ca salts).

These and other limitations often necessitated high inclusion rates, making enzyme application uneconomical.  Alternatively, other avenues for improving the nutritive value of canola meal, including pre-treatment of the meal with a blend of  enzymes, were explored.  In this regard, the canola crushing process was considered to offer some potential for such an approach and desolventized meal with its high moisture content and high temperature was targeted for enzyme application.

EXPERIMENTAL

            The preparations evaluated in the current study included some new cellulase-like enzymes  in addition to enzymes already investigated in our earlier research (ie., "-galactosidase, pectinase, phytase)(Slominski et al., 1992;  Guenter et al. 1995; Simbaya et al., 1996; Nernberg et al., 1997).  Endocellulases were employed in this research as a means to effectively target linkages within the cellulose molecule.  Seven commercial cellulase preparations were screened, along with the carbohydrase (ie., "-galactosidase) preparation, for their ability to depolymerise the non-starch polysaccharide (NSP) fraction.  As shown in Table 1, cellulase E was found to be the most effective and was chosen for further studies on pre-treatment of canola meal with a blend of carbohydrase, cellulase and phytase preparations. 

Table 1.  The effect of carbohydrase and cellulase enzymes on canola meal non-starch  polysaccharide (NSP) depolymerization

Enzyme^1	NSP Glucose^2, mg/g	Total NSP, mg/g
None (control) Carbohydrase^3 Carbohydrase + cellulase A Carbohydrase + cellulase B Carbohydrase + cellulase C Carbohydrase + cellulase D Carbohydrase + cellulase E Carbohydrase + cellulase F	63.8 63.9 57.9 58.2 61.7 57.6 52.7 62.4	178.0 175.1 161.0 159.5 169.2 163.4 148.8 170.7

¹ Added at 0.25%; ² Represents glucose originating, for the most part, from the cellulose molecule; ³ Contains "-galactosidase and pectinase activities

             In addition to partial depolymerization of the cell wall polysaccharides, which was demonstrated by the decrease in total NSP content and an increase in soluble NSP, complete hydrolysis of oligosacchrides and a significant hydrolysis of phytate was achieved (Table 2).  The efficacy of enzyme treatment, as shown by the results of a subsequent experiment, was greatly influenced by moisture content, with 70-80 % showing the highest degree of NSP and phytate hydrolysis (Table 3). 

Table 2.  Quality parameters of enzyme-treated canola meal (mg/g meal)

Enzyme	Total NSP^1	Soluble NSP	Oligosac-charide	Phytate
None (control) Carbohydrase^2 + Cellulase Carbohydrase  + Cellulase + Phytase	182.4 160.6 150.1	17.8 23.4 23.0	22.9  nd^3 nd	30.4 27.6 20.8

¹ Non-starch polysaccharide; ² Contains "-galactosidase and pectinase activities; ³ Not detected.

Table 3.  Selected quality parameters of canola meal when treated with enzyme cocktail under different moisture conditions (mg/g meal)

Enzyme added^1/ moisture content	Total NSP^2	Soluble NSP	Phytate
None, control Enzyme,   80% Enzyme,   70% Enzyme,   60% Enzyme,   50% Enzyme,   40%	173.3 145.0 147.9 150.8 158.2 162.2	16.9 23.8 22.6 23.6 22.5 21.0	28.9 20.3 22.4 24.6 25.2 26.3

¹ Contains carbohydrase, cellulase and phytase enzymes; ² Non-starch polysaccharide.

            Following enzyme evaluation studies, a large quantity of canola meal was subjected to enzyme treatment under optimal conditions (ie., 80% moisture content).  For this study, the amounts of enzymes were reduced to make enzyme application economically more feasible.  In this regard, the level of cellulase E was reduced to 0.1%, carbohydrase to 0.05% while the inclusion rate of phytase was kept constant at the 0.02% level.  These changes resulted in a lower degree of cellulose and NSP depolymerization than that observed earlier when higher inclusion rates of cellulase enzyme were used.   However, the hydrolysis of oligosaccharides was still complete and the reduction in phytate content was similar (ie., 30% reduction).

            The enzyme-treated meal was incorporated into a semi-purified diet at the 30 % level to study the effects on animal utilization in a rat growth trial.  Two control diets were used.  Control A represented canola meal with no enzyme added while Control B contained canola meal supplemented with the same enzyme blend as used for the enzyme-treated meal with identical enzyme to meal ratios.

            The comparison between control diets A and B indicated a lack of effect of dietary enzyme supplementation (Table 4).  Lack of response from the enzyme supplemented diet (ie., Control B) suggests that the survival rate of enzymes in the GI tract was minimal.  This is in agreement with our earlier research which showed low pH of the stomach to have a detrimental effect on enzyme activity (Chibowska et al., 1997).  Feeding of the enzyme-treated canola meal, however, resulted in improved weight gain and feed efficiency. This effect was most pronounced in weeks 3 and 4 of the experiment.   As a consequence of no response to enzyme-treated canola meal in weeks 1 and 2, the  performance of growing rats, as determined for the entire trial, showed only a tendency toward improved weight gain and feed efficiency.  It should be emphasized, however, that with the exception of the canola meal component, all three diets were identical and the improvement in rat performance was solely due to the quality changes in the enzyme-treated meal.  In this context, the improvement to the quality of canola meal would appear to be of high magnitude as the contribution of the meal to total dietary energy, protein and available phosphorus contents was 26, 87 and 52%, respectively. As compared to control diet A, a significant  enhancement in total NSP, soluble NSP, oligosaccharides and phytate digestibilities was observed for enzyme-treated meal (Table 5).

Table 4.  Growth performance of rats fed semipurified diets containing canola meal (CM)(Control A), enzyme-supplemented canola meal (Control B) and enzyme-treated canola meal

Treatment	1^st - 2^nd Week		3^th - 4^th Week		Overall
	Weight gain, g	Feed : Gain	Weight gain, g	Feed : Gain	Weight gain, g	Feed: Gain
Control A: CM Control B: CM + enzyme Enzyme-treated CM	91.8 89.2 92.6	2.62 2.61 2.62	109.5^ab 104.7^b 116.9^a	2.97^a 3.00^a 2.79^b	201.4 193.9 209.5	2.80 2.81 2.71

^ab P#0.05

Table  5.  The effect of enzyme on carbohydrate, phytate and dry matter digestibilities  in growing rats fed enzyme-supplemented and enzyme-treated canola meal (CM)

Treatment	Total NSP^1	Soluble NSP	Oligosac-charides	Phytate	Dry matter
Control A: CM Control B: CM + enzyme Enzyme-treated CM	1.4^c 5.5^b 9.8^a	19.8^b 17.9^b 28.0^a	65.0^a 59.4^a na^2	31.1^c 80.3^b 97.7^a	72.3^b 73.8^a 75.0^a

^ab P<0.05;  ¹ Non-starch polysaccharide; ²No raffinose and stachyose were present in the enzyme-treated diet

CONCLUSIONS

A potential for improvement to the quality of canola meal by enzyme treatment is indicated by the results of this study.  More research is needed to implement this technology on the commercial scale.

ACKNOWLEDGMENTS

The authors wish to thank Finnfeeds International Ltd., Marlborough, UK and Canadian Bio-Systems Inc., Calgary, Canada for providing enzyme supplements and the Enzyme Research  Consortium of the Canola Council of Canada, Winnipeg for financial assistance.

REFERENCES

Bell, J.M. and M.O. Keith, 1987. Feeding value for pigs of canola meral derived from Westar and triazine-tolerant cultivars. Canadian Journal of Animal Science, 67: 811-819.

Chibowska, M., B.A. Slominski, J. Gdala, W. Guenter and L.D. Campbell.  1997.  Efficacy of alpha-galactosidase enzyme preparation as influenced by loss of activity in the GI tract of the chicken. Poultry Sci. 76: 80.

Guenter, W., B.A. Slominski, J. Simbaya, A. Morgan and L.D. Campbell.  1995.  Potential for improved utilization of canola meal using exogenous enzymes.  Proceedings of the 9th International Rapeseed Congress, Cambridge, U.K., pp. 164-166.

Nernberg, L., W. Guenter and B.A. Slominski.  1997.  Improved phosphorus availability in broiler chickens fed a wheat/canola meal based diets supplemented with phytase enzyme.  Poultry Sci. 76: 80.

Sauer, W.C., R. Mosenthin, R. Ahrens and L.A. Den Hartog, 1991.  The effect of source of fibre on ileal and faecal amino acid digestibility and bacterial nitrogen excretion in growing pigs.  Journal of Animal Science,  69: 4070-4077.

Simbaya, J., B.A. Slominski, W. Guenter, A. Morgan and L.D. Campbell. 1996.  The effects of protease and carbohydrase supplementation on the nutritive value of canola meal for poultry: In vitro and in vivo studies.  Anim. Feed Sci. Technol. 61: 219-234.

Slominski, B.A. and L.D. Campbell.  1990.  Non-starch polysaccharides of low-glucosinolate rapeseed (canola) meal: quantification, digestibility in poultry and potential benefit of dietary enzyme supplementation.  J. Sci. Food Agric. 53:175-184.

Slominski, B.A., L.D. Campbell and W. Guenter.  1992.  Enhancement of the feeding value of low-glucosinolate rapeseed by the supplementation of poultry diets with exogenous enzymes.  Proceedings of the 19th World's Poultry Congress, Amsterdam, p. 241-245.

Slominski, B.A. and L.D. Campbell.  1991.  The carbohydrate content of yellow-seeded canola.  Proceedings of the 8th International Rapeseed Congress, Saskatoon, Canada, pp. 1402-1407.