INDUSTRIAL PRODUCTS FROM MICROBIAL

PROCESSES (SINGLE CELL PROTEIN)

During World War II, when there were stortages in proteins and vitamins in the diet, the Germans produced yeasts and a mould (Geotrichum candidum) in some quantity  for food; this led to the idea to produce edible proteins on a large scale by means of microorganisms during 1970s.

Several industrial giants investigated the possibility of converting cheap organic materials into protein using microorganism.

Single-Cell Protein (SCP) is a term coined at Massachusetts Institute of Technology by Prof C.L. Wilson (1966) and represents microbial cells (primary) grown in mass culture and harvested for use as protein sources in foods or animal feeds.

Single Cell Protein (SCP) is not a pure protein but refers to whole cells of bacteria, yeasts, filamentous fungi or algae.

Contains carbohydrates, lipids, nucleic acids, mineral salts and vitamins.

Carbon substrates: major substrates used in commercial SCP production is alcohols, n-alkanes, molasses, sulphite liquor and whey.

Note: Soya beans contain ~ 40% of protein.

Microbe % of Protein Nucleic acidBacteria 50-85 10-16%Yeast 45-55 5-12%Filamentous Fungi 30-55 3-10%Algae 45-65 4-6%

Animal nutrition: fattening calves, poultry, pigs and fish breading

Foodstuffs area: aroma carriers, vitamin carrier, emulsifying aids and to improve the nutritive value of baked products, in soups, in ready-to-serve meals, in diet recipes

Technical field: paper processing, leather processing and as foam stabilizers.

Not a pure protein but refer to the whole cells of bacteria, yeast, filamentous fungi or algae.

Also contains carbohydrates, lipids, nucleic acids, mineral salts and vitamins.

Bhalla et al. (2007)

Various carbon sources and microorganisms used for SCP production

Carbon substrate Microrganism

CO2 Spirulina speciesChlorella species

Liquid hydrocarbons (n-alkanes)

Saccharomyces lipolyticaCandida tropicalis

Methane Methylomonas methanicaMethylococcus capsulatus

Methanol Methylophilus methylotrophusHyphomicrobium spCandida boidiniiPichia angusta

Ethanol Candida utilis

Glucose (hydrolysed starch) Fusarium venenatum

Inulin (a polyfructan) Candida spKluyveromyces sp

Molasses Candida utilisSaccharomyces cerevisiae

Whey Kluyveromyces marxianusKluyveromyces lactisPenicillium cyclopium

Spent sulphite waste liquor Paecilomyces variotii

Rapid growth rate and high productivity (algae: 2–6 hours, yeast: 1–3 hours, bacteria: 0.5–2 hours)

High protein content, 30-80% on a dry weight basis. The ability to utilize a wide range of low cost carbon

sources, including waste materials. Strain selection and further development are relatively

straightforward, as these organisms are amendable to genetic modification.

Process occupy little land area. Ex: Algal culture can be done in space that is normally unused and so there is no need to compete for land..

Production is independent of seasonal and climatic variations.

Consistent product quality.

1) Moulds have their limitations due to lower growth rates and lower protein content.

2) Algae have cellulose in their cell walls which are not digestible. They also accumulate heavy metals which may prove harmful to living beings.

3) Since the bacterial cells are small in size and have low density, their harvesting from the fermented medium becomes difficult and costly.

4) Bacterial cells possess high nucleic acid content which may prove detrimental to human beings by increasing the uric acid level in blood.

→ Additional steps to overcome this problem make the production costly.

Medium preparation: The main carbon source may require physical or chemical pretreatment prior to use.Ex: Polymeric substrates are often hydrolysed before being incorporated with sources of nitrogen, phosphorus and other essential nutrients.

Fermentation:

Basic stages irrespective of the carbon substrate or microorganisms used:1) MEDIUM PREPARATION

Physical and chemical pretreatment of carbon sources used.Ex: Polymeric substrates are often hydrolysed before being incorporated with sources of nitrogen, phosphorus and other essential nutrients

2) FERMENTATIONMay be aseptically or run as a ‘clean’ operation depending upon the particular objectives.The fermentations process were operated at max growth rate of microorganisms used.Ex: Solid state fermentation (SSF) = growth of microorganisms on predominantly insoluble substrate where there is no free liquid.

3) SEPARATION AND DOWNSTREAM PROCESSINGThe cells are separated by filtration or centrifugation.The spent medium may be processed in order to reduce level of nucleic acids, eg: thermal shock process to inactivate cellular proteasesFurther purification may involved, eg: solvent wash, dehydration.

5 established methods:1) The Bel Process2) The Symba Process3) The Pekilo Prosess4) The Bioprotein Process5) The Pruteen Process

Different carbon source, different microbes used, different in product quality.

Whey (liquid waste of dairy industry) is used as substrate.

Whey contains approximately 45 g/L lactose and 10 g/L protein. It is particularly suitable for the production of SCP using lactose - utilizing yeast.

Ex: Kluyveromyces marxianus. The Bel process was designed by theBel Industries in

France. It was developed with the aim of reducing the pollution

load of dairy industry waste, while simultaneously producing a marketable protein product which is used for both human and animal consumption.

In this process initially 75 % of the whey proteins are precipitated.

The Symba process was developed in Sweden to produce SCP for animal feed from potato processing wastes.

A high proportion of the available substrate is starch, which many microbes cannot directly utilize.

To overcome this problem two microorganisms were selected that grow in a symbiotic association.

They are the yeasts Saccharomycopsis fibuligera, which produces the hydrolytic enzymes necessary for starch degradation and Candida utilis.

Resultant protein rich biomass contains 45% protein.

This process began operating in 1975 and was the first commercial continuously operating process for the production of a filamentous fungus.

The process was developed in Finland for the utilization of spent sulfite liquor, derived from food processing, that contains monosaccharides and acetic acid.

Supplements of other carbon sources, usually molasses, whey and hydrolyzed plant wastes were added.

The organism of interest in this process is Paecilomyces variotii.

This continuous process is operated aseptically and produces over 10,000 tonnes of SCP a year.

Resulting dried Pekiloprotein containing up to 59 % crude protein, is used in the preparation of compounded animal feed

The Bioprotein process was developed in1990s by gas-based fermentation plant, Norferm in Norway to produce protein from methane.

‡There has been a considerable amount of research into the production of SCP using alkanes as carbon sources, notably methane and liquid straight chain hydrocarbons.

‡This process uses methane rich natural gas as a sole carbon and energy source for the growth of Methylococcus capsulatus.

Methanol has several advantages over methane and many other carbon sources particularly it is miscible with water and is available in a very pure form.

Consequently the resultant protein does not have to undergo purification.

This process uses a methylotrophic bacterium, Methylophilus methylotrophus, to produce a feed protein for chickens, pigs and calves, marketed as Pruteen.

The dried unprocessed product contained 16 % nucleic acids and over 70 % crude protein.