Optimisation of distillery co-products for poultry feed
EU legislation has led to an almost ten-fold increase in bioethanol production between 2003 and 2011. The current distillery co-product, distiller’s dried grains with solubles (DDGS), is fed primarily to cattle due to the high fibre content but differentiation of the co-product stream would allow penetration of the large monogastric feed sector. The aim of this project was to evaluate a novel separation process producing a high protein yeast protein concentrate (YPC) from DDGS, and assess the potential of this product as a feed ingredient for poultry. A pilot plant study modelling the process confirmed the variability of the stillage, but highlighted the viability of the process for ameliorating some of these differences. Inter-batch variability was reduced from 10% to 1.2% in terms of protein content but dry matter content still varied by more than 8%, due to fibre contamination. The batches of yeast cream with increased fibre content had significantly reduced drying rates, from 37.3mg/min to 23.6mg/min, due to the larger particle sizes included. Additionally, the increased range of particle size introduced by fibre contamination would lead to product separation with detrimental implications for transport and handling of the dried product. It is vital to have measurements of amino acid content and digestibility for any new feed ingredient to ensure accurate feed formulation. Amino acid digestibility was measured in vivo in broiler chicks for five YPCs from potable and bioethanol sources produced using three drying technologies. Amino acid digestibility coefficients (COD) were significantly better for bioethanol produced YPC than potable (bioethanol 0.73 and 0.63 compared with 0.58 and 0.52 for potable). This is likely to be due to the addition of exogenous enzymes during the bioethanol process resulting in reduction of some of the detrimental effects of non-starch polysaccharides. Drying methodology affected both total amino acid content and digestible amino acid content, with spray drying being the least damaging method (COD 0.73 and 0.58) and ring drying the most damaging (COD 0.39). Lysine was particularly damaged during the heating process; reducing in total content from approximately 5% of protein to 2.3% of protein for ring dried material. Freeze dried YPC samples (COD 0.63 and 0.52) may have been negatively affected by the presence of fibre in the YPC due to processing inconsistencies. In terms of bird performance, bioethanol freeze dried YPC inclusion improved weight gain (p=0.003) and feed intake (p=0.006) compared with potable, again likely due to the enzyme addition during the bioethanol process. This was confirmed by the measured digesta viscosity increase in birds fed diets with increasing potable YPC inclusion (p=0.073). Spray dried YPC did not significantly affect FCR up to 20% inclusion, but both intake and bodyweight gain reduced with rate of inclusion. This may be attributed to spray drying producing a small particle size which increases feeding time and can increase viscosity, as was shown in this project (viscosity of spray dried YPC increased with RoI p=0.031). Ring dried YPC was incorporated into pelleted diets and therefore gave the best performance results. FCR for bioethanol YPC was improved from 1.68 for freeze dried material included at 9% of total diet to 1.4 for ring dried material at a higher rate of 12.5% of total diet. Finally the potential of YPC as a source of available phosphorus was considered, by assessing foot ash content of birds fed diets containing varying YPC levels. Increasing rate of YPC inclusion increased foot ash from 17.3% to 18.5% at 20% inclusion (p=0.031). YPC replaced 35% of supplemental phosphorus in chick diets with no significant effects on bone mineralization. The novel YPC from bioethanol distilleries appears to be a viable protein source for chicks at low inclusion levels (less than 6%). In pelleted diets the inclusion level could rise to 17.5% with no detrimental effects on bird performance. Additionally, YPC provides a source of available phosphorus, reducing the need for supplemental phosphorus in chick diets. The most appropriate drying method appears to be ring drying if care is taken to reduce residence time and heat damage. However there is substantial scope for further improvement of both the process and product as a feed ingredient for poultry.
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