Use of Single Cell Protein as a feed ingredient in Aquaculture

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Introduction

Wild catch and seafood are the biggest sources of protein for the industry. Since 1990, Wild-catch extent has been steadied at 90 million tons, hydroponic represents all development. Truth be told, hydroponics developed quicker than any creature protein part. Food is a significant expense in livestock growing whereas the protein content significantly rules the food cost of hydroponic. Along these lines, proficient food and especially protein transformation is fundamental to oversee the expense of production and improve the feasibility of hydroponics. Moreover, the contribution of hydroponic is very significant in the industry for animal proteins. It is concluded that there is a very significant role of SCP in the future 1.

Indeed, With decreasing incorporation of fish meal in hydroponics foods an expected deficiency extending 0.4 to 1.32 million tons amounts of the fish meal would in 2050, essentially disabling aquaculture industry development. Proteins excluding from plant source can be purified to enhance similarity with sea creatures food.

So, it is a demand that we have to find the protein contents that can stabilize the food activity, advantage hydroponics nature, balance the inventory and its transfer, and most importantly, the financial condition of the industry while its expansion. SCP can possibly convey different arrangements through multitude products and production perspective, however significant research, improvement and especially enlargement is as yet demanded. In this case, we survey ongoing improvements in the SCP preparation and the food evaluation, in extension to a concise Intro on animals and the feedstocks 1.

Single-Cell Protein Organisms

The organisms involved in the production of single-cell proteins include bacteria, yeast and microalgae 2. The organisms that have the capability to accumulate single-cell proteins are termed as oleaginous

Bacteria is suitable for SCP production due to its rapid growth and short generation time. The protein content ranges from 50-80%. Methanotrophic bacteria are used commonly for SCP production which includes Methylococcus capsulates 3.

Microalgae can be used for SCPO production because of high protein content produced 60-70% along with omega-3 fatty acids and carotenoids which possess anti-oxidant and immunostimulant properties. They grow in response to sunlight. They have good digestibility with good nutritional quality.

Yeast is being used for SCP production as they are a good source of proteins about 30-50%. Most commonly used are Sachhromyces serevisiae and Candidia utilis.Dietary hydrolyzed yeast such as Ruhodotorula mucilagenosa increased their antioxidant capacity as well as growth performance 2.

Protists

Thaustrochytrids are heterotrophic fungi,not-photosynthetic, they are involved in single-cell protein production as they are a good source of Poly Unsaturated Fatty Acids(PUFAs) as well as 10-20% protein content. They are used to produce poly-unsaturated fatty acids beneficial for animal feed.

Manufacturing Methods

The main objective of SCP is to enhance cell growth and the additional product yield which is economically feasible and the raw material must be cheap or inexpensive.

A recent survey of literature helps to find out the greatest use of waste materials, residual substances and by-product are being more utilized in more circular economy and as being more expensive.Although with the help of practical knowledge we come to know that we must pay more attention to processing cost used for the upgrading of feedstock and to meet the challenges related to them. Modern treads are employing methane, synthesis gas and off-gases feedstock in the production of SCP approaches, another example is of oxidizing bacteria along with it some other ways are being employed to produce low-cost products by dry grinding method of corn ethanol plant so, by variation indifferent feedstock variation in modes are also required which may include autotrophs, photoautotrophs, chemoautotrophs, methylotrophs, heterotrophs and mixotrophs etc. As a result, different production technologies can be utilized for the production of SCP 4.


Photoautotrophs

In this mode of action, inorganic carbon (such as CO2, CO-23, HCO-3) and light is sources of energy. The raw materials are CO2, light and water which is easily available and inexpensive therefore this mode of action is gaining incredible popularity along with this, many challenges are also there in order to meet large scale production.

Challenges

  • High Surface area: High surface area must be provided for better penetration of light in the bioreactor.
  • High Gas flow Rate: High gas flow rate should be maintained.
  • High-Density Cell: High densities of the cells are required in order to reduce the quantity of water.

Organisms used in this mode

Microalgae got first priority in this mode and some proteobacteria (like chromatiales, rhodospirillaceae) are used for the production of SCPs. 

Yen et al, presents where the technology stands, how it is commercially deployed and where the challenges persist.


Chemoautotrophs 

In this mode, growth utilizes inorganic carbon as a vital role along with an inorganic energy source. Bacteria in this domain, are greatly diverse in their growth pattern.

Organisms used in this mode 

Three types of Bacteria are used in this mode (for SCP production), variations in these bacteria helps to bring about more growth and productivity 5.

Acetogens:Acetogens consume carbon dioxide or hydrogen or carbon monoxide through  reductive acetyl-CoA pathway which is known as Wood-Ljungdahl pathway.

Methogens: They uses carbon dioxide or hydrogen to produce methane gas.

Knall gas bacteria: This bacteria is also known as hydrogen-oxidizing bacteria which uses hydrogen, CO2 and oxygen as the final electron acceptor. It has the ability of carbon dioxide fixation  by using  reverse Krebs cycle/Calvin Benson-Bassham cycle. Reason of their more demand is due to carbon fixation and inexpensive feedstock.

Challenges

  • Optimize growth rate and sufficient volumetric production.
  • High cellular mass production.
  • Gases must be solubilized such as H2

By-products which are mainly called carbon metabolites’ act as final electron acceptor such as CH3COO-, C4H7O2  for acetogens and CH4 for methogens so these co-products must be valorized. Cupravidus nectar and related organisms are used by Novo-Nutrients, Solar foods.


Methylotrophs 

In this mode, those bacteria are included that is dependent on methane and methanol as they are not fit into autotrophic and heterotrophic groups so, they have been assigned a separate category called methylotrophs. Their source is organic Carbon feedstock for carbon and energy. They have the capability to carry carbon fixation by different pathways such as ribulose biphosphate cycle (Calvin cycle) /ribulose monophosphate cycle /serine cycle. The intermediate product which is formed during the cycle is CH2O produce by oxidation of methane or methanol.

Challenges

Dissolving the feedstock methane and oxygen into  aqueous broth.

Handling of a large amount of heat produced during fermentation.

  • Pruteen was  first bacterial SCP product, produced by Methylophilus methlotrophus by Imperial chemical industry from a  methanol feedstock in the late 1970s.
  • Pronin (SCP product) made from Methylococcus capsulatus by using methane as a feedstock by Norferm. Pronin was used for aquaculture. Dupont produced a strain than also produced carotenoids, that only targeted astaxanthin. Later on, economics reject this process and now, many companies revive this process. The companies such as Lyngby Denmark use Uniprotein  by  methane feedstock. Calysta making Feedking from methane feedstock.String Bio(Bangalore, India) and KnipBio making KnipBio meal from methanol.KnipBio engineers using microbes to make carotenoids  and taurine and announced plans to scale up this with ICM.KnipBio was the first to produced genetically engineered SCP product which was GRAS recognized by Food and Drug Administration. 


Heterotrophs

In this mode, the organisms feed on organic carbon and all the sources which are used in other modes. This modality has got a wide appreciation for covering a wide range of sources. The specificity of this model is its flexibility for the production of a high rate of SCP Recent advancements in this category is the utilization of corn ethanol process for the high value of SCP. LysCell was SCP product made from S.Cerevisiae  are in the market today made by ICC. Aventine Yeast by Pacific Ethanol, NuPro by Alltech and ProPlex DY by ADM, though most are targeted for high-value applications.


Mixotrophs

In this mode, the use of a mixture of different sources can be utilized for energy and carbon. In this mode, the microbes can act as heterotrophic or autotrophs. Most commonly carbon dioxide and light along with the sugars are added to enhance the growth yield such as yield of cellular mass Spirulina and Chlorella sp. has been observed in greater extent which is far more than in photoautotroph modality. The use of mixotrophs in chemoautotrophy has proven better in metabolites production than cell production.


CONCLUSION

With the increasing population of the world and the need for animal protein, aquaculturing plays an essential role. It becomes a challenge for industries to use a long-lasting and viable ingredient that is protein enriched. Currently, fishmeal and terrestrial plant meals are used for aquaculturing. But, fishmeal and plant meal for aquaculture can not fulfil the requirements of the aquaculture industry. If fishmeal has no long-lasting and beneficial effects on the health of the oceans then it is not suitable and if plant meals do not contain essential amino acids but contain harmful compounds then it is also not suitable. The SCP based meals that are rich in protein can fulfil these requirements. It fulfils the requirements of plant meals and lessens the requirements of fishmeals. It provides benefits for culturing edible aquatic species. These attempts suggest the beneficial impacts of SCP added in the nutrition of these species. While there are several challenges in SCP production, a lot of progress was made in past years for fish species and these attempts encourage the use of SCP products.


By Zoha Khan

 

References

  1. Jones, S. W., Karpol, A., Friedman, S., Maru, B. T. & Tracy, B. P. Recent advances in single cell protein use as a feed ingredient in aquaculture. Curr. Opin. Biotechnol. 61, 189–197 (2020).
  2. Coutteau, P., Lavens, P. & Sorgeloos, P. The use of yeast as single-cell protein in aquacultural diets. Med. Fac. Landbouww. Rijksuniv. Gent 54, 1583–1592 (1989).
  3. Bharti, V., Pandey, P. K. & Koushlesh, S. K. Single Cell Proteins: A Novel Approach in Aquaculture Systems. World Aquac. 45, (2014).
  4. Nasseri, A. T., Rasoul-Amini, S., Morowvat, M. H. & Ghasemi, Y. Single cell protein: production and process. Am. J. food Technol. 6, 103–116 (2011).
  5. Harel, M. et al. Advanced DHA, EPA and ArA enrichment materials for marine aquaculture using single cell heterotrophs. Aquaculture 213, 347–362 (2002).

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