Measuring the evolution of microstructure and texture of foods during cooking is difficult because conventional techniques cannot analyze the product's internal structure while preserving its integrity. However, understanding the mechanisms occurring during the cooking of apple, one of the most consumed and processed fruit, is crucial to improve processing efficiency. Thus, an in-situ quantitative NMR approach was developed to characterize apple parenchyma during cooking. Five Malus domestica × 'Golden Delicious' fruits were sampled in four 10 mm by 5 mm cylinders, each sealed in Parafilm 'M' before being placed in the microimaging RF coil of a NMR detector. Half samples were cut parallel to the apple core, and the other half perpendicular to it (along the pores). A controlled hot air flow cooked the sampled from 20 to 60 °C. Every 2 °C the temperature was stabilized and transversal relaxation time (T2) measurements were performed with Carr-PurcellMeiboom-Gill pulse sequence (τ=125µs, TR=5s, 256 echoes, acquisition time = 2min30s). By following the internal vacuolar fluid of the sample, the T2 distribution provided information on the evolution of the internal structure. In parallel, in order to compare the in-situ measurements with texture data, firmness measurements were performed on 30 mm by 10 mm samples from Golden Delicious fruits treated at 20°C (raw), 45°C, 50°C, 53°C, 60°C and 70°C. The firmness measurements showed a significant change in apple parenchyma firmness at 53°C, and no statistical differences between the firmness at 60 and 70°C (ANOVA, α=0.05). The T2 distributions slightly change before 52°C, but then show a remarkable change at 52°C: the cytoplasmic fraction disappears and the vacuolar fraction shifts, while the cell wall fraction remains stable during the whole thermal treatment. Thus, the NMR measurements are in line with the firmness measurements. The T2 also showed significant anisotropy as differences in T2 value observed between samples cutalong the pore direction, and those along the core. However these differences collapsed along heating, showing a less structured cooked tissue as vacuolar membranes are thermally destroyed [1] and pores subsequently filled with water. This study provided valuable information on the apple parenchyma thermal softening, and shows the strong potential of in-situ NMR to investigate the evolution of fruit and vegetable microstructure and texture during cooking.