Microalgae nutritional composition

FEED Posted on 2010-05-07 Viewed: 47811 Commented: 0 Printed: 7301

 

Composition

As for higher plants, the nutritional composition of microalgae is made up mainly of proteins, carbohydrates, lipids and trace nutrients, including vitamins, antioxidants, and trace elements. Their content varies with different species, even strains and growing conditions, including nutrient supplies, temperature, sunlight, etc (Table 1).

 

 

Table 1. General composition of some animal feeds and foods, and microalgae species (% of dry matter of maximum values achieved in each commodity), adapted from Becker (1994), Fabregas and Herrero (1985), Aaronson and Dubinsky, (1982), Miles and Chapman (2009).

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Figure 1. General composition of human food sources and different algae (maximum values achieved in each commodity) expressed in a column type chart (% of dry matter). Adapted from Becker (1994), Fabregas and Herrero (1985), Aaronson and Dubinsky (1982).

 

It can be noted that there is a large variation in compositions among both conventional feeds / foods and microalgae. Indeed, depending on growth conditions, microalgae, even the same strain, can exhibit large variations in composition, with protein, carbohydrate and lipid contents, each ranging from about 15 to over 50% of dry weight. This plasticity in composition is an important attribute in their use as animal feeds.

About six decades ago, the mass production of certain protein-rich microalgae was considered as a possibility to close the predicted "food gap". Although this "gap" failed to materialize, as a result of the "green revolution", catalyzed in large part by the enormous amounts of fertilizers produced by the Harber Bosch process, the early interest in microalgae resulted in many comprehensive nutritional studies in both animal and human. These nutritional studies continued during the 60s and 70s, due in part to the following interest in microalgae for space applications, and the early commercial production of two algae species, Chlorella and Spirulina. However, by the 1970s the scale-up of commercial production to reduce production costs was not achieved, and the field of large-scale delaying this potential.

 

Essential Amino Acids

These early and extensive nutritional studies of microalgae as foods and feeds demonstrated that algal proteins are of high quality, comparable to conventional vegetable proteins in terms of their content of essential amino acids, which mainly determine the nutritional quality of a protein source (Becker, 2007).
The amino acid profile of various algae are compiled in table 2 and compared with some basic conventional food items and a reference pattern of a well-balanced protein, recommended by WHO/FAO.

Table 2. Amino acid Profile of different algae as compared with conventional protein sources and the WHO/FAO reference pattern (g per 100 protein). Adapted from Becker (2007), Fabregas and Herrero (1985), Miles and Chapman (2009).

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Figure 2. Amino acid Profile of different algae as compared with conventional protein sources and the WHO/FAO reference pattern (g per 100 protein) expressed in a column type chart. Adapted from Becker (2007), Fabregas and Herrero (1985), Miles and Chapman (2009).

 

Most of the early work in determining which amino acids could be classed as indispensable for humans and animals was carried out with rats fed on purified diets. The following ten indispensable amino acids are required for growth in the rat: Arginine, Histidine Isoleucine, Leucine, Lysine, Methionine, Phenylalanine; Threonine; Tryptophan; Valine. Some animals differ slightly in these requirements (e.g. the pig can synthesize arginine, for example), but the content of these essential amino acids determines in large measure the nutritional value of these feeds.

 

Fact 1 ________________________________________________________________

Microalgae proteins have an amino acids profile comparable with the best plant protein sources (For example: Chlorella is better than soybean in most essential amino acids).

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Vitamins and Trace Elements

A similar comparison can be made for vitamins, demonstrating that microalgae contain high levels of essential vitamins, similar to the best food sources such as bakers yeast and liver and are vastly superior to all commodity feeds (such as soybeans, corn, fishmeal, etc.) which have little if any vitamin content (see Table 3).
 

Table 3. Vitamin content of different microalgae in comparison with common foodstuffs and the recommended daily intake (RDI), values in mg.Kg-1 dry matter. Adapted from Becker (2004).

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The nutritionally necessary trace elements, of which there are about two dozen, have similarly high levels in microalgae to those of vitamins, compared to most feed sources. However, data on trace elements is more limited, contents are even more variable between and even within species, and composition more plastic, depending on growing conditions, than is the case even for the major constituents, essential amino acids or vitamins. Indeed, microalgae with desired high concentrations of trace elements could be produced on demand by adjusting the trace elements in their growth medium. 

In the case of both vitamins and trace elements, but also for essential amino acids, the bioavailability of these trace nutrients is often more important and decisive in terms of feed quality than just their bulk constituents. Bioavailability studies are more difficult than just simple analytical measurements, but, overall, bioavailability of all these components is good to high for various microalgae biomass sources studied, in most cases the microalgae already being produced commercially (e.g. Chlorella and Spirulina). 

 

Fact 2 ______________________________________________________________

Microalgae contain a much higher level of vitamins and trace elements than commodity feeds and these are generally highly bio-available.

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An also important properties of microalgae is that their biomass usually has little ash content (less than 10 % dry weight) (Aaaronson and Dubinsky, 1982).
 

 

References

Aaronson S. and Dubinsky Z. 1982. Mass production of microalgae. Experientia 38: 36-40. Article

Becker, E. W. 1994. Microalgae Biotechnology and microbiology. Cambridge University Press, Cambridge.

Becker EW. 2004. Microalgae in human and animal nutrition. In: Richmond A., editor. Handbook of Microalgae Culture. Biotechnology and Applied Phycology. Oxford: Blackwell Science. 

Becker EW. 2007. Microalgae as a source of protein. Biotechnology Advances 25: 207-210. Article

Fabregas J and Herrero C. 1985. Marine Microalgae as a potential source of single cell protein (SCP). Appl. Microbiol. Biotechnol. 23: 110-113. Article

McDonald P, Edwards R, Grenhalgh J, Morgan C. 2002. Animal Nutrition. Prentice Hall. Article

Miles R, Chapman R. 2009. The benefits of fish meal in aquaculture diets. Institute of Food and Agricultural Sciences (IFAS). University of Florida. Article

 

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