water content (according to PN-ISO1442, which involves drying the sample in an Ecocell laboratory dryer from BMT at a temperature of 103 ± 2 °C to obtain dry matter);
total ash (according to a method complying with PN-ISO936, which involves drying the analyzed sample, to be subsequently incinerated in a Snol muffle furnace at a temperature of (550 ± 25) °C, and after cooling down the mass of the residue is determined;
total nitrogen (with the Kjeldahl method in compliance with PN-75 A-04018, with conversion to protein);
fat (with the Soxhlet method in a Kjeltec 2200 apparatus manufactured by Boss. Before this, the samples were subjected to hydrolysis with hydrochloric acid);
contents of amino acids by Zeng et al. [41 (link)] (by hydrolyzing the sample with 6M HCl for 24 h at a temperature of 110 °C and rinsing with 0.1 molar solution of HCl and distilled water; the hydrolysate was then evaporated, and the residue was dissolved in a buffer of pH 2.2; the contents of amino acids were determined with the use of AAA-400 amino acid analyzer, which performs an assay based on liquid chromatography—following separation in the column, amino acids react with ninhydrin. The sulfur-containing amino acids were subjected to oxidizing hydrolysis with formic acid and hydrogen peroxide and then examined with AAA-400);
profile of fatty acids by Zhang et al. [42 (link)] (the samples were prepared following the Folch method (extraction with chloroform-methanol (2:1) mixture, methylation BF3/methanol). The profile was examined with a Varian 3400CX gas chromatograph, equipped with a flame ionization detector (FID), with the use of a CP-WAX column (length 50 m, diameter 0.53 mm); conditions of chromatograph operation: carrier gas—argon, the temperature of the dispenser −200 °C, temperature of the detector −240 °C, temperature of the column −60–220 °C). The analytical results of the fatty acid profiles were used to calculate the sum of saturated and unsaturated acids in fat. The content of amino acids and the profile of fatty acids in the fat of earthworms were determined in the material previously subjected to the freeze-drying process. Due to a lack of specific information on the chemical composition of D. veneta, research was undertaken to determine the content of protein and amino acids and the profile of fatty acids in the integumentary-muscular sacs as a possible raw material for use in product compositions for human and livestock nutrition. Thereafter, the composition of selected indicators of nutritional quality of integumentary-muscle sacs of D. veneta were compared with E. fetida, an earthworm for which much more information is available.
