3.2. Nitrogen distribution
The protein content of SCP is calculated from its total nitrogen content.
But nitrogen remains bound to the nucleic acid, nucleotide, free nitrogen bases and cell membrane amino sugars which does not have significant nutritional values.
Nitrogen distribution in various fractions of the biomass of P. sajor-cajuis presented in Table 2.
The alcohol insoluble nitrogen fraction, termed as the true protein nitrogen fraction, comprised 73.24% of the total mycelial nitrogen.
Based on the calculation alcohol insoluble nitrogen 6.25, the true protein content of P. sajor-caju was found to be 28.75%.
The protein content of five wild species of genus Pleurotus including P. Sajor-caju from Northwest
India varied from 0.98 to 2.17% on the dry weight basis.
Fermentation in whey might account for higher protein content in comparison to wild mushrooms.
Percentage of the total mycelial nitrogen of P. sajor-cajuaccounted for true protein nitrogen found to be similar to that obtained for other SCP.
The cold TCA soluble fraction contains free amino acids and peptones and comprised 16.4% of the total mycelial nitrogen.
The nucleic acid content was found to be lower than S. fragilis and ‘Bel’ yeast, but slightly higher than K. Fragilis.
The low nucleic acid content of P. sajor-cajuis significant from nutritional point of view.
Nucleic acid content is often the limiting factor for microbial foods to be considered for human consumption.
reported as high as 6e11% nucleic acid on a dry weight basis in yeast.
High nucleic acid intake causes gout due to overproduction of uric acid crystals in joints or formation of stone in the urinary tract.
More than 2 g SCP nucleic acid/ day may place normal subjects at risk.
Nucleic acids also reduce the utilization of proteins from diet.
On the basis of a maximum daily intake of 2 g SCP nucleic acid per day, P. sajor-caju biomass can be included in the diet as the sole source of protein up to 40 g per day.
Nucleic acid content can be reduced by a heat-shock with ribonuclease treatment or by an alkaline extraction and acid coagulation process.