Protein and chitin nitrogen contents and protein content in Pleurotus ostreatus var. columbinus

Proteins and chitin were extracted and purified from dried fruitbodies of P. ostreatus var. columbinus grown on wheat straw and grass hay. Water- and sodium chloride-extractable proteins were purified by dialysis and precipitated by 10% TCA. These proteins contained 15.2% nitrogen (Kjeldahl and amino acid methods). The protein/nitrogen ratio of 6.58 was found and recommended as the new conversion factor. Chitin was purified from acid- and alkali-insoluble residue by 2% KMnO4 and 15% NaHSO3. This chitin contained 5.9% nitrogen and its infrared spectrum was similar to that of commercial chitins. The chitinous nitrogen content was about 0.34% dry weight of fruitbodies. The protein content was calculated from the non-chitinous nitrogen content and the factor 6.58. It was 17.1 and 23.5% dry weight of fruitbodies on wheat straw and grass hay, respectively, rather than 18.4 and 24.4% (as total nitrogen × 6.25).