Dried biomass of certain fungi is consumed as a protein source in human food and animal feed. Such fungal biomass is termed fungal protein or mycoprotein. A few yeasts and moulds are being consumed as SCPs. Fungi grow rapidly on a wide variety of cheap raw materials. They have lesser amount of nucleic acids than the bacterial SCPs. The digestibility and acceptability of fungal protein in human intestine is high. Therefore, dried fungal biomass is consumed as a SCP.
For the time, yeast biomass was consumed as a supplement to human food by Germans during the World War. Germans mass cultured baker's yeast (Saccharomyces cerevisae ) on cane molasses and consumed when there had been a shortage for convenitional foods.
Now many yeasts are consumed as SCPs. Example- Saccharomyces fragilis, Candida utilis, Candida lipolytica, Rodotorula glutinis, Torulopsis, etc. About 0.4 million tones of yeasts has been manufactured in the world per year .
Yeasts can be grown in a wide variety of wastes by fed batch fermentation. Saccharomyces cerevisae prefers molasses and bears. Candida utilis prefers starchy wastes. Saccharomyces fragilis prefers milk whey. Rhodotorula glutinis prefers domestic sewage. Candida lipolytica prefers hydrocarbons.
To a proper waste, in organic minerals such as nitrogen, potassium, phosphorous, iron, magnesium and sulphur are added and then diluted with water. The pH is adjusted to 3.5-4.5. Medium formulated in this way is stream sterilized before use.
The sterilized medium is filled in a fermenter and a small volume of pure culture of yeast is inoculated into the medium. The temperature is maintained between 30Â°C and 40Â°C. Sterile air is pumped into the fermenter at suitable intervals for providing enough aeration to the culture and to mix the broth well.
When the culture gets reached 2 g cells/ml, the broth is harvested. An equal amount of sterile medium is pumped into the fermenter for continuous operation.
Harvested broth is diluted with a small amount of water and left undisturbed for a few hours. During this time, yeast cells settle down in the broth. The liquid portion is decanted from the vessel to get a concentrated cell suspension.
The cell suspension is then centrifuged to remove the excess of water. Then it is filtered through a rotary vacuum filter to obtain a concentrated yeast biomass on the filter.
The biomass is dried in the sunlight until its water content gets reduced to 6-10%.
The dried yeast biomass is packed in aluminium lined bags for marketing.
Yeast biomass is a rich source of protein, vitamins and minerals. So it has been consumed as a protein supplement in human food and animal feed.
A sweet protein called thaumatin is extracted from the fresh biomass of genetically engineered yeast. It is being used as a substitute for sugar based sweetners for diabetics.
Thaumatin is a great protein found in the fruit of a West African plant, Thaumatococcus daneilli. It is 5000 times sweeter than 4% sucrose. A DNA coding for thaumatin of T.danielli was introduced into the yeast Saccharomyces cerevisae. The genetically manipulated yeast accumulates thaumatin in the cells. Thaumatin is now manufactured from the yeast. In Japan, it is released in the market in the name Talin. It is used as a substitute for sugar-based sweetners for diabetics.
Some mould fungi are easily digestible and acceptable by human system. Their flavor and taste are as good as mushrooms. They have no toxic substance. They are rich in protein. They are therefore consumed as SCPs.
Examples- Aspergillus niger, Aspergillus fumigates, Trichoderma viridae, Trichoderma recsei, Penicillium cyclopium, Paecilomyces varioti etc.
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