2.2. Egg Quality

Each egg was a single unit in the quality assessment. Egg quality analysis included the determination of egg weight, yolk weight and weight of thick and thin albumen measured using RADWAG PS 750/X (Radwag, Radom, Poland) scales (± 0.01 g). The egg shape index (egg width/length) was calculated using measurements taken with a Mitutoyo Quantu Mike calliper (Mitutoyo, Wrocław, Poland). Eggshell surface area was calculated using the egg weight (W) with a formula proposed by Paganelli et al. [15]: P_s = 4.835 × W^0.662. Eggshell strength (kg/cm³) was analysed with an Egg Force Reader (Orka Food Technology Ltd., Toruń, Poland). Thick albumen height was measured with a QCD device (TSS, Poznań, Poland). Yolk colour was assessed using the 15-tone La Roche scale. Yolk colour was also assessed using a Konica Minolta colourimeter, model CR400, Japan. The device was calibrated using the white calibration plate no. 21033065 and the D₆₅ Y_86.1 x_0.3188 y_0.3362 scale. Colour was graded according to the CIE (1986) L*a*b* system (L* = lightness, a* = redness and b* = yellowness). Haugh unit (HU) scores were calculated from the formula HU = 100 lg (H + 7.7 – 1/7W ^0.37), where H is the height of the thick albumen (mm) and W is the weight of the egg (g) [16]. The specific density of thick albumen and yolk was determined using KIT-128 (for the analysis of the density of liquids and solids, Radwag, Radom, Poland) and RADWAG 750/X scales. Shells from broken eggs were collected on trays and dried for 3 hours at 105 °C in a SUB 100M drying chamber (Binder, Tuttlingen, Germany). After drying, the shells were weighed (RADWAG PS 750/X) and measured for thickness with a screw thread micrometre (TSS, Poznań, Poland). The proportion of morphological components of the egg was calculated.