Application of MRI for tissue characterisation of ‘Braeburn’ apple

Magnetic resonance imaging (MRI) has become a well-established technique for non-destructive analysis of the internal (micro)structure of food, and the related heat, gas, water and solutes transport, which is of interest for food processing (e.g., drying), physical tissue damage assessment (e.g., bruising) for online sorting purposes or detection of internal defects (e.g., internal browning), amongst others. In contrast to previous MRI studies which predominantly analysed entire fruit, small samples (diameter ∼10−2 m) of ‘Braeburn’ apple were investigated in this study with high-field MRI, providing very local, high-resolution information, in order to identify the capability of MRI for detecting differences in fruit tissue types. The focus was on MRI for tissue characterisation with respect to inner and outer cortex tissue, fertilisation treatment, storage time and internal browning (IB). For this purpose, the proton density (PD), T2 value and self-diffusion coefficient (DC) were measured. No clear distinction could be made between samples with different fertilisation treatments. Differences in storage times could be observed from an increased PD for longer storage times. Inner tissue clearly showed an increased PD, T2 value and DC, compared to the outer tissue. IB could be successfully detected, where the PD, T2 value and the DC of the affected tissue were clearly higher than those of the healthy tissue, but a dependency of these parameters on the degree of tissue degradation was identified. Especially, the DC seemed to be an appropriate parameter regarding IB detection.

► Fertilisation treatment of ‘Braeburn’ apples could not be distinguished with MRI.
► The proton density increased with increasing fruit storage time.
► Inner fruit tissue could be distinguished from outer tissue with MRI.
► Internal browning can be successfully detected with MRI.
► The diffusion coefficient seems most appropriate for internal browning detection.