Biofuel co-products as livestock feed - Opportunities and challenges

438Biofuel co-products as livestock feed – Opportunities and challengesTABLE 9Amino acid profile of a few algae compared with some conventional protein sources (g/100 g protein)Source Ile Leu Val Lys Phe Tyr Met Cys Try Thr Ala Arg Asp Glu Gly His Pro SerEgg 6.6 8.8 7.2 5.3 5.8 4.2 3.2 2.3 1.7 5.0 na 6.2 11.0 12.6 4.2 2.4 4.2 6.9Soybean 5.3 7.7 5.3 6.4 5.0 3.7 1.3 1.9 1.4 4.0 5.0 7.4 1.3 19 4.5 2.6 5.3 5.8Chlorella vulgaris 3.2 9.5 7.0 6.4 5.5 2.8 1.3 na na 5.3 9.4 6.9 9.3 13.7 6.3 2.0 5.0 5.8Dunaliella 4.2 11.0 5.8 7.0 5.8 3.7 2.3 1.2 0.7 5.4 7.3 7.3 10.4 12.7 5.5 1.8 3.3 4.6bardawilSpirulina platensis 6.7 9.8 7.1 4.8 5.3 5.3 2.5 0.9 0.3 6.2 9.5 7.3 11.8 10.3 5.7 2.2 4.2 5.1Aphanizomenonflos-aquae2.9 5.2 3.2 3.2 2.5 na 0.7 0.2 0.7 3.3 4.7 3.8 4.7 7.8 2.9 0.9 2.9 2.9Notes: na = not available. Source: Adapted from Becker, 2004.TABLE 10Major constituents of four important micro-algaeComponentAlgal biomass (% w/w)B. braunii Chlorella sp. Scenedesmus sp. Spirulina sp.Moisture 5–6 5–8 5–7 5–8Ash 10–35 8–10 6–8 10–12Fat 6.9–15 8–12 8–14 2–3Carbohydrates 9.75 12–16 10–15 15–20Protein 20.8 40–50 50–55 50–60Hydrocarbon 5–15 nd nd ndTotal chlorophyll 2.6 nd nd ndTotal carotenoids 0.7 nd nd ndPhenolics 0.77 nd nd ndNucleic acids nd 6–8 4–6 5–7Fibre nd 6–8 10–12 5–8Notes: nd = not determined. Sources: Data for B. braunii from Sarada, 2007[unpublished], and for Chlorella sp., Scenedesmus sp. and Spirulina sp. fromRavishankar et al., 2008essential amino acid (EAA) index. The amino acid profile ofthe micro-algae is comparable to that of standard proteinsources, like milk or eggs. Table 9 gives the amino acidprofile of few micro-algae. The amino acid profile is almostcomparable with that of conventional protein sources, withsome minor deficiencies in sulphur-containing amino acidssuch as methionine and cysteine.Furthermore, micro-algae are good sources of carbohydrates,found in the form of starch, cellulose, sugars andother polysaccharides. The extractable micro-algal polysaccharidescan be used as emulsifiers in the food industry.The available carbohydrates have good overall digestibilityand are therefore suitable for feed applications. The spentbiomass is rich in cellulosic polysaccharides and can alsobe utilized as a diet ingredient in ruminant feed mix asthey have good cellulose digestibility. Addition of algaeto the diet of cows resulted in a lower natural breakdownof unsaturated fatty acids and a higher concentration ofbeneficial compounds in meat and milk. It was observedthat sewage-grown algae (supplemented at 5 percent)could replace 25 percent soybean meal used in broilermash (Becker, 2004). In addition the crude fibre contentof the spent algae could be used for therapeutic purposes.Many experiments with supplementation of whole algaebiomass, from species such as Spirulina, Scenedesmus andChlorella, showed hypo-cholesterolemic effect. In Chlorellaspecies, an important compound of therapeutic value isβ-1,3-glucan, which is immuno stimulatory, with blood lipidreducing effects. Efficacy of this compound against gastriculcers and hypercholesterolemia has also been reported,and there is some anti tumour effect (Spolaore et al., 2006;Lee, Park and Kims, 2008).Unconventional food and feed sources contain certaincompounds, like nucleic acids, that are sources of purines,when consumed increase plasma uric acid concentrations,which are considered in humans to contribute to gout anduric acid stones in the kidney. The nucleic acid contentof micro-algae varies normally between 4 and 6 percent(w/w), while other single-cell protein sources, like yeastand bacteria, are 8–12.5 and 20 percent, respectively(Becker, 2004). Compared with other sources, micro-algaeas a source of feed is relatively safe, but it is recommendedthat intake of nucleic acids should not exceed 2.0 g fromunconventional sources, indicating maximum intake ofalgal biomass not beyond 20 g/day or 0.3 g of algae perkg body weight. Extracts of the hydrocarbon-rich algaB. braunii showed significant antioxidant activity, and wasnon-toxic when whole biomass was supplemented as partof the diet for experimental animals. The antioxidant activitywas attributed to carotenoids, especially lutein, which