Fig. 11 Solid state NMR difference spectra of ¹³C–glucose supplemented samples incubated under anaerobic conditions four weeks at A, 15°C and pH 4.3; B, 25°C and pH 4.3; C, 15°C and pH 6.8; D, 25°C and pH 6.8. Spinning side bands of ¹³C–glucose C are denoted as x