2.4. Sampling, analytical procedures and subsequent calculations

The sample received for analysis was milled and thoroughly mixed. Two analytical samples were taken from it by the quartering method [17]. Analytical samples were added to preliminarily dried and weighed beakers. Beakers and analytical samples in beakers were weighed and placed in a drying cabinet. Analytical samples were dried to constant weight at a temperature 105 ± 2 °C. The mass ratio of moisture in analytical sample W in percent was calculated by the formula:

where m1 is the mass of moist substrate with a beaker;

The result of the analysis was taken as the arithmetic mean of the results of two parallel determinations. The mass ratio of dry weight in analytical sample DW in percent was calculated by the formula:

To determine the ash content of analytical samples, the crucibles were placed in a muffle furnace and calcined at a temperature of 575 ± 25 °C [18]. After calcinations, the crucibles were cooled to room temperature and weighed. Then the dried analytical sample was placed in the calcined crucible and their total weight was determined. The crucible with the analytical sample was transferred to a muffle furnace, where it was kept at a temperature of 575 ± 25 °C for at least 3 h or until visible traces of carbon compounds disappeared. The ash content of the sample was calculated by the formula:

where Ash content is the mass of ash, referred to the mass of the sample dried at 105 °C, expressed in percentages.

Trends in changes in the chemical composition of the substrate during the cultivation of oyster mushrooms were identified by examining three samples of the substrate from the experimental group 9 (Table 1). The chemical composition of three samples of the untreated substrate (wheat straw) and fruiting bodies was also studied.

The content of cellulose, hemicellulose, and lignin in the untreated and spent substrates was determined by the detergent method [19]. The carbon content in the samples was measured on a Flash EA 1112 series; Thermo Finnigan, Milan, Italy analyzer. Crude fat content in the samples was determined by the Rushkovsky method [20]. The content of the available carbohydrate in the dried analytical samples of fruiting bodies was determined by the following equation:

where fat, protein, ash and crude fiber is the content of these substances in the tested material [21].

The total nitrogen content was determined by the Kjeldahl method [22]. The protein content of the wheat straw and spent substrate samples was determined by multiplying the total nitrogen content by a factor of 6.25 [23], while a factor of 4.38 was used to calculate the protein content in the fruiting bodies [24].

The total phosphorus content in the samples was determined by the molybdate method [25]. Potassium was determined by flame photometry [26]. Calcium and magnesium were determined by the complexometric method with Trilon B by back titration [20].

Based on the results of the analysis, the carbon balance equation was compiled for the cultivation vessel:

where Cinit is the initial mass of carbon in the untreated substrate;

Multiplying each term in equation (9) by 100/Cinit gave this equation expressed as a percentage.

The mass of carbon CCO2 was determined from equation (9):

The distribution of biogenic elements between the spent substrate and fruiting bodies, expressed as a percentage, was determined according to the equations:

where miss is the proportion of the i-th element in the substrate, %;

The content of the unidentified substances in the substrate samples was calculated as the difference between 100% and the sum of the identified substances as a percentage.