Contribution of individual electron captures to the neutronization close to the centre as a function of the mass coordinate for a Chandrasekhar-mass model with (a) ρ_c = 2 × 10⁹ g cm⁻³(model C2), (b) ρ_c = 3 × 10⁹ g cm⁻³(model C3), (c) ρ_c = 4 × 10⁹ g cm⁻³(model C4), and (d) ρ_c = 5 × 10⁹ g cm⁻³(model C5). In panel c, the curves are labelled with the species name. In all panels, the contribution from protons has been scaled down by a factor ten.