Effect of Processing Technique on the Non-Starch Polysaccharide Content of Canola Meal

Non-starch polysaccharides (NSP) have a considerable impact on digestibility in broilers, dictating nutrient availability and energy utilization. The high NSP content of the hulls in canola meal are one factor limiting its effective use in poultry diets. The major NSP present in canola meal include cellulose, pectic polysaccharides and a variety of non-cellulosic polysaccharides, including arabinoxylans (AX). Attempts have been made to increase utilization of canola meal through the use of NSP-degrading enzymes, including xylanase (Kocher et al., 2000; Mushtaq et al, 2007), but there have been mixed responses. Processing method influences the nutritive value of canola meal, including its NSP composition. The aim of this study was to compare the soluble and insoluble NSP and AX content of solvent-extracted, expeller-pressed and cold-pressed canola meal. Twenty-one samples of solvent-extracted, thirteen samples of expeller-pressed and eighteen samples of cold-pressed canola meal were collected from across Australia. Soluble and insoluble NSP and AX were analysed by an enzymatic-chemical method, involving determination of the released constituent sugars by gas chromatography.

Table 1 - Soluble and insoluble non-starch polysaccharide composition of solvent-extracted, expeller-pressed and cold-pressed canola meal (g/100g).

Processing technique diversely impacted NSP and AX composition (Table 1), suggesting susceptibility to NSP-ase degradation varies greatly depending on the quantity and specific polymer composition of the canola meal fed. The greatest abundance of soluble and insoluble NSP and AX was observed in the cold-pressed canola meals, possibly due to lessened heat damage to the polysaccharides or dilution effect of the oil. There was also more variability within the cold-pressed canola samples, suggesting that this technique results in a less consistent fibre content compared to the other two. Therefore, the necessity for NSP-ase application to combat the anti-nutritional effects of NSP, particularly insoluble NSP on encapsulating nutrients, is comparatively greater in birds fed this form of canola meal. Solvent-extracted and cold-pressed canola had very similar soluble and insoluble AX content, suggesting their response to xylanase is alike, although bird performance is generally enhanced in birds fed cold-pressed canola. Interestingly, the expeller-pressed canola meal presented the lowest NSP and AX content, as opposed to the solvent-extracted samples as predicted, possibly due to the higher heat application and oil content in expeller meal. This study highlights the need for heightened focus on the impact of processing technique on the NSP composition of canola meal and its resulting impact on NSP-ase efficacy.